Flow mechanism of production decline during natural depletion after hydraulic fracturing of horizontal wells in tight oil reservoirs

Abstract

Currently, there are problems regarding decreasing production rates and low recovery factors in the field test during depletion development of staged fractured horizontal wells in tight reservoirs. However, the production decline mechanism during the depletion development process is not clear at present; so, it is necessary to further explore the pressure distribution law and production decline mechanism in order to guide subsequent tight reservoir exploitation and to improve the recovery factor. In this study, a multi-point pressure measurement physical simulation experiment system, a pressure distribution mathematic model, and a mathematic productivity model were developed. After fitting the model with the experimental data, the production decline mechanism during depletion development of tight oil reservoirs was analyzed from four aspects. The results show that in lower permeability tight reservoir facies, the pressure propagation distance is shorter. The pressure gradient of tight oil reservoirs during depletion development is four times higher than that of low permeability reservoirs. As the permeability decreases, the seepage resistance coefficient increases exponentially. The seepage resistance in tight oil reservoirs is nearly six times higher than that in low permeability reservoirs. Compared with traditional enhanced oil recovery (EOR) techniques, inter-fracture flooding has obvious mechanism advantages in the EOR of tight reservoirs.