A few years ago, following an extensive field study in North Kuwait, several wells were sidetracked and converted as horizontal openhole water injectors to support reservoir pressures as part of a secondary recovery plan. Production improvement was immediate, but injection rates soon started to decline and injection pressures were rising, eventually jeopardizing oil recovery. Conventional acid stimulation only led to short-lived improvements, and more elaborate methodologies rapidly became uneconomical. A new stimulation strategy was needed.
In these carbonate reservoirs, marked, sustainable improvements in injectivity can only be obtained through accurate placement of stimulation fluid across the entire interval, away from high-intake zones that develop as a consequence of repeated blind acidizing practices. A real-time, pump-through downhole flow measurement tool was used with coiled tubing (CT) to profile the openhole sections and identify thief and tight zones prior to treatment. The tool enabled adaptation of the stimulation strategy and was then used to ensure proper fluid placement during the pumping stages. Both profiling and pumping were performed in just one trip.
This innovative tool and its cost-effective workflow unlock a new level of operational efficiency. Whereas previous approaches required mobilization of additional equipment, the proposed methodology allows profiling horizontal sections and treating them in a single run with the same bottomhole assembly (BHA). For the water injectors presented in this study, this represented a saving of 3 days of operations and the associated logistics costs as compared to using logging tools and tractors for profiling. Moreover, real-time downhole flow monitoring with CT opens new avenues for treatment optimization, and ultimately, stimulation effectiveness. It allows for a better control of fluid resources and placement while the treatment is in progress. Flow sensors can be used to obtain the initial injection profile in lieu of distributed temperature sensing (DTS), which typically requires long acquisition times in water injectors. In this study, the wells treated with this approach showed a sustained 100% increase in injection rate, with the injection pressure dropping to nearly 0 psi. The volume of stimulation fluid needed was also lower than expected, yielding additional cost savings.
By providing direct, real-time downhole flow measurement, this new tool brings acid stimulation execution to a new level of effectiveness, an advance necessary to the sustainability of many production enhancement projects in Kuwait. Furthermore, the use of this new monitoring capability is more cost-effective than conventional stimulation approaches that have proven either inefficient or detrimental to wells in the long run.