Loading...
Compositional modeling of gas injection in tight oil reservoirs
Tian, Ye
Tian, Ye
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2021
Date Submitted
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
The commercial development of tight oil reservoirs has reshaped the landscape of the petroleum industry in North America. However, the recovery factor (RF) of tight oil with primary depletion is very low, mostly below 10%. With a large volume of remaining oil in tight oil reservoirs, the successful execution of Improved/Enhanced Oil Recovery (IOR/EOR), even with a minor improvement of 1%, would prompt a substantial production increase. Based on various field pilots, gas injection is by far the most promising IOR/EOR technology for tight oil reservoirs. This work developed an improved compositional model and its associated simulator to understand the complex multiphase and multicomponent behaviors during gas injection into tight oil reservoirs. The model accounts for the key physics in tight oil reservoirs, including nanopore confinement, multicomponent diffusion, and their coupling with geomechanics. Firstly, a hybrid algorithm combining the Successive Substitution and Newton's method was presented to improve the phase equilibrium calculation under confinement. Secondly, a modified formulation of the Maxwell-Stefan equation was presented to better quantify the multicomponent diffusion driven by the chemical potential gradient. A physics-based improvement was then proposed for the advection-diffusion model in fractured reservoirs, where fracture, matrix, and their interface are represented by three different yet interconnected continua to better capture the transient mass exchange between fracture and matrix. Thirdly, the transport is fully coupled with geomechanics during the computation of both primary and secondary variables. The numerical technique of solving the proposed model is also detailed, with special considerations to handle the numerical issues encountered during gas injection modeling. With the more general compositional model presented above, major modifications are implemented in Fortran to update the in-house simulator MSFLOW-COM for better modeling the gas injection processes in tight oil reservoirs. Fourthly, the implemented multicomponent diffusion formulation is validated with both intraphase and interphase diffusion experimental data. For the matrix-fracture mass transfer, the implemented MINC approach with three continua can better match the results of the fine grid model than the conventional double-porosity approach. The developed simulator MSFLOW-COM is validated with a commercial compositional simulator for both primary depletion and gas injection. After validation, the simulator is used to carry out two case studies. The first case study based on the Eagle Ford play investigates the impact of nanopore confinement, geomechanics, and their coupling. The simulation shows that the nanopore confinement has a minimal impact on RF for depletion and the early cycles of gas huff-n-puff (HnP), but in the long run, it reduces RF of the light components and increases RF of the heavy components. Geomechanics is an important factor in production but not always detrimental. The second case study based on the Permian Basin Wolfcamp Shale investigates the effect of multicomponent diffusion within the fractured tight oil reservoir. The simulation reveals that multicomponent diffusion has a minor impact on the performance of depletion as oil is the dominant phase. For gas injection, the simulation neglecting diffusion will underestimate the oil RF. With the diffusion included in the model, gas HnP becomes more sensitive to the soaking time than that without diffusion. Though a longer soaking time will achieve a higher RF after considering diffusion, the incremental oil is not high enough to justify a prolonged soaking time. Simulation using the double-porosity approach leads to a similar cumulative oil RF but overestimates the RF of heavy components compared with the MINC approach with three continua. To the best of the author's knowledge, the above studies cannot be done with any commercial simulators, which neglect fundamental physics, including nanopore confinement, multicomponent diffusion, and their coupling with geomechanics. The developed model and its associated simulator in this work can help researchers better understand the complex multiphase and multicomponent behaviors in tight oil production as well as be of great use for engineers to optimize gas injection parameters in field applications.
Associated Publications
Rights
Copyright of the original work is retained by the author.