Hydro has produced oil from horizontal wells in the thin oil layer on Troll West since 1995. The main challenge is to efficiently drain the thin target sands, within a remaining oil column of 0-20 meters, covering an area of approximately 500 km2. New horizontal producers are continuously being drilled and multi-disciplinary collaboration between geophysicists, geologists, reservoir and production engineers is crucial for optimizing new wells. Delegation of operational responsibility to the well group is a vital factor for obtaining an effective work process. Vertical geosteering is performed on a centimeter scale and quick decision-making within the well teams is needed to optimize the well paths while drilling. By combining real-time data with high-quality 3D and 4D seismic, detailed geological models, reservoir and production data, cost-effective and highly profitable wells are routinely planned and drilled on Troll West.
The Troll field is currently the largest producing oil and gas field on the Norwegian continental shelf. It is located in the northern North Sea, near the west coast of Norway, on the margin of the Viking Graben, Fig. 1. The field is divided by two major north-south trending faults, which separate the field into three provinces, named Troll West Oil Province (TWOP), Troll West Gas Province (TWGP) and Troll East, Fig. 2. Since 1995, Hydro has produced oil from horizontal wells on TWOP and TWGP where the initial oil column was 22-27 m and 11-13 m respectively1. More than 150 horizontal producers have been drilled on Troll West and approximately two thirds of the total oil reserves of 1.4 billion barrels have been produced. The oil column on Troll East is 1-4 m and so far only the huge gas cap has been considered commercial.
Figure 1: The Troll field is located in the North Sea near the west coast of Norway. The field is divided into three provinces: TWOP, TWGP and Troll East. (Available in full paper)
Figure 2: Structural map of Top Reservoir indicating the two major NS trending faults separating the field into the three provinces TWOP, TWGP and Troll East. Numerous minor NW-SE orientated faults define the different reservoir compartments. (Available in full paper)
The main challenge is to efficiently drain the thin target sands within the thin oil column. New horizontal producers are continuously being drilled in the progressively thinning oil layer. Well planning and drilling are becoming increasingly difficult due to the ever-larger number of existing producers, the consequent decrease in remaining targets and movement of the fluid contacts due to production, Fig. 3. Multi-disciplinary collaboration between geophysicists, geologists, and reservoir and production engineers is crucial to meet this challenging task.
Figure 3: Structural map of top reservoir cut by the initial OWC. The thin oil column extends over a huge area. A large number of horizontal wells have been drilled. (Available in full paper)
The Troll field is located within three large tilted fault blocks at the edge of the Horda Platform, Figs. 2, 3 and 4. The reservoir consists of stacked off-lapping shallow marine sandstones and intervening siltstones mostly belonging to the Upper Jurassic (Oxfordian) Sognefjord Formation, Fig. 5.