川东南五峰组-龙马溪组深层、超深层页岩储层特征及其页岩气勘探意义

Characteristics of the deep and ultra⁃deep shale reservoirs of the Wufeng-Longmaxi formations in the southeastern Sichuan Basin and the significance of shale gas exploration

四川盆地东南地区上奥陶统五峰组—下志留统龙马溪组中深层领域页岩气勘探及页岩储层特征与主控因素的研究已经取得了丰硕成果,而作为当前页岩气勘探重点的深层、超深层领域,由于受钻井等因素的制约,对于其储层发育特征及与中深层页岩储层的差异等研究还不够深入。为了明确五峰组—龙马溪组深层、超深层页岩储层特征,为勘探部署提供依据,选取川东南地区4口埋深在2000~6000 m的典型页岩气钻井,系统开展了深层、超深层页岩储层发育特征及差异对比研究,探讨了储层孔隙发育的成因。研究表明:(1)埋深在6000 m以内,五峰组—龙马溪组页岩储层依然能够发育高孔有效储层,且随埋深的增大孔隙度无明显变化,但是有机质孔的形态、孔隙结构及连通性存在一定差异,即随着埋深的增大,有机质孔孔径相对变小,孔隙连通性变差;(2)明确了生物成因的硅质是孔隙发育的基础,流体超压是储层孔隙保持的关键,在两者联合作用下,深层、超深层页岩高孔隙优质储层得以发育和保持;(3)基于储层发育的研究,将页岩气勘探拓深至6000 m,明确了下一步页岩气勘探方向。初步评价四川盆地及周缘五峰组—龙马溪组深层、超深层页岩气(埋深为4000~5000 m)资源量超2×10^(12)m^(3)。

Fruitful achievements have been made in shale gas exploration in the middle and deep areas from the Upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation in the southeastern Sichuan Basin,and in the research on shale reservoir characteristics and main controlling factors.As the key direction of current shale exploration,the deep and ultra⁃deep areas are limited by drilling and other factors,and the research on reservoir development characteristics and differences with the middle and deep shale reservoirs is insufficient.In order to clarify the characteristics of the deep and ultra⁃deep shale reservoirs of the Wufeng-Longmaxi forma⁃tiosns,four typical shale gas wells at the depth of 2000-6000 m in the southeastern Sichuan exploration area were selected to systematically carry out a comparative study of deep and ultra⁃deep shale reservoir development characteristics and differences,and the causes of pore development were discussed.The results show that:(1)With a burial depth of less than 6000 m,the shale reservoirs of the Wufeng-Longmaxi formations are effective reservoirs with high porosity,and the porosity has no obvious change with the change of burial depth.However,there are certain differences in the morphology,structure and connectivity of organic matter pores,that is,with the increase of burial depth,the size of organic matter pores relatively decreases,and the pore connectivity deteriorates;(2)It has been clarified that biogenic silica is the foundation of pore development,and fluid overpressure is the key to maintaining reservoir pores.Under the combined action of biogenic silica and biogenic silica,the deep and ultra⁃deep shale reservoirs with high porosity and high quality can be developed and maintained;(3)Based on the research of reservoir development,shale gas exploration will be extended to 6000 m,which provides a clear direction for shale gas exploration in the next step.It is preliminarily assessed that the deep and ultra⁃deep shale gas(buried depth of 4000-5000 m)resources in the Wufeng-Longmaxi formations in the Sichuan Basin and its surrounding areas exceed 2×10^(12)m^(3).