Controlling Water Production Using Gelled Polymer Systems
- G. Paul Willhite (U. of Kansas) | Richard E. Pancake (Murfin Drilling Company Inc)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- June 2008
- Document Type
- Journal Paper
- 454 - 465
- 2008. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 3.2.6 Produced Water Management, 3 Production and Well Operations, 4.1.5 Processing Equipment, 1.6.9 Coring, Fishing, 5.2.1 Phase Behavior and PVT Measurements, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.2.3 Materials and Corrosion, 2.2.2 Perforating, 5.6.4 Drillstem/Well Testing, 5.1 Reservoir Characterisation
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Arbuckle reservoirs in central Kansas produce by natural waterdrive. Although clean oil is usually produced on initial completion of a well, the water cut increases with time. Water cuts of 99% and water production rates of 400 to 3,000 B/D are common. Wells cannot be pumped off. Water production has been reduced selectively by treating wells with a chrome acetate-polyacrylamide gelant. In most cases, incremental oil is produced following the treatment.
This paper describes results from a seven-well program in which production wells were treated with chrome acetate-polyacrylamide gelant. Pressure data were obtained before the treatment, during the gel treatment and after gel treatment. Buildup data were interpreted to estimate kh prior to the treatment, and the extent of permeability reduction to oil and water caused by the treatment. Bottomhole-pressure (BHP) data obtained during the treatment provided were used to monitor gelant placement. Production data following the treatments were analyzed to determine incremental oil production and correlate the treatments to the production response. Water-production rates were reduced in every well, and reductions were persistent during intervals ranging from 7 to 36 months. Incremental oil was produced in four of seven wells treated in the program. The amount of incremental oil increased with volume of gelant injected in wells with openhole completions. Results of this test program suggest how to distinguish wells that are likely to take large treatments from those that can be treated only with small amounts of gelant. These results should improve treatment design and identify wells that are good candidates for successful treatment.
The Arbuckle reservoirs in central Kansas are a major source of oil production. These reservoirs produce by natural waterdrive, yielding millions of bbl of fluid during 40 years with little decline in pressure from discovery pressures. In many reservoirs, a thick oil column is believed to be underlain by an extensive aquifer, as shown in Fig. 1, and development was accomplished by completing the wells open hole in the upper 2 to 10 ft. Penetration was limited because deeper completions often led to production of large volumes of water. The nature of the connection with the water aquifer is not understood. However, water/oil ratios increased with time, and ratios of 100:1 or higher are common when production becomes uneconomic. Other Arbuckle reservoirs appear to consist of multiple permeable layers separated by lower-porosity intervals (Franseen et al. 2003; Mulling and Ireland 1967), as shown in Fig. 2. In these reservoirs, wells are completed by setting the casing through the entire productive interval and perforating selective intervals. The wells also produce large volumes of water with time, but the contributions of each interval to the production of oil and water are not known.
Arbuckle reservoir rock is a dolomite with highly variable properties. Permeabilities vary from a few millidarcies to several darcies (Mulling and Ireland 1967). Because of the completion practices, Arbuckle cores are limited. Complete cores through the entire productive interval are not available in the major Arbuckle reservoirs, such as that shown in Fig. 1, so net thickness is uncertain.
Arbuckle wells frequently have high initial production rates that are considered to be inconsistent with flow through matrix rock. A typical reservoir description of wells completed (as shown in Fig. 1) usually contains a hypothetical fracture system connected to the aquifer to explain the high water-production rates. Consequently, water-shutoff programs usually are developed with the objective of treating the fractures, shutting off direct flow of water to the producing well, and forcing the water through matrix rock where oil can be displaced. Some Arbuckle core is not fractured, leading to the possibility that vugs and other permeable flow paths exist within Arbuckle reservoirs. Arbuckle reservoirs (such as that shown in Fig. 2) consist of alternating oil- and water-saturated intervals. There is no evidence of communication between separate zones in Fig. 2, and it is common to find water-saturated zones above oil-saturated zones.
An important characteristic of the Arbuckle reservoirs is the strong pressure support from either bottomwater or edgewater aquifers (Franseen et al. 2003; Mulling and Ireland 1967). Fig. 3 shows a pressure buildup from Hadley A#3. The well was produced at a rate of 740 B/D (733 BWPD and 7.5 BOPD) with a producing BHP of 896 psi. Pressure buildup was rapid and was complete within 1 hour after the well was shut-in. As described in the section "Pressure Buildup During Gel Injection," pressure buildup after the completion of a polymer-gel treatment was also rapid, indicating a good hydraulic connection with the source of reservoir pressure after the gel treatment.
Gelled-polymer treatments have been used successfully to reduce water production in Arbuckle wells, prolonging the life of some wells and increasing oil recovery (Moffitt 1993; Sloat 1975; Portwood 1999, 2005). Since 1989, more than 1,400 treatments have been applied. This paper describes results from a seven-well program in which production wells were treated with chrome acetate-polyacrylamide gelant to reduce water production and increase oil production. Pressure data were obtained before the treatment to estimate reservoir permeability. BHP data obtained during some gel treatments provided insight into the behavior of gelant during placement. Finally, buildup data were obtained after gel treatment to determine the extent of permeability reduction to oil and water caused by the treatment.
|File Size||3 MB||Number of Pages||12|
Franseen, E.K., Byrnes, A.P., Cansler, J.R., Steinhauff, D.M., Carr, T.R.,and Dubois, M.K. 2003. Geologic Controls on Variable Character of ArbuckleReservoirs in Kansas: An Emerging Picture. Kansas Geological Survey,Open-file Report no. 2003-59. Lawrence, Kansas: University of Kansas.
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