Unlocking flow pathways in complex carbonate reservoirs: Benefits of an integrated subsurface study from the Cretaceous Mauddud Formation, North Kuwait

Despite its long production history (since 1958) and extensive reservoir stimulation by water injection, the Mauddud reservoir of the Sabiriyah field (SAMA) in northern Kuwait has been plagued by relatively disappointing oil production increase, low oil-by-water replacement ratios, and early water-breakthrough observations. The work described in this paper indicates that reservoir complexity and associated permeability heterogeneity are at the root cause of this and are the result of the interplay between sedimentology, diagenesis and the structural evolution of the area. A multi-disciplinary study involving structural geology, sedimentology, diagenesis, reservoir engineering and geomechanics identified the geological processes responsible for the development of principal high-permeability (High-K) elements in SAMA. Their 3D distribution has been characterized and reservoir property ranges have been established, based on integrated evaluation of static (e.g., seismic, core, borehole image, wireline logs, and drilling information such as losses) and dynamic information (e.g., production and injection logging tools, well test information, pressure data, historical production data and tracer information). Feedback loops between geological realizations and dynamic simulations allowed the testing of various concepts and property ranges with learnings implemented in updates of the geological realizations. This approach increases the confidence level in the conceptual geological models. Three principal plumbing elements contribute to the reservoir and property heterogeneity in the SAMA reservoir. Firstly, relatively thin (one to several decimeters) cemented zones characterized by low matrix porosity but significant secondary vuggy and fracture porosity with high permeability occur in two distinct stratigraphic intervals in the reservoir. These intervals occur near sequence boundaries when the carbonates likely experienced brief periods of exposure. They are interpreted to be cemented cycle tops formed during meteoric diagenesis and represent key flow zones for the initial hydrocarbon production as well as for later high-rate production of formation water and injected water, as identified by production/injection logging tools. Faults and associated fault (damage) zones with abundant fractures are the second key plumbing element. Core recovery and observations from wells located closely to a fault zone identified from detailed seismic interpretation highlight the o