摘要
当白云石含量超过一定范围后,白云岩孔隙度随着白云石含量增高而增大,这是否意味着白云岩化作用导致新生孔隙产生,这是值得深究的问题。选取川东北地区下三叠统飞仙关组鲕粒滩储层为对象,进行细致的岩石矿物学观察,并开展白云岩段和灰岩段对比分析工作。结果表明:当白云石含量大于40%,随着白云石含量增加,白云石的抗压实压溶作用使得鲕粒岩中压溶再沉淀成因的第三期粒间方解石胶结物含量不断减少,理应被其占据的粒间孔隙不断空出,并成为现今孔隙的主体,由此导致了岩石孔隙度与白云石含量之间的协同增长关系。由此提出,白云岩化并非为鲕粒滩储层贡献了新生孔隙,而是有效地保存了早期孔隙。研究还揭示了现今鲕粒滩体不同部位白云岩物性迥异根源于白云岩结构差异演化。沉积旋回内灰岩岩性及其分布特征的不同引发了这种白云岩结构差异演化;早期大气水淋滤对鲕粒岩结构、矿物组成以及稳定性等方面的效应是鲕粒原始结构保存与否的根本原因;重结晶和深埋藏溶蚀作用加剧原始鲕粒离散和结构破坏,趋向于形成最终的结晶云岩。
A progressive increase in dolomite content over a certain range is usually accompanied by an increase in poro-sity of dolostone.It is challenging to clarify whether dolomitization is capable of creating new pores or not,and this deserves special attention.We assessed this process in the oolitic shoal reservoirs in the Lower Triassic Feixianguan Formation in the northeastern Sichuan Basin,China,through petrographic observations and comparisons of petrologic and mine-ralogical features of the limestones and dolostones.The results show that the content of intergranular calcite cement of phase 3,the product of pressure solution and re-precipitation in oolite,continuously decreases with the increase of dolomite content after the content of dolomite exceeds 40%.Then the intergranular pore space,which was supposedly occupied by the calcite cements in the precursor lithologies,would have increased and developed into the present porosity.This observation explains well the trend of porosity increasing with dolomite content.That is,rather than creating new pores,dolomitization in the oolitic grainstone layers was more likely to have helped to preserve the early pores.We also found that the variation of petrophysical properties of the dolostones in different parts of the present oolitic shoal bodies originated from the differential evolution of dolostone fabric,which was initiated by the difference in lithologies and their distribution patterns in one depositional cycle.The effects of eogenetic freshwater infiltration on oolitic fabric,mineral composition and stability have exerted substantial influence on preservation of the original textures of the oolites.Recrystallization and deep buried dolomite dissolution further obliterated the oolites and the original fabrics of the precursor lithologies,resulting in the final crystallized dolomites.
作者
李开开
张学丰
贺训云
范俊佳
Li Kaikai;Zhang Xuefeng;He Xunyun;Fan Junjia(School of Energy Resources,China University of Geosciences(Beijing),Beijing 100083,China;Key Laboratory for Marine Reservoir Evolution and Hydrocarbon Abundance Mechanism(Ministry of Education),China University of Geosciences(Beijing),Beijing 100083, China;Institute of Oil and Gas,Peking University,Beijing 100871,China;Key Laboratory of Carbonate Reservoirs,CNPC,Hangzhou Research Institute of Geology,PetroChina,Hangzhou,Zhejiang 310023,China;Key Laboratory of Basin Structure&Hydrocarbon Accumulation,CNPC,Research Institute of Petroleum Exploration&Development,PetroChina,Beijing 100083,China)
出处
《石油与天然气地质》
EI
CAS
CSCD
北大核心
2018年第4期706-718,共13页
Oil & Gas Geology
基金
国家自然科学基金项目(41572129)
中央高校基本科研业务专项资金项目(2652017299)
关键词
鲕粒滩
白云岩结构
白云岩化
孔隙保存
飞仙关组
四川盆地
oolitic shoal
dolostone fabric
dolomitization
porosity preservation
Feixianguan Formation
Sichuan Basin
