Geochemical Source Fingerprinting of Leak Fluids from a Shallow Water Well Blowout: A Case Study in West Kuwait

Summary A gas blowout event occurred in a shallow brackish aquifer water well, Minagish oil field, West Kuwait, March 2023. As part of an integrated, multidisciplinary investigation into its origins, geochemical fingerprinting analyses were undertaken to aid in determination of leak fluids source reservoir(s) and pathway to surface. Scales modelling of leak brine + aquifer water mixtures was also carried out, as was an assessment of shallow well corrosion, both in support of wider study conclusions. A data review with QA/QC was undertaken and gaps were identified, leading to a priority sampling programme. The chemical fingerprints of leak oil, gas and brine samples – based on a range of compositional measurements, including stable isotopes – were compared with those of local reservoirs to pinpoint origins. Sulphate scales modelling involved simulating mixing of saline leak brines with aquifer water to assess the potential for scale precipitation (including trace radioactive radium sulphate) around well casings. An example of severe shallow well corrosion was evaluated in respect of local aquifer geochemical conditions. Leak fluids fingerprinting demonstrated gas and oil to be from the main Minagish Oolite reservoir, with no evidence for interaction with other local hydrocarbon reservoirs. Leak gas was identified as non-native injection gas, which forms a crestal gas cap. Integrated with geological, geomechanical and well integrity findings, geochemistry results were key to concluding on a direct (well) path to surface, and to narrowing down suspect wells to ∼20 out of the ∼600 wellbores in the field. A saline reservoir brine component of leak fluids was also confirmed. While source fingerprinting of this proved challenging, it was demonstrated that stable isotopes could provide a means to differentiate between local reservoir brines, with analyses pointing to an overlying Wara / Burgan source for leak water. Scale modelling supported (radioactive) sulphate scale deposition associated with shallow leak brine crossflow as the cause of widespread well gamma ray anomalies, while at least one identified case of severe well casing / tubing corrosion was concluded as microbial, fed by sulphate rich aquifer waters. The wider integrated study concluded that the blowout was primarily due to internal and external well casing corrosion in several wells, exacerbated by challenging cement placement in loss prone shallower hole sections. The integrated multidisciplinary nature of the study and the application of chemical analyses to narrow down well suspects was key to evaluating the most likely mechanism and specific wells of concern.