Abstract:

The Cambrian Longwangmiao Formation in the Gaoshti area of the Sichuan Basin is abundant in natural gas resources. However, studies on pore diversity among different beach bodies are still insufficient. Based on core observations and thin-section analysis,four distinct microfacies assemblages within the parasequences of the Longwangmiao Formation have been identified. These assemblages exhibit significant differences in diagenetic processes at various stages,particularly in the upper sections of each microfacies: (1)The sandstone shoal-oolitic shoal primarily develops intergranular dissolution pores due to meteoric freshwater dissolution,with porosity ranging from 2% to 6%.(2)The intershoal sea-sandstone shoal experiences both meteoric freshwater dissolution and dissolution during medium-deep burial stages, as well as extensive cementation,resulting in intergranular dissolution pores with porosity ranging from 1.5% to 5%.(3)The sandstone shoal-dolomite flat is influenced by meteoric freshwater dissolution,dissolution during medium-deep burial stages,and recrystallization,leading to the development of intergranular pores,intragranular dissolution pores,and intercrystalline dissolution pores with distinct pore size differentiation,exhibiting porosity ranging from 2% to 8%.(4)The medium-high energy sandstone shoal shows a strong correlation between burial dissolution intensity and late-stage cementation,resulting in intergranular dissolution pores with significant pore size variation,with porosity ranging from 1.4% to 5.8%. Therefore,the porosity of the four types of microfacies assemblages,ranked from highest to lowest,is as follows: sandstone shoal-dolomite flat (2%~8%),sandstone shoal-oolitic shoal (2%~6%),medium-high energy sandstone shoal (1.4%~5.8%),and intershoal sea-sandstone shoal (1.5%~5%). This study provides valuable insights into the types and evolutionary characteristics of secondary pores in rocks within the parasequences, which is crucial for evaluating the differences in various reservoir types.

Key words: Sichuan Basin, Gaoshiti area, Longwangmiao Formation, parasequence, microfacies assemblage, diagenesis, pore genesis

摘要：

四川盆地高石梯地区寒武系第二统龙王庙组天然气资源十分丰富,但不同滩体的孔隙差异性研究仍有不足。基于岩心观察和薄片鉴定,认为龙王庙组准层序中发育由不同类型滩体组成的4种微相组合,分别为砂屑滩—鲕粒滩型、滩间海—砂屑滩型、砂屑滩—云坪型、中-高能砂屑滩型。这4种微相组合在不同成岩阶段的成岩作用存在明显差异,且主要体现在各微相组合的上部岩石中: 砂屑滩—鲕粒滩型上部主要发育受大气淡水溶蚀影响的粒间溶孔,面孔率介于2%~6%之间; 滩间海—砂屑滩的粒间溶孔经历了大气淡水溶蚀和中-深埋藏期溶蚀和大量胶结物的充填,面孔率介于1.5%~5%之间; 砂屑滩—云坪型受到大气淡水溶蚀、中-深埋藏期溶蚀控制,发育孔径分异明显的粒间孔、粒内溶孔和晶间溶孔,面孔率介于2%~8%之间; 中-高能砂屑滩型埋藏期溶蚀强度与晚期胶结物发育关系密切,形成的粒间溶孔孔径差异较大,面孔率介于1.4%~5.8%之间。因此,4类微相组合的孔隙度由高到低依次为砂屑滩—云坪型、砂屑滩—鲕粒滩型、中-高能砂屑滩型、滩间海—砂屑滩型。上述研究成果提供了一个分析准层序下不同微相发育的次生孔隙类型及演化特征的实例,对于进一步评价不同类型储集层的差异性具有重要意义。

关键词: 四川盆地, 高石梯地区, 龙王庙组, 准层序, 微相组合, 成岩作用, 孔隙成因

CLC Number: 

• P618.130.2+1