裂缝性致密碳酸盐岩储层酸压多场耦合数值模拟与应用

Numerical simulation and application of multi-field coupling of acid fracturing in fractured tight carbonate reservoirs

深层高温致密裂缝性碳酸盐岩储层中,酸液在天然裂缝中的动态滤失减弱了酸液对水力裂缝的刻蚀,影响了酸压改造效果。为了提高此类储层酸压设计的准确性及有效性,建立了耦合裂缝扩展与天然裂缝动态滤失的"流场-温度场-化学场"三场耦合前置液酸压模型。以磨溪气田龙王庙组X井为例,采用所建立的酸压模型,基于酸压施工压力数据拟合获取了储层天然裂缝特征参数,分析了天然裂缝动态滤失特征及其对酸压裂缝参数的影响;基于无因次产能指数综合评价了不同施工参数下的酸压改造效果。研究结果表明:(1)酸液在天然裂缝的动态滤失对缝内流动、温度均存在较大影响,天然裂缝滤失的精确计算是准确模拟预测酸压效果的关键;(2)裂缝性储层中的酸液滤失量并不随注酸时间的增加而降低,而是随着沟通天然裂缝数量的增加呈现出锯齿状的动态平衡;(3)在裂缝性致密碳酸盐岩储层中,最优注酸排量随注酸量的增加而提高,天然裂缝滤失是施工参数优化最重要的影响因素;(4)综合考虑施工条件及经济因素,X井的最优注酸参数中注酸量为500~600 m^3、注酸排量为6 m^3/min,优化后计算得到的无因次产能指数为拟合所得的2.5倍。

In deep,high-temperature and tight fractured carbonate reservoirs,the dynamic leak-off of acid in natural fractures weakens the etching effect of acid on hydraulic fractures,thus affecting the effect of acid fracturing treatment.To improve the accuracy and effectiveness of acid fracturing design of such kind of reservoir,this study establishes an acid fracturing model for the"flow field-temperature field-chemical field"coupling of the fracture propagation and the dynamic leak-off of natural fractures.Taking Well X of the Longwangmiao Formation in the Moxi Gas Field as an example,using the established acid fracturing model,based on the fitting of acid fracturing treatment pressure data,this study obtains the characteristic parameters of natural fractures in the reservoir,and analyzes the dynamic leak-off characteristics of natural fractures and their effect on the parameters of acid fracturing fractures;additionally,based on the dimensionless productivity index,it comprehensively evaluates the effect of acid fracturing treatment under different treatment parameters.The results show that:(1)the dynamic leak-off of acid in natural fractures has a great influence on the flow and temperature.Accurately calculating the dynamic leak-off is the key to precisely simulate and predict the results of acid fracturing;(2)in fractured reservoirs,the leak-off of acid does not decrease with the increase of acid injection time,but shows a zigzag dynamic balance with the increase of communicating natural fractures;(3)in fractured tight carbonate reservoirs,the optimal acid injection displacement increases with the increasing injection acid volume.The leak-off of natural fractures is the most important factor for the optimization of construction parameters;(4)as comprehensively considering treatment conditions and economic factors,the optimal acid injection parameters of Well X are determined as:acid injection of 500-600 m^3,acid injection displacement of 6 m^3/min,and the dimensionless productivity index obtained after optimization is 2.5 times greater than the fitting result.