Study On Reservoir Characteristics Of The Lower Carboniferous Donghe Sandstone In The South-South Slope Of Lunnan

Based on the multidissiplinary theories,such as sedimentary petrology and reservoir geology,the core,logging and cross-hole seismic data were used to study the reservoirs characteristics of Carboniferous Donghe sandstone section of the east slope of Lunnan,Tarim Basin.Reservoir distribution characteristics in vertical and horizontal directions are described based on the analysis of petrologic feature,reservoir space type,physical properties and reservoir types,combined with the evaluation criteria.And then,the reservoir control factors,such as lithology and diagenesis etc,were used to predict the favorable areas of reservoir.The main results are as follows:The main rock types in Donghe sandstone section in the research area are the quartz sandstone,lithic quartz sandstone and lithic sandstone,etc.The main types of sedimentary facies include the alluvial fan,wave-controlled shore,tidal flat and continental shelf.The reservoir space includes the original hole,secondary hole,crack and primary intergranular pore-interparticle dissolution pore.The average porosity of the rocks in Donghe sandstone section is 9.24%on average,and the permeability characteristiced as the bimodal distribution in the permeability histogram.The permeability of front peak is between 0.01mD and 1mD,indicating the low porosity and low permeability reservoir of calcareous sandstone;The back peak is between 100mD and 500mD,indicating the middle porosity and middle permeability reservoir of medium sandstone and fine sandstone.In the study area,the reservoir types are dominated with type II and III,while there are fewer type I reservoirs.There are effective reservoirs within the pinch-out boundary of Donghe sandstone section,and the thickness of effective reservoir gradually increases towards the direction of Caohu depression.The thickness of non-effective sandstone reservoir from the Lunnan Well 48 to Cao Well 4 block is relatively large.Whereas,the thickness of effective reservoir of the sandstone in the southern and northern areas of the study area is obviously increased and well developed.The changes in effective reservoir thickness and sandstone thickness are synchronized.In the study area,the main controlling factors of sandstone reservoir of Donghe sandstone section are the deposition and diagenesis.In the sedimentation process,the coastal environment causes the poor separation of sandstone composition and weak petrophysical basis.During the diagenesis,the compaction,pressolution and cementation are the main destructive digenesis,while organic acid dissolution is the main constructive digenesis,which have incured augment of porosity 4%-9%.Combined with the main controlling factors,the reservoir distribution is predicted and the reservoir in Donghe sandstone section is divided into four types:type? to ? reservoir distributed in the area from Cao Well 3,Quema Well 4 to Lunnan Well 60 block;Cao Well 4 block is type II reservoir;type III reservoir limited within the Lunnan Well 48 to Jiefang Well 122 block.The long and narrow area between the pinch-out boundaries of stratum and sandstone in Donghe sandstone section is distributed as type IV non-reservoir.