Overview of CO2 Injection and WAG Sensitivity in SACROC

Abstract

This paper presents an overview of the SACROC Unit's activity focusing on different CO 2 injection and WAG projects that have made the SACROC Unit one of the most successful CO 2 injection projects in the world. The main objective of this work was to review CO 2 injection and injection rate losses due to the CO 2 /WAG miscible displacement process in the SACROC Unit and recommend an injection strategy for WAG-sensitive patterns.Two types of pattern CO 2 /WAG injection rate performance were observed, 1) WAG-sensitive and 2) WAG insensitive. WAG-sensitive patterns displayed loss of CO 2 injectivity, exceeding 80% in some patterns, during water-alternating-gas (WAG) injection, and an apparent reduction in water injectivity during the follow-up brine injection. This injectivity loss was observed in over 150 injection patterns. Over time, CO 2 injectivity tended to return to prior-to-WAG values. WAG-insensitive patterns suffer from these injectivity losses and were characterized by differences in 1) injectivity profiles, 2) Dykstra-Parsons coefficients, and 3) injectivity indexes.In the majority of WAG-sensitive patterns, injectivity profiles redistributed after CO 2 injection, while WAG-insensitive patterns did not show a significant change in their injectivity profiles over time. In a limited data set, the mean Dykstra-Parsons coefficient calculated for WAG-sensitive patterns was 0.83, while for WAG-insensitive patterns the mean Dykstra-Parsons coefficient was 0.76. However it was observed that in the lower Dykstra-Parsons patterns (WAG-insensitive patterns) much larger injectivity indexes were also observed; 19.5 bbl/day/psi, compared to 8.5 bbl/day/psi for higher Dykstra-Parsons patterns. This suggests that the WAG-insensitive patterns were dominated by fracture flow rather than matrix flow. These observations indicate that the WAG injection process in these heterogeneous SA-CROC wells is successful in diverting the injected fluids from zones with higher permeability to zones with lower permeability.For wells with injectivity values of less than 10 bbl/day/psi it is recommended to begin CO 2 /WAG injection with a long CO 2 cycle since they are likely to show sensitivity to WAG.A simulated 5-spot pattern was used to study the injection schedule for WAG-sensitive patterns. Longer CO 2 cycles and shorter water cycles improved the injectivity and pattern production. Most importantly, it was observed that increasing producing BHP to MMP resulted in significantly lower GOR.

Innovative CO2 Injection Strategies in Carbonates and Advanced Modeling for Numerical Investigation

“…This fact produces changes on the bottom hole pressure and flow rate injected on site due to the fluid properties and the injection sequence used, which induced an injectivity decrease during the testing period. Ghahfarokhi et al [37] concluded similar conclusions for porous mediums in their study of the SACROC EOR project in Texas (USA).…”

“…On the other hand, tests conducted in the flow rate control mode showed the pressure increases at the well-head to hold a constant flow rate value. The discussion is focused on whether these results correspond to wellbore effects in the short-term, as de Dios et al [11] proposed according to the results from Hontomín hydraulic characterization, or whether they set a trend on the long-term behavior of the pair seal-reservoir [37].…”

“…The terms of the BHP recovery depend on fluid transmissivity through the fracture network, which usually produces a slower pressure recovery than in the porous medium [11,38], as it happens in the case of the study as well. The recovery term also depends on the alternative injection (brine/CO 2 ) [37] because of the different hydraulic properties of each fluid (relative permeability) in the fractures [19] and on the cumulative CO 2 injected on site. Therefore, it is also necessary to demonstrate if this recovery trend is due to short-term effects occurred in the well vicinity or corresponds to the long-term behavior of the reservoir.…”

Techno-socio-economic analysis of geological carbon sequestration opportunities

“…This project is recorded as one of those which injected the largest amounts of CO 2 so far, globally. 17 In this project, CO 2 injection facilitates enhanced oil recovery (EOR). In this CO 2 -EOR project, about 100 million tonnes of CO 2 have been stored.…”

“…24 Current plans are outlined for pilot testing followed by field testing over an approximately 5 year period. At the pilot site, CO 2 injection and comprehensive monitoring of safety risks will occur in conjunction with lab testing and modelling work meant to monitor changes in formation permeability under sequestration conditions; 17 assuming the pilot will succeed, a larger-scale commercial site will be chosen for quantifying the field-scale efficiency of CO 2 injectivity as well as for conducting a techno-economic analysis. Best practice procedures could be learned from Australia, where carbon sequestration in deep un-mineable coal seams has been attempted.…”