Fracability Evaluation Of Shale Gas Reservoirs In Zhaotong District

Shale gas reservoirs have low porosity and low even ultra low permeability.Usually,more than 90% of the shale gas wells should be fractured to realize commercial production.Hydraulic fracturing is a widely used stimulation techniques in the petroleum industry for enhanced hydrocarbon recovery from low permeable reservoirs,which has been adopted for the development of shale gas wells.Even though hydraulic fracturing has been used for a half century and achieved good results in low permeable reservoirs,recently,petroleum industries are still facing a number of issues: fracturing of arbitrarily oriented wellbores,role of performation practices and existing of natural weak plane.Therefore,fracability evaluation and the estimation of hydraulic facture initiation should be conducted using well logging data to avoid fracturing blindly.In order to solve these issues,this paper presents a set of methodology to evaluate the facability of shale gas reservoirs.With the full application of array acoustic logging and electrical imaging logging data,the hydraulic fracture initiation pressure of an arbitrarily oriented wellbore in an arbitrarily stess regimes is predicted for different formation conditions.At last,the fracability index is proposed to evaluate the fracturing performance of shale gas reservoirs,combining the brittleness and fracture toughness.Some content includes:1.A detailed research of mechanical properties in isotropic and transversely isotropic formation has been conduted.Proper calculation models of rock mechanical parameters were established on the foundation of rock mechanic experimental data.2.Combined with the statistical experimental data,a sonic velocity model was built by fully considering the influence of porosity,organic content and effective stress on sonic velocity.A new pore pressure prediction method for shale gas reservoirs was proposed based on this model.3.According to the mini-fracture,the horizontal stress models in isotropic and transversely isotropic formations.were corrected for Zhaotong District.The influence of an arbitrarily oriented wellbore,an arbitrary stress regime and weak plane on hydraulic fracture initiation pressure was discussed.The initiation pressure model for vertical and horizontal wellbore were proposed.4.The impact of brittleness,fracture toughness and naturally weak plane on facability were discussed in this paper,and the fracability index was calculated by a proper model to evaluate the fracturing performance.