Gas Injection Pilot Design Simulation Model in Eagle Ford
Authors: Basbug Basar , Sarak Hulya , Firincioglu Tuba , Ozgen Chet , Parada Machado Claudia , Yuan Chengwu , Chapman Philip 
Published: April 2022

The primary objectives of this study are to design a gas injection pilot in the Eagle Ford and to estimate the benefits of gas injection under different operational scenarios. This pilot design study entails the construction of multiple reservoir simulation models to understand the hydraulic fracturing and flow dynamics of multiple wells and gas injection operations in the Eagle Ford.

Two DSUs with multiple hydraulically fractured wells were studied to achieve the proposed objectives. One of the DSUs was identified as the main study area to design a huff-and-puff gas injection pilot. Having an existing gas injection operation, the other DSU was selected to improve our understanding of the physics associated with gas injection. A dual porosity numerical reservoir simulation model coupled with geo-mechanics was built to replicate the historical well performances of the pilot area using a sophisticated numerical reservoir simulator. Another dual porosity simulation model was constructed to assimilate the existing huff-and-puff performance of the second DSU in which data was only publically available.

The methodology used in this study integrates the hydraulic fracturing process, multi-phase flow, geo-mechanics, and proppant transport within the reservoir simulation. The simulation model was calibrated to match the historical hydraulic fracture treatment, fluid flow back and post-stimulation production. The proppant entrapment and migration from child well to the parent well was captured. The calibrated simulation model was then utilized to design a huff-and-puff gas injection pilot. Learnings and observations obtained from modeling of the existing gas injection operation in the second DSU were integrated into the pilot model. Additional sensitivity runs were performed to examine the potential benefits of gas injection under different operational scenarios.

The calibration results indicated that the stimulated rock volume geometries of pilot study wells vary based on their completion practices. The historically observed well interference and frac hits between parent and child wells were captured by establishing a proper connectivity between wells during calibration. Proppant entrapment and movement of the proppant impacted the well performance. The results showed that significant amount of depletion leads to considerable matrix permeability reduction around wells. The most important knowledge gained from the calibration of the second DSU with huff-and-puff data is the identification of reservoir model characteristics that have the largest impact on the huff-and-puff performance.

This study allows us to identify opportunities to design and improve huff-and-puff operation as well as estimating benefits of gas injection under different operational scenarios. The utilized technology in this study is unique and novel as it solves the geomechanics and flow in a single process. Proppant flow and entrapment was captured successfully. The multi-well calibration of the simulation model provides physics-based explanations for the historical well performances in the Eagle Ford.