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.