Integration of discrete fracture reconstruction and dual porosity/dual permeability models for gas production analysis in a deformable fractured shale reservoir

Permeability of gas shale in Changning region is exceptionally low and ranges from 0.76 x 10(-4) to 1.56 x 10(-4) mD, and fracturing stimulation measures can produce high diversion channels. Therefore, the technology of multi-stage fractured horizontal wells (MFHWs) is essential for commercial exploitations. Microseismic hydraulic fracture mapping (MSM) can effectively provide visual information (spatial position, hydraulic fracture geometry, and distribution complexity) and has now been currently used to evaluate and optimize the fracturing operations and well completions. The shale gas pressure changes with production time after injection and stimulation treatments, which can result in the dynamic evolution and redistribution for in-situ stresses. This study established a poroelastic porosity and permeability model for triple-continuum incorporating desorption-induced deformation, Knudsen diffusion, and viscous flow. The discrete fracture network (DFN) was interpreted by the robust occurrence calculation method based on the Random Sample Consensus (RANSAC) algorithm. This dual porosity/dual permeability (DPDP) model was more accurate than the other four classical models that were based on the single porosity and permeability model. The porosity and permeability for matrix and natural fractures decreased exponentially with production time, and the reduction ranges were less than 1% in the whole production, and the variation ranges for hydraulic fractures can reach nearly 5%. Meanwhile, the induced deformations under the same in situ stresses were maximum for the hydraulic fractures, and minimum for the inorganic pores, while intermediate for the natural fractures. Furthermore, this study compared the equilibrium desorption mechanism (EDM) with the non-equilibrium desorption/adsorption mechanism (NEDAM) on cumulative production. It was discovered that NEDAM exposed the delayed effect for the shale gas, and the calculated production for NEDAM was smaller and more reasonable than EDM. This study provided a workflow from fracture interpretation to reservoir evaluation by an effective geophysical method.

Automated summary

This study established a model to compare the effects of different desorption mechanisms on shale gas production and evaluated and optimized fracturing operations and well completions using microseismic hydraulic fracture mapping technology. The results showed that the DPDP model was more accurate than other classical models, and the variation range for hydraulic fractures could reach nearly 5%.