Study on Coupled Percolation Mechanism of Low Permeability Layer-High Permeability Layer-Wellbore in Giant Thick Gas Reservoir

Abstract

AbstractAB2 gas field in Tarim Basin is gas reservoir with huge thickness, abnormal high pressure and water, and its reservoir thickness is 300–400 m. Its physical properties are mainly low-medium porosity, medium-high permeability. The permeability differential coefficient in the gas reservoir is large (up to 120000). The traditional theory holds that the high permeability and low permeability reservoirs supply gas to the wellbore at the same time. Although the high permeability layer is dominant, the output of low permeability layer can not be ignored because of its great thickness.However, the actual data show that the production of gas wells is obviously non-uniform, the high permeability layer is the main channel of early gas production and late water production, and the low permeability layer does not even have direct production contribution. But with the production of the high permeability layer, the formation pressure of the low permeability layer decreases basically synchronously with the high permeability layer, and the reserves of the low permeability layer are also effectively used.In order to reveal this phenomenon, this paper makes a comprehensive analysis by comparing the measured data, establishing a theoretical model and carrying out numerical simulation research, the multi-stage coupled percolation mechanism with low-permeability-high-permeability and high-permeability wellbore flow is put forward. And the real cause of non-uniform water invasion and non-uniform water production in gas wells is revealed.Based on this understanding, aiming at the heterogeneous gas reservoir with huge thickness, this paper puts forward the technical policy of producing in the middle permeability layer and draining in the low permeability layer, which has important guiding value for the next development.KeywordsGiant thick gas reservoirLow permeability layer-high permeability layer-wellboreCoupled seepage flowExtremely poor permeabilityNon-uniformityTechnical policy