吉木萨尔致密油储层脆性及可压裂性预测

Brittleness and fracability prediction for tight oil reservoir in Jimsar Sag,Junggar Basin

致密油气储层具有非均质性强、物性差、单井产量低、开发难度大等特点,为了准确识别高脆性层段,建立地层可压裂性模型,总结、比较了现有脆性指数在致密油气储层脆性评价中的适用性,提出了适用于吉木萨尔地区的改进矿物组分法脆性指数,并在此基础上,分析了地层可压裂性与岩石脆性、断裂韧性、抗压强度的关系,提出了三者结合的可压裂性指数。研究表明:基于数据驱动的方法,认为白云石、长石和黄铁矿含量是影响吉木萨尔地区致密油储层岩石脆性的主要因素;致密油储层地层条件复杂,高脆性指数地层不一定具有良好的可压裂性,仅利用岩石脆性描述可压裂性还不够完善;新的可压裂性指数表明,具有较高岩石脆性指数、较低断裂韧性和抗压强度的地层为有利压裂层段。将新方法用于吉木萨尔J174井可压裂性预测,优选可压裂层段,对指导水力压裂施工具有重要意义。

Tight oil and gas reservoirs are characterized by significant heterogeneity,poor physical properties,low single-well production,and great difficulties in the development.In order to identify high brittle formations and establish accurately a fracability prediction model,we summarize and compare the applicability of the existing brittleness index for the brittleness evaluation of tight oil reservoirs,and put forward a modified mineralogical brittleness index with favorable applicability in Jimsar Sag,Junggar Basin.On this basis,we analyze the relationships between fracability and brittleness,fracability and fracture toughness,and fracability and compressive strength.Finally we propose a new fracability index.Based on our study,the following understandings are obtained:a.The contents of dolomite,feldspar,and pyrite are the main factors which affect rock brittleness of tight oil reservoirs in Jimsar Sag;b.Formations with high brittleness index do not necessarily have good fracturing candidate due to the complex condition of tight oil reservoir,only brittleness alone cannot characterize accurately the fracability;c.Based on the new fracability index,formations with higher brittleness,lower fracture toughness and compressive strength are considered as good fracturing layers.This new method is applied in the fracability prediction for the Well J174 in Jimsar Sag,which optimizes fractured sections to guide hydraulic fracturing operations.