Injecting Polyacrylamide Into Gulf Coast Sands: The White Castle Q Sand Polymer-Injectivity Test
- G.T. Shahin (Shell Development Co.) | D.R. Thigpen (Shell Development Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- August 1996
- Document Type
- Journal Paper
- 174 - 180
- 1996. Society of Petroleum Engineers
- 5.6.4 Drillstem/Well Testing, 3.3 Well & Reservoir Surveillance and Monitoring, 5.1.2 Faults and Fracture Characterisation, 2.2.2 Perforating, 5.1.1 Exploration, Development, Structural Geology, 5.2 Reservoir Fluid Dynamics, 5.6.5 Tracers, 5.3.2 Multiphase Flow, 5.5.8 History Matching, 5.1.8 Seismic Modelling, 5.6.3 Pressure Transient Testing, 3.2.4 Acidising, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 2.4.3 Sand/Solids Control
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A polymer injectivity test designed to control mobility in cosurfactant-enhanced alkaline flooding was performed in the Q-Sand of the White Castle Field, Louisiana. Analysis of test data indicates that a polymer bank with an average viscosity of 4 cp was propagated as far as 90 feet into the reservoir with no measurable sign of degradation. It is estimated from pilot and laboratory data that injection of 500 ppm polyacrylamide through perforations at a rate of at least 32 bbl/day/ (in. of perforation) into Gulf Coast sands is feasible. Monitoring of back produced reservoir samples indicates that to date, no detectable change in viscosity has occurred over a two-year period.
The "White Castle Field, located some 20 miles south of Baton Rouge, LA, was chosen as the site of Shell's Enhanced Alkaline Flooding Pilot due to its onshore location and proximity to a freshwater source. The cosurfactant-enhanced alkaline flooding pilot was designed to evaluate technology slated for the significant enhanced oil recovery reserves in the Gulf of Mexico. Over the course of several years, a three-stage piloting strategy was adopted: (1) injection of chemical slug without mobility control into the Q Sand of the White Castle Field, (2) limited injection of polymer-assisted chemical slug into the Q Sand, and (3) full injection of polymer-assisted chemical slug into the 01-Sand.
The second stage of the project was designed to evaluate whether injection of polyacrylamide was feasible in Gulf Coast sands. The design of the pilot, the facilities required to meet design specifications, the results of evaluating the integrity of in-situ polymer, predicting maximum injection rates, and monitoring the integrity of the polymer solution over extended periods of time are discussed in this paper.
DESIGN OF THE POLYMER INJECTIVITY TEST
The test was conducted in Reservoir A of the Q-Sand fault block. (Refer to Figure 1 and Table 1.) The reservoir is bounded in the updip direction by an impermeable shale sheath associated with a piercement salt dome and by sealing faults to the north and south. To the west, the reservoir communicates with a strong aquifer drive across a nonsealing fault. Dip angle within the pilot area is approximately 45, while permeability and porosity were measured on average to be 2 darcies and 0.32, respectively.
The wells in place for the test were one downdip injection well (Wilbert 264), two updip production wells (Wilbert 267 and 269), a sampling well (Wilbert 25), and two fiberglass logging observation wells (Wilbert 268 and 286). Design of the Polymer Injectivity Test consisted of acidizing Wilbert 264 and performing a downhole-shut-in pressure transient test to infer the skin and permeability of the reservoir in the absence of polymer. Wilbert 264 was then reworked to include a plastic-coated string, a Monel screen and liner, and a total of 12 perforations per foot over a 10-foot injection interval. (Big hole charges with a nominal 3/4-inch diameter were used in this recompletion.) It is estimated from the work of Maerker that no more than a 50% reduction in screen factor and 10% loss of mobility would be incurred with this perforation density.
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