冀中坳陷廊固凹陷河西务构造带古近系沙河街组四段储集层孔隙度演化定量研究

Quantitative research on porosity evolution of reservoirs in the Member 4 of Paleogene Shahejie Formation in Hexiwu structural zone of Langgu sag,Jizhong Depression

薄片鉴定、流体包裹体分析、埋藏演化史与有机质热演化史分析、膏岩层脱水及黏土矿物转化分析等研究表明:河西务构造带古近系沙河街组四段储集层经历了碱性→酸性→碱性→弱酸性→弱碱性的成岩环境演化过程;成岩作用演化序列为:压实作用→长石溶蚀和(或)石英加大→碳酸盐胶结和(或)硬石膏胶结→少量碳酸盐胶结物溶解→少量黄铁矿胶结。利用"反演回剥"的原理,以铸体薄片资料为基础,计算了各关键成岩作用对储集层面孔率的贡献量,并利用面孔率—孔隙度的函数关系,结合机械压实校正,定量地恢复了不同成岩特征储集层的实际孔隙度演化史。根据孔隙度演化史与油气成藏史匹配关系,河西务构造带沙四段储集层第1期油气成藏时期储集物性较好,孔隙度高达20%左右。第2期油气成藏时期,北部区块储集层碳酸盐胶结强烈,孔隙度急剧降低至7%左右,不利于油气充注补充;而南部区块储集层碳酸盐胶结作用弱,孔隙度仍以大于10%为主,有利于油气充注补充和成藏,成为有利勘探目标。

Based on methods of rock thin section identification, fluid inclusion uniform temperature test, burial history and organic matter thermal history analysis, gypsum bed dehydration and clay mineral transformation analysis, it was shown that reservoirs in the Member 4 of the Shahejie Formation in Hexiwu structural zone had experienced alkaline→acidic→alkaline→weak acidic→weak alkaline diagenetic envi- ronment during their evolution process. Moreover, the diagenetic evolution sequences were compaction→feldspar dissolution and/or secondary enlargement of the quartz→carbonate cementation and/or anhydrite cementation→little carbonate cement dissolution→little pyrite cementation. According to the principle of inversion and back-stripplng, the authors calculated each of the key diagenetic contributions on reservoir plane porosity quantitatively on the basis of casting thin sections with different diagenetic characteristics in the study area. Furthermore, the actural porosity was calculated by using the functional relationship with porosity. Finally, the evolution histories of actual porosity with different diagenetic characteristics have been established quantitatively combined with the mechanical compaction correction. In summary, from the matching relationship between porosity evolution and hydrocarbon accumulation period, in the first pe- riod of hydrocarbon accumulation, the reservoir physical properties were good with porosity up to about 20%. In the second period of hydrocarbon accumulation, the reservoir porosity rapidly decreased to about 7% in the northern block as a result of intense carbonate cementation, and was not good for hydrocarbon accumulation. However, carbonate cementation in the southern block was weak, and most of the reservoir porosity is bigger than 10%. Therefore, the southern block was good for hydrocarbon accumulation, and became the favorable exploration target.