Impact of Natural Fractures in a Predominantly Non-Fractured Carbonate field, Sabiriyah Mauddud

Abstract

Summary Production from the mid-Cretaceous Sabiriyah Mauddud Formation results to a large extent from waterflood, yet field data indicate that reservoir performance is impacted by large permeability contrasts in the reservoir. High permeability (high-K) elements in the reservoir are likely the product of sedimentological and diagenetic processes as well as the structural evolution of the field. In this abstract, we concentrate on the fault and fracture components of an integrated study with included carbonate and structural geology, seismic interpretation diagenesis, geomechanics and reservoir engineering. One of the key outcomes of the study is an improved understanding of the complex High-K pathways summarized in a so-called plumbing diagram. The two first order elements for the High-K plumbing system are 1) cemented low porosity cycle tops that are sequence stratigraphically controlled and where dissolution enlarged open fractures and vugs make up flow paths and 2) fault damage zones with increased fracture density in cemented layers. While it has been observed that, statically, the reservoir is characterized by the presence of faults and fractures contributing to flow paths, from a dynamic-response point of view, the reservoir behaves overall as an unfractured reservoir.