Oil & Gas Geology ›› 2018, Vol. 39 ›› Issue (4): 823-832,838.doi: 10.11743/ogg20180419

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Calculation and analysis of unsteady production of different fractured injection-production patterns in low permeability reservoirs

Pu Jun1,2,3, Qin Xuejie1, Gou Feifei1, Fang Wenchao1   

  1. 1. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China;
    2. Institute of Porous Flow and Fluid Mechanics, Chinese Academy of Sciences, Langfang, Hebei 065007, China;
    3. University of Chinese Academy of Sciences, Beijing 100190, China
  • Received:2018-04-23 Revised:2018-05-21 Online:2018-08-28 Published:2018-07-23

Abstract:

Waterflooding in fractured reservoirs,an important way to develop low permeability reservoirs,can effectively improve the flow field effectiveness and increase oil discharge area. Rapid and accurate prediction of production of low permeability reservoirs with water injection can establish a foundation for optimal design of development. However,the flow field of water injecting into low permeability reservoirs presents unsteady and nonlinear flow characteristics,so the calculation methods based on Darcy's law are not applicable. After the analysis of flow fields,the equivalent flow units are divided. Taking the threshold pressure gradient of oil-water two-phase flow into consideration,we established the analytical calculation method for unsteady oil production with injection in different fracturing modes,based on the flow line integral method. And the method is simpler and faster compared with physical and numerical simulations,so it is applicable for optimizing fracturing injection and production well patterns and water injection development strategies in low permeability reservoirs. Besides,this method was used to calculate and analyze the effects of threshold pressure gradient,fracturing injection and production methods and fracture lengths on the productivity of oil wells. The results show that (1) the greater threshold pressure gradient leads to larger seepage resistance,so the well productivity is lower than that without considering the threshold pressure gradient; (2) the well productivity is controlled by flow units,so with different fracturing injection and production modes,the effects of production increase and the time of water breakthrough are completely different. Although the increase of production with simultaneous fracturing injection and production is the best,being 3.1 times that of other modes,the water breakthrough time is just 24 months; (3) with the increase of fracture length,the oil production increases,whereas the effect of increased oil production is not obvious any more when the fracture length exceeds the optimum length.

Key words: threshold pressure gradient, flow line integral method, non-steady production, seepage resistance, fracturing injection and production mode, low permeability reservoir

CLC Number: