渤海海域石臼坨—辽西凸起覆盖型潜山储集层发育特征与分布模式*

渤海海域发育勘探潜力巨大的覆盖型潜山,这类潜山储集层的发育特征及分布模式是当前潜山油气勘探研究的重点和难点。利用地震、测井、铸体薄片、井壁岩心、常规物性、扫描电镜和X衍射等资料,开展了石臼坨—辽西凸起覆盖型潜山储集层的发育特征、主控因素和分布模式研究。研究结果表明: (1)覆盖型潜山以长英质含量较高的混合花岗岩为主,发育多种类型的溶蚀孔隙和裂缝,其中构造裂缝是最主要的储集空间。储集层平均孔隙度为2.2%,平均渗透率为0.445×10^-3 μm²。覆盖型潜山自上而下可划分为风化黏土带、风化砂砾岩带、风化裂缝带、裂缝发育带、相对致密带和基岩带。 (2)富长英质的岩石为裂缝型储集层的形成提供了物质基础,较高的长英质含量利于构造成缝和风化、淋滤、溶蚀改造。 (3)印支期—燕山期的强烈隆升是形成优质风化壳储集层的必要条件,而多期次构造作用叠加是潜山规模裂缝型储集层形成的关键,储集层距印支—燕山主控断裂的远近和所处构造部位进一步影响了裂缝的发育。 (4)风化淋滤对于覆盖型潜山储集层的改造具有重要作用,是控制储集层垂向分带性的主要因素。 (5)建立了覆盖型潜山储集层的分布模式,叠合破碎带的风化裂缝带和裂缝发育带是优质储集层的有利发育部位,二层结构潜山风化壳更为发育,多期构造活动叠加区域潜山内幕裂缝带厚度更大,裂缝发育带和破碎带发育更为密集。

Characteristics and distribution pattern of the covered buried-hill reservoirs in Shijiutuo-Liaoxi uplift,Bohai Sea

The Archaean covered buried hills with great potential are developed in the Bohai sea area. The characteristics and distribution pattern of such buried-hill reservoirs are the focus and difficulty in the current research of buried-hill oil and gas exploration. Using seismic data,well-log data,thin sections,sidewall cores,conventional physical property,scanning electron microscopy and X diffraction,the current research explored the characteristics,controlling factors and documented distribution patterns of Archaean covered buried-hill reservoirs in Shijiutuo-Liaoxi uplift of the Bohai Bay Basin,resulting in five main lines of observations and results. First,observations from the current study suggest that the documented Archaean buried hills is composed mainly of mixed granites and developed various types of dissolution pores and fractures,among which structural fractures are the most important reservoir space. The reservoir has an average porosity of 2.2% and average permeability of 0.445×10^-3 μm². The Archaean covered buried-hill reservoirs are composed from base to top of weathered clay zone,weathered conglomerate zone,weathered fracture zone,fracture-developed zone,tight zone and bedrock zone. Second,rocks rich in felsic minerals provided the material basis for the formation of fractured reservoirs. Higher felsic content is conducive to fracture formation and weathering,leaching and dissolution. Third,multi-stage tectonics are key to the formation of large-scale fractured,buried-hill reservoirs. The strong uplift of Indosinian and Yanshanian is the necessary condition for the formation of high-quality weathered crust reservoirs. More specifically,the development of fractures was affected by the different structural positions and the distance between the buried-hill reservoirs and main faults(i.e. the Indosinian and Yanshanian faults). Fourth,weathering and leaching of atmospheric fresh water facilitated the reworking of fractured and is the main factor controlling the vertical zonation of reservoirs. Fifth,the distribution pattern of Archaean covered buried-hill reservoirs was established. The overlapped fracture zones in weathered fracture zones and fracture-developed zones represent two main zones for the development of high-quality buried-hill reservoirs. The thickness of weathering crust of two-story buried hill is larger. The thickness of inner fracture zone is larger and the fracture-developed zone and fracture zone of buried hill are more densely developed in the superposition area of multi-stage tectonic activity.