页岩气工程甜点评价方法——以四川盆地焦石坝页岩气田为例

An evaluation method of engineering sweet spots of shale gas reservoir development: A case study from the Jiaoshiba Gas Field, Sichuan Basin

页岩气工程甜点的定量评价对于评判页岩气的开发难易程度及开发成本高低都具有重要的参考价值。为了寻求一种高精度的页岩气工程甜点定量评价方法,以四川盆地焦石坝页岩气田为例,结合国内外的研究成果,首先定性分析了脆性指数、应力差异系数、泥质含量和破裂压力等工程甜点参数对压裂加砂量及加液量的影响;在此基础上,采用相关系数法进行定量分析,确定主要工程甜点参数和表征页岩气工程甜点的目标评价参数;然后,采用单一参数评价、雷达面积模型和独立性权重系数模型等3种方法来评价页岩气工程甜点,并对比其结果。研究结果表明:(1)泥质含量、脆性指数、钙质含量和应力差异系数等4个参数为主要的工程甜点参数;(2)采用携砂比来表征页岩气工程甜点可以有效回避用加砂量和加液量来表征时所存在的多目标评价问题;(3)独立性权重系数模型评价工程甜点精度最高,其次是雷达面积模型,单一参数评价的精度较低。现场3口压裂井的应用效果也表明,利用独立性权重系数模型定量评价页岩气工程甜点所得到的评价结果可靠。结论认为,宜采用独立性权重系数模型对页岩气工程甜点进行定量评价。

The quantitative evaluation of engineering sweet spots in shale gas reservoir development provides important reference for forecast on difficulties and costs in such projects. In this paper, the Jiaoshiba Shale Gas Field in the Sichuan Basin was taken as an example to search for a high-precision quantitative engineering sweet spot evaluation method. Firstly, the effects of engineering sweet spot parameters （e.g. brittleness index, stress difference coefficient, shale content and fracture pressure） on fracturing sand volume and fluid volume were qualitatively analyzed. Then, a quantitative analysis was conducted by means of the correlation coefficient to determine principal engineering sweet spot parameters and the corresponding target evaluation indexes which characterize shale gas reservoir development. Finally, such shale gas engineering sweet spots were evaluated based on three models （i.e., single parameter model, radar area model and independence weight coefficient model） and the evaluation results were compared. The following research results were obtained. First, shale content, brittleness index, calcareous content and stress difference coefficient are the main engineering sweet spot parameters. Second, the multi-target evaluation problem, which occurs when the engineering sweep spot is characterized by using sand volume and fluid volume, can be avoided effectively by characterizing the engineering sweet spots by means of sand carrying ratio. Third, the evaluation precision of engineering sweet spots is the highest in the independence weight coefficient model, secondary in the radar area model and the lowest in the single parameter model. Field application effects in three fracturing wells also show that the quantitative evaluation result of engineering sweet spots in shale formations by the independence weight coefficient model is reliable. To sum up, it is appropriate to adopt the independence weight coefficient model to quantitatively evaluate the engineering sweet spots in shale gas reservoir development.