Water-sensitive characterization and its controlling factors in clastic reservoir: A case study of Jurassic Ahe Formation in Northern tectonic zone of Kuqa depression

Abstract

Water-sensitivity is a factor that must be paid attention to in the reservoir development stage of oil and gas fields. As a clastic reservoir, the water effect of Ahe formation in the northern structural belt of Kuqa is strong as a whole, but the mechanism analysis of medium and strong water-sensitivity effect is restricted by the evaluation method with permeability damage rate as the main parameter. Taking the shape of water-sensitivity test curve as the starting point, combined with the analysis of microscopic pore throat and clay minerals, the difference of permeability change rate measured by samples is characterized. The strong to medium water-sensitivity effects in the study layer are divided into three types: The permeability gradually decreases in the early stage-the rapid decrease in the late stage, the continuous decrease in the permeability, and the rapid decrease in the early stage-the slow decrease in the later stage. As a widely developed reservoir space in the study section, the micropore not only has the characteristics of fine pore size and easy blockage, but also serves as the occurrence space of the main water-sensitive mineral illite-smectite mixed layer. Therefore, the change types of the above different water sensitivity test curves are mainly controlled by the difference of micropore content. When the micropore content is low, the permeability decreases slowly in the early stage and decreases rapidly in the later stage (type I), while when the micropore content is high, the permeability decreases rapidly in the early stage and slowly decreases in the later stage (type II), while when the micropore content is medium, the permeability decreases continuously, and there is no obvious rate change (type III) before and after the micropore content. The results show that the structural characteristics and relative content differences of micropores in the samples are the internal mechanism of the difference of water sensitivity effect types.