Carbonated Waterflood Implementation and Its Impact on Material Performance in a Pilot Project

Abstract

SPE Member Abstract Carbonated waterflooding is an enhanced oil recovery process developed in the early 1950's that may have potential application in several West Texas reservoirs. The process consists of saturating injection water with CO2 in order to swell the remaining oil-in-place, and thereby increase the amount of recoverable oil in a reservoir. The process usually involves less investment and CO2 demand than miscible CO2 flooding. The effects of carbonated waterflooding on equipment material performance were monitored during a two well carbonated water injection pilot test conducted by Amoco Production Company in the Slaughter Field, Hockley County, Texas. Stainless steel and aluminum bronze material showed no deterioration during the test period. However, severe problems were encountered at holidays in the internal plastic coating of carbon steel pipe and fittings. Injection well material performance data and observations are presented to support these findings. In addition, the surface equipment design used to saturate injection water with CO2 will be presented. No attempt will be made to discuss the impact of carbonated waterflooding on injection well or reservoir performance. Introduction Corrosion and plugging problems were encountered in wellhead equipment during operation of a two well carbonated waterflood injection pilot. The carbonated waterflood injection pilot, located within the currently active Central Mallet Unit CO2 miscible flood, was placed in operation on July 25, 1985, and operated continuously until termination on March 4, 1986. Performance of surface injection wellhead equipment and materials during the 7 1/2 month pilot period is provided along with recommendations for future carbonated waterflood wellhead equipment designs. DESIGN DATA AND BACKGROUND INFORMATION Initial design data for the two carbonated waterflood pilot wells is summarized below: Well A Well B Design Water Rate 1050 BWIPD 990 BWIPD Desired Surface Operating Press. 1200 PSIG 1490 PSIG Target Solubility 101 SCF CO2/Bbl 104 SCF CO2/Bbl Prior to initiating carbonated water injection, both wells were on water injection at the design water rates and surface pressures noted in the table. The wells were equipped for CO2 injection; however, neither well had been placed on CO2 injection prior to carbonated water injection. WELLHEAD EQUIPMENT DESIGN Wellhead equipment for the carbonated waterflood pilot wells consisted of separate CO2 and water injection skids upstream of a 316 stainless steel static mixing unit. The static mixing unit provided sufficient intimate contact to saturate injection water with CO2 prior to entry into an aluminum bronze wellhead assembly. As shown in Figures No. 1 – 4, CO2 was injected in to the water stream through a 1/2" nozzle in the side of the static mixer prior to entering the mixing elements. P. 55^