Deepwater Gas Injector Wells: Overcoming the Challenge of Achieving Matrix Injectivity

Abstract

As fields mature, they start depleting and require assistance to help extend production and enhance hydrocarbon recovery. The introduction of injector wells in producing fields is a commonly used pressure maintenance method which consists of injecting water or gas to maintain reservoir pressure and/or sweep hydrocarbons toward producer wells. Injector wells, requiring matrix injectivity, are typically drilled using reservoir drill-in fluids (RDIF) as they minimize near wellbore damage while drilling and lay down a high-quality acid-soluble filtercake (Dick et al. 2003). The slow and uniform dissolution of the filtercake is achieved by spotting a delayed breaker solution to allow time for pulling out the lower completion running string and closing the formation isolation valve (FIV) without causing losses. For two deepwater gas injector wells recently drilled in the Guyana Surinam Basin, a 11.9 lbm/gal RDIF was necessary and presented a design challenge of meeting both the deepwater reservoir drill-in and post-completion matrix injectivity requirements. A reversible non-aqueous RDIF system using a calcium bromide brine as the internal phase and formulated at 50/50 oil-water ratio (OWR) was selected to meet the drilling challenges. Such challenges included maintaining wellbore stability while drilling interbedded shale and controlling equivalent circulating density (ECD) below the fracture gradient at the desired rate of penetration (ROP). They also included depositing a thin, ultra-low permeability and acid-soluble filtercake. A newly developed breaker was customized to provide a 4-hour delay at bottom-hole temperature (250°F) permitting a safe pull out of the inner string above the FIV and then slowly dissolve the filtercake to restore near wellbore permeability and enable matrix injectivity. Both the recommended RDIF and delayed breaker formulations were d used in the field during reservoir drill-in and lower completion operations of the two deepwater gas injector wells. Post-completion well tests confirmed that the two wells have achieved maximum gas injectivity below fracture gradient, meeting customer expectations. This paper discusses the results of extensive laboratory tests that were necessary for the selection and the customization of both the RDIF and the delayed breaker and the field performance of the two fluids.