Favorable Diagenesis and Pore Evolution of The Qi-2 Member Reservoir in the Hechuan-Tongnan Area

Abstract This article takes the Qi-2 member dolomite reservoir in the Hechuan-Tongnan area as the research object, and combines research methods such as drilling cores, thin section analysis, CT scanning, and geochemical analysis to deeply explore the pore structure characteristics, diagenetic characteristics, and influencing factors on pore evolution of the Qi-2 member dolomite reservoir. This results indicate that: ①The Qi-2 member should develop two types of reservoir spaces: pores and fractures. The reservoir space is mainly composed of intercrystalline dissolved pores (0.5∼5%), dissolved fractures and dissolved cavities (2∼4%). The intercrystalline pores are relatively evenly distributed, and the fractures improve the connectivity of pores. The reservoir space of the poor gas layer is mainly composed of biocast pores and intragranular dissolved pores (1∼2%), which are relatively isolated; ② The matrix pores of the Qi-2 member are relatively evenly distributed, with a radius of 200μm~600μm is the main focus. The throat radius is mainly 20μm~60μm fine throats.③According to the effect of diagenesis on pore evolution of dolomite reservoir in Qi-2 formation, it can be divided into constructive and destructive. The formation of reservoir space is mainly caused by quasi-syngenetic atmospheric fresh water erosion, and the matrix pores are mainly intercrystalline pores and intercrystalline dissolved pores. The early dolomitization is the key factor of pore preservation. The geological study of dolomite reservoir of the Qixia Formation in the Daqing exploration area has been enhanced, providing strong basis for reservoir prediction and deployment in the later stage.