库车坳陷迪那气田古近系裂缝发育的多样性与差异性

以岩心观察和薄片鉴定为基础，辅以扫描电镜、粘土矿物X-衍射、流体包裹体、油层物性分析等手段，结合区域地质研究成果，系统研究塔里木盆地库车坳陷迪那气田古近系低渗-特低渗砂岩储层裂缝的多样性和差异性。结果表明：宏、微观裂缝主要为构造裂缝，其余依次为溶蚀裂缝、成岩裂缝和超压裂缝。构造裂缝分为剪切裂缝、扩张裂缝和震裂缝3种主要类型（以剪切裂缝为主）和3个发育期次；其中对储集烃类最为有效的裂缝形成于晚喜马拉雅期（上新世末期，即2.6~1.81 Ma）的构造挤压作用；溶蚀裂缝、成岩裂缝与超压裂缝与油气注入引起的溶蚀作用、粘土矿物脱水收缩、强烈构造挤压、快速深埋及流体增压造成的地层超压有关，主要形成时间为库车末期至西域期（2 Ma至现今）。裂缝发育的差异性主要受岩石类型、沉积相带、单层厚度和与主控断层距离的控制。位于气田中部的水下分流河道以粉细砂岩为主，裂缝最发育，单井产能高。裂缝线密度与单层厚度呈“座椅”式负相关，随着与主控断层距离增大而减小；泥岩裂缝线密度小于0.4条/m，且与单层厚度无关。

Diversities and disparities of fracture systems in the Paleogene in DN gas field,Kuqa Depression,Tarim Basin

The diversities and disparities of fracture systems in low-and ultra-low-permeability sandstone reservoirs in the Paleogene in DN gas field of Kuqa Depression,Tarim Basin,were scrutinized through a combination of analytic means such as core and thin section observation,SEM,as well as analyses of clay mineral XRD,fluid inclusion,and physical properties of oil-bearing formations,with regional geological understanding.The results show that the fracture systems are dominated by tectonic fractures,followed successively by dissolution fractures,diagenetic fractures,and overpressured fractures.The tectonic fractures have 3 types (shear fractures,extension fractures,and seismic-related fractures) and 3 development stages.It was the late Himalayan stage (i.e.the end of Pliocene,2.6-1.81 Ma) when certain tectonic compression process generated the most favorable fractures for hydrocarbon accumulations.The formation of the other three kinds of fractures,i.e.the dissolution fractures,diagenetic fractures,and overpressured fractures,is suggested to be happening during the period from the late Kuqua to Xiyu (2Ma-present) and associated with dissolution by hydrocarbon charging,shrinkage by dehydration of clay minerals,and a formation overpressure by intensive tectonic compression,rapid burial processes and pressurized fluids.The disparities of the fracture systems are mainly controlled by rock types,sedimentary facies belts,the single layer thickness and the distance to major controlling faults.The underwater distributary channels in the central part of the gas field are dominated by silty and fine sandstone where the fractures are highly developed and well productivity is high.The linear density of fractures are found to be negatively related to the thickness of single layers (a s-shaped correlation),and decreases as the distance to the major controlling faults increases.The linear density of fractures in mudstone is less than 0.4 lines per meter and is observed to have no connection with single layer thickness.