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

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 the 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 scope 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.