The Jurassic-age Marrat Reservoir at Humma Field, Partitioned Neutral Zone (PNZ), Saudi Arabia and Kuwait - Utilization of a Probabilistic, Two Stage Design of Experiments-based Workflow for Reservoir Characterization and Management during Early Field Development and Delineation

Abstract

Abstract The Jurassic-age Humma Marrat carbonate reservoir is mainly located in the southwest corner of the Partitioned Neutral Zone (PNZ) between Saudi Arabia and Kuwait. The reservoir was discovered in 1998. The reservoir depth is about 9000 ft subsea. The gross reservoir interval is approximately 730 ft thick (110 ft net). The lowermost Marrat E zone contributes 80–90% of the production based on PLT data. The productivity of the Marrat E is dominated by a forty-foot thick, largely dolomitized interval with 15–20% porosity and 20–100 mD permeability. The upper zones contribute 10–20% of the production from thin intervals with 12–15% porosity and 2–5 mD permeability. A two stage design of experiments (DoE) based workflow was used to evaluate and optimize primary reservoir development. Reservoir uncertainties affecting volume and connectivity were assessed in the first stage of the workflow. The second stage of the workflow focused on dynamic uncertainties. The results of the workflow defined the P10, P50, and P90 models used for development optimization. Economic analysis showed that 640-acre primary development using vertical wells was the most attractive option. Pressure data obtained during field delineation in 2005 and 2006 showed the reservoir to be approaching bubble point pressure in the Marrat E zone main compartment. On-going dynamic modeling showed that only a limited number of additional wells were needed and the primary development project scope decreased considerably. Data acquired during delineation drilling in 2005 and 2006 continued to reduce reservoir uncertainties. Additional dynamic simulation was done in 2006 to refine development options. Rather than redo the entire DoE-based workflow, a series of dynamic models were generated in 2006 that incorporated the new well data and preserved the capability of giving probabilistic results. The modified DoE approach was shown to be an efficient tool for final assessment of primary development options and reserves. Introduction In the past few years design of experiments (DoE) based workflows have been used to assess reservoir uncertainty (Peng and Gupta, 2004, Friedman et al, 2003; White and Royer, 2003, White et al., 2001). Note that DoE is also referred to as experimental design or ED in the literature. DoE-based workflows are often used in reservoir fluid flow simulation studies to reduce the number of simulation runs (Kabir et al., 2004, Narahara et al., 2004, Peng and Gupta, 2003, Sanhi (2003)). DoE-based workflows are also being used to assess static reservoir uncertainties that effect original oil in place (OOIP) and connectivity or drained volume (Meddaugh and Griest, 2006; Meddaugh et al., 2006a). The basic principles, background, and methods of DoE are discussed by Barrentine (1999), Anderson and Whitcomb (2000), Montgomery (2001), and Mason et al. (2003). The Humma Marrat reservoir evaluation project, with which this paper is concerned, began in early 2004 as part of an effort to determine if the Humma Marrat reservoir should be developed and if so, what would be the likely development plan for primary production. Given anticipated well costs, likely primary development well spacing (160-acre based on analogs), and surface facility costs, the project was considered to be a major capital project and thus subject to rigorous internal technical review. As limited time was available to develop a decision support package and considerable reservoir uncertainties existed due to limited data, a two stage, design of experiments (DoE) based approach was used. In the first stage, the DoE-based workflow evaluated uncertainties related to OOIP and connectivity. The first stage results were used to build P10, P50, and P90 models for the second stage of the DoE workflow during which the dynamic uncertainties were evaluated. The results of the second stage of the DoE workflow were used to generate P10, P50, P90 models for development optimization and economic analysis. Optimization runs and preliminary economic analysis suggested that primary development on a 160 or 320-acre spacing was appropriate for the Humma Marrat reservoir.