精细化壁面重构下的酸蚀裂缝导流能力研究

Study on the conductivity of acid etched fracture under the precise reconstruction of fracture surface

酸化压裂是碳酸盐岩储层开采的主要手段,利用酸液对裂缝壁面的非均匀溶蚀,在裂缝壁面形成沟糟状刻蚀,这样形成的酸蚀裂缝在闭合压力作用下仍具有一定的导流能力,最终达到改善渗流条件、油气增产的目的。酸压后的裂缝导流能力是酸压效果的重要评价指标,因此对于裂缝导流能力的研究至关重要,酸蚀后的裂缝壁面形态以及支撑体的高度是计算酸蚀裂缝导流能力重要影响因素,它有助于预测酸蚀裂缝导流能力和评价酸蚀效果。利用原始高度数据绘制的壁面形貌图不能准确地重构真正的酸蚀形态,原始获得支撑体高度的方法也有误差,因此需要寻找一种能准确地重构酸蚀裂缝壁面形态获得支撑体高度的方法。通过空间插值的方法精细化重构裂缝壁面可以大幅度提高裂缝壁面支撑体高度数据的精度,并且有效修补在扫描获取初始数据时由于技术原因缺失的高度数据。本文主要考虑了不同酸蚀裂缝壁面岩石力学形态参数以及力学性质的非均一性,建立了基于支撑体高度的酸蚀裂缝导流能力的模型,通过裂缝壁面精细化重构插值得到了其中关键参数壁面高度相关数据,精确化确定模型参数,以获得最佳分析结果;将精确化得到的数据应用到裂缝导流能力模型中,同时进行了不同时间下的酸蚀导流系列实验,将碳酸盐岩岩样过酸后进行导流能力测试,获得不同酸蚀时间下的裂缝导流能力,将实验所得裂缝导流能力数据与模型获得的数据对比后证明了此模型可以更为准确的表现出裂缝导流能力的变化,并且通过数据结果得到了在一定闭合压力下的最佳酸蚀时间范围,论证了利用不规则网格插值方法在裂缝导流能力研究中应用的可行性和适应性。

Acid fracturing is a major method of carbonate reservoir exploitation.The non-uniform dissolution of acid liquid on the fracture surface is utilized,which results the grooving corrosion on the fracture surface.The formed acid etching fracture still has a certain fluid conductivity under the effect of closing pressure,which can improve the seepage conditions and increase oil and gas production.The fracture conductivity after acid fracture is an important evaluation index of the acid fracturing effect.Therefore,it is very important to study the fracture conductivity properties.According to the nail-bed model,the fracture surface shape and height of the support are essential factors for calculating the fluid conductivity of acid etched fracture,which can predict the fluid conductivity of acid etched fracture and evaluate the effect of acid etching.The wall topography illustrated with the original height data can’t accurately reconstruct the real acid etched form,and the original methods to obtain the height of support also are different.So an approach to precisely reconstruct the acid etched fracture surface to obtain the support height must be found out.Through the spatial interpolation of irregular triangular mesh method,the precision of the height data of the support body on the fracture surface should be greatly improved,and the height data missing due to technical reasons should be effectively repaired when the initial data are obtained by scanning.A conductivity model of the stress-varying acid-etched fracture was established in this paper,and the heterogeneity of mechanical parameters and mechanical properties of rocks with different acid etched fracture surfaces were mainly considered.Through interpolation of irregular triangular mesh reconstruction,the height data of key parameters were obtained,which accurately could determine the model parameters and finally got the best results.The precise data were applied to the fracture conductivity model.Meanwhile,acid etching fluid directing series experiments were conducted,and the fracture fluid conductivities of different acid etching time were gained.By comparing the data obtained by the fracture conductivity experiments with the model one,it was proved that the model could show the change of fracture conductivity more accurately.Another,the optimal etching time under a certain closing pressure was obtained.The feasibility and adaptability of the irregular grid interpolation methods in the study of fracture conductivity were demonstrated.