The BZ 34-1 oilfield is a typical gas cap edge water reservoir in the Bohai oilfield. The main characteristics of the oilfield were multi-phase sand body stacking and the sand body was composed of three parts: gas cap...The BZ 34-1 oilfield is a typical gas cap edge water reservoir in the Bohai oilfield. The main characteristics of the oilfield were multi-phase sand body stacking and the sand body was composed of three parts: gas cap, oil reservoir, and edge water. The actual production site results show that the permeability difference of multi-layer sand bodies has a serious impact on the development effect. This article establishes a typical reservoir model numerical model based on the total recovery degree of the reservoir and the recovery degree of each layer, and analyzes the impact of permeability gradient. As the permeability gradient increases, the total recovery degree of all four well patterns decreases, and the total recovery degree gradually decreases. The recovery degree of low permeability layers gradually decreases, and the recovery degree of high permeability layers gradually increases. As the permeability gradient increases, the degree of recovery gradually decreases under different water contents. As the permeability gradient increases, the reduction rate of remaining oil saturation in low permeability layers is slower, while the reduction rate of remaining oil saturation in high permeability layers was faster. By analyzing the impact of permeability gradient on the development effect of oil fields, we could further deepen our understanding of gas cap edge water reservoirs and guide the development of this type of oil field.展开更多
For thin oil rim reservoir with gas cap and edge water, it is helpful to improve the development effect to find out the distribution law of remaining oil in this kind of reservoirs. For this reason, taking the narrow ...For thin oil rim reservoir with gas cap and edge water, it is helpful to improve the development effect to find out the distribution law of remaining oil in this kind of reservoirs. For this reason, taking the narrow oil rim reservoir with gas cap and edge water of Oilfield A in Bohai Sea as a case, the main controlling factors, including reservoir structure, fault, gas cap energy, edge water energy and well pattern, affecting the distribution of residual oil in this kind of reservoir were analyzed by using the data of core, logging, paleogeomorphology and production. Then, the distribution law of remaining oil was summarized. Generally, the remaining oil distribution is mainly potato-shaped or strip-shaped in plane. Vertically, it depends on the energy of gas cap and edge water. For the reservoir with big gas gap and weak edge water, the remaining oil mainly lies in the bottom of oil column. And for the reservoir with small gas gap and strong edge water, the remaining oil mainly locates at the top of oil column. Aiming at different distribution modes of remaining oil, the corresponding potential tapping strategies of horizontal wells are put forward: in the late stage of development, for the reservoir with big gas gap and weak edge water, the remaining oil concentrates at the bottom of the oil column, and the position of horizontal well should be placed at the lower 1/3 to the lower 1/5 of the oil column;for the reservoir with small gas cap and strong edge water, the remaining oil locates at the top of the oil column, and the position of horizontal well should be put at the upper 1/5 to the upper 1/3 of the oil column height, vertically. Based on the study on remaining oil of Oilfield A, a potential tapping strategy of well pattern thickening and vertical position optimization of horizontal well was proposed. This strategy guided the efficient implementation of the comprehensive adjustment plan of the oilfield. Moreover, 18 infill development wells were implemented in Oilfield A, and the average production of the infill wells is 2.1 times that of the surrounding old wells. It is estimated that the ultimate recovery factor of the oilfield will reach 33.9%, which is 2.3% higher than that before infilling wells. This study can be used for reference in the development of similar reservoirs.展开更多
The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The ch...The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The chemical properties of reservoir water are very important for reservoir evaluation and are significant indicators of the sealing of reservoir oil and gas resources.Therefore,the caprock of the Chang 6 reservoir in the Yanchang Formation was evaluated.The authors tested and analyzed the chemical characteristics of water samples selected from 30 wells in the Chang 6 reservoir of Ansai Oilfield in the Ordos Basin.The results show that the Chang 6 reservoir water in Ansai Oilfield is dominated by calcium-chloride water type with a sodium chloride coefficient of generally less than 0.5.The chloride magnesium coefficients are between 33.7 and 925.5,most of which are greater than 200.The desulfurization coefficients range from 0.21 to 13.4,with an average of 2.227.The carbonate balance coefficients are mainly concentrated below 0.01,with an average of 0.008.The calcium and magnesium coefficients are between 0.08 and 0.003,with an average of 0.01.Combined with the characteristics of the four-corner layout of the reservoir water,the above results show that the graphics are basically consistent.The study indicates that the Chang 6 reservoir in Ansai Oilfield in the Ordos Basin is a favorable block for oil and gas storage with good sealing properties,great preservation conditions of oil and gas,and high pore connectivity.展开更多
The irreducible water saturation(Swir) is a significant parameter for relative permeability prediction and initial hydrocarbon reserves estimation.However,the complex pore structures of the tight rocks and multiple fa...The irreducible water saturation(Swir) is a significant parameter for relative permeability prediction and initial hydrocarbon reserves estimation.However,the complex pore structures of the tight rocks and multiple factors of the formation conditions make the parameter difficult to be accurately predicted by the conventional methods in tight gas reservoirs.In this study,a new model was derived to calculate Swir based on the capillary model and the fractal theory.The model incorporated different types of immobile water and considered the stress effect.The dead or stationary water(DSW) was considered in this model,which described the phenomena of water trapped in the dead-end pores due to detour flow and complex pore structures.The water film,stress effect and formation temperature were also considered in the proposed model.The results calculated by the proposed model are in a good agreement with the experimental data.This proves that for tight sandstone gas reservoirs the Swir calculated from the new model is more accurate.The irreducible water saturation calculated from the new model reveals that Swir is controlled by the critical capillary radius,DSW coefficient,effective stress and formation temperature.展开更多
As we all know, cyclic gas injection is one of the most effective development methods to improve condensate oil recovery. When dealing with the calculation of the reserves, the injection-production differences and wat...As we all know, cyclic gas injection is one of the most effective development methods to improve condensate oil recovery. When dealing with the calculation of the reserves, the injection-production differences and water influx create great influence on the accuracy. Based on the existing research, we proposed a new material balance equation which considered the differences of composition between produced and injected fluids and the effect of water influx, and a solution was provided in this paper. The results of the method are closer to the actual situation because they are built on the law of conservation of mass, and the using of curve fitting method can not only avoid the use of water influx coefficient but also obtain the water influx rate and reserves at the same time. The YH-23 gas condensate reservoir is taking as a typical subject to do the research, which has been exploited by cycle gas injection for 14 years. Three different methods are used to calculate the reserves, and the results show that the method proposed in this paper has minimum error of 2.96%.展开更多
The studies of water, gas and isotope chemistry indicate that the formation of geothermal water in the Henjing area is not related to the magmatic and volcanic sources. The geothermal water mainly derives from the met...The studies of water, gas and isotope chemistry indicate that the formation of geothermal water in the Henjing area is not related to the magmatic and volcanic sources. The geothermal water mainly derives from the meteoric source, and the gas components originate from the mixing of meteoric, crustal and mantle sources. Moreover, the geothermal water is in a low to moderate temperature geothermal reservoir. The results calculated by the quartz geothermometer and the silicaenthalpy diagram demonstrate that the lowest temperature of geothermal reservoir is in the range 78℃ to 134 ℃ and the highest temperature is in the range 95℃C to 155℃. Based on isotopic data, the possible elevation of recharge water is about 337. 5 m to 743. 6 m, which corresponds to the Wunizhang area.展开更多
Marine shale gas resources have great potential in the south of the Sichuan Basin in China.At present,the high-quality shale gas resources at depth of 2000–3500 m are under effective development,and strategic breakth...Marine shale gas resources have great potential in the south of the Sichuan Basin in China.At present,the high-quality shale gas resources at depth of 2000–3500 m are under effective development,and strategic breakthroughs have been made in deeper shale gas resources at depth of 3500–4500 m.To promote the effective production of shale gas in this area,this study examines key factors controlling high shale gas production and presents the next exploration direction in the southern Sichuan Basin based on summarizing the geological understandings from the Lower Silurian Longmaxi Formation shale gas exploration combined with the latest results of geological evaluation.The results show that:(1)The relative sea depth in marine shelf sedimentary environment controls the development and distribution of reservoirs.In the relatively deep water area in deep-water shelf,grade-I reservoirs with a larger continuous thickness develop.The relative depth of sea in marine shelf sedimentary environment can be determined by redox conditions.The research shows that the uranium to thorium mass ratio greater than 1.25 indicates relatively deep water in anoxic reduction environment,and the uranium to thorium mass ratio of 0.75–1.25 indicates semi-deep water in weak reduction and weak oxidation environment,and the uranium to thorium mass ratio less than 0.75 indicates relatively shallow water in strong oxidation environment.(2)The propped fractures in shale reservoirs subject to fracturing treatment are generally 10–12 m high,if grade-I reservoirs are more than 10 m in continuous thickness,then all the propped section would be high-quality reserves;in this case,the longer the continuous thickness of penetrated grade-I reservoirs,the higher the production will be.(3)The shale gas reservoirs at 3500–4500 m depth in southern Sichuan are characterized by high formation pressure,high pressure coefficient,well preserved pores,good pore structure and high proportion of free gas,making them the most favorable new field for shale gas exploration;and the pressure coefficient greater than 1.2 is a necessary condition for shale gas wells to obtain high production.(4)High production wells in the deep shale gas reservoirs are those in areas where Long11-Long13 sub-beds are more than 10 m thick,with 1500 m long horizontal section,grade-I reservoirs penetration rate of over 90%,and fractured by dense cutting+high intensity sand injection+large displacement+large liquid volume.(5)The relatively deep-water area in the deep-water shelf and the area at depth of 3500–4500 m well overlap in the southern Sichuan,and the overlapping area is the most favorable shale gas exploration and development zones in the southern Sichuan in the future.With advancement in theory and technology,annual shale gas production in the southern Sichuan is expected to reach 450×108 m3.展开更多
Large-scale gas accumulation areas in large oil-gas basins in central and Western China have multiple special accumulation mechanisms and different accumulation effects.Based on the geological theory and method of nat...Large-scale gas accumulation areas in large oil-gas basins in central and Western China have multiple special accumulation mechanisms and different accumulation effects.Based on the geological theory and method of natural gas reservoir formation,this study examined the regional geological and structural background,formation burial evolution,basic characteristics of gas reservoirs,and fluid geology and geochemistry of typical petroliferous basins.The results show that the geological processes such as structural pumping,mudstone water absorption,water-soluble gas degasification and fluid sequestration caused by uplift and denudation since Himalayan stage all can form large-scale gas accumulation and different geological effects of gas accumulation.For example,the large-scale structural pumping effect and fluid sequestration effect are conducive to the occurrence of regional ultra-high pressure fluid and the formation of large-scale ultra-high pressure gas field;mudstone water absorption effect in the formation with low thickness ratio of sandstone to formation is conducive to the development of regional low-pressure and water free gas reservoir;the water-soluble gas degasification effect in large-scale thick sandstone can not only form large-scale natural gas accumulation;moreover,the degasification of water-soluble gas produced by the lateral migration of formation water will produce regional and regular isotopic fractionation effect of natural gas,that is,the farther the migration distance of water-soluble gas is,the heavier the carbon isotopic composition of methane formed by the accumulation.展开更多
Vast amounts of world oil reservoirs are in natural fractured reservoirs. There are different methods for increasing recovery from fractured reservoirs. Miscible injection of water alternating CO2?is a good choice amo...Vast amounts of world oil reservoirs are in natural fractured reservoirs. There are different methods for increasing recovery from fractured reservoirs. Miscible injection of water alternating CO2?is a good choice among EOR methods. In this method, water and CO2?slugs are injected alternatively in reservoir as miscible agent into reservoir. This paper studies water injection scenario and miscible injection of water and CO2?in a two dimensional, inhomogeneous fractured reservoir. The results show that miscible water alternating CO2?gas injection leads to 3.95% increase in final oil recovery and total water production decrease of 3.89% comparing to water injection scenario.展开更多
Although significant amount of H_(2)S(sour gas)rich natural gas is estimated globally,but not much attention has been given to the application of H_(2)S in the oil recovery process.Recent studies on the use of H_(2)S ...Although significant amount of H_(2)S(sour gas)rich natural gas is estimated globally,but not much attention has been given to the application of H_(2)S in the oil recovery process.Recent studies on the use of H_(2)S in oil recovery processes showed that H_(2)S has the potential of improving the oil recovery,and it can be even more effective than using CO_(2) in some processes.H_(2)S can equally dissolve in the water,react with the reservoir rock to change its surface charge,porosity,and permeability.However,previous in-vestigations on H_(2)S oil recovery attributed the improved oil recoveries to the higher miscibility of H_(2)S in the oil,and the reduction in the oil viscosity.Therefore,there is limited understanding on the H_(2)S-oil-brine-rock geochemical interactions,and how they impact the oil recovery process.This study aims to investigate the interactions between H_(2)S,oil,and carbonate formations,and to assess how the combi-nation of H_(2)S and low salinity water can impact the wettability and porosity of the reservoirs.A triple layer surface complexation model was used to understand the influence of key parameters(e.g.,pressure,brine salinity,and composition)on the H_(2)S-brine-oil-rock interactions.Moreover,the effects of mineral content of the carbonate rock on H_(2)S interactions were studied.Thereafter,the results of the H_(2)S-oil-brine-rock interactions were compared with a study where CO_(2) was used as the injected gas.Results of the study showed that the seawater and its diluted forms yielded identicalζ-potential values of about 3.31 mV at a pH of 3.24.This indicates that at very low pH condition,pH controls the ζ-potential of the oil-brine interface regardless of the brine's ionic strength.The study further demonstrated that the presence of other minerals in the carbonate rock greatly reduced the calcite dissolution.For instance,the calcite dissolution was reduced by 4.5%when anhydrite mineral was present in the carbonate rock.Findings from the simulation also indicated that CO_(2) produced negative ζ-potential values for the car-bonate rocks,and these values were reduced by 18.4%-20% when H_(2)S was used as the gas phase.This implies that the H_(2)S shifted the carbonate rockζ-potentials towards positive.The outcomes of this study can be applied when designing CO_(2) flooding and CO_(2) storage where the gas stream contains H_(2)S gas since H_(2)S greatly influences the dissolution of the carbonate mineral.展开更多
The development of natural gas in China has entered a golden and leap-forward stage, which is a necessary bridge to clean energy. This in-depth study on the status quo, theory, technology and prospect of natural gas d...The development of natural gas in China has entered a golden and leap-forward stage, which is a necessary bridge to clean energy. This in-depth study on the status quo, theory, technology and prospect of natural gas development shows:(1) The global remaining proven recoverable reserves of natural gas are 186×1012 m3, and the reserves-production ratio is 52.4, indicating a solid resource base for long-term and rapid development.(2) Ten formation and distribution laws of conventional and unconventional natural gas reservoirs have been proposed. In terms of exploration geology, the theory of conventional "monolithic" giant gas fields with different gas sources, and an unconventional gas accumulation theory with continuous distribution of "sweet areas" in different lithologic reservoirs have been established; in terms of development geology, a development theory of conventional structural gas reservoirs is oriented to "controlling water intrusion", while a development theory of unconventional gas is concentrated on man-made gas reservoirs.(3) With the geological resources(excluding hydrates) of 210×1012 m3 and the total proven rate of the resources less than 2% at present, the natural gas in China will see a constant increase in reserve and production; by 2030, the proven geological reserves of natural gas are expected to reach about(6 000-7 000)×108 m3, the production of conventional and unconventional natural gas each will reach about 1 000×108 m3, and the gas consumption will reach 5 500×108 m3. The dependence on imported natural gas may be 64% by 2030, and 70% by 2050.(4) Ten measures for future development of natural gas have been proposed, including strengthening exploration in large-scale resource areas, increasing the development benefits of unconventional gas, and enhancing the peak adjusting capacity of gas storage and scale construction of liquified natural gas.展开更多
Through analyzing the development of large ultra-deep structural gas fields in China,strategies for the efficient development of such gas fields are proposed based on their geological characteristics and production pe...Through analyzing the development of large ultra-deep structural gas fields in China,strategies for the efficient development of such gas fields are proposed based on their geological characteristics and production performance.According to matrix properties,fracture development degree and configuration between matrix and fractures,the reservoirs are classified into three types:single porosity single permeability system,dual porosity dual permeability system,and dual porosity single permeability system.These three types of gas reservoirs show remarkable differences in different scales of permeability,the ratio of dynamic reserves to volumetric reserves and water invasion risk.It is pointed out that the key factors affecting development efficiency of these gas fields are determination of production scale and rapid identification of water invasion.Figuring out the characteristics of the gas fields and working out pertinent technical policies are the keys to achieve efficient development.The specific strategies include reinforcing early production appraisal before full scale production by deploying high precision development seismic survey,deploying development appraisal wells in batches and scale production test to get a clear understanding on the structure,reservoir type,distribution pattern of gas and water,and recoverable reserves,controlling production construction pace to ensure enough evaluation time and accurate evaluation results in the early stage,in line with the development program made according to the recoverable reserves,working out proper development strategies,optimizing pattern and proration of wells based on water invasion risk and gas supply capacity of matrix,and reinforcing research and development of key technologies.展开更多
Carbonate reservoirs in China have the characteristics of diversified accumulation pattern, complex structure and varying reservoir conditions. Concerning these characteristics, this article tracks the technical break...Carbonate reservoirs in China have the characteristics of diversified accumulation pattern, complex structure and varying reservoir conditions. Concerning these characteristics, this article tracks the technical breakthroughs and related practices since the 1950 s, summarizes the developed theory and technologies of carbonate reservoir development, analyzes their adaptability and problems, and proposes their development trend. The following theory and technologies have come into being:(1) carbonate reservoir formation mechanisms and compound flow mechanisms in complex medium;(2) reservoir identification and description technologies based on geophysics and discrete fracture-vuggy modeling method;(3) well testing analysis technology and numerical simulation method of coupling free flow and porous media flow;(4) enhanced oil recovery techniques for nitrogen single well huff and puff, and water flooding development techniques with well pattern design in spatial structure, changed intensity water injection, water plugging and channel blocking as the core;(5) drilling and completion techniques, acid fracturing techniques and its production increasing techniques. To realize the efficient development of carbonate oil and gas reservoirs, researches in four aspects need to be done:(1) complex reservoir description technology with higher accuracy;(2) various enhanced oil recovery techniques;(3) improving the drilling method and acid fracturing method for ultra-deep carbonate reservoir and significantly cutting engineering cost;(4) strengthening the technological integration of information, big data, cloud computation, and artificial intelligence in oilfield development to realize the smart development of oilfield.展开更多
Gas production from hydrate reservoir by the combination of warm water flooding and depressurization is proposed,which can overcome the deficiency of single production method.Based on the combination production method...Gas production from hydrate reservoir by the combination of warm water flooding and depressurization is proposed,which can overcome the deficiency of single production method.Based on the combination production method,the physical and mathematical models are developed to simulate the hydrate dissociation.The mathematical model can be used to analyze the effects of the flow of multiphase fluid,the kinetic process of hydrate dissociation,the endothermic process of hydrate dissociation,ice-water phase equilibrium,the convection and conduction on the hydrate dissociation and gas and water production.The mechanism of gas production by the combination of warm water flooding and depressurization is revealed by the numerical simulation.The evolutions of such physical variables as pressure,temperature,saturations and gas and water rates are analyzed.Numerical results show that under certain conditions the combination method has the advantage of longer stable period of high gas rate than the single producing method.展开更多
Shaly sands reservoir is one of the most distributive types of the oil(gas)-bearing reservoirs discovered in China, and low resistivity oil(gas)-bearing reservoirs are mostly shaly sands reservoirs. Therefore, shaly s...Shaly sands reservoir is one of the most distributive types of the oil(gas)-bearing reservoirs discovered in China, and low resistivity oil(gas)-bearing reservoirs are mostly shaly sands reservoirs. Therefore, shaly sands reservoir conductive model is the key to evaluate low resistivity oil(gas)-bearing reservoirs using logging information. Some defects were found when we studied the clay distribution type conductive model, dual-water conductive model, conductive rock matrix model, etc. Some models could not distinguish the conductive path and nature of microporosity water and clay water and some models did not consider the clay distribution type and the mount of clay volume. So, we utilize the merits,overcome the defects of the above models, and put forward a new shaly sands conductive model-dual water clay matrix conductive model (DWCMCM) in which dual water is the free water and the microporosity water in shaly sands and the clay matrix(wet clay) is the clay grain containing water. DWCMCM is presented here, the advantages of which can tell the nature and conductive path from different water (microporosity water and freewater), in consid-eration of the clay distribution type and the mount of clay volume in shaly sands. So, the results of logging interpretation in the oil(gas)-bearing reservoirs in the north of Tarim Basin area, China with DWCMCM are better than those interpreted by the above models.展开更多
Flowability of gas and water through low-permeability coal plays crucial roles in coalbed methane(CBM)recovery from coal reservoirs.To better understand this phenomenon,experiments examining the displacement of water ...Flowability of gas and water through low-permeability coal plays crucial roles in coalbed methane(CBM)recovery from coal reservoirs.To better understand this phenomenon,experiments examining the displacement of water by gas under different displacement pressures were systematically carried out based on nuclear magnetic resonance(NMR)technology using low-permeability coal samples of medium-high coal rank from Yunnan and Guizhou,China.The results reveal that both the residual water content(W_(r))and residual water saturation(S_(r))of coal gradually decrease as the displacement pressure(P)decreases.When P is 0-2 MPa,the decline rates of W_(r) and S_(r) are fastest,beyond which they slow down gradually.Coal samples with higher permeability exhibit higher water flowability and larger decreases in W_(r) and S_(r).Compared with medium-rank coal,high-rank coal shows weaker fluidity and a higher proportion of irreducible water.The relationship between P and the cumulative displaced water content(W_(c))can be described by a Langmuir-like equation,W_(c)=WLP/(PL+P),showing an increase in W_(c) in coal with an increase in P.In the low-pressure stage from 0 to 2 MPa,W_(c) increases most rapidly,while in the high-pressure stage(P>2 MPa),W_(c) tends to be stable.The minimum pore diameter(d′)at which water can be displaced under different displacement pressures was also calibrated.The d′value decreases as P increases in a power relationship;i.e.,d′the coal gradually decreases with the gradual increase in P.Furthermore,the d′values of most of the coal samples are close to 20 nm under a P of 10 MPa.展开更多
It is known from macrocomparisons and microresearches of bioherm reservoirs in main sedimentary basins of the South China Sea through deep-water petroleum explorations and by means of 2D/3D seismic data and a whole-co...It is known from macrocomparisons and microresearches of bioherm reservoirs in main sedimentary basins of the South China Sea through deep-water petroleum explorations and by means of 2D/3D seismic data and a whole-coring core from the Xisha (西沙) Islands that there are great differences between deep-sea oil and gas fields in the world and those in the South China Sea,as reservoir systems of the former are mainly clastic rocks,whereas the latter have organic reefs that act as reservoirs of their largest oil and gas fields,which are represented by large Liuhua (流花) 11-1 reef oilfield in the north and super-large L reef gas field in the south of the South China Sea.Therefore,it is of great significance to study deep-water bioherm reservoirs in the South China Sea.Comparisons of organic reefs in the four large islands of the South China Sea give evidences that such reefs in main sedimentary basins came into being during Cenozoic,especially in Neogene,and mainly occur as tower (point) reef,massive reef,platform-edge reef,and patch reef in shape,which show different reservoir physical properties and seismic reflection configurations and make up carbonate rock-bioherm formations in the island reef and sedimentary basin areas.Generally,the south and north parts differ from the east and the west of the South China Sea in geologic conditions,as their corresponding continental shelf/island shelf areas are relatively wide/narrow,large stream current systems are well developed/not so well developed,and terrigenous sediments are relatively sufficient/insufficient.The southeast and south parts of the South China Sea had organic reefs built up earlier than the north and the reef building mainly took place in Neogene;these Neogene organic reefs all belong to plant algal reef rocks.Liuhua oilfield in the Pearl River Mouth basin is found to mainly have red algal bindstone,Malampaya reef in the northern Palawan basin is rich in both red algal bindstone and green algal reef segmented rock,and especially Miocene red algal framestone and green algal segmented rock are discovered in the Xisha Islands.These algal reefs created different sedimentary microfacies as well as various rock structures and types,and through recent researches on the mechanism of dolomitization,freshwater dolomite was discovered and grouped under products from dolomitization in mixed water that was regression reefal dolomite of good reservoir properties.展开更多
Gas hydrate is one kind of potential energy resources that is buried under deep seafloor or frozen areas.The first trial offshore production from the silty reservoir was conducted in the South China Sea by the China G...Gas hydrate is one kind of potential energy resources that is buried under deep seafloor or frozen areas.The first trial offshore production from the silty reservoir was conducted in the South China Sea by the China Geological Survey(CGS).During this test,there were many unique characteristics different from the sand reservoir,which was believed to be related to the clayed silt physical properties.In this paper,simulation experiments,facilities analysis,and theoretical calculation were used to confirm the hydrate structure,reservoir thermo-physical property,and bond water movement rule.And the behavior of how they affected production efficiency was analyzed.The results showed that:It was reasonable to use the structure I rather than structure II methane hydrate phase equilibrium data to make the production plan;the dissociation heat absorbed by hydrate was large enough to cause hydrate self-protection or reformation depend on the reservoir thermal transfer and gas supply;clayed silt got better thermal conductivity compared to coarse grain,but poor thermal convection especially with hydrate;clayed silt sediment was easy to bond water,but the irreducible water can be exchanged to free water under high production pressure,and the most obvious pressure range of water increment was 1.9–4.9 MPa.展开更多
文摘The BZ 34-1 oilfield is a typical gas cap edge water reservoir in the Bohai oilfield. The main characteristics of the oilfield were multi-phase sand body stacking and the sand body was composed of three parts: gas cap, oil reservoir, and edge water. The actual production site results show that the permeability difference of multi-layer sand bodies has a serious impact on the development effect. This article establishes a typical reservoir model numerical model based on the total recovery degree of the reservoir and the recovery degree of each layer, and analyzes the impact of permeability gradient. As the permeability gradient increases, the total recovery degree of all four well patterns decreases, and the total recovery degree gradually decreases. The recovery degree of low permeability layers gradually decreases, and the recovery degree of high permeability layers gradually increases. As the permeability gradient increases, the degree of recovery gradually decreases under different water contents. As the permeability gradient increases, the reduction rate of remaining oil saturation in low permeability layers is slower, while the reduction rate of remaining oil saturation in high permeability layers was faster. By analyzing the impact of permeability gradient on the development effect of oil fields, we could further deepen our understanding of gas cap edge water reservoirs and guide the development of this type of oil field.
文摘For thin oil rim reservoir with gas cap and edge water, it is helpful to improve the development effect to find out the distribution law of remaining oil in this kind of reservoirs. For this reason, taking the narrow oil rim reservoir with gas cap and edge water of Oilfield A in Bohai Sea as a case, the main controlling factors, including reservoir structure, fault, gas cap energy, edge water energy and well pattern, affecting the distribution of residual oil in this kind of reservoir were analyzed by using the data of core, logging, paleogeomorphology and production. Then, the distribution law of remaining oil was summarized. Generally, the remaining oil distribution is mainly potato-shaped or strip-shaped in plane. Vertically, it depends on the energy of gas cap and edge water. For the reservoir with big gas gap and weak edge water, the remaining oil mainly lies in the bottom of oil column. And for the reservoir with small gas gap and strong edge water, the remaining oil mainly locates at the top of oil column. Aiming at different distribution modes of remaining oil, the corresponding potential tapping strategies of horizontal wells are put forward: in the late stage of development, for the reservoir with big gas gap and weak edge water, the remaining oil concentrates at the bottom of the oil column, and the position of horizontal well should be placed at the lower 1/3 to the lower 1/5 of the oil column;for the reservoir with small gas cap and strong edge water, the remaining oil locates at the top of the oil column, and the position of horizontal well should be put at the upper 1/5 to the upper 1/3 of the oil column height, vertically. Based on the study on remaining oil of Oilfield A, a potential tapping strategy of well pattern thickening and vertical position optimization of horizontal well was proposed. This strategy guided the efficient implementation of the comprehensive adjustment plan of the oilfield. Moreover, 18 infill development wells were implemented in Oilfield A, and the average production of the infill wells is 2.1 times that of the surrounding old wells. It is estimated that the ultimate recovery factor of the oilfield will reach 33.9%, which is 2.3% higher than that before infilling wells. This study can be used for reference in the development of similar reservoirs.
基金supported by the Jiangsu Natural Science Foundation project(SBK2021045820)the Chongqing Natural Science Foundation general Project(cstc2021jcyj-msxmX0624)+1 种基金the Graduate Innovation Program of China University of Mining and Technology(2022WLKXJ002)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX22_2600).
文摘The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The chemical properties of reservoir water are very important for reservoir evaluation and are significant indicators of the sealing of reservoir oil and gas resources.Therefore,the caprock of the Chang 6 reservoir in the Yanchang Formation was evaluated.The authors tested and analyzed the chemical characteristics of water samples selected from 30 wells in the Chang 6 reservoir of Ansai Oilfield in the Ordos Basin.The results show that the Chang 6 reservoir water in Ansai Oilfield is dominated by calcium-chloride water type with a sodium chloride coefficient of generally less than 0.5.The chloride magnesium coefficients are between 33.7 and 925.5,most of which are greater than 200.The desulfurization coefficients range from 0.21 to 13.4,with an average of 2.227.The carbonate balance coefficients are mainly concentrated below 0.01,with an average of 0.008.The calcium and magnesium coefficients are between 0.08 and 0.003,with an average of 0.01.Combined with the characteristics of the four-corner layout of the reservoir water,the above results show that the graphics are basically consistent.The study indicates that the Chang 6 reservoir in Ansai Oilfield in the Ordos Basin is a favorable block for oil and gas storage with good sealing properties,great preservation conditions of oil and gas,and high pore connectivity.
基金supported by the National Science Foundation (51904324, 51674279, 51804328)the Major National Science and Technology Project (2017ZX05009-001, 2017ZX05072)+3 种基金the Key Research and Development Program (2018GSF116004)the China Postdoctoral Science Foundation (2019T120616)the Funding for Scientific Research of China University of Petroleum East China (YJ20170013)Graduate Innovative Engineering project (YCX2019023)。
文摘The irreducible water saturation(Swir) is a significant parameter for relative permeability prediction and initial hydrocarbon reserves estimation.However,the complex pore structures of the tight rocks and multiple factors of the formation conditions make the parameter difficult to be accurately predicted by the conventional methods in tight gas reservoirs.In this study,a new model was derived to calculate Swir based on the capillary model and the fractal theory.The model incorporated different types of immobile water and considered the stress effect.The dead or stationary water(DSW) was considered in this model,which described the phenomena of water trapped in the dead-end pores due to detour flow and complex pore structures.The water film,stress effect and formation temperature were also considered in the proposed model.The results calculated by the proposed model are in a good agreement with the experimental data.This proves that for tight sandstone gas reservoirs the Swir calculated from the new model is more accurate.The irreducible water saturation calculated from the new model reveals that Swir is controlled by the critical capillary radius,DSW coefficient,effective stress and formation temperature.
文摘As we all know, cyclic gas injection is one of the most effective development methods to improve condensate oil recovery. When dealing with the calculation of the reserves, the injection-production differences and water influx create great influence on the accuracy. Based on the existing research, we proposed a new material balance equation which considered the differences of composition between produced and injected fluids and the effect of water influx, and a solution was provided in this paper. The results of the method are closer to the actual situation because they are built on the law of conservation of mass, and the using of curve fitting method can not only avoid the use of water influx coefficient but also obtain the water influx rate and reserves at the same time. The YH-23 gas condensate reservoir is taking as a typical subject to do the research, which has been exploited by cycle gas injection for 14 years. Three different methods are used to calculate the reserves, and the results show that the method proposed in this paper has minimum error of 2.96%.
文摘The studies of water, gas and isotope chemistry indicate that the formation of geothermal water in the Henjing area is not related to the magmatic and volcanic sources. The geothermal water mainly derives from the meteoric source, and the gas components originate from the mixing of meteoric, crustal and mantle sources. Moreover, the geothermal water is in a low to moderate temperature geothermal reservoir. The results calculated by the quartz geothermometer and the silicaenthalpy diagram demonstrate that the lowest temperature of geothermal reservoir is in the range 78℃ to 134 ℃ and the highest temperature is in the range 95℃C to 155℃. Based on isotopic data, the possible elevation of recharge water is about 337. 5 m to 743. 6 m, which corresponds to the Wunizhang area.
基金Supported by the China National Science and Technology Major Project(2016ZX05062)the PetroChina Science and Technology Major Project(2016E-0611)
文摘Marine shale gas resources have great potential in the south of the Sichuan Basin in China.At present,the high-quality shale gas resources at depth of 2000–3500 m are under effective development,and strategic breakthroughs have been made in deeper shale gas resources at depth of 3500–4500 m.To promote the effective production of shale gas in this area,this study examines key factors controlling high shale gas production and presents the next exploration direction in the southern Sichuan Basin based on summarizing the geological understandings from the Lower Silurian Longmaxi Formation shale gas exploration combined with the latest results of geological evaluation.The results show that:(1)The relative sea depth in marine shelf sedimentary environment controls the development and distribution of reservoirs.In the relatively deep water area in deep-water shelf,grade-I reservoirs with a larger continuous thickness develop.The relative depth of sea in marine shelf sedimentary environment can be determined by redox conditions.The research shows that the uranium to thorium mass ratio greater than 1.25 indicates relatively deep water in anoxic reduction environment,and the uranium to thorium mass ratio of 0.75–1.25 indicates semi-deep water in weak reduction and weak oxidation environment,and the uranium to thorium mass ratio less than 0.75 indicates relatively shallow water in strong oxidation environment.(2)The propped fractures in shale reservoirs subject to fracturing treatment are generally 10–12 m high,if grade-I reservoirs are more than 10 m in continuous thickness,then all the propped section would be high-quality reserves;in this case,the longer the continuous thickness of penetrated grade-I reservoirs,the higher the production will be.(3)The shale gas reservoirs at 3500–4500 m depth in southern Sichuan are characterized by high formation pressure,high pressure coefficient,well preserved pores,good pore structure and high proportion of free gas,making them the most favorable new field for shale gas exploration;and the pressure coefficient greater than 1.2 is a necessary condition for shale gas wells to obtain high production.(4)High production wells in the deep shale gas reservoirs are those in areas where Long11-Long13 sub-beds are more than 10 m thick,with 1500 m long horizontal section,grade-I reservoirs penetration rate of over 90%,and fractured by dense cutting+high intensity sand injection+large displacement+large liquid volume.(5)The relatively deep-water area in the deep-water shelf and the area at depth of 3500–4500 m well overlap in the southern Sichuan,and the overlapping area is the most favorable shale gas exploration and development zones in the southern Sichuan in the future.With advancement in theory and technology,annual shale gas production in the southern Sichuan is expected to reach 450×108 m3.
基金Supported by the National Science and Technology Major Project(2016ZX05003-002)Scientific Research Project of Petro China Company Limited(2016E-0601)
文摘Large-scale gas accumulation areas in large oil-gas basins in central and Western China have multiple special accumulation mechanisms and different accumulation effects.Based on the geological theory and method of natural gas reservoir formation,this study examined the regional geological and structural background,formation burial evolution,basic characteristics of gas reservoirs,and fluid geology and geochemistry of typical petroliferous basins.The results show that the geological processes such as structural pumping,mudstone water absorption,water-soluble gas degasification and fluid sequestration caused by uplift and denudation since Himalayan stage all can form large-scale gas accumulation and different geological effects of gas accumulation.For example,the large-scale structural pumping effect and fluid sequestration effect are conducive to the occurrence of regional ultra-high pressure fluid and the formation of large-scale ultra-high pressure gas field;mudstone water absorption effect in the formation with low thickness ratio of sandstone to formation is conducive to the development of regional low-pressure and water free gas reservoir;the water-soluble gas degasification effect in large-scale thick sandstone can not only form large-scale natural gas accumulation;moreover,the degasification of water-soluble gas produced by the lateral migration of formation water will produce regional and regular isotopic fractionation effect of natural gas,that is,the farther the migration distance of water-soluble gas is,the heavier the carbon isotopic composition of methane formed by the accumulation.
文摘Vast amounts of world oil reservoirs are in natural fractured reservoirs. There are different methods for increasing recovery from fractured reservoirs. Miscible injection of water alternating CO2?is a good choice among EOR methods. In this method, water and CO2?slugs are injected alternatively in reservoir as miscible agent into reservoir. This paper studies water injection scenario and miscible injection of water and CO2?in a two dimensional, inhomogeneous fractured reservoir. The results show that miscible water alternating CO2?gas injection leads to 3.95% increase in final oil recovery and total water production decrease of 3.89% comparing to water injection scenario.
文摘Although significant amount of H_(2)S(sour gas)rich natural gas is estimated globally,but not much attention has been given to the application of H_(2)S in the oil recovery process.Recent studies on the use of H_(2)S in oil recovery processes showed that H_(2)S has the potential of improving the oil recovery,and it can be even more effective than using CO_(2) in some processes.H_(2)S can equally dissolve in the water,react with the reservoir rock to change its surface charge,porosity,and permeability.However,previous in-vestigations on H_(2)S oil recovery attributed the improved oil recoveries to the higher miscibility of H_(2)S in the oil,and the reduction in the oil viscosity.Therefore,there is limited understanding on the H_(2)S-oil-brine-rock geochemical interactions,and how they impact the oil recovery process.This study aims to investigate the interactions between H_(2)S,oil,and carbonate formations,and to assess how the combi-nation of H_(2)S and low salinity water can impact the wettability and porosity of the reservoirs.A triple layer surface complexation model was used to understand the influence of key parameters(e.g.,pressure,brine salinity,and composition)on the H_(2)S-brine-oil-rock interactions.Moreover,the effects of mineral content of the carbonate rock on H_(2)S interactions were studied.Thereafter,the results of the H_(2)S-oil-brine-rock interactions were compared with a study where CO_(2) was used as the injected gas.Results of the study showed that the seawater and its diluted forms yielded identicalζ-potential values of about 3.31 mV at a pH of 3.24.This indicates that at very low pH condition,pH controls the ζ-potential of the oil-brine interface regardless of the brine's ionic strength.The study further demonstrated that the presence of other minerals in the carbonate rock greatly reduced the calcite dissolution.For instance,the calcite dissolution was reduced by 4.5%when anhydrite mineral was present in the carbonate rock.Findings from the simulation also indicated that CO_(2) produced negative ζ-potential values for the car-bonate rocks,and these values were reduced by 18.4%-20% when H_(2)S was used as the gas phase.This implies that the H_(2)S shifted the carbonate rockζ-potentials towards positive.The outcomes of this study can be applied when designing CO_(2) flooding and CO_(2) storage where the gas stream contains H_(2)S gas since H_(2)S greatly influences the dissolution of the carbonate mineral.
基金Supported by the National Science and Technology Major Project of China(2016ZX05047,2016ZX05015)the National Basic Research Program of China(973 Program)(014CB239000)
文摘The development of natural gas in China has entered a golden and leap-forward stage, which is a necessary bridge to clean energy. This in-depth study on the status quo, theory, technology and prospect of natural gas development shows:(1) The global remaining proven recoverable reserves of natural gas are 186×1012 m3, and the reserves-production ratio is 52.4, indicating a solid resource base for long-term and rapid development.(2) Ten formation and distribution laws of conventional and unconventional natural gas reservoirs have been proposed. In terms of exploration geology, the theory of conventional "monolithic" giant gas fields with different gas sources, and an unconventional gas accumulation theory with continuous distribution of "sweet areas" in different lithologic reservoirs have been established; in terms of development geology, a development theory of conventional structural gas reservoirs is oriented to "controlling water intrusion", while a development theory of unconventional gas is concentrated on man-made gas reservoirs.(3) With the geological resources(excluding hydrates) of 210×1012 m3 and the total proven rate of the resources less than 2% at present, the natural gas in China will see a constant increase in reserve and production; by 2030, the proven geological reserves of natural gas are expected to reach about(6 000-7 000)×108 m3, the production of conventional and unconventional natural gas each will reach about 1 000×108 m3, and the gas consumption will reach 5 500×108 m3. The dependence on imported natural gas may be 64% by 2030, and 70% by 2050.(4) Ten measures for future development of natural gas have been proposed, including strengthening exploration in large-scale resource areas, increasing the development benefits of unconventional gas, and enhancing the peak adjusting capacity of gas storage and scale construction of liquified natural gas.
文摘Through analyzing the development of large ultra-deep structural gas fields in China,strategies for the efficient development of such gas fields are proposed based on their geological characteristics and production performance.According to matrix properties,fracture development degree and configuration between matrix and fractures,the reservoirs are classified into three types:single porosity single permeability system,dual porosity dual permeability system,and dual porosity single permeability system.These three types of gas reservoirs show remarkable differences in different scales of permeability,the ratio of dynamic reserves to volumetric reserves and water invasion risk.It is pointed out that the key factors affecting development efficiency of these gas fields are determination of production scale and rapid identification of water invasion.Figuring out the characteristics of the gas fields and working out pertinent technical policies are the keys to achieve efficient development.The specific strategies include reinforcing early production appraisal before full scale production by deploying high precision development seismic survey,deploying development appraisal wells in batches and scale production test to get a clear understanding on the structure,reservoir type,distribution pattern of gas and water,and recoverable reserves,controlling production construction pace to ensure enough evaluation time and accurate evaluation results in the early stage,in line with the development program made according to the recoverable reserves,working out proper development strategies,optimizing pattern and proration of wells based on water invasion risk and gas supply capacity of matrix,and reinforcing research and development of key technologies.
基金Supported by the China National Science and Technology Major Project(2016ZX05014)
文摘Carbonate reservoirs in China have the characteristics of diversified accumulation pattern, complex structure and varying reservoir conditions. Concerning these characteristics, this article tracks the technical breakthroughs and related practices since the 1950 s, summarizes the developed theory and technologies of carbonate reservoir development, analyzes their adaptability and problems, and proposes their development trend. The following theory and technologies have come into being:(1) carbonate reservoir formation mechanisms and compound flow mechanisms in complex medium;(2) reservoir identification and description technologies based on geophysics and discrete fracture-vuggy modeling method;(3) well testing analysis technology and numerical simulation method of coupling free flow and porous media flow;(4) enhanced oil recovery techniques for nitrogen single well huff and puff, and water flooding development techniques with well pattern design in spatial structure, changed intensity water injection, water plugging and channel blocking as the core;(5) drilling and completion techniques, acid fracturing techniques and its production increasing techniques. To realize the efficient development of carbonate oil and gas reservoirs, researches in four aspects need to be done:(1) complex reservoir description technology with higher accuracy;(2) various enhanced oil recovery techniques;(3) improving the drilling method and acid fracturing method for ultra-deep carbonate reservoir and significantly cutting engineering cost;(4) strengthening the technological integration of information, big data, cloud computation, and artificial intelligence in oilfield development to realize the smart development of oilfield.
基金financially supported by the National High Technology Research and Development Program of China (863 Program) (Grant No. 2006AA09A209)the National Basic Research Program of China (Grant No. 2009CB219507)
文摘Gas production from hydrate reservoir by the combination of warm water flooding and depressurization is proposed,which can overcome the deficiency of single production method.Based on the combination production method,the physical and mathematical models are developed to simulate the hydrate dissociation.The mathematical model can be used to analyze the effects of the flow of multiphase fluid,the kinetic process of hydrate dissociation,the endothermic process of hydrate dissociation,ice-water phase equilibrium,the convection and conduction on the hydrate dissociation and gas and water production.The mechanism of gas production by the combination of warm water flooding and depressurization is revealed by the numerical simulation.The evolutions of such physical variables as pressure,temperature,saturations and gas and water rates are analyzed.Numerical results show that under certain conditions the combination method has the advantage of longer stable period of high gas rate than the single producing method.
基金National Natural Science Foundation of China (Grant No.49474235) and Northwest Petroleum Company (CNSPC) Foundation of China (Grant No. 9806). We thank Science & Technology Department and Well Logging Center of Northwest Petroleum Company of China for
文摘Shaly sands reservoir is one of the most distributive types of the oil(gas)-bearing reservoirs discovered in China, and low resistivity oil(gas)-bearing reservoirs are mostly shaly sands reservoirs. Therefore, shaly sands reservoir conductive model is the key to evaluate low resistivity oil(gas)-bearing reservoirs using logging information. Some defects were found when we studied the clay distribution type conductive model, dual-water conductive model, conductive rock matrix model, etc. Some models could not distinguish the conductive path and nature of microporosity water and clay water and some models did not consider the clay distribution type and the mount of clay volume. So, we utilize the merits,overcome the defects of the above models, and put forward a new shaly sands conductive model-dual water clay matrix conductive model (DWCMCM) in which dual water is the free water and the microporosity water in shaly sands and the clay matrix(wet clay) is the clay grain containing water. DWCMCM is presented here, the advantages of which can tell the nature and conductive path from different water (microporosity water and freewater), in consid-eration of the clay distribution type and the mount of clay volume in shaly sands. So, the results of logging interpretation in the oil(gas)-bearing reservoirs in the north of Tarim Basin area, China with DWCMCM are better than those interpreted by the above models.
基金Financial support for this work was provided by the National Natural Science Foundation of China(Grant No.41772155)the Advanced Basic Research Projects of China National Petroleum Corporation(2019B-4910).
文摘Flowability of gas and water through low-permeability coal plays crucial roles in coalbed methane(CBM)recovery from coal reservoirs.To better understand this phenomenon,experiments examining the displacement of water by gas under different displacement pressures were systematically carried out based on nuclear magnetic resonance(NMR)technology using low-permeability coal samples of medium-high coal rank from Yunnan and Guizhou,China.The results reveal that both the residual water content(W_(r))and residual water saturation(S_(r))of coal gradually decrease as the displacement pressure(P)decreases.When P is 0-2 MPa,the decline rates of W_(r) and S_(r) are fastest,beyond which they slow down gradually.Coal samples with higher permeability exhibit higher water flowability and larger decreases in W_(r) and S_(r).Compared with medium-rank coal,high-rank coal shows weaker fluidity and a higher proportion of irreducible water.The relationship between P and the cumulative displaced water content(W_(c))can be described by a Langmuir-like equation,W_(c)=WLP/(PL+P),showing an increase in W_(c) in coal with an increase in P.In the low-pressure stage from 0 to 2 MPa,W_(c) increases most rapidly,while in the high-pressure stage(P>2 MPa),W_(c) tends to be stable.The minimum pore diameter(d′)at which water can be displaced under different displacement pressures was also calibrated.The d′value decreases as P increases in a power relationship;i.e.,d′the coal gradually decreases with the gradual increase in P.Furthermore,the d′values of most of the coal samples are close to 20 nm under a P of 10 MPa.
基金supported by the National Natural Science Foundation of China (Nos.49206061 and 41106064)the Major National Oil and Gas Special Programs (Nos.2008ZX05025-03 and 2011ZX05025-002)the 973 Program of China (No.2012CB956004)
文摘It is known from macrocomparisons and microresearches of bioherm reservoirs in main sedimentary basins of the South China Sea through deep-water petroleum explorations and by means of 2D/3D seismic data and a whole-coring core from the Xisha (西沙) Islands that there are great differences between deep-sea oil and gas fields in the world and those in the South China Sea,as reservoir systems of the former are mainly clastic rocks,whereas the latter have organic reefs that act as reservoirs of their largest oil and gas fields,which are represented by large Liuhua (流花) 11-1 reef oilfield in the north and super-large L reef gas field in the south of the South China Sea.Therefore,it is of great significance to study deep-water bioherm reservoirs in the South China Sea.Comparisons of organic reefs in the four large islands of the South China Sea give evidences that such reefs in main sedimentary basins came into being during Cenozoic,especially in Neogene,and mainly occur as tower (point) reef,massive reef,platform-edge reef,and patch reef in shape,which show different reservoir physical properties and seismic reflection configurations and make up carbonate rock-bioherm formations in the island reef and sedimentary basin areas.Generally,the south and north parts differ from the east and the west of the South China Sea in geologic conditions,as their corresponding continental shelf/island shelf areas are relatively wide/narrow,large stream current systems are well developed/not so well developed,and terrigenous sediments are relatively sufficient/insufficient.The southeast and south parts of the South China Sea had organic reefs built up earlier than the north and the reef building mainly took place in Neogene;these Neogene organic reefs all belong to plant algal reef rocks.Liuhua oilfield in the Pearl River Mouth basin is found to mainly have red algal bindstone,Malampaya reef in the northern Palawan basin is rich in both red algal bindstone and green algal reef segmented rock,and especially Miocene red algal framestone and green algal segmented rock are discovered in the Xisha Islands.These algal reefs created different sedimentary microfacies as well as various rock structures and types,and through recent researches on the mechanism of dolomitization,freshwater dolomite was discovered and grouped under products from dolomitization in mixed water that was regression reefal dolomite of good reservoir properties.
基金funded by the National Key Research and Development Program of China(2017YFC0307600)the China Geological Survey Program(DD20190231).
文摘Gas hydrate is one kind of potential energy resources that is buried under deep seafloor or frozen areas.The first trial offshore production from the silty reservoir was conducted in the South China Sea by the China Geological Survey(CGS).During this test,there were many unique characteristics different from the sand reservoir,which was believed to be related to the clayed silt physical properties.In this paper,simulation experiments,facilities analysis,and theoretical calculation were used to confirm the hydrate structure,reservoir thermo-physical property,and bond water movement rule.And the behavior of how they affected production efficiency was analyzed.The results showed that:It was reasonable to use the structure I rather than structure II methane hydrate phase equilibrium data to make the production plan;the dissociation heat absorbed by hydrate was large enough to cause hydrate self-protection or reformation depend on the reservoir thermal transfer and gas supply;clayed silt got better thermal conductivity compared to coarse grain,but poor thermal convection especially with hydrate;clayed silt sediment was easy to bond water,but the irreducible water can be exchanged to free water under high production pressure,and the most obvious pressure range of water increment was 1.9–4.9 MPa.
