歧口凹陷北大港构造带奥陶系潜山储层特征、主控因素及发育模式

Characteristics,main controlling factors and development model of Ordovician buried-hill reservoir in Beidagang structural belt,Qikou sag

奥陶系碳酸盐岩潜山是歧口凹陷重要的油气勘探对象,由于其储层的非均质性强,勘探进展缓慢。在分析宏观构造背景、钻井、录井、常规测井、成像测井、试油和地震等资料的基础上,明确了北大港构造带奥陶系潜山的储层特征和储层主控因素,提出了多期次岩溶发育模式。北大港构造带潜山储层的岩性主要为白云岩和膏溶角砾岩,储集空间以溶洞、粒间溶孔、晶间孔和裂缝为主,储层发育主要受控于岩性组合,以及晚加里东期—早海西期、印支期—燕山期和喜马拉雅期3期古岩溶的综合改造。基于恢复的岩溶古地貌、试油表现、溶洞充填物和构造背景,建立了3期古岩溶改造模式,即晚加里东期—早海西期的准平原化岩溶残丘—斜坡—洼地改造模式、印支期—燕山期总体岩溶斜坡背景下的次级残丘—洼地模式、喜马拉雅期的断裂岩溶改造模式。其中,晚加里东期—早海西期是北大港构造带最重要的储层改造阶段,印支期—燕山期古岩溶储层的改造作用仅在千米桥潜山带较明显,而喜马拉雅期的古岩溶改造仅发育于古近系凹陷的边界断裂带,改造了晚加里东期—早海西期的古岩溶地层。

Ordovician carbonate buried hill is an important hydrocarbon exploration target in Qikou sag where the strong heterogeneity of reservoir leads to the exploration in slow progress.Based on the systematic analysis of macro-structural background,drilling and logging,conventional logging,imaging logging,oil testing,seismic and other geological data,the characteristics and main controlling factors of Ordovician buried-hill reservoirs in Beidagang structural belt are identified to propose a multi-stage karst development model.The lithology of buried-hill reservoir in Beidagang structural belt is dominated by dolomite and gypsum-karst breccia.The reserving spaces mainly include karst caves,intergranular dissolution pores,intergranular pores and fractures.The reservoir development is primarily controlled by lithologic assemblage and the comprehensive reformation of Late Caledonian-Early Hercynian,Indosinian-Yanshanian and Himalayan stages.On the basis of the restored karst paleogeomorphology,oil test performance,filling materials of karst caves and tectonic settings,the models for three stages of paleo-karst transformation are established,i.e.,the Late Caledonian-Early Hercynian peneplain karst residual hill-slope-sag transformation model,and the Indosinian-Yanshanian secondary residual hill-sag model under the whole background of karst slope,and the Himalaya fault karst transformation model.Among them,the Late Caledonian-Early Hercynian period is the most important stage of reservoir reformation in Beidagang structural belt.The Indosinian-Yanshanian paleo-karst reservoir transformation only had obvious effects in the Qianmiqiao buried-hill zone,while the Himalayan paleo-karst transformation only occurred in the boundary fault zone of the Paleogene sag,leading to the transformation of the Late Caledonian-Early Hercynian paleo-karst reservoirs.