Research status and discussion of horizontal well interference in shale oil and gas reservoirs

Low-permeability shale reservoirs can hardly form industrial oil and gas flow naturally, and their commercial production is commonly realized by using horizontal well and hydraulic fracturing to create hydraulic fracture networks. As large-scale infill well deployment and fracturing is conducted, however, horizontal well spacing gets short and stimulated reservoir volume (SRV) is increased, so interference induced by hydraulic fractures occurs between wells, which impacts the wellhead pressure and production rate of the neighboring well and even induces the problems of well control, casing damage and proppant invasion and seriously results in the abandonment of horizontal well, so as to impact the production efficiency greatly. In addition, the depletion of old wells can lead to the dynamic evolution of reservoir geostress on the basis of the in-situ geostress to form the complex geostress state, which will impact the reservoir stimulation effects of infill horizontal wells and refracturing wells and restrict the productivity performance of well pads. The development of the shale oil and gas resources in the Junggar Basin, the Sichuan Basin and the Ordos Basin of China has stepped into the stage of small well spacing and infill well deployment, so well interference has already impact the normal production obviously. Therefore, it is in urgent to carry out specific studies. In this paper, domestic and foreign well interference phenomena, mechanism studies and diagnosis methods of shale oil and gas were introduced in details, and the intervention countermeasures were proposed. It is indicated that accurate characterization and prediction of fractured horizontal well interference shall be carried out in the framework of geology and engineering integration. The accurate understanding of natural fractures, faults, in-situ geostress and reservoir rock mechanical characteristics is the prerequisite to evaluate well interference. The modeling and characterization of formation depletion induced dynamic geostress and complex hydraulic fracture network is the key means to quantitatively evaluate the interconnection of complex fracture network between wells, as well as the effective method to quantitatively predict the impact of well interference on the estimated ultimate reserve (EUR) of well pad. Well shutdown, liquid injection into old well, refracturing, well spacing optimization and fracturing optimization are the means to intervene or diminish well interference.