Draugen Field development; the role of gravity drainage and horizontal wells

The Draugen Field is an elongate, low relief, anticline containing mainly multi-Darcy sandstones. Oil initially in-place (STOOIP) is 182 x 10 6 Sm 3 . The 1987 Plan for Development and Operation (PDO) assumed a central cluster of 6 deviated production wells and 3 subsea water injectors at each end of the field. In addition two subsea wells would provide early production. Unsteady state relative permeability data indicate a residual oil saturation of 35%. In the full field simulation model this was increased to 40% to account for small-scale heterogeneity. The model yielded a recovery of some 67 x 10 6 Sm 3 . Modern steady state and centrifuge techniques have since demonstrated a long tail of very low oil relative permeability before reaching a residual oil saturation of some 15%. Fine grid simulations translated this into a gravity segregation process behind the displacement front. Other fine grid models reveal that horizontal wells will yield a slower build up of water cut than vertical wells. The increased productivity of the horizontal wells reduced the required number of platform producers from 6 to 5. Pseudo-relative permeabilities were developed to represent fine grid model performance in a new sophisticated full field model. This model predicted an ultimate recovery of 94 x 10 6 Sm 3 (40% increase). The additional predicted recovery is attributed to a reduction of the effective residual saturation and delayed water production associated with horizontal wells. In October 1993 Draugen started production from one horizontal subsea well, which has since demonstrated a better than expected coning performance. Production from platform wells was initiated in June 1994 with initial well rates up to 8000 Sm 3 per day, confirming the expected high productivity of horizontal wells. Optimization and tuning of facilities has since allowed the peak production rate for the field to be increased from the planned 17 500 Sm 3 per day to a present actual level of 24 600 Sm 3 per day. Further de-bottlenecking is ongoing with the aim of increasing process capacity.