Development Planning For The Statfjord Field Using Three-Dimensional And Areal Reservoir Simulation
Authors: Chauvin A.L. , Jackson R.F. , McGee P.R. , McMichael C.L. 
Published: December 2007

Rapidly increasing costs associated with North Sea development have produced an environment in which good field development planning is imperative. Reservoir management is the keystone of any plan. This paper reviews the geology of the Statfjord Field and paper reviews the geology of the Statfjord Field and describes the latest reservoir simulation techniques being used for the evaluation of producing alternatives.

The Statfjord Field is comprised of two geologically complex reservoirs; the Brent and the Statfjord. The overall development plan calls for pressure maintenance by waterflood in the Brent and pressure maintenance by waterflood in the Brent and a combination gas and waterflood in the Statfjord. The first platform, Statfjord "A" is in place in the field and the second, Statfjord "B", is under construction. These two platforms will go in the center and southern part of the field, respectively. The development program for the northern part of the field and the optimum utilization of the associated gas have not been resolved.

The simulation approach chosen employs several three-dimensional cross section models to evaluate the impact of reservoir property variations and water and gas coning and cusping. Special performance functions are developed from the three-dimensional modeling for use in a two-dimensional field model. Prior to their use in the field model, the validity Prior to their use in the field model, the validity of the special functions is established by comparison of three-dimensional cross section results with the results from a corresponding two-dimensional model in which the functions have been used. The field model is used to examine field development alternatives.

Introduction

The Statfjord Field is located in the North Sea about 150 km east of the Shetlands Islands and 200 km northwest of the city of Bergen, Norway. Figure 1 shows its location in relation to other North Sea Fields. The largest part of the field lies on the Norwegian side of the United Kingdom - Norway International offshore boundary within License 037. The remainder of the field lies within United Kingdom License P104. Water depth in the field averages a relatively uniform 144 m (470 feet).

The first exploratory well in the Statfjord field, well 211/24-1, was drilled during 1973 on the southwest side of the structure. Water-bearing but good quality Brent and Statfjord formation sands were encountered. It is now known that the well was drilled just 150 meters west of the Brent Formation oil/water contact (Figure 2).

The discovery well, 33/12-1, was drilled on the crest of the structure in March, 1974. The entire Brent reservoir section, 160 meters, was found oil-bearing. The oil from test samples was undersaturated by approximately 1500 Psi at the pressure datum depth of 2469 meters. No gas cap was pressure datum depth of 2469 meters. No gas cap was found and from the well location it was concluded that none existed in the reservoir. This has since been confirmed by other wells. Sands were encountered in the deeper Statfjord Formation but these were in water at this location (Figure 3).

The confirmation well, 33/9-1, encountered the Brent Formation oil column and a well defined oil/water contact at 2584 meters subsea. Sand accumulation was found in the Statfjord Formation but, as in the discovery well, it was water-bearing.

The second major oil reservoir was discovered by the third well, 33/12-2. The well encountered 124 meters of oil accumulation in the Statfjord Formation and an abbreviated but oil-bearing Brent Formation. Lowest oil saturation in the well was 2805 meters subsea at an oil/shale contact. As in the case of the Brent Reservoir no gas cap was observed. Reservoir crude from well tests was undersaturated by over 2700 psi at the depth of 2701 meters, and it was therefore concluded that the reservoir had no gas cap.