Development of a Crude Oil Sulfonate for Micellar/Polymer Flooding of the Salt Creek Field in Natrona County, Wyoming

Abstract

Summary Development of a sulfonate for use in a proposed 3-acre (12 129-m ) pilot test and a potential 200-acre (809 200-m ) commercial demonstration in the Salt Creek field Second Wall Creek reservoir (WC2) is summarized. Work emphasized development of a sulfonate manufactured from Salt Creek crude oil (CROS) or a feed stream from Amoco's Casper, WY, refinery. Advantages of the CROS product are in its expected long-term cost advantage, consistent feed stream quality, availability of feed stream, and reduced transportation cost when manufactured at or near a field location. This paper addresses the optimization and laboratory selection that went into defining the final product for more extensive fluid development studies. Experimental products were evaluated primarily on the criteria of micellar fluid stability and the oil displacement performance of single-phase micellar fluids. Core test studies evaluated the effects of manufacturing conditions and micellar formulation variables on oil displacement. Topping (light ends removal) of the WC2 crude before sulfonation was the most significant variable affecting the salinity tolerance of the products as well as the oil displacement performance. A 35% topping level was found to be optimum. Topping beyond this level further reduced salinity tolerance and reduced the oil displacement performance. Average equivalent weights and equivalent weight distributions were determined for selected products. Typically, oil-soluble alcohol cosurfactants, such as n-hexyl alcohol or Alfonic 610–50R (TM), improved oil displacements of CROS products. Salinities of in-place brines had little effect on the oil displacement performance over the range from about 8,700 to about 119,000 ppm TDS in core tests. Introduction The object of this work was to determine the feasibility of developing a crude oil sulfonate from a Salt Creek area stream that would be competitive in performance with a reference vacuum gas oil (VGO) sulfonate. This objective has been attained. The salinity tolerance range and oil displacing ability of CROS formulations indicate performance comparable with the VGO. Coupled with the other advantages of a CROS, it appears that a viable sulfonate candidate exists. The Salt Creek field is located in central Wyoming about 60 miles (96 km) north of Casper. In Aug. 1917, the WC2 producing zone of the Salt Creek field was discovered. The Light Oil Unit, which encompasses a major portion of the WC2 zone. has been the most productive portion of the field, producing more than 300 million bbl (47 × 10 m ) of oil since discovery. Waterflooding began in the WC2 reservoir in 1962. It is anticipated that waterflooding will extend the economic life of the WC2 reservoir until the mid-1990's. The WC2 formation is a muddy sandstone with a net pay of approximately 75 ft (22.86 m). Porosities range from 15 to 20% and absolute brine permeabilities are 10 to 100 md. Original water in place was low in satinity (13,367 ppm TDS), with less than 50 ppm hardness. Water from the Madison formation has been injected throughout the waterflood. Although low in salinity (about 2,500 ppm TDS), this water has a total hardness of about 350 ppm. The net effect has been to harden the clays in the waterflooded portions of the reservoir. This resulting satinity/hardness condition has been studied by Griffith. Because of this condition. ion exchange conditioning of the 3-acre (12 129-m ) pilot is being considered. Removal of calcium by ion exchange would be accomplished, before micellar injection, by injecting a bank of high-salinity water followed by fresh water. Crude produced from WC2 is somewhat waxy, and there is no measurable gas production at this time. JPT P. 2283^