基于G函数曲线分析的压后裂缝复杂性评估研究

Evaluative Research for the Fracture Complexity after Fracturing Based on the G-function Curves Analysis

页岩储层压裂成败的关键在于是否能沟通天然裂缝并形成裂缝网络,裂缝的复杂性直接影响着压后单井的增产效果。在经典G函数理论基础上分析了天然裂缝开启时的压裂液滤失行为;通过引入自由变量ω修正了天然裂缝闭合阶段的滤失系数并建立了考虑天然裂缝开启的压降模型;对比分析了简单主裂缝、沟通一条天然裂缝与沟通多条天然裂缝的一阶导数dp/d G、叠加导数ISIP-Gdp/d G和Gdp/d G的曲线形状。涪陵气田三口压裂井的实例分析表明,G函数曲线形态与产量有较好的相关性,证明了运用修正后的G函数曲线能够解释压后裂缝形态的复杂性,从而为后续气田区块优化压裂施工参数、改进压裂施工方案、合理部署开发提供技术指导。

The key to the successful hydraulic fracturing in shale reservoir is whether the working communicates the artificial fractures with the natural fractures and forms fracture network or not. The complexity of fracture directly affects the stimulation effect of single well after fracturing. On the basis of the classical theory of G function,the fracturing fluid leak off with the situation of natural fractures opening was analyzed. The factor,ω,is introduced as a free variable to correct the leak off coefficient during the natural fractures closure and establish the pressure drop model with considering natural fractures opening. What＇s more,the curves＇ shape of the first derivative dp / d G,the superposition derivative ISIP-Gdp / d G,Gdp / d G for the main fracture,communicating single nature fracture and communicating several nature fractures were compared. The example analysis of three fractured wells in Fuling shale gas field shows that the G function curves have a good correlation with the production and proves the correctness of using the corrected G function curves to judge the complexity of fracture. It provides supports on optimizing the fracturing parameters,improving the fracturing scheme and deploying reasonable development plan for the shale gas field in further.