Optimization of Hydraulic Fracturing Parameters and Evolution of the In Situ Stress Field During Waterflooding: A Case Study of the Lower Karamay Formation Reservoir in the Bai 21 Well Block

This research investigates strategies for improving oil recovery from the highly heterogeneous conglomerate deposits of the Lower Karamay Formation in the Bai 21 Well Block of the Junggar Basin. Particular attention is given to the coordinated application of hydraulic fracturing and waterflooding to enhance the effectiveness of infill well development. An integrated approach combining geomechanical modeling, numerical hydraulic-fracturing simulation, and reservoir performance analysis was employed to systematically investigate the effects of proppant ratio, temporary plugging, and proppant placement intensity on fracture propagation, waterflood response, and stress-field evolution. The results show that a proppant ratio of 0.15 and a proppant placement intensity of 2.5 m3/m, combined with temporary plugging and diversion fracturing, can generate short and wide fractures with half-lengths of 40–45 m, effectively mitigating early water channeling and reducing interwell interference. In situ, stress-field simulations further indicate that the stress field evolves non-uniformly during injection and production. The average formation stress initially decreases and subsequently increases, with a maximum reduction of 13.7% relative to the initial value. As waterflooding progresses, the stress gradually recovers, resulting in a final reduction of 10.7%. These findings provide an important reference for the coordinated design of infill-well hydraulic fracturing and waterflooding development in similarly highly heterogeneous conglomerate reservoirs.