Alkaline Waterflooding: Design and Implementation of a Field Pilot
Authors: Raimondi P. , Gallagher B.J. , Ehrlich R. , Messmer J.H. , Bennett G.S. 
Published: December 2007

Raimondi, P., SPE-AIME, Gulf Research and Development Co. Gallagher, B.J., SPE-AIME, Gulf Energy and Minerals Co.-U.S. Ehrlich, R., SPE-AIME, Gulf Research and Development Co. Messmer, J.H., SPE-AIME, Gulf Research and Development Co. Bennett, G.S., SPE-AIME, Gulf Research and Development Co.

A field trial of caustic waterflooding in a Queen sand lens in the North Ward-Estes field is described. Comparison of results with projections for a conventional waterflood, while uncertain, indicate that about 25 percent more oil was produced. Operational problems are discussed.

Introduction

The North Ward-Estes field, Ward and Winkler Counties, Tex., has been under successful water drive for many years. However, a considerable amount of oil is left behind even in the water-swept zones. Laboratory tests have indicated that the oil displacement efficiency could be improved significantly by adding a high-concentration slug of sodium hydroxide (NaOH or caustic) to the flood water. In the swept zone, the laboratory-measured improvement was about 125 bbl/acre-ft. This is attributed to generation of surfactants by the reaction of caustic with organic acids in the oil and the effect of these surfactants on multiphase flow, primarily a wettability shift in the water-wet direction. These mechanisms have been discussed in other papers.

The field test is being conducted in the Queen sand, East Flat area of the North Ward-Estes field. This area was discovered in 1969 and development drilling was completed during 1970 with the drilling of 20 additional wells. The oil production rate peaked at 85,000 bbl/ month during mid-1970, followed by a rapid decline in rate resulting from the highly undersaturated nature of the oil. To offset this decline, full-scale water injection was begun in late 1970. Production response to water injection was almost immediate and a peak rate of 40,000 bbl/month was reached in early 1971.

To test the laboratory results, a 5-acre inverted fivespot pattern was developed by drilling four water-injection wells, WI-79 through WI-82. around an existing producing well, Well 874 (Figs. 1 and 2) in an area of the field that was presumed to have not yet been affected by the ongoing waterflood. The objective was to determine the effect of a caustic slug injected early in the life of a waterflood.

This paper describes the test area, the laboratory evaluation, the design and conduct of the test, the production behavior and an analysis of the recovery. The production behavior and an analysis of the recovery. The test was still in progress when this paper was written.

Reservoir Description

Geologically, the Queen sand is a channel-type deposit. These deposits exhibit strongly directional permeabilities, generally northwest-southeast. Normal to permeabilities, generally northwest-southeast. Normal to this, the permeability is reduced to one-fourth or less of the dominant permeability. The East Flat Queen sand is rather fine-grained argillaceous, becoming increasingly anhydritic and dolomitic away from the central portion until reservoir development ceases to occur. Permeability and porosity pinchouts control the reservoir limits. However, northwest of Well 838 (Fig. 1) and along the southwest boundary, little geologic control is available and some water influx may have occurred.

Fig. 3 shows a typical log section. The presence of gypsum and dolomite above and below the sand is evident from visual and other observations. X-ray diffraction analysis of producing sands gave 80 percent quartz and 10 percent feldspar as well as varying amounts of illite and montmorillonite clays.

JPT

P. 1359