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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Fast Appraisal and Maturation of Heterogeneous Carbonate Fields in a Shuaiba Stratigraphic Play, North Oman

Anouk Creusen1; Mariano Carrera1; Lawrence Grant-Wooley1; Issa Mahruqi1; Maniesh Singh1; Murali Raghunathan1; Richard Spiteri1; Harry Soek1

(1) ONPL, Petroleum Development Oman LLC, Muscat, Oman.

We present two case studies discussing the synergy between appraisal and maturation activities of a heterogeneous carbonate play in North Oman. Key aspects are the effects of the complex geology on how quickly new fields can be brought on stream after discovery.

The Upper Shuaiba Formation was deposited as a series prograding clinoforms on either side of the Bab basin. The clinoforms comprise thick rudist build-ups, high-energy oolitic grainstone shoals and thin restricted miliolid oolitic grainstone sheets, are around 800 - 1000 meter wide, over 10 kilometres long, 5 to 25 meters thick and have high net-to-gross ratios. In both fields, the clinoforms are separated by non-permeable argillaceous facies, forming stratigraphic traps below the Nahr Umr unconformity. The extend of the reservoirs, the distribution of good quality reservoir, the heterogeneity and impact of fractures remain as the key uncertainties.

Owing to low permeability of the facies, horizontal wells are preferred. Horizontal well placement in thick parts of the reservoir requires precise geosteering of injectors and producers in the top and base of the reservoir in order to maximize recovery. Well placement requires a balanced decision regarding the use of azimuthal geosteering tools in certain appraisal wells. Thinner units may require a more intensive azimuthal geosteering strategy as the heterogeneity of the shoals may lead to patchy reservoir quality and thickness, not detectable on seismic. In order to be able to make cost effective decisions regarding facilities and drilling costs, the pattern design and geosteering strategy require an upfront decision on producer-injector spacing, flexible to deal with the heterogeneity encountered while drilling.

Water-flooding was selected as the optimal recovery mechanism and box-models were designed to simulate the physics of the process. Data acquired from RCA, SCAL, PVT analysis, MDT and VIT are utilized to build simplistic dynamic models. Based on the results of the simulations, the optimal producer-injector spacing for varying thicknesses across the fields was tested. A maturation plan based on various wells spacings was developed. Well scheduling focuses on maturation of the projects and volumes associated, mitigating appraisal and performance risks.

The appraisal strategy includes drilling vertical pilot holes with a horizontal sidetracks. Azimuthal geosteering technology is used to place the wells at desired distance to bed boundary.