Injectivity decline in water-injection wells: An offshore Gulf of Mexico case study

A decline in injectivity in water injection wells can have a large impact o n the economic feasibility of offshore water disposal operations. A case st udy is presented for an offshore Gulf of Mexico water injection project. Da ta are presented for five typical offshore wells for which a rapid decline in injectivity was observed due to water injection. The wells were successf ully acidized every few months over a period of 2 years. An analysis of the data indicates that in injection wells that are not fractured, such declin es in injectivity may be expected even for relatively clean injection water . A comparison of the different completion types indicates that both open h ole and perforated completions would have yielded similar results. Cleaner water would have improved the situation but at a substantial cost. Fracturi ng the injection wells appears to be the only plausible way of substantiall y increasing the half life of such injectors. In cages where reservoir cond itions dictate that the wells not be fractured, the economics of periodic s timulation vs. the cost of installing surface facilities for cleaning up th e water should be evaluated using models for injectivity decline. "What if" simulations conducted to study the impact of different process parameters such as injected particle size and concentration, injection rate and reserv oir properties were found to be a useful tool in specifying water quality r equirements.