The present study is devoted to understanding the evolution of the Upper Jurassic Sab'atayn Formation in the Marib-Shabwa Basin,Yemen,through a sequence stratigraphic analysis based on integrating datasets of sedi...The present study is devoted to understanding the evolution of the Upper Jurassic Sab'atayn Formation in the Marib-Shabwa Basin,Yemen,through a sequence stratigraphic analysis based on integrating datasets of sedimentology,seismic sections,and well logs.The Sab'atayn Formation(Tithonian age)is represented by a series of clastic and evaporites that were deposited under fluvio-deltaic to prodeltaic settings.It is divided into four members including Yah(at the base),upwards to Seen,Alif,and Safir at the top.Two third-order depositional sequences were determined for the Tithonian succession which were separated by three sequence boundaries.These sequences were classified into their systems tracts signifying several sedimentation patterns of progradational,aggradational,and retrogradational parasequence sets.The first depositional sequence corresponds to the early-middle Tithonian Yah and Seen units that can be classified into lowstand,transgressive,and highstand systems tracts.The second sequence comprises the late Tithonian Alif unit that can be subdivided into transgressive and highstand systems tracts.The sandy deposits of the Alif Member(highstand deposits)represent the most productive hydrocarbon reservoir in the basin.The Upper Jurassic sediments in the study area were resulted from a combination of eustatic and tectonic effects.展开更多
Log-analysts typically distinguish three types of shale distribution in clastic reservoirs,that is,laminated,dispersed and structural distribution,which tend to influence the effective porosity and permeability of res...Log-analysts typically distinguish three types of shale distribution in clastic reservoirs,that is,laminated,dispersed and structural distribution,which tend to influence the effective porosity and permeability of reservoirs.The Alif Member is made up of sandstone interbedded with some shale,with shale dominating on top and at the bottom.In sedimentary formations,the gamma ray log normally reflects the shale content.The gamma ray log and neutron-density porosity crossplot is used to estimate a reservoir's shale volume(Vsh),according to which the Alif Member is divided into three zones.In addition,shale types are recognized by neutron-density porosity crossplot,and the correlation coefficients of gamma ray log-based Vsh and neutron-density porosity-based Vsh are suggested to be reliable.The Vsh and shale types of the three zones are compared against the reservoir's potential to yield hydrocarbons.The major oil intervals mainly concentrate in shaly sand and sandstone zones of dispersed and laminated shale types.The third zone,the lowermost interval,contains pure shale of laminated type and is considered out of reservoir standards in hydrocarbon production due to its excessive shale volume.Quantitative assessment of shale type distribution and Vsh by crossplot approach could not furnish correct information to evaluate massive shale intervals.展开更多
文摘The present study is devoted to understanding the evolution of the Upper Jurassic Sab'atayn Formation in the Marib-Shabwa Basin,Yemen,through a sequence stratigraphic analysis based on integrating datasets of sedimentology,seismic sections,and well logs.The Sab'atayn Formation(Tithonian age)is represented by a series of clastic and evaporites that were deposited under fluvio-deltaic to prodeltaic settings.It is divided into four members including Yah(at the base),upwards to Seen,Alif,and Safir at the top.Two third-order depositional sequences were determined for the Tithonian succession which were separated by three sequence boundaries.These sequences were classified into their systems tracts signifying several sedimentation patterns of progradational,aggradational,and retrogradational parasequence sets.The first depositional sequence corresponds to the early-middle Tithonian Yah and Seen units that can be classified into lowstand,transgressive,and highstand systems tracts.The second sequence comprises the late Tithonian Alif unit that can be subdivided into transgressive and highstand systems tracts.The sandy deposits of the Alif Member(highstand deposits)represent the most productive hydrocarbon reservoir in the basin.The Upper Jurassic sediments in the study area were resulted from a combination of eustatic and tectonic effects.
文摘Log-analysts typically distinguish three types of shale distribution in clastic reservoirs,that is,laminated,dispersed and structural distribution,which tend to influence the effective porosity and permeability of reservoirs.The Alif Member is made up of sandstone interbedded with some shale,with shale dominating on top and at the bottom.In sedimentary formations,the gamma ray log normally reflects the shale content.The gamma ray log and neutron-density porosity crossplot is used to estimate a reservoir's shale volume(Vsh),according to which the Alif Member is divided into three zones.In addition,shale types are recognized by neutron-density porosity crossplot,and the correlation coefficients of gamma ray log-based Vsh and neutron-density porosity-based Vsh are suggested to be reliable.The Vsh and shale types of the three zones are compared against the reservoir's potential to yield hydrocarbons.The major oil intervals mainly concentrate in shaly sand and sandstone zones of dispersed and laminated shale types.The third zone,the lowermost interval,contains pure shale of laminated type and is considered out of reservoir standards in hydrocarbon production due to its excessive shale volume.Quantitative assessment of shale type distribution and Vsh by crossplot approach could not furnish correct information to evaluate massive shale intervals.
