Abstract：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 la-yers.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.
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