Boosting Oil Recovery in Naturally Fractured Shale Using CO2 Huff-n-Puff

Abstract

Although hydraulic fracturing in Liquid-Rich Unconventional Reservoirs (LUR) have become a norm, the recovery factor continues to be low. Use of Enhanced Oil Recovery (EOR) techniques in LUR have recently become more popular to improve the recovery. The objective of this study is to numerically investigate the advantages and disadvantages of the application of CO2 huff-n-puff technique in the LUR formations having complex fracture networks. The study explores the fluid flow mechanisms for oil recovery in the naturally fractured reservoir. A calibrated 3D mechanical earth model with geomechanical and petrophysical property from the Eagle Ford was used for the study. Complex hydraulic fracture model was used to simulate the hydraulic fractures, proppant and fluid distribution around the wellbore. Numerical reservoir simulation on a Perpendicular Bi-section (PEBI) grid was used to capture the permeability, porosity and conductivity distribution due to the proppants in the hydraulic fractures. CO2 huff-n-puff technique using numerical reservoir simulation is used to determine the well performance and recovery factor arising from reservoir fluid viscosity reduction and gas expansion. Effect of fluid thermodynamics to recovery systems in the low permeability reservoir medium is fully captured in approach. Equation of state prepared for simulating the CO2 impact on the oil is prepared with correlating the collected down hole oil sample. Numerical reservoir simulation study coupled with the complex fracture simulation model presents the insights of new means to improve RF in LUR through the injection of CO2. Such EOR method would be critical to increase the long term economic benefits. The study demonstrates that the infill well requirements can be mitigated if the EOR method of Huff-n-puff is utilized in cyclic modes over various time periods of production. Up to 9% extra RF was observed when CO2 Huff-n-puff technique was used as compared to production dependent only on hydraulic fracture stimulation. Parametric sensitivity on job sizes and start timing of EOR in a producing well is used to evaluate the RF. However, the hydraulic fracture geometry and the created footprint along with the time of injection has a larger effect in improving the EOR effectiveness. The methodology provides the demonstration of simulating the EOR methods in unconventional reservoirs for economic assessment. The workflow demonstrates modeling CO2 flooding as an EOR technique on the full wellbore level with complex hydraulic fracture geometry. The approach demonstrated here can be applied to other basins in the unconventional formations to improve the recovery factor.

Huff-n-Puff Technology for Enhanced Oil Recovery in Shale/Tight Oil Reservoirs: Progress, Gaps, and Perspectives

“…Immersed-core H-n-P experimental setups have been meticulously documented . The ∼70% of shale oil recovery was increased through H-n-P technology . The technique is widely considered to be a cost-effective gas-EOR method that works more efficiently in highly heterogeneous permeability systems …”

“…Subsequently, with an integration of these mechanisms, oil is driven back to the fractures and then to the wellbore. Schlumberger researchers assessed the effectiveness of CO 2 H-n-P in the Eagle Ford (EF) reservoir by accounting for the presence of natural cracks, diffusion coefficients, and oil characteristics . They proposed that hydraulic fracturing alone would result in an extra 9% oil recovery.…”

A New Mechanism for Enhanced Oil Recovery by CO2 in Shale Oil Reservoirs

“…Figure 9 depicts average oil saturation in the core after three days. The gas saturation (Figure 8) of the improved case has reached 20% after 12 hours, which indicates an acceptable response time compared to normal huff and puff time-scales suggested for shale oils [3,13,[15][16][17]. On the other hand, using conventional approach, no gas was formed in the grid block as shown with pink curve on Figure 8, which indicates the importance of using realistic parameters for EOS.…”

Stimulation and Sequestration Mechanism of CO2 Waterless Fracturing for Continental Tight Oil Reservoirs

“…These reactions can increase the porosity and permeability of reservoirs and improve crude oil flowability. As a result, CO 2 fracturing could significantly enhance oil recovery and CO 2 sequestration. − Although the interaction mechanism and sequestration effect of CO 2 -enhanced oil recovery (CO 2 -EOR) under relatively low pressure and injection rates have been quite widely investigated, − the stimulation and sequestration mechanisms of CO 2 fracturing under higher pressure and injection rates have not been widely reported . Some researchers investigated the effect of CO 2 –rock interactions on porosity, permeability, and mechanical properties for the Lujiaping and Longmaxi formations of the marine sedimentary Sichuan Basin during the CO 2 fracturing treatment .…”