Well Leak Assessment After Shallow Water Well Blowout: A Case Study in West Kuwait

Abstract A gas blowout event occurred in a shallow water well, conventionally used as a brackish water source for drilling rigs, in the Minagish Field located in West Kuwait on March 2023. After 16 months of continuous production, the well was effectively controlled by drilling vent wells. A study was undertaken to assess the specific source reservoir gas leak path(s) from the deeper Minagish formations to the shallow water formation, assessing geological leak paths, well integrity and narrowing down the possible problem well(s) from the ~600 wellbores in the field. A review and quality control of a very large volume of subsurface and wells data was undertaken by an integrated team of discipline subject matter experts. Production Chemistry fingerprint work identified the primary source of the gas to narrow the focus of the review. In the water formation, a characterisation study was performed using mud loss data (presence of vugs, high permeability channels, fracture channels, etc..), to highlight the main karst distribution both areally and vertically which was then mapped. The maps provided both guidance on leak flow paths and possible locations of future vent wells if required. The study concluded that the gas leak was primarily due to internal and external casing corrosion in a number of wells, exacerbated by the challenging cement placement in the loss prone shallower hole sections. By defining and adopting a range of leak evaluation criteria, the ~600 suspect wellbores were reduced to 24 possible potential leak wells connecting the Minagish reservoir to the water formation, two of them classified as high risk and another one as medium. In support of this well leak path conclusion, this study also concluded the leak is "unlikely a geological leak path", which might require a leak path from the Minagish formation through multiple reservoirs and seals. There was firm geomechanical and chemical evidence supporting this conclusion, including: Several seals that were presentOver-pressured or depleted zones that could act as a natural flow barrierNo evidence of deeper faults reaching the water formationNo data supporting fracturing caprock or fault re-activation in the overburdenDirect leak path to the water formation - the blowout hydrocarbons comprised of native Minagish reservoir oil and injection gas, with no evidence of interaction with fluids from other reservoirs. The integrated multidisciplined nature of the study and the application of chemical analysis to narrow the well suspects was the key to evaluating the most likely mechanism and specific wells of concern.