Abstract

The Middle Cretaceous Upper Burgan and Wara sandstone reservoirs in the Minagish field are exhibiting variable clastic depositional settings ranging from fluvial, fluvio-tidal to tidal wave sands. The sand bodies are highly heterogeneous in terms of the stratigraphic architecture implying extensive lateral facies variations, stacked sand bodies and varying petrophysical properties. Modeling the target sand channels and optimizing subsurface well placement and geo-steering requires high resolution geological and seismic data integration in order to minimize uncertainities related to correlations of multiple auto-cyclic ravinement surfaces, channels geometry and sub-seismic fault network.

Within Upper Burgan and Wara sand bodies there are different lobes that have varying degree of minerals like glauconite, pyrite and hematite with other cementing materials such as calcite and dolomite. The presence of glauconite has a strong impact on petrophysical evaluation, whereas the presence of shale poses several challenges during geosteering.

Geostatistical modeling for sand distribution were integrated using seismic data, core and sedimentological models, electrofacies and petrophysical intrepretations. High resolution seismic data including pre-stack depth mighration and pre-stack simultaneous inversion have been utilized with well log curve shales and elastic impedance to trace accurately the good quality sand. High resolution sequence stratigraphic model were attempted on this complex Upper Burgan and Wara formations. The formation evaluation and geosteering challenges were addressed to ensure the successful drilling and completion of horizontal producers.

The wells drilled in this complex settings are geostreed with high definition inversion based distance to boundary technology having a higher precision and accuracy of resistivity contrasts. Formation capture cross section (sigma) saturation was of great value in "mixed lithologies" of Upper Burgan and Wara as resistivity frequently polarized from the proximity to bed boundaries and in these portions traditional resistivity logs proved ineffective for saturation evaluations. In addition the real time permeability estimation using spectroscopy analysis was very beneficial to ICD design.

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