准噶尔盆地腹部侏罗系深部优质储层成因

Origin of Jurassic deep burial high-quality reservoirs in the central Junggar Basin

准噶尔盆地腹部侏罗系主要发育辫状河、三角洲和湖泊等沉积相类型,其岩石类型以成分成熟度低的岩屑砂岩和长石质岩屑砂岩为主,压实作用是控制储层质量的主要成岩作用。通过铸体薄片和物性资料综合分析,认为准噶尔盆地莫索湾地区在埋深3 500～4 500m发育孔隙度和渗透率较高的优质砂岩储层带,且此深部优质储层带是原生孔隙带,而非次生溶蚀孔隙带。结合测井资料分析,认为莫索湾地区存在欠压实带,该区莫13井、莫15井、盆5井等在欠压实带均表现出高声波时差、低视电阻率等异常。该区欠压实引起的异常高压大大削弱了正常压实作用对深部地层的影响,是造成该区深部优质储层发育的主要原因。研究区欠压实砂岩储层分布具有明显规律,即砂泥比越低,泥岩层厚度越大,越容易发育欠压实砂岩储层。

The Jurassic system in the central Junggar Basin mainly developed various deposits including braided river,delta and lake facies,and their rocks are mainly lithic sandstones and feldspathic litharenites.Strong compaction is the most important diagenesis to control reservoir qualities in the study area.Based on comprehensive investigation of casting thin sections and physical properties of rocks,the present paper proposed that there was a high-quality sandstone reservoir zone with relatively high porosity and permeability at the depths of 3500m to 4500m in the Mosuowan region and this deep burial high-quality reservoir zone was identified as a primary porosity zone rather than a secondary dissolution porosity zone.The combination of logging data indicated that there was an uncompacted belt in the Mosuowan region and anomalies of high acoustic interval transit time and low resistivity occurred in the uncompacted belt of wells Mo-13,Mo-15 and Pen-5.Overpressure resulted from uncompaction had greatly reduced the effect of a normal compaction on deep strata,significantly resulting in the development of high-quality reservoirs in deep strata of this area.The distribution of uncompacted sandstone reservoirs in the study area showed an obvious tendency,i.e.the lower the sand-to-shale ratio,and the thicker the depth of mudstones,the more readily the uncompacted sandstone reservoirs develop.