川西坳陷洛带构造沉积成岩作用对油气聚集的控制

CONTROL OF SEDIMENTARY DIAGENESIS ON HYDROCARBON ACCUMULATION IN LUODAI STRUCTURE OF WESTERN SICHUAN DEPRESSION

油气的聚集是以储集空间为基础的,对于川西坳陷的碎屑岩储层来说,油气聚集的储集空间以孔隙为主,裂缝次之。孔隙空间的发生、发展和演化严格受沉积成岩作用的控制,而油气的聚集则取决于有利孔隙、裂隙发育的深度及部位。从川西坳陷洛带构造(J2s)所发现的气藏来看,皆具有三高一低即高致密度、高含水饱和度、高异常流体压力及低孔渗的特征。储层非均质性强,常被分隔成孤立的、独具压力系统的"储集体"。研究表明,有利的沉积作用控制着储层的展布,而差异成岩作用则控制着储层储集性能的优劣,也是形成储层非均质性的主要原因,从而导致储层在纵向上、横向上油气丰度的差异性。文中以洛带构造上沙溪庙组(J2s)为例,阐明沉积成岩作用对油气聚集的控制性,进一步查明该区有利的沉积成岩相带的展布,为预测油气的潜在分布提供重要依据。

The storage space of clastic reservoirs in western Sichuan Depression is dominated by pores with some fractures. Development and evolution of pores were strictly controlled by sedimentry diagenesis and hydrocarbon accumulation was determined by favourable depth and position of pore and fracture development. In terms of gas reservoirs in Luodai structure of western Sichuan Depression, the reservoirs were characterized by high tightness, high water saturability, high overpressure and low porosity and permeability. They were highly nonhomogeneous and were divided into isolated 'reservoir' with independent pressure system. Distribution of reservoirs was controlled by sedimentation and their quality was controlled by different diagenesis, which resulted in anisotropy and differences of hydrocarbon accumulation. Took Shaximiao formation in Luodai structure as an example, controls of sedimentary diagenesis on hydrocarbon accumulation were analyzed and favourable zones for hydrocarbon habitat were suggested.