Liu Huifeng, Baletabieke Bahedaer, Wang Gang, Guo Jianchun, Xia Fuguo, Chen Zhangxin
CNPC Engineering Technology R&D Company Limited, National Engineering Research Center for Oil & Gas Drilling and Completion Technology, Bejing 102206, China.
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China.
Heliyon. 2022 Nov 18;8(11):e11659. doi: 10.1016/j.heliyon.2022.e11659. eCollection 2022 Nov.
During acid fracturing, acid-rock reaction heat has a significant influence on temperature profiles in fractures and consequently on etched fracture dimensions, but it is usually neglected or simplified in acid fracturing models. This can lead to misestimating of etched fracture dimensions. A model for calculating real-time acid-rock reaction enthalpy, which is a function of temperature, pressure and volumetric work of carbon dioxide produced by reactions, is coupled into a heat transfer model and a fracture growth model, and its effect on etched fracture dimensions is simulated. True experimental data from SL oilfield in China is used for simulation. The results show that acid-rock reaction heat reduces the effective etched fracture length by around 10%, and the effect of reaction heat on the etched fracture length in limestone is 10%-15% larger than in dolomite. Acid-rock reaction heat makes the etched width profile along a fracture more inhomogeneous. With consideration of acid-rock reaction heat, etched fracture widths are 15%-20% larger near the wellbore and over 20% narrower at fracture tip, and its effects are more intense in limestone than in dolomite. The influences of acid-rock reaction heat on etched fracture dimensions are stronger when the initial formation temperature is lower and when acid of high concentration is used. When the pump rate of acid fracturing is increased, the effect of acid-rock reaction heat on etched fracture dimensions is weakened. The new coupled models were used in carbonate reservoirs in Tarim Basin, China for acid fracturing optimization. A scenario comparison showed that the designed treatment parameters of acid fracturing should be different when acid-rock reaction heat was fully considered. The application of the optimized scenario resulted in at least three folds of production rate increase compared to that before stimulation.
在酸压裂过程中，酸岩反应热对裂缝中的温度分布有显著影响，进而影响酸蚀裂缝尺寸，但在酸压裂模型中通常被忽略或简化。这可能导致对酸蚀裂缝尺寸的错误估计。将一个计算实时酸岩反应焓的模型（该模型是温度、压力以及反应产生的二氧化碳体积功的函数）耦合到传热模型和裂缝扩展模型中，并模拟其对酸蚀裂缝尺寸的影响。使用中国SL油田的真实实验数据进行模拟。结果表明，酸岩反应热使有效酸蚀裂缝长度减少约10%，且反应热对石灰岩中酸蚀裂缝长度的影响比对白云岩大10%-15%。酸岩反应热使沿裂缝的酸蚀宽度剖面更加不均匀。考虑酸岩反应热后，酸蚀裂缝宽度在井筒附近大15%-20%，在裂缝尖端窄20%以上，且其影响在石灰岩中比在白云岩中更强烈。当初始地层温度较低且使用高浓度酸时，酸岩反应热对酸蚀裂缝尺寸的影响更强。当酸压裂泵注速率增加时，酸岩反应热对酸蚀裂缝尺寸的影响减弱。新的耦合模型被用于中国塔里木盆地碳酸盐岩储层的酸压裂优化。情景比较表明，当充分考虑酸岩反应热时，酸压裂设计的施工参数应有所不同。优化方案的应用使产量比增产措施实施前至少提高了三倍。
