Optimization of Shut-in Time between the First and Second Fracturing by means of Pressure Decline Analysis
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摘要: 第二次压裂与第一次压裂之间有一段停泵时间,停泵时间的长短目前主要依靠经验确定,容易产生较大误差,从而影响第二次压裂的效果.为此,在前人研究成果的基础上,将压裂前后的整个过程分成了注入阶段、续流阶段、裂缝闭合阶段和裂缝闭合后等4个阶段;考虑压裂液的续流效应和支撑剂体积的影响,并根据裂缝闭合后的压降分析,建立了续流阶段和裂缝闭合阶段时间及地层压力趋于稳定时间的计算模型.利用X区块压裂井的基本施工参数,对压裂液的续流时间、裂缝的净闭合时间进行了计算,对裂缝闭合后的压降进行了分析,对多口压裂井的第二次压裂效果进行了对比.实例分析发现,地层压力趋于稳定的时间即为第一二次压裂间合理的停泵时间,地层压力稳定的时间点为最佳停泵时间,在该点可以获得最佳压裂效果.研究表明,模拟结果和压裂后日产量对应的最佳停泵时间与模型计算结果相吻合,建立的模型可以较为准确地预测最佳停泵时间,这对于现场施工具有一定的指导作用.Abstract: It is necessary to shut in the well between the first and second fracturing, with the time interval often determined by prior experience, which may result a significant error. Moreover, the selection of shut-in time will directly affect the performance of secondary fracturing. Based on previous efforts, this paper divides the fracturing process into four stages:pumping, frac fluid after-flow, fracture closure and after-closure. Considering the influences of frac fluid after-flow and proppant volume, and through the pressure decline analysis of after-closure, the calculation model was established for after-flow time and fracture closure time and the time when formation pressure became stable. By using basic fracturing parameters of the X block, the after-flow time and fracture closure times were calculated, the pressure decline after fracture closure was analyzed, and the performance of the secondary fracturing for several wells was compared. The results showed that the time when the formation pressure was stable corresponded to a reasonable shut-in time between the first and second fracturing and it marked the optimum point in time at which the best fracturing performance could be achieved. The optimum shut-in time gained from the simulation results and production after fracturing were consistent with that calculated by the model, which demonstrated that the model could accurately predict the optimum shut-in time which could be significant for guiding fracturing operations.
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Keywords:
- fracturing /
- fracturing fluid /
- shut-in time /
- pressure decline /
- mathematical model
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