Light-Oil Steamdrive Pilot Test at NPR-1, Elk Hills, California
- F.J. Gangle (U.S. DOE) | H.V. Weyland (U.S. DOE) | J.P. Lassiter (Chevron U.S.A. Inc.) | E.J. Veith (Bechtel Petroleum Operations Inc.) | T.A. Garner (Bechtel Petroleum Operations Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- August 1992
- Document Type
- Journal Paper
- 315 - 320
- 1992. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 5.3.4 Reduction of Residual Oil Saturation, 1.2.3 Rock properties, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.2 Reservoir Fluid Dynamics, 5.6.5 Tracers, 6.1.5 Human Resources, Competence and Training, 5.1.5 Geologic Modeling, 5.4.6 Thermal Methods, 5.4.1 Waterflooding, 4.3.4 Scale, 7.1.10 Field Economic Analysis, 5.2.1 Phase Behavior and PVT Measurements, 2.4.3 Sand/Solids Control, 4.2 Pipelines, Flowlines and Risers, 5.4.2 Gas Injection Methods, 5.1.1 Exploration, Development, Structural Geology, 5.1.2 Faults and Fracture Characterisation, 7.1.9 Project Economic Analysis, 2.2.2 Perforating
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A steamdrive pilot was run on a light-oil reservoir at the Naval PetroleumReserve No. 1 (NPR-1) in the Elk Hills oil field, Kern County, CA. From areservoir perspective, the steamdrive process behaved much as expected. Thefirst event to occur was the appearance of freshened water productionaccompanied by CO2 gas 3 months from startup of steam injection. The secondevent, an increase in crude gravity, appeared 3 months later, or 6 months intothe project. Finally, the third event was the arrival of the heat front at theproducing wells 13 months after startup. From a production perspective, CO2 inthe freshened produced water caused wellbore scale damage and loss of wellproductivity. The steamdrive, however, mobilized residual oil, which mostly wascaptured outside the pilot pattern area. Acid stimulations to restore wellproductivity were done by injecting inhibitor in the steam feedwater and bydesigning acid cleanup treatments on the basis of results from laboratorytests.
NPR-1 in the Elk Hills oil field, located 25 miles [40 km] southwest ofBakersfield in Kern County, CA (see Fig. 1), was discovered in 1919, unitizedin 1944, and opened to full production in 1976. The U.S. DOE and Chevron U.S.A.Inc. are unit partners. Bechtel Petroleum Operations Inc. operates the unitunder contract to the DOE. The shallow oil zone (SOZ) is found at an averagedepth of 3,000 ft [900 m]. Since discovery in 1919, it has been under primaryrecovery and is currently producing about 19% of the total primary recovery andis currently producing about 19% of the total crude from the field. The pilot,shown in Fig. 2 as four inverted fivespot patterns, had the objective ofcommercial full-scale steamdrive development. The unproved reserves in the SOZare estimated to be as much as 100 million bbl [15.9 X 10(6) m3] of thermaloil. The Elk Hills pilot behaved in a similar way to several earlier steamdriveprojects at the Brea, Shiells Canyon, and Buena Vista Hills oil fields inCalifornia. Pilot configuration was based on the geology and reservoircharacterization given in Table 1. Actual field data, however, compared poorlywith predictions from numerical simulation. The difference between actualperformance and the predictions was explained by poor well performance and thepredictions was explained by poor well recoveries, which resulted from wellborescaling and lack of steam confinement to the pilot pattern area.
Geology of Steamdrive Area
The steamdrive pilot project is on the southeastern flank of the Elk Hillsanticline, a geological structure about 10 miles [16 km] long and 3 miles [4.8km] wide with about 750 ft [230 m] of closure. Throughout the pilot area,normal faulting is extensive, with fault angles ranging from 75 degrees to nearvertical. The southernmost fault was originally believed to be confining (seeFig. 2). This normal fault has 80 ft [24 m] of displacement, yet it did notfully confine the movement of reservoir fluids. Other minor faults were mappedwith 20 ft [6 in] of displacement or less. Formation beds in the pilot areahave no more than 4 degrees of dip. Throughout the pilot area, the interbeddedsand and shale sequences are areally continuous, as suggested in the A-A' crosssection of Fig. 3. For the purposes of the steamdrive, the sands making upInterval SS-1 were designated as five discrete sand lobes labeled Intervals A,B, C, D, and E (see the type log of Fig. 4). Thin interbedded shales, rangingfrom 1 to 5 ft [0.3 to 1.5 m], were barriers to fluid movement. The sandswithin these lobes are friable; fine to medium grained, ranging in some casesto coarse grained; silty; well sorted; and range from 5 to 15 ft [1.5 to 4.6 m]thick. Porosity ranges from 27% to 35% and air permeabilities from 100 to 2,000md. Table 2 gives the average reservoir data.
Light-Oil Steamdrive Process
One of the earliest light-oil steamdrive projects was in Schoonebeek, TheNetherlands, in 1961. It was first reported in 1968. Blevins et al. depicted asimplistic view of the light-oil steamdrive process (see Fig. 5). Field data atElk Hills suggested that process (see Fig. 5). Field data at Elk Hillssuggested that the hot-water zone was made up of fresh water containing CO2gas. A heat front was behind the oil-distillate bank shown in Fig. 5 as a steamzone. Steam breakthrough did not occur when the heat front appeared at theproducers. In the steamdrive process, steam vaporizes a fraction of theresidual oil and transports it to the steam front where it condenses to form adistillate oil bank. This process, the vaporization and transport of theresidual oil, which condenses into a miscible distillate bank, is known toreduce steam-swept pore space to a residual oil saturation (ROS) as low as 5%.This pore space to a residual oil saturation (ROS) as low as 5%. This was adistinct advantage over waterflooding, where no miscible distillate bankdevelops to reduce ROS to such low values.
The Elk Hills steamdrive pilot location was selected on the basis of thecriteria listed in Table 1: geologic confinement, net oil-sand thickness, oilsaturation, and depth to pay. Other screening guides provided in theliteratures were considered but not used. The Elk Hills guides were consideredmore rigorous than those reported by Blevins et al. The pilot design alsobenefited greatly from Chevron's Buena Vista Hills steamdrive field experience,unpublished Chevron steamdrive technical reports, and Hong's simulationstudy.
Field Pilot Objectives
The possibility of categorizing 100 million bbl [15.9 x 10(6) m3] as provedreserves prompted management approval for the pilot project. The primaryobjective to develop a commercial fieldwide project. The primary objective todevelop a commercial fieldwide steamdrive venture required more rigorousobjectives for evaluating the potential for light-oil steamdrive at Elk Hills(see Table 3). For example, well spacing determines the number of patternsrequired and subsequently the number of steam generators needed. These factorsgovern capital and operating costs. Completion techniques and profile controlare interrelated factors required for achieving good steam-injectionconformance, a definite key to high recovery. Operator training was mandatoryat Elk Hills because thermal technology was new to the field. Finally, thedevelopment of a useful reservoir numerical model was required to justify anyexpansion of the steamdrive to other parts of the SOZ. It was initially hopedthat the project economics could be evaluated on the basis of steamdriveincremental oil. This paper, however, does not give that evaluation. As a pointof interest, simple economics indicated that the pilot was a break-even ventureif production response outside the pattern is incorporated into the overallproject. Costs and revenues were about $13 million each. Current plans call forconverting the pilot to conventional water and gas injection.
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