考虑岩矿非均质性的前置液酸压模拟研究

前置液酸压工艺采用高黏非反应性前置压裂液压开储层形成水力裂缝,然后高压挤入酸液刻蚀裂缝表面,形成非均匀溶蚀缝面以此来增强裂缝的导流能力。为了给深部碳酸盐岩储层的前置液酸压改造提供理论依据,在建立多种矿物存在的裂缝酸化数学模型的基础上,结合裂缝拟三维延伸模型,构建了能够正确描述前置液酸压物理、化学过程的综合控制方程组;基于控制方程,模拟分析了岩矿层理、岩矿组分占比和排量等关键因素对前置液酸压改造效果的影响。结果表明:(1)岩矿层理对酸蚀裂缝形态起主导作用,且水平层理有助于提高酸液的有效作用距离;(2)石灰岩在碳酸盐岩矿物中所占比例越大,酸液有效作用距离越短;(3)在考虑岩矿非均质性的前置液酸压改造中,大排量能增加酸液的有效作用距离,但酸蚀缝宽相应变窄。结论认为:(1)与常规酸压模拟方法相比,该方法充分考虑了受地质沉积影响的岩矿分布特点,较真实地模拟了岩矿非均质性所引起的裂缝非均匀刻蚀形态;(2)该研究成果为碳酸盐岩储层前置液酸压改造优化设计提供了新的方法和手段,丰富了碳酸盐岩储层改造理论。

A simulation study on the preflush acid fracturing considering rock heterogeneity

When the preflush acid fracturing technology is carried out, a high-viscosity nonreactive pad fracturing fluid is used to fracture the reservoirs and generate hydraulic fractures. Then, an acidizing fluid is injected at high pressures to etch the surface of the fractures, so that a nonuniform surface of dissolved fractures is formed to increase the flow conductivity of fractures. For providing the theoretical basis for the preflush acid fracturing of deep carbonate reservoirs, a mathematical model for fracture acidizing in the cases with multiple minerals was established. Then, based on the pseudo-three dimensional fracture propagation model, a comprehensive control equation set was prepared to accurately describe the physical and chemical courses of preflush acid fracturing. Based on the control equation, the influences of key factors (e.g. rock bedding, rock composition percentage and flow rate) on the stimulation effects of preflush acid fracturing were simulated and analyzed. And the following research results were obtained. First, the rock bedding plays a leading role for the morphologies of etched fractures and horizontal beddings is conducive to increase the effective distance of acidizing fluid. Second, the higher the content of limestone in carbonate minerals, the shorter the effective distance of acidizing fluid. Third, if the rock heterogeneity is considered in the preflush acid fracturing, a high flow rate can increase the effective distance of acidizing fluid, but the etched fractures become narrow correspondingly. It is concluded that different from conventional acid fracturing simulation methods, this method fully considers the rock distribution characteristics that are affected by geologic sedimentation and it can simulate authentically the nonuniform etch morphologies of fractures caused by rock heterogeneity. The research results provide a new method for the design optimization of the preflush acid fracturing in carbonate reservoirs and enrich the carbonate reservoir stimulation theories.