GUO Yu-xin

(Exploration and Development Research Institute, Shengli Oilfield Company, Sinopec, Dongying 257022, China)

Abstract: The type of constructive diagenesis, diagenetic evolution process and its influence on the our selected dolomite reservoir of the Lower Paleozoic Yeli-Liangjiashan Formation in the Zhuanghai area of Jiyang Depression have been studied in this paper by using methods of the casting thin section, cathodoluminescence, scanning electron microscopy, imaging logging data, and carbon and oxygen isotope analysis, combined with the diagenetic evolution characteristics of the study area. Constructive diagenesis mainly includes dolomitization, fracturing, and dissolution. The dolomite of the area mainly includes micro- to fine-sized crystalline dolomite, with a small amount of fine- to medium-sized crystalline dolomite and micritic to microcrystalline dolomite. The carbon and oxygen isotopic characteristics show that the dolomite was formed by the dolomitization, including major burial dolomitization and occasional penecontemporaneous dolomitization, which was mainly developed in the early Caledonian and the middle and late Hercynian periods. Dolomitization can result in the formation of dolomite reservoir in which intercrystalline pores were developed. Comparing to the limestone, the dolomite reservoir has relatively high porosity and permeability which are favorable foundation for the development of late-stage fracturing and fluid dissolution phenomena in the dolomite. Fracturing was mainly developed in periods of the late Indosinian, Yanshan, and early Himalayan movements. Multi-phase tectonic movements result in the development of structural fractures which acted as channels for the fluid caused the following dissolution of dolomite. Dissolution occurred in all stages of tectonic movement. It includes the superficial atmospheric freshwater dissolution, hydrothermal dissolution, and organic acid dissolution. It has obvious effect on the reservoir reconstruction. Generally, dolomitization, fracturing, and dissolution are the respective basic, pre-conditional, and key controlling factors for the formation of high-quality dolomite reservoir. The superposition of these three kinds of activities had conducted the development and subsequent transformation of secondary pores in the dolomite, improved physical properties of the reservoir, and controlled the formation of high-quality dolomite reservoirs.

Keywords: Dolomitization; fracturing; dissolution; Yeli－Liangjiashan Formation; Zhuanghai area; Jiyang Depression

ACTA MINERALOGICA SINICA Vol. 41, No.2, 2021, page 163-170