Rock mechanical properties and fracability evaluation of deep tight hybrid sedimentary rocks reservoirs-a case study of Lucaogou formation in Jimsar Sag, Junggar Basin

The exploration and development of the tight reservoirs in the Lucaogou Formation of the Junggar Basin have been poorly stable due to poorly understanding of rock mechanical properties and the lack of a reasonable fracability evaluation plan. Firstly, the impacts of confining pressure on the rock mechanical parameters such as compressive strength, Young’s modulus, Poisson’s ratio, and tensile strength were analyzed, through the trial mechanical test under multilevel confining pressure, the whole mineral analysis with X-ray diffraction (XRD), and Brazilian test on hybrid sedimentary rocks. Subsequently, the relation between fracability and brittleness, fracture toughness, difference coefficient of horizontal principal stress and compressive strength of the rock were systematically studied. Then, quantitative evaluation model of fracability was established via the analytic hierarchy process. The results indicated that the compressive strength of rock increased, the elastic modulus increased, Poisson’s ratio decreased, along with the increase of confining pressure. Additionally, the difference of horizontal principal stress determined the ductility of fractures, and the horizontal principal stress difference coefficient determined the complexity of fractures. Finally, test results illustrated that productivity index was positively correlated with fracability index. The micro-seismic monitoring results further confirmed that the fracability evaluation model established had good applicability to the tight hybrid sedimentary reservoir of Lucaogou Formation. This study could provide important reference and theoretical basis for and completion practice of deep tight oil and gas evaluation and drilling $${\sigma _c}$$ $${\sigma _V}$$ $${\sigma _h}$$ $${\sigma _H}$$ .