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鄂尔多斯盆地大牛地气田二叠系下石盒子组储层砂岩具有成分成熟度低,结构成熟度中等到好的特点,岩性以岩屑石英砂岩和岩屑砂岩为主。砂岩属于特低孔特低渗储层,以次生溶蚀粒间孔为主要储集空间。储层成岩作用主要包括压实、溶解、胶结和交代4种,目前处于中成岩阶段B期。成岩作用对储集物性的影响主要表现在孔隙度和渗透率两方面。机械压实作用主要发育于成岩阶段早期,是造成下石盒子组储层埋深小于2 350 m砂岩原生孔隙大量丧失、渗透率急剧减小的主要原因,随着埋藏深度的增加,其对储层物性的影响逐渐减弱。胶结作用对储层物性的破坏主要表现为各种胶结物的沉淀析出、充填孔隙及堵塞喉道,其中孔隙衬里绿泥石和碳酸盐胶结物对储层物性的影响具有双重性,孔隙衬里绿泥石对储集物性的建设性大于破坏性,其减弱了机械压实强度,抑制了硅质胶结物的发育,并为后期酸性有机流体的进入以及溶解产物的带出提供了有效通道,有利于溶蚀孔隙的发育;早期碳酸盐胶结物减弱了压实作用对储集物性的破坏强度,并为后期溶解作用的发育提供了物质基础,而后期碳酸盐胶结物充填孔隙,堵塞喉道,对储集物性起破坏作用。溶解作用是导致次生孔隙发育及改善砂岩储集性能的主要因素,下石盒子组储层在埋深2 400、2 500和2 670 m附近存在3个次生溶蚀孔隙发育带。
The Permian Xiashihezi Formation reservoir sandstones of the Daniudi Gas Field in the Ordos Basin are characterized by low maturity and moderate structural maturity. The lithology is dominated by lithic quartz sandstone and lithic sandstone. Sandstone belongs to ultra-low porosity and ultra-low permeability reservoirs, with secondary dissolution of intergranular pores as the main reservoir space. The diagenesis of reservoirs mainly consists of four types of compaction, dissolution, cementation and alteration, and is currently in stage B of diagenetic stage. Diagenesis on reservoir properties mainly in the porosity and permeability of both. Mechanical compaction mainly occurs in the early stage of diagenesis, which is the main reason for the large loss of primary porosity of sandstone below 2 350 m in Lower Shihezi Formation and the sharp decrease of permeability. With the increase of burial depth, The impact of the physical properties gradually weakened. The physical and chemical damage of the cementation is mainly caused by the precipitation of various cements, the filling of pores and the clogging of the throat. The effects of pore-lining chlorite and carbonate cementation on the physical properties of the reservoir are dual, Debris is more constructive than destructive for reservoir properties, which weakens mechanical compaction strength, inhibits the development of siliceous cements, and provides an effective channel for the subsequent entry of acidic organic fluids and the carry-over of dissolved products. There are Which is conducive to the development of dissolution pores. Early carbonate cements weaken the crushing effect on reservoir properties and provide the material basis for the development of later dissolution, while the later carbonate cements fill the pores and block the throat , The destruction of the physical properties of storage. Dissolution is the main factor that leads to the development of secondary pores and the improvement of sandstone reservoir performance. There are three secondary dissolution pore development zones in Xiashihezi Formation near depths of 2 400, 2500 and 2670 m.