Evidence of Reopened Microfractures in Production Data Analysis of Hydraulically Fractured Shale Gas Wells

Abstract

Abstract The triple porosity analytical model provides a way to account for shale gas production from multiple hydraulic fractured horizontal wells that may have reopened a network of microfractures in the shale during hydraulic fracturing. This behavior has also been analytically modeled as multiple parallel finite conductivity hydraulic fractures in a dual porosity formation. In theory these models may reveal a series of flow regimes exhibiting linear, bilinear, and even trilinear flow. In practice, characterizing the various flow regimes is challenging because typically only one or two of them are likely to appear in any one transient data set. This work concludes possible theoretical flow regime combinations which may be seen in fractured shale gas wells based on the dual and triple porosity models. Then sensitivity studies are investigated using typical shale gas formation and completion parameters to identify under what conditions in practice the transient data may reveal the flow regimes sensitive to microfractures and how likely or unlikely the those flow regimes could be present in field data. Investigation of production rate and pressure field data from Barnett and Horn River shale formations illustrates that confirmation of a reopened fracture network, or "complexity", as this has been called by some authors, is not obvious even though some cases show the model related to reopened fracture network yield better matches than the homogeneous model. This work emphasizes that interpretation using different models may yield significantly different results while still matching the observed behaviors equally well. Though buildup data may help to reduce uncertainties of parameters related to features visible at very early time, the variation of production forecast and recovery estimation is still expected if the model predicts large volume of reopened fracture network with ultra-low shale matrix permeability.