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渤中凹陷奥陶系碳酸盐岩具有明显深埋环境下溶蚀特征,溶蚀形成的次生孔隙有效改善了储层物性。通过岩石薄片鉴定、扫描电镜观察、阴极发光观察、流体包裹体分析及天然气碳同位素分析等手段对研究区溶蚀成因进行了系统分析。结果显示:研究区奥陶系储层以灰岩、白云岩及灰质白云岩为主,储集空间以多期溶蚀形成的次生孔隙及裂缝为主。该储层经历了正常海水、大气淡水及深埋藏3个成岩环境,其成岩作用则以胶结及溶蚀作用交互为特征。深埋藏环境下碳酸盐矿物溶蚀主要受控于沿深大断裂注入的幔源CO_2、H_2S及硫酸盐热化学反应形成的酸性流体和晚期成藏过程中有机质成熟产生的有机酸和酸性气体。综合分析认为由于更易受到深大断裂及表生溶蚀作用影响,研究区东南侧高部位是奥陶系碳酸盐岩优质储层有利发育区。
The Ordovician carbonate rocks in Bozhong Depression have obvious erosional characteristics under deep burial environment. The secondary pores formed by dissolution effectively improve reservoir physical properties. The causes of erosion in the study area were systematically analyzed by means of identification of rock slices, scanning electron microscopy, cathodoluminescence observation, fluid inclusion analysis and natural gas carbon isotope analysis. The results show that the Ordovician reservoirs in the study area are dominated by limestone, dolomite and gray dolomite. Secondary pores and fractures formed by multi-stage dissolution of reservoir space are the main reservoirs. The reservoir experienced normal seawater, atmospheric fresh water and deep buried three diagenetic environment, its diagenesis is characterized by cementation and dissolution interaction. The dissolution of carbonate minerals under deep burial environment is mainly controlled by the acidic fluids formed by the mantle-derived CO_2, H_2S and sulfate chemical reactions injected into the deep faults and the organic acids and acid gases produced by organic maturation in the late accumulation. The comprehensive analysis shows that due to being more susceptible to deep faults and superficial dissolution, the high southeast part of the study area is a favorable area for the development of Ordovician carbonate high-quality reservoirs.