Increase Productive Life and Add to Inplace Oil in Mature Reservoirs with Integrated Studies: Zubair Reservoir in Kuwait

Azim, Saikh A.; Al-Anezi, Salah; Kostic, Boris; Hoppe, Markus; Al-Blayees, Mariam; Al-Qattan, Sarah; Al-Saad, Bader

The Zubair reservoir is an Albian siliciclastic reservoir on production for the last six decades. Cumulative production indicates a higher oil recovery factor than expected. An integrated study involving sequence stratigraphy, sedimentology, biostratigraphy, petrophysics and modeling technique resulted in a better understanding of rock fabric, mineralogical composition, depositional settings and their evolution leading to discovery of more inplace oil and a rejuvenated development plan.

Petrographically, the formation comprises highly mature clastic deposits with variable and heterogeneously distributed argillaceous matter. The fine to medium-grained sandstones are weakly overprinted by authigenic mineral precipitates. Whole rock and clay-fraction XRD indicate very low expandable clay minerals.

The deposits were rationalized into three levels of comprehensive descriptive and interpretative schemes. The expected geometries, dimensions, internal heterogeneities and reservoir qualities of the various facies associations were upscaled into Gross Depositional Environments (GDE) to increase the confidence and consistency of sedimentological interpretations from openhole logs alone. The palynologically constrained GDE indicate increased importance of deltaic as opposed to previously envisaged shallow marine processes.

Four low-order sequence stratigraphic sequences were identified: A basal transgressive set, a heterogeneous highstand deltaic and more homogeneous channel-dominated lowstand set, which in turn are capped by transgressive deltaic to open marine deposits.

Focused core studies on hot gammaray intervals showed the presence of conductive heavy minerals in net sands. Intercalation of shale laminations with oil stained sands contributed to high gammaray values in some layers. Realistic assessment of net pay in these zones was possible from formation evaluation using resistivity anisotropy tools calibrated to cores.

Identification of arenaceous deltaic sandstones enhanced the net to gross ratio in the reservoir intervals. High pressure mercury injection data from SCAL studies confirmed the conclusion. A detailed layering scheme with layer specific modeling techniques backed by a combination of deterministic sand trend maps and stochastic modeling realized the envisaged model.

An accelerated development with water injection is underway to exploit the discovered reserves. The paper describes the studies leading to enhanced value of the asset in detail.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013