渤海海域渤南低凸起碳酸盐岩潜山储层特征及形成机制

碳酸盐岩潜山是渤南低凸起潜山中重要的油气勘探和开发目标,运用钻井、地震、岩心、薄片、测井等资料,以BZ28-1碳酸盐岩潜山油气田为例,对碳酸盐岩储层特征及形成机制进行了综合分析。渤南低凸起碳酸盐岩潜山包括风化壳岩溶型储层和内幕溶蚀型储层2套储集系统,岩性主要为白云岩,其次为灰岩,储集空间主要为晶间孔、裂缝和溶蚀孔隙。物性分析表明,白云岩中的不等粒白云岩、粉—细晶白云岩和粉晶白云岩物性最好,且普遍好于灰岩。渤南低凸起碳酸盐岩潜山储层的形成主要受沉积相、岩溶作用和构造破裂作用的控制:(1)沉积相是储层形成的基础,有利的储层主要分布在局限海、潮间坪和潮坪中的白云岩和部分灰岩中;(2)岩溶作用是储层形成的关键,风化壳岩溶型储层和内幕溶蚀型储层主要分布在不整合面顶部以下0~250 m和0~150 m的范围内,岩溶古地貌中的岩溶高地和宽缓的岩溶斜坡相带是岩溶储层发育最有利的部位;(3)构造破裂作用是储层形成的纽带,在不整合面附近的半充填或未充填的构造缝和溶蚀缝,既可作为油气的储集空间和渗流通道,也可与溶蚀孔隙复合,形成裂缝—孔隙型和孔隙—裂缝型储层,大大改善了储集性能。

Characteristics and formation mechanisms of buried hill carbonate reservoirs in Bonan Low Uplift,Bohai Bay

The carbonate rock buried hills are important exploration and development targets in the Bonan Low Uplift of the Bohai Bay. Based on drilling, seismic, core, thin section and well logging data, the characteristics and formation mechanisms of the buried hill carbonate reservoirs were studied. They were divided into two reservoir systems, including the weathering crust karst reservoir and the inner dissolution reservoir. Dolomites were dominant, while limestones took second place. Reservoir space mainly included intercrystalline porosity, fractures and dissolved pores. The results of physical characteristic analysis showed that inequality grain dolomites, powder crystal-aplitic dolomites and silt crystal dolomites were better than limestones. Sedimentary facies, karstification and tectonic disruption were recognized as the main formation mechanisms of the buried hill carbonate reservoirs in the Bonan Low Uplift. (1) Sedimentary facies were the basis of reservoir formation. Favorable reservoirs mainly distributed in the dolomites and limestones of restricted sea, intertidal flat and tidal flat facies. (2) Karstification was the key to the formation of buried hill carbonate reservoirs. Weathering crust karst reservoirs and inner dissolution reservoirs developed within 0-250 and 0-150 meters under the top of the unconformity. Favorable karst reservoirs developed in the karst highland and karst slope of karst palaeogeomorphology. (3) Tectonic disruption was the connection of the formation of buried hill carbonate reservoir. Semi-filled or unfilled structural fractures and dissolution fractures provided important reservoir porosity and migration channels. When combined with dissolution pores, they formed fracture-pore and pore-fracture reservoirs, which improved reservoir performance.