--> Abstract: Stochastic Structural Modeling of Troll West with Special Emphasis on the Thin Oil Zone, by T. Hoye and E. Damsleth; #90990 (1993).

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HOYE, TROND, and EIVIND DAMSLETH, Norsk Hydro, Stabekk, Norway

ABSTRACT: Stochastic Structural Modeling of Troll West with Special Emphasis on the Thin Oil Zone

The Troll field is a giant gas field located in the Norwegian sector of the North Sea. In the Troll West Oil Province (TWOP) and Troll West Gas Province (TWGP), the field also contains a thin oil zone (22-26 m in TWOP, 12-14 m in TWGP), with an estimated STOOIP of approximately 600 10{6} Scu m.

The Troll reservoir is described as a coastal deltaic deposition characterized by high-permeable sands alternating with micaceous low-permeable sands. The combination of a near-horizontal layered structure and a thin oil leg makes the predicted target locations very sensitive to small changes in the structural model. Only minor vertical adjustments of the high-permeable sands may lead to significant changes in the lateral position of these oil prospects.

A stochastic structural model has been developed to be able to study the effects of the various uncertainties (seismic interpretation, depth conversion, well tie, OWC and GOC, reservoir zonation, etc.) on the location of the oil prospects and related volumes. The model is basically a multivariable two-dimensional Gaussian model for the different layer thicknesses, conditioned on the interpreted seismic reflectors and observations from about 20 wells. In the modeling, we have combined standard software for generating multi-Gaussian stochastic fields with a program system for grid manipulation and mapping.

Based on a large number of realizations of the model, we can produce "probability maps," showing the areal probability of various events, e.g., that the oil leg coincides with a high-permeable sand. These maps can be used as input in planning for appraisal and future production well locations. The same realizations can also be used to give probability distributions for the bulk volume of reservoir sands in the oil zone, and become a framework for stochastic three-dimensional petrophysical modeling.

Although our approach to stochastic structural modeling contains only basic elements from the geostatistical and grid-manipulating tool box, we believe that this is the first study of its kind where the results have had a direct impact on the further field development strategy. Several elements in our approach, although tailored to the Troll field, should be directly applicable to other fields where uncertainty in the structural model is important.

These data and interpretations represent the view of Norsk Hydro, and do not necessarily represent those of the entire partnership group.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.