Using Laboratory Flow Experiments and Reactive Chemical Transport Modeling for Designing Waterflooding of the Agua Fría Reservoir, Poza Rica-Altamira Field, Mexico

Abstract

Using Laboratory Flow Experiments and Reactive Chemical Transport Modeling for Designing Waterflooding of the Agua Fria Reservoir, Poza Rica- Altamira Field, Mexico P. Birkle, Instituto de Investigaciones Electricas; K. Pruess, SPE, and T. Xu, Lawrence Berkeley National Laboratory; R.A. Hernandez Figueroa, and M. Diaz Lopez, Petroleos Mexicanos; and E. Contreras Lopez, Instituto de Investigaciones Electricas Abstract Waterflooding for enhanced oil recovery requires that injected waters must be chemically compatible with connate reservoir waters, in order to avoid mineral dissolution-and-precipitation cycles that could seriously degrade formation permeability and injectivity. Formation plugging is a concern especially in reservoirs with a large content of carbonates, such as calcite and dolomite, as such minerals typically react rapidly with an aqueous phase, and have strongly temperature-dependent solubility. Clay swelling can also pose problems. During a preliminary waterflooding pilot project, the Poza Rica-Altamira oil field, bordering the Gulf coast in the eastern part of Mexico, experienced injectivity loss after five months of reinjection of formation waters into well AF-847 in 1999. Acidizing with HCl restored injectivity. We report on laboratory experiments and reactive chemistry modeling studies that were undertaken in preparation for long-term waterflooding at Agua Fria. Using analogous core plugs obtained from the same reservoir interval, laboratory coreflood experiments were conducted to examine sensitivity of mineral dissolution and precipitation effects to water composition. Native reservoir water, chemically altered waters, and distilled water were used, and temporal changes in core permeability, mineral abundances and aqueous concentrations of solutes were monitored. The experiments were simulated with the multi-phase, non- isothermal reactive transport code TOUGHREACT, and reasonable to good agreement was obtained for changes in solute concentrations. Clay swelling caused an additional impact on permability behaviour during coreflood experiments, whereas the modeled permeability depends exclusively on chemical processes. TOUGHREACT was then used for reservoir-scale simulation of injecting ambient-temperature water (30 o C, 86 o F) into a reservoir with initial temperature of 80 o C (176 o F). Untreated native reservoir water was found to cause serious porosity and permeability reduction due to calcite precipitation, which is promoted by the retrograde solubility of this mineral. Using treated water that performed well in the laboratory flow experiments was found to avoid excessive precipitation, and allowed injection to proceed. Introduction The Poza Rica – Altamira oilfield forms part of the Chicontepec region, located in the eastern part of Central Mexico in the State of Veracruz, about five km from the town of Poza Rica and 250 km NE from Mexico City (Fig. 1). The thick, low-permeable accumulation of Paleocene-age sediments within the Chicontepec paleochannel contains an estimated 139 billion barrels [22 billion m 3 ] of original oil in place and 50 Tcf [1.4 Trillion m 3 ] of gas 1 . A total of 951 production wells were completed from 1951 to 2002, with initial production rates on the order of 70 to 300 BPD (barrels of oil per day) [11 to 48 m 3 /d]. Recently, PEMEX initiated an aggressive strategy to increase field production from an average of 2,500 BPD [397 m 3 /d] and 12 MMcf/D [344,000 m 3 /d] in 2002 to reach 39,000 BPD [6,200 m 3 /d] and 50 MMcf/D [1.4 million m 3 /d] in 2006 2 . Central to the success is the construction of high productivity wells, as well as waterflooding as part of an enhanced oil recovery program.