ABSTRACT
The objective of this paper was to evaluate corrosion problems in casing vapor recovery system from a production field utilizing steam recovery processes with a view of determining the optimum corrosion management approach considering routine maintenance, corrosion mitigation, inspections, material selection and cost-effective solutions.
Aqueous corrosion issues in gas gathering and transmission lines are not new to Oil and Gas production and pipeline operators. Produced gas naturally contains carbon dioxide, CO2, hydrogen sulfide, H2S and oxygen as the principal corrosives with the composition of the corrosives varying throughout the life of the reservoir due to shifting formation chemistry and other souring mechanisms such as microbiological activities. Water vapor is produced with the formation fluid or introduced into the formation through enhanced recovery methods such as steam flooding.
Erosion-Corrosion effect resulting from corrosion by-products specifically ‘Black Iron Powder’ was also evaluated. Failure frequency impact on operation and high maintenance costs were the main consideration used to determine the appropriate corrosion mitigation and management strategy.
INTRODUCTION
Steam flooding is one of the matured techniques used in enhanced thermal recovery of heavy crude oil mostly from shallow reservoirs. Steam injected into the reservoir via injection wells heats up the crude oil in the formation thus reducing its viscosity and enhancing easy seepage of oil towards the production wells. The design of the production wells is such that distilled light components and produced gas are recovered through the casing annulus while the bulk fluid is recovered through the production tubing.
Casing vapor recovery is an integral part of steam flooding enhanced oil recovery process. The production field under consideration has casing vapor recovery system that collects casing gas from 450 production wells from the central zone of the field and 300 production wells from the south end of the field. Storage tanks vapor recovery systems also tie-in to the casing vapor recovery system upstream of the central compressor. The gas is then scrubbed and desulfurized in a sulfatreat reactor before being utilized as combustion fuel in steam generators.