辽河盆地西部凹陷古潜山天然裂缝特征及其影响因素

Characteristics of natural fractures and their influencing factors in the paleo-buried-hill reservoirs of the Western Sag in the Liaohe Basin,China

古潜山储层是辽河盆地西部凹陷油气勘探的重要领域,天然裂缝发育的非均质性是影响古潜山储层油气富集和单井产能的主要因素之一。通过相似野外露头、岩心、薄片、扫描电镜和成像测井等资料分析,对辽河盆地西部凹陷古潜山储层天然裂缝类型和发育特征进行了研究,并讨论了影响古潜山储层天然裂缝发育的主要因素。辽河盆地西部凹陷古潜山储层天然裂缝按照地质成因可以划分为构造裂缝、风化裂缝和溶蚀裂缝。构造裂缝是天然裂缝的主要类型,其发育的优势方位为NNE-SSW向。铸体薄片和扫描电镜等资料分析表明古潜山储层中发育有矿物晶间缝、解理缝、裂纹缝和破碎缝。其中矿物破碎缝的开度和规模较大,开度通常分布在20~40μm,规模不受矿物颗粒的限制。古潜山储层天然裂缝发育的非均质性主要受构造运动、岩性和成岩作用的控制。加里东运动、印支运动和燕山运动是天然裂缝形成的主要时期;古潜山储层变质岩中的花岗岩类、碳酸盐岩中的白云岩以及火山岩中的中酸性岩石为天然裂缝发育的优势岩性;成岩作用中表生风化作用、溶蚀作用和变质作用是天然裂缝发育的建设性作用,而充填作用和交代蚀变作用属于破坏性作用。研究成果为辽河盆地西部凹陷古潜山储层油气藏的勘探开发提供了科学的地质依据。

The paleo-buried-hill reservoirs are important targets for hydrocarbon exploration in the Western Sag of Liaohe Basin,China.The heterogeneity in natural fracture development is one of the main factors affecting the hydrocarbon enrichment and single well productivity in the area.Based on the analysis of analogous outcrops,drilling cores,thin sections,scanning electron microscopy(SEM)and image logging data,we study the types and developmental characteristics of natural fractures therein,and discuss the main factors affecting the development of natural fractures in the area.According to the geological genesis,natural fractures in these buried hills can be divided into 3 groups,namely tectonic,weathering,and dissolution fractures with the dominant orientation of NNE-SSW strikes.Thin section and SEM observation indicates that mineral intercrystalline fractures,cleavage fractures,cracks and mechanical fractures were developed in these reservoirs.Among others,mineral intercrystalline fractures have the largest aperture and scale with an aperture of 20-40μm and the scale unlimited by mineral particles.The heterogeneity of natural fractures is controlled by tectonic movements,lithology,and diagenesis of the paleo-buried-hill reservoirs.The Caledonian,Indosinian and Yanshan movements are the main periods of natural fracture development.The granitoids in the metamorphic rocks,dolomites in the carbonate rocks and medium-acid rocks in the volcanic rocks are advantageous to the development of natural fractures.The supergene weathering,dissolution,and metamorphism are the constructive diageneses for natural fracture development,while the filling and metasomatic dissolusion are the destructive ones.The results provide a sound geological basis for the exploration and development of the paleo-buried-hill reservoirs in the Western Sag of Liaohe Basin.