For many years, all the untreated production water from the Groningen gas field in The Netherlands had been injected into a dedicated water disposal well without problems. Recently, however, the injectivity of this well reduced significantly as a result of downhole blockages. Various remedial injection well clean ups and acidisations were executed without much long-lasting success. Early 2001, a dedicated study was conducted to identify the causes of the problems and come up with remedial actions. In particular, the question was whether the well plugging was due to the the low quality of the injection water, which would imply building dedicated water treatment faclities in order to remediate the problem, or whether the blockages were due to some other mechanism.
By carrying out a thorough analysis of all the injection data over the years, and combining this analysis with water injection computer simulations, it was concluded that the injectivity problems had nothing to do with the low injection water quality, but were the result of sand production during shut-ins. This result appeared surprising at first sight as the disposal water is injected into a fairly competent sandstone. It led to a set of recommendations for an improved way of operating the disposal well. The recommendations have been followed up, as a result of which the well has been in operation trouble-free over the last six months.