渤中凹陷中生界火山岩储层裂隙发育程度实验研究:以安山岩为例

Experiment on microfractures of Mesozoic volcanic rock reservoirs in the Bozhong Sag: A case of andesite reservoir

渤海湾盆地中生界火山岩发育广泛,但含油气性横向变化较大,失利井较多,勘探风险大,了解火山岩潜山储层内部裂隙发育程度及规律可为中生界火山岩潜山勘探提供理论依据。本文选取中生界安山岩,开展不同构造环境下岩石微裂隙发育程度实验,分析安山岩在不同应力状态下微裂隙发育规模、频率以及微裂隙空间分布,探讨张性和压性构造应力环境下中生界火山岩微裂隙发育能力及空间展布规律。实验结果表明:安山岩在压性和张性环境下均有微裂隙发育;安山岩在较低的压应力作用下产生大量微裂隙,微裂隙发育规模不随应力增大而升高,其原因可能是安山岩本身含有大量先存构造缝、溶蚀缝和溶蚀孔,受较小的应力后“再活化”产生微裂隙;结合渤中凹陷的构造演化过程,安山岩经历了燕山早期北东向压扭、中期伸展,燕山晚期右旋压扭及喜山期伸展,导致其内部裂隙较为发育,其运储能力提升,具备成为优质储层的基本条件。

The Mesozoic volcanic rocks are widely developed in the Bohai Bay Basin,North China.However,the regional oil-gas reserves vary greatly in lateral direction,and many wells frequently failed and exploration is facing high risk.Understanding the development of internal fractures of volcanic rocks can provide a theoretical basis for the exploration of Mesozoic volcanic buried-hill.We selected the Mesozoic andesite to carry out microfractures experiments under the action of tensile stress and compressive stress,in which the development ability and spatial distribution of microfractures in andesite rocks were analyzed.Results show that andesite generated microfractures in both compressive and tensile stress.Many microfractures occur under low compressive stress,and the size of microfractures does not increase with the increase of compressive stress.The reason may be that andesite contains many pre-existing structural fracture,dissolution-assisted fractures,and/or dissolution pores,which are“reactivated”to generate microfractures after small stress.Considering the tectonic evolution of the Bozhong Sag,we believed that andesite had experienced NE compression-shearing in early Yanshanian,extension in middle Yanshanian,dextral compressionshearing in late Yanshanian,and extension in the Himalayan,resulting in relatively well-developed internal fractures and improved the transportation and storage capacity,which have met the basic conditions of forming a high-quality reservoir.