Evaluation of Flood Water Quality in the West Montalvo Field

Abstract

One of the most important factors affecting success of waterflood performance is maintenance of water quality. Determining minimum water quality is difficult because water quality requirements are as varied as the formations to be flooded. Previously, attempts have been made to set quantitative standards based on simple tests for water quality. However, injection water quality is best measured by formation core flooding at conditions that model fullscale injection operations. While acceptability of source water can be determined in the laboratory by flooding formation core material, it is difficult to acquire representative water samples because of water instability. On-site core flooding at sand face injection temperature with water from a pilot treating plant minimizes water quality uncertainty and permits continuous, on-line screening for development of treating and filtering requirements. Water injection acceptability and pilot plant evaluation provide determination of corrosivity, filtration efficiency, treatment additive compatibility and treatment economics. This source water evaluation method improves waterflooding economics in two important ways:minimum treatment cost to maintain continuous injection without permeability decline is established; andthe possibility of injection well damage is reduced. Introduction An evaluation study of an injection water source is described. In addition to the usual determinations of bacterial activity and corrosivity, this on-site pilot plant study evaluated particle plugging tendency, scaling tendency, treating chemical compatibility and potential clay problems by formation core flooding at sand face injection temperature. The purpose was to provide an economic means of maintaining injectivity in West Montalvo field, Oxnard, Calif., by developing a chemical treatment and filtration system from core flood tests. Injection History Water injection in the West Montalvo field began in 1963, with the injection of produced brine into the McGrath pool. Immediate injection problems resulted from inadequate water treatment. In mid-1964, a shallow source well was drilled on the ocean shore to supply saline injection water for both the McGrath and Colonia pools. Water analysis and injection tests performed in the laboratory indicated the new water to be suitable after minor chemical treatment and filtration. Injection into a Colonia zone well began in Sept., 1964, at an average rate of 600 BWPD at 3,000 psig. However, the rate declined to 440 BWPD at 4,600 psia within 3 months. Injection wells continued to plug and required repeated acid stimulations to maintain injection (Fig. 1). Injection in the initial injector could not be maintained economically, and in April, 1966, the well was shut in. Reservoir characteristics peculiar to the Colonia zone were apparently part of the problem because injectivity was much better in the McGrath pool. The Colonia zone is a thick, non-marine, Oligocene section comprising a series of thin oil- and water-bearing sand lenses interbedded with shales. Petrographic analysis of core material indicated sufficient kaolinite. illite and montmorillonite to cause permeability damage from clay migration. Clay sensitivity and poor water quality were probable causes of damage to Colonia zone injectors; therefore, a flow test program was designed to evaluate injection problems. JPT P. 683ˆ

Water Quality Aspects of North Sea Injection Water

“…3,[5][6][7][8][9][10] Generally, formation and injection water analysis, membrane filter techniques, and core injectivity studies have been used in the industry to monitor suspended solids and evaluate water quality.…”

Reservoir Characterization, Production Characteristics, and Research Needs for Fluvial/Alluvial Reservoirs in the United States

“…A relatively high clay content (kaolinite, illite and montmorillonite) at West Montalvo Field reduced permeability and rendered the field unsuitable for then current injection methods in the @d 1960s (Farley and Redline 1967). By 1993 production from the Colonia Zone at West Montalvo Field was restricted to the offshore part of the reservoir (Conservation Committee of California Oil and Gas producers 1994).…”