Integrated Reservoir Characterisation of Cycle III, Brent Group, Brent Field, UK North Sea for Reservoir Management
Published:January 01, 1991
I.D. Bryant, A.H.M. Paardekam, P. Davies, M.C. Budding, 1991. "Integrated Reservoir Characterisation of Cycle III, Brent Group, Brent Field, UK North Sea for Reservoir Management", The Integration of Geology, Geophysics, Petrophysics and Petroleum Engineering in Reservoir Delineation, Description and Management, Robert Sneider, Wulf Massell, Rob Mathis, Dennis Loren, Paul Wichmann
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Data transfer between geologists and reservoir engineers has traditionally been by means of maps of reservoir properties averaged over the whole reservoir or over several reservoir intervals. These averaged descriptions of the reservoir are often adequate to guide decisions concerning early field development (e.g. how many platforms are required to develop a given field) but lack sufficient detail to guide later stage reservoir management when much more information is usually available (Slatt & Hopkins 1988; Weber & van Geuns 1989). At this stage of field development a major problem is the time and manpower required to integrate the available data into a detailed reservoir model (Johnson 1989). Even if such a model is successfully created, all too often the detail present in the model is lost during transfer to reservoir engineering simulators.
Recent developments in data managementtechnology have resulted in the creation of a number of detailed, computer-based reservoir modelling systems (Abib et al. 1988; Pajot et al. 1988; Hastings et al. 1989). The reservoir models generated by these systems may be used as data bases that are accessible to a variety of petroleum engineering disciplinesand constitute a common, multi-discplinarydescription of the reservoir that may subsequently be transferred to reservoir simulators. This methodology represents a significant advance from traditional methods since much more informationis containedwithin these modelsthan in maps of average properties.
This paper discusses the use of workstation-based log manipulation and reservoir modelling software to generate a detailed 3-D model of part of the Brent Group in the
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The Integration of Geology, Geophysics, Petrophysics and Petroleum Engineering in Reservoir Delineation, Description and Management
Bima Field, offshore northwest Java, is a sizeable reservoir containing reserves of approximately 700 MM bbls OOIP with a 50 BCF gas cap. At present only the northern 1/3 of the field is developed, with 7 platforms and 54 producing wells, of which 20 are horizontal. The field has multiple drive mechanisms and high viscosity oil (21 cp), resulting in rapid GOR and water-cut increase after 3 years of production. The high stakes (both reserves and facility investments) and the reservoir's complexities, make an effective reservoir management scheme critical. For this reason an integrated geological, geophysical and engineering description was carried out to provide a 3-D Reservoir Simulation Model to evaluate development options. Geologically, the Oligo-Miocene age Batu Raja Limestone was deposited on the Seribu Platform, a basement-controlled, fault- bounded structure. The Upper Batu Raja carbonate build-up is thickest on the structurally highest parts of the platform where the rock comprises a series of "cleaning upwards" cycles (muddy deposits overlain by progressively more grain-rich sediments). A Lower Miocene drop in sea-level caused subaerial exposure of much of the platform and leaching by meteoric fluids. This diagenetic event resulted in contrasts in the reservoir quality (porosity, permeability, fluid saturations) at various intervals of the Upper Batu Raja. Based on these dissimilarities, the reservoir was zoned into 6 model layers. Once zonation was established, well logs could be calibrated to whole and sidewall core. A dense grid of seismic data were used to map the Batu Raja structure. From these data, color seismic inversion sections were produced and calibrated to the well logs. The calibrated seismic data were then used to map the top of structure, the carbonate build-up's edges, the total thickness of the Upper Batu Raja (needed to control aquifer size in the model) and the thickness of the main pay zone (layers 1-3). Engineering reservoir description began with a detailed compilation of capillary pressure, relative permeability, production and DST data. The 3-D simulation model required special treatments, including varying the GOC depths to honor separate gas cap closures; making permeability pressure dependent in poorly-consolidated zones; and setting up horizontal well completion treatments. Results suggest that water injection into the oil rim and gas cap is an effective approach toward maximizing recoveries and minimizing gas cap resaturation. However, waterflood reserves are sensitive to injection timing. The synergistic approach of geological, engineering and geophysical input into the Bima reservoir study has had impact by delivering a reservoir management tool that can evaluate future development expansion and possible gas sales. The simulation model can also track fluid migration during the field's producing life. The geological/geophysical model led to an enhanced understanding of Batu Raja depositional and diagenetic processes that has potential in regional exploration strategies.