Fractuability Evaluation of Chang 8 Tight Sandstone Reservoir in Ordos Basin: Construction of Geological-Engineering Dual Sweet Spot Model and Multi-factor Collaborative Mechanism Study

Aiming at the low development benefit of the Chang 8 tight sandstone reservoir in Yongning River Area, Ordos Basin, the main controlling factors of its frac ability were studied, and a comprehensive evaluation model of the coordination of geological and engineering parameters was established to provide a basis for the optimization of fracturing sweet spot. The micro-pore structure of the reservoir was analyzed by casting thin slice, scanning electron microscope and high pressure mercury injection experiment. The static/dynamic elastic modulus and Poisson's ratio of rock are obtained by triaxial mechanics experiments. Based on brittleness index, fracture toughness and horizontal stress difference, an evaluation model of geological engineering is established by using the independent weight coefficient method and grey correlation analysis. The results show that the reservoir in the study area is dominated by class I pore throat (average pore throat radius 0.101μm), and the horizontal stress difference (50.54~61.84MPa) dominates the fracture propagation direction. Brittleness index (weight 0.4792) and porosity (weight 0.2591) are the core indexes of frac ability. The reservoirs are divided into three types in the model, and Class I has the highest comprehensive compressibility index (7 points), which has the potential of complex fracture network formation. A geology-engineering double dessert evaluation model is proposed, and the independent weight coefficient method is combined with grey correlation analysis for the first time to quantify the weight of main control factors, which provides a new method for efficient fracturing of tight sandstone reservoirs and has important engineering application value.