江汉油田盐间非砂岩储层的特征及裂缝的成因

CHARACTERISTICS OF INTER-SALT NON-SANDSTONE RESERVOIRS AND GENESIS OF FRACTURES IN THE JIANGHAN OIL FIELD

江汉盆地潜江凹陷盐韵律发育,部分韵律层段存在有工业价值的油藏,岩性主要为泥岩、泥膏岩、含膏泥岩、钙芒硝质白云岩等,储集空间有孔隙、孔洞和裂缝,以裂缝为主。同一储层中多种储集类型共存。在该类储层中,渗透率的高低不完全取决于孔隙度的大小,而与孔隙结构的分选性,即孔喉的大小、形状、连通程度和裂缝发育情况、充填程度等有关。孔隙结构整体以微喉为主,综合评价属中孔、低渗-特低渗储层。通过大量岩心观察、薄片分析、试井资料和裂缝的形态、产状、密度、分布范围研究后认为,裂缝主要是在高压异常、差异压实、成岩、构造等综合作用下形成的,其中成岩作用是水平层间缝、构造作用是各类扩张缝和剪切缝的主导因素。

Salt rhythms are well developed in the Qianjiang subbasin, Jianghan basin, and some rhythms contain oil accumulations of commercial value. The rocks consist predominantly of mudstone, evaporite, gypseous mudstone and glauberite dolostone. The reservoir spaces mainly include pores, cavities and fractures, with fractures predominating. There are several types of reservoir spaces in one reservoir. In such reservoirs, permeability does not completely depend upon porosity but is related to ;he size, shape and degree of connection of pore throats, as well as the development of fractures and degree of filling. The reservoir belongs to a medium-porosity, low- to very low-permeability one. Based on core observations, thin-section analysis, well tests and study of the shape, attitudes, density and distribution SCOl~ of the fractures, the authors consider that the fractures mainly formed under the integrative effects of high abnormal pressures, differential compaction, diagenesis and tectonism, of which diagenesis was the main factor for the formation of horizontal interlayer fractures and tectonism is the main factor for the formation of swelling and shear fractures.