Bench-Scale Experiments and Field Tests of Water Flooding Among Horizontal Wells with Zipper Fractures in Tight Oil Reservoir

Changqing Oilfield has the typical characteristics of low pressure, low permeability, and low abundance. The application of horizontal well and volumetric fracturing has greatly improved the production of single wells. However, there are problems such as ineffective water flooding in five-spot pattern for horizontal wells and rapid production decline with natural depletion. To tackle these issues, we put forward a new development technology of injecting water among horizontal wells with zipper fractures to improve the water flooding efficiency. This technology transforms the traditional inter-well displacement scheme to inter-fracture displacement and imbibition to replenish reservoir energy. Bench-scale lab experiments using outcrops showed that linear displacement can be formed between zipper fractures of the injector and producer provided reasonable fracture spacing and fracture length, increasing the sweep efficiency and oil recovery. The monitored pressure profile displayed a smooth front under linear displacement and advanced uniformly with injection. Experimental results showed that most of the produced oil was gathered before water breakthrough, after which water reached fractures of the producer and water cut spiked rapidly. Therefore, reasonable technical measures should be adopted to extend the oil production period before breakthrough as much as possible. According to the principle of similarity, the horizontal well spacing and fracture spacing were optimized to be 200 m and 150 m, respectively. Field tests were carried out for 12 wells in Chang6 reservoir of Heshui Oilfield. Compared with the conventional flooding scheme in five-spot pattern nearby, the formation pressure in the tested horizontal wells was stable and increased steadily, successfully retarding the production decline. This novel zipper fracture water flooding technology provides a technical means for replenishing reservoir energy and improving oil recovery in horizontal well development of tight oil reservoirs with low natural energy.