The effect of natural fracture's closure on long-term gas production from unconventional resources

Abstract

The future U.S. and world energy supply is supported by the observed trends of long-term production forecasts from unconventional resources. Also, recent innovations in multi-pad horizontal drilling and hydraulic fracturing empower such trends to be economically viable. Nevertheless, the triggered fractures in an unconventional reservoir rapidly shrink, as a result of produced gas that leads to a significant loss in long-term production. Hence, it is critical to quantify the effect of fracture closure on long-term production for to reach an accurate production forecast. In this paper, the permeability changes of secondary fractures network are investigated with respect to their effect on the long-term gas production from unconventional resources.An analytical trilinear model is revised and improved in order to handle the constant bottom-hole pressure production scenario and hence analyzing the cumulative gas production by considering the effect of stress on natural fracture permeability. In addition, a comprehensive sensitivity study is performed to rank the influence of uncertain parameters on cumulative production and consequently identify a condition in which a severe effect of pressure-dependent natural fracture on production is observed. It is concluded that the pressure-dependent natural fracture permeability can cause up to ten percent less cumulative production than considering the constant natural fracture permeability. Also, the improved analytical model is very fast and robust compared to the commercial numerical simulators. The advantage of this approach is to obtain a quick and accurate assessment of the complex production behavior of unconventional reservoirs. The findings of this paper provide valuable insights into long-term investment on unconventional reservoirs and guide decision making for the secondary or tertiary enhancement treatments of unconventional wells, such as re-fracturing.