Alkaline/Surfactant/Polymer Flood: Single-Well Chemical-Tracer Tests - Design, Implementation, and Performance

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 130042, ’Alkaline/ Surfactant/Polymer Flood: Single-Well Chemical-Tracer Tests - Design, Im plement ation, and Performance,’ by S.N. Oyemade, S.A. Al Harthy, H.F. Jaspers, SPE, J. Van Wunnik, SPE, and A. de Kruijf, SPE, Petroleum Development Oman, and M. Stoll, SPE, Shell Technology Oman, prepared for the 2010 SPE EOR Conference at Oil & Gas West Asia, Muscat, Oman, 11-13 April. The paper has not been peer reviewed. Studies of mature fields in Oman have shown that alkaline/surfactant/polymer (ASP) flooding can yield significant incremental recoveries compared with waterflooding. However, the technique has risks: poor injectivity of the ASP slug, effectiveness of reservoir sweep, formation of scale in the wells and facilities, and persistent emulsions in the produced fluids. Analysis of these risks highlighted the need for pilot testing. Introduction A study indicated that ASP flooding could increase recovery in several fields, ranging from heavy-oil sandstone fields in southern Oman to light-oil carbonate fields in northern Oman. Several key risks that must be mitigated include extent of desaturation by ASP, ASP stability, emulsion breaking, and scaling. Tests were planned to reduce these uncertainties before making the significant investments associated with full-field implementation. Reservoirs were identified that could benefit from enhanced-oil-recovery (EOR) methods such as steam, chemical, and gas. Bottle tests are a subset of the coreflood tests and check various combinations of EOR chemicals—particularly alkali, surfactant, and polymer. Chemical EOR floods have been implemented with different combinations such as alkali/surfactant, alkali/polymer, and surfactant/polymer. From the bottle tests, different concentrations of chemical combinations were tried in coreflood tests. The optimum recipe for each reservoir was identified by flooding cores from the reservoir with reservoir fluids and the chemical mixtures. Following the coreflood tests, several tests could be run to determine desaturation. The single-well chemical-tracer (SWCT) test was chosen as an efficient means of confirming the effectiveness of laboratory results at a larger scale (well) and in situ (reservoir). SWCT tests are nondestructive (i.e., after the production step, the formation is returned to its original condition), which allows oil-saturation measurements before and after an EOR injection from a single well. The objective of the ASP SWCT tests was to mitigate risks of recovery and injectivity on a well or single-reservoir level. Three fields were selected for the ASP SWCT testing. Two fields are sandstone, and the third is a carbonate. Field X has had active waterflood support for more than 10 years, while fields Y and Z have no waterflood support. Following the SWCT test, a continuous-injection-pilot test may be planned for one of the fields. Candidate Selection Wells were selected from each of the three fields. The candidate-selection procedure for one of the three fields (Field X) is detailed in the full-length paper. Field X had 123 oil-producing wells. The screening criteria included gross production rate, high permeability, high water cut, possibility to log the well, well shape and deviation, casing integrity, interval homogeneity, and lack of interference with neighboring wells.