Abstract

The focus of most waterflood or pressure maintenance projects is on the performance of the production and injection systems to ensure maximizing field rates and efficiencies. Yet there is a third leg to this operational triangle: the water supply system including wells and gathering system. This paper presents a case study of operational strategies and programs developed from experience from mature Field "B," and then translated to a revitalized re-started Field "F." These strategies include the use of tubeless completions of the water supply wells to maximize the water production rate and the subsequent implementation of a "build-down" strategy consisting of the installation of smaller casing sizes to isolate impaired casing sections and well monitoring with corrosion logs to address casing integrity issues.

Over time, the casing profiles became smaller, the rate of casing integrity issues accelerated and the overall supply well rates could not meet the increased injection demand. These casing integrity issues (up to 60% metal loss in some wells) necessitated a shift in strategy from the mechanical "build-down" to a mitigation strategy to extend the life of the existing supply wells. The "build-down" strategy was effective from 1975 to approximately 2006 in isolating casing integrity issues. The initial chemical squeeze inhibition campaign completed from 1979 to 1981 floundered on the monthly treatment requirements and the attendant high cost for these treatments. As casing profiles become smaller over time, a revamped corrosion inhibitor treatment program was completed quarterly and has been found to extend the well service life by 7 years so far. Furthermore, this case study will review the efficiency of the use of the same corrosion mitigation squeeze strategy in the revitalized Field "F."

Introduction to the Water Supply System of Field "B"
General Background

The mature Field "B" has been in service since 1967 with a peripheral waterflood operation for pressure maintenance since 1972 into the two primary oil producing zones. Waterflood operations are supported by the use of water supply wells completed in a regional water aquifer, sandstone characterized by very high deliverability, with rates of up to 70,000 barrels of water per day (BWPD). This supply water flows to the surface supported by the formation pressure with surface flowing wellhead pressures (WHPs) of between 100 to 125 psig. Initial injection requirements were in the order of 250,000 BWPD in 1983 and have expanded to approximately 363,000 BWPD as of July 2013. At injection startup, there were 21 supply wells, and at July 2013 there are 18 active supply wells. Supply water is gathered from the wells through two flanks to the main operational facilities where the water is pumped into the various water injection wells. It should be noted that these main operational facilities are located within 1500 meters of the Arabian Gulf.

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