Abstract
Understanding the changes of the near-wellbore pore pressure associated with the reservoir depletion is greatly significant for the development of ultra-deep natural gas reservoirs. However, there is still a great challenge for the fluid flow and geomechanics in the reservoir depletion. In this study, a fully coupled model was developed to simulate the near-wellbore and reservoir physics caused by pore pressure in ultra-deep natural gas reservoirs. The stress-dependent porosity and permeability models as well as geomechanics deformation induced by pore pressure were considered in this model, and the COMSOL Multiphysics was used to implement and solve the problem. The numerical model was validated by the reservoir depletion from Dabei gas field in China, and the effects of reservoir properties and production parameters on gas production, near-wellbore pore pressure and permeability evolution were discussed. The results show that the gas production rate increases nonlinearly with the increase in porosity, permeability and Young’s modulus. The lower reservoir porosity will result in the greater near-wellbore pore pressure and the larger rock deformation. The permeability changes have little effect on geomechanics deformation while it affects greatly the gas production rate in the reservoir depletion. With the increase in the gas production rate, the near-wellbore pore pressure and permeability decrease rapidly and tend to balance with time. The reservoir rocks with higher deformation capacity will cause the greater near-wellbore pore pressure.
Highlights
With the rapid advances of the oil and gas exploration and development, ultra-deep oil and gas resources have become the hot spot of the exploration and development around the world (Tong et al 2018)
0.28 implies that the gas production rate has a great impact on the rock deformation in reservoirs, and too high gas production rate is not conducive to the stable production capacity in the reservoir depletion
The rock Young's modulus and Poisson's ratio describe the rock deformation response under the deformation condition, which considers as the significant mechanical properties and can be used to predict the geomechanical behavior in
Summary
With the rapid advances of the oil and gas exploration and development, ultra-deep oil and gas resources have become the hot spot of the exploration and development around the world (Tong et al 2018). The exploration and development of ultra-deep natural gas reservoirs are faced with the complex environments of high temperature, high pressure and high in situ stress, and there exist the complex multiphysics-coupled processes of the fluid flow between the reservoir and the wellbore (Selvadurai et al 2018; Lei et al 2021). In the depletion of ultra-deep natural gas reservoirs, the reservoir deformation caused by overburden pressure results in considerable change of porosity and permeability, which will affect the reservoir production performance. There is a significant necessity to understand the coupled geomechanics and fluid flow behavior on these extreme conditions so as to optimize extraction conditions and maximize gas productivity in ultra-deep natural gas reservoirs. A mathematic model was developed to describe the coupled fluid flow and geomechanics deformation caused by pore pressure in ultra-deep natural gas reservoirs. The effects of reservoir properties and production parameters on gas production, near-wellbore pore pressure and permeability evolution were discussed
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