Long term effect of natural fractures closure on gas production from unconventional reservoirs

Observed trends of long-term production forecasts of unconventional assets tend to secure US energy supply for decades to come. Also, recent innovations in horizontal drilling and hydraulic fracturing support such trends to be economically viable. However, triggered fractures in an unconventional reservoir rapidly shrink and will result in significant long-term production loss. Hence, it is essential to quantify the effect of fracture closure on long-term production. In this paper, the permeability changes of secondary fracture network are investigated with respect to the effect on the long-term gas production from unconventional reservoirs. A simple analytical trilinear model is improved in order to handle the constant bottom-hole pressure production and analyze the cumulative gas production by considering the effect of stress on natural fracture permeability. Moreover, a sensitivity study is performed to identify the influence of uncertain parameters on cumulative production and consequently detect a condition in which the pressure-dependent natural fracture effects on production are severe. It is observed that the pressure-dependent natural fracture permeability can cause up to ten percent less cumulative production than the constant natural fracture permeability conditions. The improved analytical model is very fast compared to the commercial numerical simulators. The advantage of this approach is in obtaining a quick and accurate assessment for operators in the pre-evaluation process of the complex production behavior of their unconventional resources. The findings of this paper provide insights into long-term investment of unconventional reservoirs and guide decision making for the secondary or tertiary enhancement treatments of unconventional wells, such as re-fracturing.