Plains CO2 Reduction (PCOR) Partnership (Phase II) - Williston Basin Field Demonstration, Northwest McGregor CO2 Huff 'n' Puff - Regional Technology Implementation Plan (RTIP)

The Plains CO2 Reduction (PCOR) Partnership has conducted field and laboratory activities to determine the effects of injecting carbon dioxide (CO2) into a Williston Basin oil field. The purpose of the activities was to evaluate the potential dual purpose of CO2 storage and enhanced oil recovery (EOR) in carbonate rocks deeper than 8000 ft. Activities were conducted to 1) establish the baseline geological characteristics of the injection site, 2) determine the effect that CO2 has on the ability of the oil reservoir to store CO2 and produce incremental oil, and 3) evaluate the ability of Schlumberger’s reservoir saturation tool (RST) and vertical seismic profile (VSP) technologies to detect a small-volume CO2 plume in a deep carbonate reservoir.

While the CO2-based EOR operations at the Weyburn and Midale fields in Saskatchewan are good examples of economically and technically successful injection of CO2 for simultaneous EOR and sequestration, the depths of injection in those fields are relatively shallow (ca. 4600 ft) and not necessarily representative of many large Williston Basin oil fields. One of the primary goals of the PCOR Partnership Phase II Williston Basin Field Validation Test was to evaluate the effectiveness of CO2 for EOR and sequestration in oil fields at depths greater than 8000 ft. To achieve that goal, a CO2 huff ‘n’ puff (HnP) test was conducted on a well that is currently producing oil from the Mission Canyon Formation at a depth of approximately 8050 ft in the Northwest McGregor oil field in Williams County, North Dakota. During the test, 440 tons of CO2 was injected into a single well and allowed to “soak” for 2 weeks, after which the well was put back onto production. Unique elements of the Northwest McGregor Mission Canyon reservoir as compared to other HnP operations in the literature, include the following: 1) at a depth of 8052 ft, it would be among the deepest; 2) pressure (3000 psig) and temperature (180°F) would be among the highest; and 3) most HnPs in the literature are in clastic reservoirs, while the Northwest McGregor Mission Canyon reservoir is a carbonate reservoir.

The dynamic response of the injection zone was evaluated for changes over the course of the project using the RST and VSP, pressure monitoring, and fluids analysis from the injection well and another nearby producing oil well. Using a petrophysical model of the reservoir, iterative dynamic simulations of the fate of CO2 in the target reservoir were developed. Each iteration was based on the acquisition of new data over the course of the baseline characterization, injection, and postinjection activities. These simulations were compared to actual postinjection reservoir conditions as monitored over the duration of the study period.

The simulations demonstrated the importance of considering the effects of fracture networks on CO2 movement when CO2 mobility and fate are predicted. The results of the RST and VSP indicated that the CO2 penetrated approximately 300 feet horizontally and as much as 100 feet vertically into the reservoir. Productivity of the oil well was observed to more than double over the course of a 3-month production period, increasing from a baseline oil production rate of 1.5 stock tank barrels (STB) a day to 3 to 7 STB a day. The percentage of oil in the produced fluid, commonly referred to as the “oil cut,” also more than doubled, going from 2.8% to 6%. Overall, the results of the field demonstration indicate that 1) CO2-based HnP operations may be a viable option for EOR in deep carbonate oil reservoirs and 2) the RST and VSP technologies may be effective MVA tools for deep carbonate oil reservoirs.

Tags: CCS, CO2, EOR, PCOR, Phase II, Williston Basin