AAPG Bulletin, V. 83 ( October 1999), No. 10, P. 1535-1551.

Correlation Techniques, Perforation Strategies, and Recovery Factors: An Integrated 3-D Reservoir Modeling Study, Sirikit Field, Thailand¹

R. Bruce Ainsworth,² Montree Sanlung,³ and S. Theo C. Duivenvoorden⁴

©Copyright 1999.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received March 26, 1998; revised manuscript received February 16, 1999; final acceptance March 31, 1999.
²Thai Shell Exploration and Production Company Ltd., Shell House, PO Box 345, Bangkok 10501, Thailand. Present address: Woodside Energy Ltd., 1 Adelaide Terrace, Perth WA 6000, Australia; e-mail: [email protected]
³Thai Shell Exploration and Production Company Ltd., Shell House, PO Box 345, Bangkok 10501, Thailand; e-mail: [email protected]
⁴Thai Shell Exploration and Production Company Ltd., Shell House, PO Box 345, Bangkok 10501, Thailand. Present address: Nederlandse Aardolie Maatschappij B.V., PO Box 1, 7760 AA Schoonebeek, Netherlands; e-mail: [email protected]
 

The authors thank Thai Shell Exploration and Production Company and joint venture partners Petroleum Authority of Thailand Exploration and Production Company (PTTEP) for their permission to publish this paper. We are grateful to Bulletin reviewers Harald Poelchau, Fred Wehr, and AAPG Editor Neil Hurley for their constructive comments, which have significantly improved this manuscript. Thanks are also due to Huw Williams for sharing his views on chronostratigraphic correlation techniques and to Chris Clayton and Amy Newland for reviewing a final version of the paper. Lastly, Peter Colleran, John Hoppe, and Gerard Mäkel should be singled out for their support of this project. 

ABSTRACT

Production in the Sirikit oil field of the Phitsanulok basin, Thailand, commenced in 1982. The field has an STOIIP (stock tank oil initially in place) of approximately 800 MMbbl (million barrels). To date, more than 130 wells have been drilled and over 100 MMbbl produced. Reservoir management studies into optimizing recovery and identifying unswept oil volumes are ongoing so as to maximize the venture's profitability. This work includes 3-D (three-dimensional) static and dynamic modeling. This study is one such exercise whereby different geological correlation techniques and perforation strategies were analyzed for their potential impact on recovery factors.

The Sirikit field and adjacent satellite fields are composed of predominantly lacustrine mouth-bar and fluvial deposits. Two correlation techniques, lithostratigraphy and chronostratigraphy, were employed to generate two 3-D reservoir architectures using the Shell proprietary 3-D static reservoir modeling system GEOCAP. Significantly different recovery factors are derived from 3-D dynamic flow simulation of these architectures (no vertical upscaling, 2 X 2 areal upscaling) within the Shell proprietary reservoir simulator MORES. When good-quality sands observed on well logs are perforated in both models, the lithostratigraphic correlation model results in an absolute 3% higher recovery factor than that of the chronostratigraphic correlation model. In relative terms, this represents a 43% higher recovery factor. This suggests that if a lithostratigraphic correlation model is assumed, then for this perforation strategy, the recovery factor would be overestimated by 3% absolute and 43% relative, if the chronostratigraphic interpretation represents the actual subsurface architecture.

In addition, the architecture of the chronostratigraphic model results in the lateral correlation of the thicker upper mouth-bar sands with good-quality, thin-bedded toeset sands and shales (heterolithics). These thin-bedded sands are only marginally resolvable on wireline logs and have not generally been perforated in the Sirikit field. When these thin-bedded heterolithics are additionally perforated in the 3-D model, an absolute increase in recovery factor of 2% is observed over the same model that has only the upper mouth-bar sands perforated. In relative terms, this represents a 28% improvement in the recovery factor.

This work confirms and partially quantifies the impact that the choice of mouth-bar correlation style can have on recovery factors as predicted by 3-D dynamic reservoir models. However, the chronostratigraphic model described in this paper represents an end-member connectivity scenario whereby sand-body continuity is relatively low due to continuous dipping shale barriers. Further work is required to quantify the recovery factors for the whole spectrum of potential chronostratigraphic model connectivity scenarios.