页岩油层水力压裂注入水返排量计算的数学模型

Mathematical model of the flowback volume of the injected water for shale-oil hydraulic fracturing

开采页岩油气水力压裂过程中需要消耗大量的水资源,但这些注入水在水力压裂之后部分又回流到了地面。因此,分析压裂后回流水的来源和压裂注入水的回收比例对水力压裂技术发展至关重要。以现场采集的水力压裂回流水组分检测统计数据为基础,结合压裂后回流水的矿化度测试和同位素测试分析了回流水来源,建立了注入水返排量数学计算模型。现场测试表明回流水主要由水力压裂注入水和存在于天然裂缝中的地层水所构成,回流水矿化度的增加主要是由于地层水与注入水的混合所导致。采用该数学模型计算的压裂注入水在回流水中的比例与现场采集数据的吻合度较高,说明建立的数学模型正确合理,该模型为优化页岩油层水力压裂用水量提供了重要技术支持。

In the process of shale oil and gas hydraulic fracturing,a large amount of water resource is needed,but most of these injected water returns to the ground after the hydraulic fracturing.Therefore,it is very important for the development and improvement of the hydraulic fracturing technology to analyze the source of the postfrac backwater and the recovered proportion of the injected water.On the basis of the tested statistical data of the backwater components collected in the field,combined with the salinity and isotopic tests of the backflow water after the fracturing,the source of the backwater was analyzed,and the mathematical calculating model of the injected water flowback volume was established.The results show that the field tests prove the backwater is mainly composed of the fracturing injected water and the formation water existing in the natural fractures,and the increase of the backwater salinity is mainly caused by the mixture of the formation water and injected water.The proportion of the fracturing injected water in the bacwater calculated by the adopted mathematical model is in good agreement with the data collected in the field,which shows that the established mathematical model is correct and reasonable.This model can provide the important technical support for optimizing the water volume used in the hydraulic fracturing of the shale oil.