Simulation Study Of CO₂ Huff-n-Puff In Tight Oil Reservoirs

Tight oil formation is formation with an ultra-low permeability(less than 0.1×10^-3μm²).The exploitation of tight oil reservoirs has been becoming a topic of interest to many researchers.The combination of multi-stage hydraulic fracturing and horizontal drilling has improved the overall profitability of tight oil reservoir by enhancing the wellbore-matrix connectivity.However,the primary oil recovery factor is very low and typically less than 10%,resulting in oil resource remaining in place.The choice of methods and techniques also depends on the characteristics of reservoir and fluid properties.A new idea is to use EOR methods to improve the recovery of tight oil reservoir,in which,the CO₂huff-n-puff is one of the potential recovery method.In this study,the Middle Bakken member is used for our base case.We created a model based on its rock and fluid properties.By employing compositional model simulation,miscible gas injections were simulated and the reservoir behavior was analyzed.Reservoir and fracture properties were modified for analyzing their impact on the oil recovery performance for CO₂injection.Simulation results have shown the increase of oil recovery factor from 2.56%to 8.97%of OOIP over 30 years.Results from simulation have revealed that the improve of oil recovery depends on some key parameters such as reservoir permeability,number of fractures per stage,fracture permeability,CO₂injection rate,CO₂injection time,CO₂soaking time,number of CO₂ huff-n-puff cycle.Besides,an investigation has proved that the increase of some parameters such as the number of fracture per stage,CO₂injection rate,and CO₂soaking time does not really affect the oil recovery depending on the case.However,the fracture permeability and the CO₂injection time usually affect consequently the oil recovery.It also revealed that there is an optimal value for some parameters such as CO₂ soaking time,after which any increase will not increase the oil recovery.The development of some regression equations has revealed that the best fit is the polynomial regression.The overestimation of oil reserve by Duong model is evaluated when the flow regime changes from linear flow.Gas injection EOR project is integrated project,and the viability of a project also depends on different economic conditions.