The primary purpose of underground gas storages is to provide gas for seasonal consumptions or strategic reserve.The periodical operations of gas injection and extraction lead to cyclic loading on the walls and surrou...The primary purpose of underground gas storages is to provide gas for seasonal consumptions or strategic reserve.The periodical operations of gas injection and extraction lead to cyclic loading on the walls and surrounding rocks of gas storages.To investigate the mechanical behaviors of different host rocks in bedded salt deposit,laboratory experiments were conducted on the samples of rock salt,thenardite,glauberite and gypsum.The mechanical properties of rock samples under monotonic and cyclic loadings were studied.Testing results show that,under monotonic loading,the uniaxial compressive stress（UCS） of glauberite is the largest（17.3 MPa）,while that of rock salt is the smallest（14.0 MPa）.The UCSs of thenardite and gypsum are 16.3 and 14.6 MPa,respectively.The maximum strain at the peak strength of rock salt（halite） is much greater than those of the other three rocks.The elastic moduli of halite,thenardite,glauberite and gypsum are 3.0,4.2,5.1 and 6.8 GPa,respectively.Under cyclic loading,the peak strengths of the rock specimens are deteriorated except for rock salt.The peak strengths of thenardite,glauberite and gypsum decrease by 33.7%,19.1% and 35.5%,respectively;and the strains of the three rocks at the peak strengths are almost the same.However,the strain of rock salt at the peak strength increases by 1.98%,twice more than that under monotonic loading.Under monotonic loading,deformation of the tested rock salt,thenardite and glauberite shows in an elastoplastic style.However,it changes to a ductile style under cyclic loading.Brittle deformation and failure are only observed for gypsum.The results should be helpful for engineering design and operation of gas storage in bedded salt deposit.展开更多
A tracking algorithm based on improved Camshift and UKF is proposed in this paper to deal with the problems which exist in traditional Camshift algorithm, such as artificial orientation and tracking failure under colo...A tracking algorithm based on improved Camshift and UKF is proposed in this paper to deal with the problems which exist in traditional Camshift algorithm, such as artificial orientation and tracking failure under color interference as well as object’s changed illumination occlusion. Meanwhile, in order to solve the sheltered problem, the UKF is combined with improved Camshift algorithm to predict the position of the target effectively. Experiment results show that the proposed algorithm can avoid the interference of the background color and solve the sheltered problem of the object, so that achieving a precise and timely tracking of moving objects. Also it has better robustness to color noises and occlusion when the object’s scale changes and deformation occurs.展开更多
Injection-induced fracture reactivation during hydraulic fracturing processes in shale gas development as well as coal bed methane(CBM)and other unconventional oil and gas recovery is widely investigated because of po...Injection-induced fracture reactivation during hydraulic fracturing processes in shale gas development as well as coal bed methane(CBM)and other unconventional oil and gas recovery is widely investigated because of potential permeability enhancement impacts.Less attention is paid to induced fracture reactivation during oil and gas production and its impacts on reservoir permeability,despite its relatively common occurrence.During production,a reservoir tends to shrink as effective stresses increase,and the deviatoric effective stresses also increase.These changes in the principal effective stresses may cause Coulomb fracture slip in existing natural fractures,depending on their strength,orientation,and initial stress conditions.In this work,an extended finite element model with contact constraints is used to investigate different fracture slip scenarios induced by general reservoir pressure depletion.The numerical experiments assess the effect of Young’s modulus,the crack orientation,and the frictional coefficient of the crack surface on the distribution of stress and displacement after some reservoir depletion.Results show that the crack orientation significantly affects the state of stress and displacement,particularly in the vicinity of the crack.Slip can only occur in permitted directions,as determined by the magnitudes of the principal stresses and the frictional coefficient.Lastly,a larger frictional coefficient(i.e.,a rougher natural fracture surface)makes the crack less prone to shear slip.展开更多
基金Supported by the Program for New Century Excellent Talents in University of China (NCET-07-0594)the National Natural Science Foundation of China (50874078 and 50804033)the Special Support for National Excellent Ph.D.Thesis (200959)
文摘The primary purpose of underground gas storages is to provide gas for seasonal consumptions or strategic reserve.The periodical operations of gas injection and extraction lead to cyclic loading on the walls and surrounding rocks of gas storages.To investigate the mechanical behaviors of different host rocks in bedded salt deposit,laboratory experiments were conducted on the samples of rock salt,thenardite,glauberite and gypsum.The mechanical properties of rock samples under monotonic and cyclic loadings were studied.Testing results show that,under monotonic loading,the uniaxial compressive stress（UCS） of glauberite is the largest（17.3 MPa）,while that of rock salt is the smallest（14.0 MPa）.The UCSs of thenardite and gypsum are 16.3 and 14.6 MPa,respectively.The maximum strain at the peak strength of rock salt（halite） is much greater than those of the other three rocks.The elastic moduli of halite,thenardite,glauberite and gypsum are 3.0,4.2,5.1 and 6.8 GPa,respectively.Under cyclic loading,the peak strengths of the rock specimens are deteriorated except for rock salt.The peak strengths of thenardite,glauberite and gypsum decrease by 33.7%,19.1% and 35.5%,respectively;and the strains of the three rocks at the peak strengths are almost the same.However,the strain of rock salt at the peak strength increases by 1.98%,twice more than that under monotonic loading.Under monotonic loading,deformation of the tested rock salt,thenardite and glauberite shows in an elastoplastic style.However,it changes to a ductile style under cyclic loading.Brittle deformation and failure are only observed for gypsum.The results should be helpful for engineering design and operation of gas storage in bedded salt deposit.
文摘A tracking algorithm based on improved Camshift and UKF is proposed in this paper to deal with the problems which exist in traditional Camshift algorithm, such as artificial orientation and tracking failure under color interference as well as object’s changed illumination occlusion. Meanwhile, in order to solve the sheltered problem, the UKF is combined with improved Camshift algorithm to predict the position of the target effectively. Experiment results show that the proposed algorithm can avoid the interference of the background color and solve the sheltered problem of the object, so that achieving a precise and timely tracking of moving objects. Also it has better robustness to color noises and occlusion when the object’s scale changes and deformation occurs.
文摘Injection-induced fracture reactivation during hydraulic fracturing processes in shale gas development as well as coal bed methane(CBM)and other unconventional oil and gas recovery is widely investigated because of potential permeability enhancement impacts.Less attention is paid to induced fracture reactivation during oil and gas production and its impacts on reservoir permeability,despite its relatively common occurrence.During production,a reservoir tends to shrink as effective stresses increase,and the deviatoric effective stresses also increase.These changes in the principal effective stresses may cause Coulomb fracture slip in existing natural fractures,depending on their strength,orientation,and initial stress conditions.In this work,an extended finite element model with contact constraints is used to investigate different fracture slip scenarios induced by general reservoir pressure depletion.The numerical experiments assess the effect of Young’s modulus,the crack orientation,and the frictional coefficient of the crack surface on the distribution of stress and displacement after some reservoir depletion.Results show that the crack orientation significantly affects the state of stress and displacement,particularly in the vicinity of the crack.Slip can only occur in permitted directions,as determined by the magnitudes of the principal stresses and the frictional coefficient.Lastly,a larger frictional coefficient(i.e.,a rougher natural fracture surface)makes the crack less prone to shear slip.
