Abstract:

Following the discovery of the Anyue extra-large gas field in central Sichuan,significant exploration breakthroughs have been achieved in Member 2 of Dengying Formation in the Penglai area of northern Sichuan Basin in recent years. However,the exploration and development of this region remain constrained due to the complex microfacies types,considerable burial depth and strong heterogeneity of microbial mounds and shoals within the Dengying Formation. Based on core data from Well Wang-1C—a fully cored scientific exploration well located in northern Sichuan Basin—this study systematically investigates the microfacies types,sedimentary evolution,and reservoir characteristics of microbial mounds-bank complex in the Member 2 of Dengying Formation. The main findings are as follows: (1)Four primary dolomite lithofacies are identified in the Member 2 of Dengying Formation at Well Wang-1C: microbial dolomite,granular dolomite,crystalline dolomite,and dolomite breccia. Among these,laminated stromatolite dolomite,thrombolite dolomite,botryoidal dolomite,and mud-crystalline dolomite are the most developed. (2)Member 2 is predominantly composed of restricted platform deposits,with key microfacies including basal mound,core mound,mound crest,grain bank,and subtidal flat. (3)Three distinct microfacies assemblages can be recognized within the microbial mound-bank system: (Ⅰ)subtidal flat-basal mound-core mound,(Ⅱ)subtidal flat-grain dolomite bank,and(Ⅲ)subtidal flat-basal mound-core mound-grain dolomite bank. Each assemblage exhibits a substantial thickness,typically ranging from 25 to 50 m. (4)Reservoir spaces in the microbial mound-bank complex include primary pores and secondary dissolution pores. Reservoir development is primarily controlled by microfacies distribution,high-frequency sea-level fluctuations,and diagenetic processes. Notably,the microbial mound-core and mound-crest facies exhibit the most favorable reservoir properties,followed by granular shoal facies,whereas the subtidal flat facies displays the poorest physical characteristics. The above results can provide geological theoretical basis for the prediction of the distribution of ultra-deep microbial mound and flat reservoirs,and the exploration and development of natural gas in the northern Sichuan Basin.

Key words: microbial mound, grain bank, microfacies assemblage, reservoir characteristics, reservoir main control factors, Dengying Formation, Sichuan Basin

摘要：

近年来在川北蓬莱地区灯影组二段勘探取得重大发现和突破,但由于该地区灯二段埋深大,取心资料少,微生物丘滩微相类型复杂,储集层非均质性强,制约了该区勘探开发进程。以川北地区全取心的科学探索井——旺1C井资料为基础,对该区灯二段微生物丘滩微相类型、微相组合序列、沉积相演化和储集层特征进行了研究。 结果表明: (1)旺1C井灯二段主要发育微生物白云岩、颗粒白云岩、晶粒白云岩和白云质角砾岩等,以藻叠层白云岩、藻凝块白云岩、葡萄花边白云岩、砂屑白云岩和泥晶白云岩最为发育; (2)灯二段主要为一套局限台地沉积,细分为微生物丘、颗粒滩、潮坪3种亚相以及丘基、丘核、丘顶、砂屑滩、潮下云坪等微相; (3)灯二段与微生物丘滩沉积相关的微相组合可分为潮下云坪—丘基—丘核、潮下云坪—砂屑滩、潮下云坪—丘基—丘核—砂屑滩等3种类型,单个微相组合序列厚度规模较大,一般在25~50 m之间; (4)灯二段微生物丘滩储集层发育原生孔隙和次生溶蚀孔隙等储集空间,该区储集层主要受微相、高频层序和成岩作用等因素控制,其中丘核和丘顶微相储集层物性相对较好,其次为砂屑滩微相,潮下云坪微相储集层物性最差。研究成果可为川北地区超深层微生物丘滩储集层分布预测和天然气勘探开发提供地质理论依据。

关键词: 微生物丘, 颗粒滩, 微相组合序列, 储集层特征, 储集层主控因素, 灯影组, 四川盆地

CLC Number: 

• P588.245