鄂尔多斯盆地姬塬地区长8致密储层溶蚀作用模拟及其影响因素

Dissolution Simulation of Chang-8 Tight Reservoir in Jiyuan Area of Ordos Basin,China and Its Influencing Factors

在明确鄂尔多斯盆地姬塬地区西部长8致密储层基本特点的基础上,利用高温高压储层流体-岩石相互作用模拟仪,模拟了长8储层岩石与有机酸溶蚀反应的过程。依据地质条件,采用0.15mol·L-1乙酸溶液(pH=2.65)作为反应溶液,模拟温度选溶蚀窗口对应深度的实际古地温(87℃~103℃),模拟压力范围为24.70~30.18MPa。通过反应前后样品储层特征的变化及溶蚀率对比,分析了长8致密储层的溶蚀特征及影响因素,探讨了其溶蚀过程及溶蚀增孔过程。结果表明:在乙酸的作用下,致密储层长石(钠长石、钾长石)和方解石矿物发生明显的溶蚀反应,并产生沉淀物;根据矿物相对溶蚀率发现,碳酸盐矿物的溶解速率整体上大于长石矿物,其中方解石大于白云石,斜长石大于钾长石;随着温度和压力的增加,方解石溶蚀率先增加后不变,而长石溶蚀率基本呈线性增加,但是方解石刚开始溶蚀率高于长石;致密储层溶蚀过程主要分为3个阶段,分别为方解石胶结物溶蚀过程、长石溶蚀过程和溶蚀后沉淀物充填过程。溶蚀作用使得致密储层的孔隙明显增加,是致密储层增孔的主要成岩作用类型,也是寻找致密储层中"甜点"的关键因素之一。

Based on the study of the basic features of Chang-8tight reservoir in western Jiyuanarea of Ordos Basin,the process of dissolution reaction of rock and organic acid of Chang-8reservoir was simulated by the fluid-rock interaction simulator of high temperature and pressure reservoir.According to the geological conditions,0.15mol·L-1 acetic acid solution with pH=2.65 was used as the reaction solution, the simulated temperature was the actual paleogeotemperature（87℃-103℃）corresponding with the depth of dissolution window,and the simulated pressure was 24.70-30.18 MPa.The reservoir features and dissolution rates of samples before and after the reaction were compared,and the dissolution features and influencing factors of Chang-8tight reservoir were analyzed,and the dissolution process and porosity enhancement were discussed.The results show that under the action of acetic acid,the dissolution reaction of feldspars（albite and K-feldspar）and calcite minerals occurs obviously,and produces sediments;according to the relative dissolution rate of minerals,the dissolution velocity of mineral is larger than that of feldspar in whole,and that of calcite is larger than dolomite,and that of plagioclase is larger than potassium feldspar;with the increase of temperature and pressure,the dissolution rates of calcites remain unchanged after the first increase,and the dissolution rates of feldspar increase linearly,but the dissolution rates of calcite are higher than that of feldspars at the beginning;the dissolution process of tight reservoir is divided into three stages,including calcite cement dissolution process,feldspar dissolution process and sediment filling process after dissolution.Dissolution makes the pores of tight reservoirs increasing significantly,and is a main diagenetic type of tight reservoir porosity enhancement,and is also one of the key factors to find the＂sweet spot＂of tight reservoir.