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ABSTRACT: High-Resolution Stochastic Inversion in Tight Oman Carbonates -The Makarem Field (Buah Fm.) Case Study

Shanor, Gordy G.1, Montri Rawanchaikul1, Mark Sams2, Roland M. Muggli3, Graham Tiley4, and Junaid M. Ghulam5
(1) Jason Geosystems Middle East, Dubai, United Arab Emirates
(2) Jason Geosystems Asia, Singapore, Singapore
(3) XGP/3, 113 Muscat, Oman
(4) XEM/3, 113 Muscat, Oman
(5) Gas Dept, 113 Muscat, Oman

This paper presents the workflow and results of an integrated stochastic inversion study of tight, gas bearing Pre-Cambrian Buah dolomites of the Makarem Field in Northern Oman. The study formed part of an integrated project to investigate different field development scenarios. The objectives and deliverables of this study were to produce multiple, detailed reservoir porosity models, capturing the reservoir heterogeneity at high resolution, for use as inputs to flow simulation modeling.

Three wells on the structure have been drilled and tested to-date: Two wells indicated high flow rates, while one well tested a tight zone within the reservoir. Early review of seismic impedance data suggested relations between test results and zones of higher dolomite impedance related to lower matrix porosity. Reservoir porosity is typically between 0 to 5% at a depth of around 4,500 m.

Review of initial inversion results led to re-interpretation of existing horizons and new horizon definitions, using the acoustic impedance (AI) data. The AI cube provided a superior data set for identifying intra-reservoir layers compared to the seismic reflectivity data.

High-resolution models of complex reservoirs were obtained through stochastic inversion combined with lithology simulation. The models must honor all seismic, log and geologic input data. Generation of multiple models then permits reservoir uncertainties to be quantified. Stochastic inversion at high resolution models the properties of individual reservoir units, which are not resolved by conventional seismic reflection imaging techniques.

The study concluded with the generation of a number of high-resolution porosity models that are currently being used in the building of the dynamic flow simulation model.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia