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This paper summarizes the response from foam injection in a pilot test conducted at the East Vacuum Grayburg/San Andres Unit (EVGSAU), including results of the reservoir characterization effort and an extensive monitoring program. The paper specifically presents (1) the positive injection-well response (documented with injectivity data and profile logs), (2) the positive production-well response, and (3) the economics of the foam test.
A pilot pattern (Fig. 1) in the EVGSAU, operated by Phillips Petroleum Co., was selected for a comprehensive evaluation of the use of foam for improving the effectiveness of a CO2 flood. This 4-year field trial was jointly funded by the EVGSAU working-interest owners, the U.S. Dept. of Energy (DOE), and the State of New Mexico. The Petroleum Recovery Research Center (PRRC), a division of the New Mexico Inst. of Mining & Technology, provided laboratory and research support.
Although the overall CO2 project performance at EVGSAU has been very encouraging, certain wells/patterns have shown anomalously high CO2 production. This has resulted in isolated cases of poor pattern sweep efficiency, inefficient CO2 utilization, and increased recycling costs and compression requirements. We suspected that these problems resulted from channeling of injected fluids through high-permeability zones, most likely exacerbated by dissolution of anhydrite in these zones.
The goal of the field trial was to investigate foam for conformance control to aid in suppressing this rapid CO2 breakthrough. Foam may improve injection conformance in two directions: (1) in a horizontal direction by increasing areal sweep efficiency and 2) in a vertical direction by diverting fluids to other, underinjected zones. Specifically, the prime directive of the trial was to prove that a foam could be generated and that it could change the mobility of CO2 in the reservoir. Proving or even determining economics or optimizing the size of the foam slug, while important, was not the original goal.
A geologic study delineated the major flow units and identified high-permeability layers that were channeling CO2 to a producing well in the pilot pattern. Production and injection logs were run in the producer and the injector and confirmed the channel. Laboratory work was performed at three different laboratories to determine which surfactant was most compatible with EVGSAU reservoir rock and fluids. Refs. 3 through 6 give details of that laboratory work, and Ref. 7 summarizes the work.
Siemers, W.T. (Phillips Petroleum Company) | Tisdale, M.G. (Phillips Petroleum Company) | Hallenbeck, L.D. (Phillips Petroleum Company) | Howard, J.J. (Phillips Petroleum Company) | Prezbindowski, D.R. (International Petrology Research, Inc.)
Abstract The East Vacuum Grayburg-San Andres Unit (EVGSAU) is located in the Permian Basin, Lea County, New Mexico. The EVGSAU was unitized in 1978 and has been under waterflood operations since 1979. CO2/water injection (WAG injection) commenced in 1986. An interdisciplinary reservoir study was initiated in 1994 to integrate the unit's geological character and reservoir performance in order to optimize the CO2/waterflood. This paper examines the sedimentologic and stratigraphic framework, lithologic character, pore system, quality and continuity, and architecture and internal geometry of the reservoir and their application to safeguarding prime CO2 flood performance within the reservoir. The Permian-aged San Andres Formation is composed of two major, eustatically controlled, upward-shallowing carbonate ramp sequences that contain multiple, anhydritic, dolomitized successions in which subtidal grain-rich lithofacies grade upward siliciclastic, lowstand tidal flat unit, the Lovington sand, caps the lower sequence and separates the formation into the Lower and Upper San Andres. Grainstones and packstones deposited as high-energy shoals and bars are the primary reservoir lithologies. Diagenetic processes critical to the development of good reservoir porosity and quality are;early dolomitization of the carbonate section, intense dissolution and alteration of anhydrite to gypsum, and dissolution of dolomite. Four correlatable subtidal grain-rich intervals constitute the chief flow units and the only continuous waterfloodable intervals across the field. Relationships between the distribution of the subtidal grain-rich lithofacies, porosity content, anhydrite and gypsum abundances, and structural position exhibit considerable potential for mapping reservoir flow units and for defining reservoir quality within flow units. This geological model provided the architectural basis for the reservoir simulation pattern model used to evaluate reservoir performances and to modify EVGSAU operating plans to ensure optimum flooding. The geological model helped determine; 1) Upper San Andres vs. Lower San Andres performance, 2) infill spacing within the Upper and Lower San Andres, 3) the potential for horizontal injection in the Upper and Lower San Andres, and 4) repressurization volumes required for the Upper San Andres. Introduction The East Vacuum Field, Grayburg-San Andres Unit, (EVGSAU) constitutes the eastern portion of the Vacuum Field, located roughly 15 miles northwest of Hobbs, New Mexico (Figure 1). The initial waterflood development of EVGSAU was based on 80 acre inverted nine spot patterns. In 1993, a 12-well infill program was instituted which included coring 5 of the wells. The wells were drilled in strategic locations within the field to test the viability of an intensive infill drilling program and to evaluate the conversion to 40 acre, 5 spot patterns or to line drive patterns. A reservoir study linking the geological character and reservoir performance of the EVGSAU was conducted to evaluate the EVGSAU operating plans. Significant performance variation demonstrated by the waterflood and early CO2 injection was thought to be closely linked to reservoir architecture, and optimization of the flood could not be achieved without a thorough knowledge of this architecture. This geological study identified the flow units that control reservoir performance and determined flow unit character and continuity within the reservoir.
The East Vacuum Grayburg San Andres Unit (EVGSAU) operated by Phillips Petroleum, is the site selected for a comprehensive evaluation of the use of foam for improving the sweep efficiency of a CO2 flood. The four-year project is jointly funded by the EVGSAU Working Interest Owners (WIO), the U.S. Department of Energy (DOE), and the State of New Mexico. The Petroleum Recovery Research Center (PRRC), a division of the New Mexico Institute of Mining and Technology (NMIMT), is providing laboratory and research support for the project. A Joint Project Advisory Team (JPAT) composed of technical representatives from numerous major oil companies, PRRC, and DOE provides input, review and guidance for the project.
This paper is the second in a series of papers detailing various aspects of the CO2 Foam Field Verification Pilot test at EVGSAU. An earlier paper summarized the project plans and detailed the laboratory work leading to the selection of a surfactant for the field trial. This paper presents: 1) an overview of the operating plan for the project, 2) details of the foam injection schedule and design criteria, and 3) a discussion of the data collection program and performance criteria to be used in evaluating successful application of foam for mobility control in the EVGSAU CO2 project.
Specific items discussed in the foam injection design include the determination of surfactant volume and concentration, selection of the surfactant-alternating-gas (SAG) injection sequence for foam generation, field facilities, operations during foam injection, and contingency plans. An extensive data collection program for the project is discussed including production testing, injection well pressure and rate monitoring, injection profiles, production well logging, observation well logging program, and both gas and water phase tracer programs.
The EVGSAU, located about 15 miles northwest of Hobbs in Lea County is the site of the first full-scale miscible carbon dioxide injection project in the state of New Mexico. CO2 injection at EVGSAU began in September, 1985. The CO2 project area covers 5000 acres developed using an 80-acre inverted nine-spot flood pattern. The total CO2 injection rate is about 30 MMcf/D. A water-alternating-gas (WAG) ratio of 2:1 (time basis) is used in the project, resulting in about one-third of the project area being on CO2 injection at any one time. In any given area, a WAG cycle consists of about four months of CO2 injection followed by eight months of water injection. This results in approximately 1.5 to 2% hydrocarbon pore volume (HCPV) CO2 injection and 3 to 4% HCPV brine injection per WAG cycle. The project is currently in the seventh WAG cycle. The tertiary oil response at EVGSAU to date has been very favorable. As shown in Figure 1, the waterflood decline established prior to CO2 injection has been arrested, and oil production has held approximately constant near the current 9000 BOPD Unit total for the past six years.
Abstract The East Vacuum Grayburg San Andres Unit (EVGSAU) began CO2 injection in 1985 which is still continuing today. Performance of CO2 injection has been very favorable in the main pay zone with oil recoveries exceeding 45 percent overall in the unit. Technical challenges remain in maintaining and increasing oil recovery but future opportunities also exist such as CO2 flooding the transition/residual oil zone and improving overall volumetric sweep efficiency. Waterflooding in EVGSAU began in 1980 to pressure up the reservoir in preparation for CO2 flooding. CO2 injection began in 1985 with a 2:1 water: alternating gas (WAG) ratio to help provide conformance control. Overall oil recovery from the main portion of the reservoir in the CO2 flooding area alone is above 55 % OOIP. Approximately 12.5 % OOIP recovery has been due to CO2 flooding. This paper will detail some of the challenges experienced during CO2 flooding which include maintaining reservoir pressure above minimum miscibility pressure, maintaining high injection rates in WAG injection wells, and handling large volumes of produced gas. During the early 2000's, 19 laterals were drilled out of existing vertical wells which assisted the unit in increasing oil production rates and reducing gas coning. Future opportunities include expansion of the current gas plant to handle the increasing gas-oil ratio of produced oil as the CO2 flood continues to mature, CO2 flooding the transition/residual oil zone, infill drilling in the main pay zone to increase areal sweep efficiency and polymer gel treatments to address poor vertical conformance. A foam treatment is also being planned for EVGSAU. CO2 flooding in the EVGSAU has been impacted during its history by changing oil and CO2 prices and many technical challenges. Despite these challenges, oil recovery by CO2 flooding has been favorable and further steps are being taken to increase long-term oil recovery.