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鄂尔多斯盆地地质历史上的2次烃源充注使得以CO2为主的气体进入砂岩储层,导致储层内发生了以水-岩反应为主的成岩作用,最终使储层发生高度致密化。鉴于储层致密化过程研究对有利储层的评价和预测极其重要,以鄂尔多斯盆地东北部下石盒子组8段致密储层为例,在实测水化学、矿物等数据的基础上,运用岩石学测试分析及数值模拟方法,利用简化的二维地质模型,采用多相、多组分反应溶质运移程序TOUGHREACT,研究不同碎屑矿物条件下,CO2进入储层后所发生的水-岩反应及其对储层孔隙度的影响,确定了最有利于储层致密化形成的碎屑矿物条件。结果表明,长石类矿物溶解所产生的自生高岭石、伊利石及铁白云石是造成储层孔隙度和渗透率减小的主要矿物。绿泥石在CO2-水-岩作用的过程中,极易发生溶蚀,主要产物为铁白云石。碎屑组成中较高含量的含钙矿物对于储层的致密化有重要意义。含钙矿物总体积分数为0.315时,在CO2参与下发生的水-岩反应中,孔隙度最大降幅可达40.0%。
In the geological history of Ordos Basin, two times of hydrocarbon source filling cause CO2-dominated gas to enter sandstone reservoirs, leading to diagenesis that is mainly water-rock reaction in the reservoir, finally resulting in highly densified reservoirs. In view of the fact that the study of reservoir densification process is very important for the evaluation and prediction of favorable reservoirs, taking the 8th-order tight reservoirs of Lower Shihezi Formation in the northeastern Ordos Basin as an example, based on the measured data of water chemistry and minerals, Analysis and numerical simulation methods, the use of simplified two-dimensional geological model, the use of multi-phase, multi-component reaction solute transport program TOUGHREACT study of different detritus conditions, CO2 into the reservoir after the water-rock reaction and its The influence of reservoir porosity on the formation of detrital minerals densified the most favorable conditions. The results show that the authigenic kaolinite, illite and iron dolomite produced by the dissolution of feldspar minerals are the main minerals that cause the decrease of porosity and permeability of reservoirs. Chlorite in the CO2-water-rock process, prone to corrosion, the main product is iron dolomite. The higher content of calcium-bearing minerals in the detrital composition is of great significance for the densification of the reservoir. When the total volume fraction of calcium minerals is 0.315, the maximum porosity decrease can reach 40.0% in the water-rock reaction with the participation of CO2.