川中地区龙王庙组花斑白云岩储层特征及成因机理

花斑白云岩是四川盆地下寒武统龙王庙组最主要的储集岩类，储集性能良好，发育广泛，不同岩石组分之间储集性能及含油气性具有明显差异。基于岩心观察、薄片鉴定、荧光反应、阴极发光与扫描电镜观察及地球化学特征等，对川中地区龙王庙组花斑白云岩储层特征及成因机理开展研究。结果表明：川中龙王庙组花斑白云岩呈暗色斑块(暗斑)与浅色基岩(白斑)不规则交错分布，暗斑部分孔隙发育但被沥青充填，白斑部分岩性致密孔隙不发育。川中地区龙王庙组花斑白云岩储层中识别出2类沥青，结合下寒武统龙王庙组埋藏史与热演化史可知，固体沥青主要来源于下寒武统筇竹寺组烃源岩，油质沥青主要来源于下志留统龙马溪组烃源岩。川中地区龙王庙组储层根据花斑形态及孔隙发育情况，划分为花斑孔隙型、花斑孔洞型、花斑岩溶型3种储层类型，不同储层类型具有不同的特征和成因：花斑孔隙型储层主要发育在晶粒白云岩中，储集空间以晶间溶孔为主，由大气淡水沿生物潜穴选择性溶蚀所形成；花斑孔洞型储层是由颗粒白云岩差异性溶蚀作用所形成，储集空间主要为粒(晶)间溶孔及溶蚀扩大孔、洞；花斑岩溶型储层主要发育在泥晶(砂屑)白云岩中，储集空间以溶缝和溶洞为主，成因与表生岩溶作用有关。

Reservoir characteristics and genetic mechanism of mottled dolomite of Longwangmiao Formation in central Sichuan Basin

The “mottled” dolomite is the most important reservoir rock of Lower Cambrian Longwangmiao Formation in Sichuan Basin. It has good reservoir performance and extensive development， with obvious heterogeneity in reservoir performance and oil and gas bearing among different rock components. Based on field observation， thin section identification， fluorescence reaction， cathode luminescence and scanning electron microscopy measurement and geochemical characteristics analysis， the characteristics and genetic mechanism of mottled dolomite reservoir in Longwangmiao Formation in central Sichuan were studied. The results show that the "mottled" dolomite of Longwangmiao Formation in central Sichuan basin is irregularly interlaced with dark mottles （dark mottles） and light bedrock （white mottle）. The “mottled” dolomite has strong heterogeneity， because dark mottles have developed pores very well but are almost filled up with bitumen， while the white mottles are very dense with less pores and are not filled with bitumen. Based on the analysis of burial history and thermal evolution history of the Lower Cambrian Longwangmiao Formation， two kinds of bitumen can be recognized. The solid bitumen in the reservoir of the Lower Cambrian Longwangmiao Formation in central Sichuan Basin mainly came from the Lower Cambrian source rock， while the oil bitumen mainly came from the Lower Silurian Longmaxi Formation. According to the piebald shape and void relationship， the Longwangmiao Formation reservoirs in the central Sichuan Basin can be divided into three types： Mottled porous reservoir， mottled vuggy reservoir and mottled karst reservoir， and different reservoir types have different lithology and genesis. The mottled porous reservoir was formed by the selective dissolution of micritic dolomite along biological burrows， while the mottled vuggy reservoir was formed by selective dissolution of granular dolomite， and the mottled karst reservoir was mainly formed by the epigenetic karstification of micritic （psammitic） dolomite.