A regular 5-spot Alkaline Surfactant Polymer (ASP) pilot is planned for a giant carbonate reservoir in Kuwait where a suitable formulation compatible with harsh salinity and temperature conditions was developed. However, it is vital to address uncertainties introduced through historical development schemes that are not necessarily compatible with original EOR plans. This paper sheds light on the importance of incorporating water flooding data and learnings to optimize the design of subsequent EOR deployment.
An integrated workflow was adopted involving acquisition and analysis of relevant surveillance data to establish a solid understanding of water flooding preceding EOR deployment. The considered surveillance data covered pressure responses, rates, a variety of passive tracers, injection step rate tests followed by fall off tests, production/injection logs, high precision temperature logs, spectral noise logs and water injection into reservoir cores. The extent of thermal and reservoir depletion effects on reducing fracture initiation pressure was also investigated.
The study focuses first on understanding the microscopic and macroscopic aspects underlying overall sweep efficiency due to water flooding, a key requirement to upscale the Pilot results to full field development. The macroscopic sweep efficiency was found to be strongly affected by the native permeability contrast attributed to geological heterogeneities as well as induced fractures. Induced fractures were triggered by different mechanisms related to cold water injection, reservoir pressure depletion, injected water quality and relatively high injection rates targets for a comparatively low permeability carbonate reservoir.
The findings related to induced fractures have a well-established impact on the design and operating philosophy of the desired ASP Pilot with relatively short well spacing and active surrounding production/injection wells. Premature breakthrough of chemical injectants will not only impact the sweep efficiency of ASP flooding, but will potentially bring about operational complications due to inorganic scaling and produced fluids separation, thus introducing additional uncertainties in relation to the acquisition and interpretation of the Pilot data. The original Pilot design is being revisited by means of an integrated workflow to better understand and adequately mitigate poor conformance challenges during the softened water injection phase that will be followed by the ASP injection phase using a fit-for-purpose surveillance program. This workflow involves geological characterization and detailed analysis of water flooding performance in pursuit of improved conformance control to pave the way for efficient ASP flooding.
The findings of this study underscore the importance of integrated field development planning and comprehensive surveillance to derive important waterflooding insights that can be used to de-risk ASP flooding under harsh reservoir conditions.