No abstract

Shale reservoirs play an increasingly important role in energy supply worldwide. Horizontal wells and hydraulic fracturing have created a new mandate for a better understanding of the resulted production amounts from these shale reservoirs. A parametric study, based on Marcellus shale laboratory Precision Petrophysical Analysis Laboratory (PPAL) experimental data, and reservoir simulation is conducted to understand the effects of gas slippage effect and the geomechanical effects on gas production prediction and completion design. Therefore by analyzing the critical conductivity of a reservoir prior to production it is possible to design a fracture treatment (i.e. proppant pumping strategy) which will have positive impacts on the well performance and increased ROFI (Return on Fracturing Investment). The study is conducted for three shale reservoir scenarios; non-naturally fractured reservoir, low permeable naturally fractured reservoir, and high permeable naturally fractured reservoir. In this study, we perform a comprehensive parametric study by running reservoir simulations using empirical permeability correlations developed by means of steady-state permeability data obtained under varying stress and pore pressure conditions. The full correlation incorporates both the gas slippage effect and the geomechanic effect. The contrast correlations consider either one of the effects or no effects at all. A simulation of the fluid flow in the hydraulic fracture and matrix are performed by a three-dimensional finite-difference based reservoir model. The primary and natural fractures are modeled explicitly as discrete grid blocks. Additionally, we study the impact of the two matrix permeability effects on the critical conductivity results for different bottomhole pressures, propped fracture lengths, and fracture half spacings. A similar study is also performed for the naturally fractured shale reservoir scenario. The impacts of the slippage effect (matrix) and the geomechanical effects (matrix & natural fracture) are investigated in the same way. Furthermore, an analysis of the geomechanical effect in just the natural fractures is performed, and finally an economic analysis based on the overlying trends from the study is implemented. The following are key results found throughout the study. First, the gas slippage effect (matrix) appears to play a significant role at lower pore pressures below 1000 psi, and the geomechanical effect (matrix) is significant throughout all pressure levels (250-4500 psi) for the Marcellus Shale sample. Since most production pressure never goes below 1000 psi, it is apparent that the pore pressure effect is negligible. For the production prediction study the following results were determined for all three reservoir types (non-naturally fractured reservoir, low permeable naturally fractured reservoir, and high permeable naturally fractured reservoir). If the geomechanical effect (matrix) is ignored than production will be overestimated 2.3 to 14% from 1 to 20 years. If the pore pressure effect (...