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Abstract

A two level design of experiments (DoE) workflow was used to evaluate the Humma Marrat reservoir in the Partitioned Neutral Zone (PNZ) between Saudi Arabia and Kuwait. The Jurassic-age Humma Marrat reservoir consists of productive limestone and dolomite intervals separated by very tight limestone and/or shaly limestone zones. The reservoir depth is about 9000 ft subsea and the gross reservoir interval is about 730 ft thick. The partially dolomitized lowermost interval (informally known as the Marrat E) is the most porous and permeable zone. The porosity within productive zones is 6-20% and permeability is generally < 20 md. Fracture-controlled production may be important in the uppermost zone (Marrat A). The middle Marrat C zone is very tight. Discovered in 1998, the reservoir currently produces from five wells. Additional delineation wells and production wells are planned for 2006 and 2007.

Reservoir uncertainties were assessed via finite difference dynamic simulation of earth models generated using parameter combinations specified by a Plackett-Burman DoE table. Cumulative oil production was used as the response variable in the DoE-based workflow. The first level DoE evaluated uncertainty sources related to reservoir volume and connectivity including structural uncertainty, facies distribution, porosity histogram, water saturation histogram, original oil/water contact, porosity semivariogram range, permeability multiplier, fault compartmentalization, and fault transmissibility. Only the porosity histogram uncertainty was determined to be statistically significant. The results from the first level DoE work were used to define earth models for the second level DoE, in which the following “dynamic” uncertainty sources were assessed: aquifer support, rock compressibility, extent of heavier oil, vertical to horizontal permeability ratio (kv/kh), PI multiplier, residual oil saturation (Sorw), and relative permeability (krw @ Sorw). The results of the second level DoE work showed that only the earth model and PI multiplier uncertainties were statistically significant. The results from the second level of the DoE-based workflow were used to generate the reservoir models for development optimization and economic analysis. The P50 model was used to screen development options that included well spacing, well type, and horizontal well length. Economic analyses were conducted to select the optimum development scenario using the P10, P50, and P90 reservoir models.

This paper focuses on the initial DoE-based evaluation of the Humma Marrat reservoir that was completed in mid-2004. The work illustrates the DoE-based approach to assess and model reservoir uncertainties. As significant additional data (e.g., reprocessed 3D seismic, revised velocity model, additional MDT and PLT pressure data, and delineation wells) became available after the initial evaluation was complete, the DoE uncertainty tables and models were updated. Since this paper is a case history, reservoir evaluation work based on data acquired or re-interpreted since the fourth quarter of 2004 also is included, although only critical aspects of the post-2004 work are discussed in detail. A companion paper in this volume (Meddaugh and Griest, 2006) provides a historical assessment of OOIP uncertainty for the Humma Marrat reservoir from pre-drill through the end of 2005.

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