The Winter Horizontal Well project was started in 1988 as a pilot of two horizontal wells. In 1989 three more horizontal wells were drilled. The performance proved to be encouraging. Central facilities of mainly a free water knockout and two treaters, and water disposal plant were constructed. Since 1990 some wells (7–15) are drilled annually to maintain a certain level of production. By the end of 1997 there were 88 horizontal wells drilled in the field producing at peak rate of 1000 m3/d of oil. When new wells are drilled they are placed on production and older watered out wells are shut in.
When oil price is high enough wells are drilled to keep the central facilities running at capacity. When oil price is low fewer wells are drilled to maintain economic operation of the field without producing reserves at low return. A new horizontal well starts at high oil rate with high decline rate. The first year of production produces half the reserves, four years produces the remaining half at increasing water cuts. No wells were drilled in 1998 due to the slump in oil prices. The recovery factor of a good watered out well is about 6- 11% of OOIP (25 % if calculated based on the volume of the triangular prism with the well at the apex and the W/O contact as the base of the prism).
The water plant and the disposal wells became the limiting parameters to the productivity of the field. Thus, in order to improve economic performance and oil rate there are two identifiable areas to improve the performance, namely, increase recovery factor and improve the economics of water handling. The current paper addresses the two issues. There is enough evidence and proof that one issue was completely addressed (water handling) while the recovery improvement was not fully addressed at the time of writing this paper.
The Winter Field (Figure 1) has been developed utilizing horizontal wells to produce heavy oil (13.7 API oil of 2800- 3800 cp. Insitu viscosity) in a 12-m (37-ft) thick Cummings sand underlain by a very strong aquifer. Fluid production is flow-lined to a central facility located at 12-32-42-25W3. Gathered fluid enters a single free water knock out where the bulk of the water is removed and directed to the water plant. The oil emulsion goes to a pair of oil treaters where the remaining water above sales specification is removed. The treated oil is blended with condensate and piped to sales.
The water plant pumps the purified water through an eight inch (20 cm) pipeline, 2 miles (3.6 km) long to three disposal wells. The volume of disposal water reached a peek of 11,000 m3/d (77,000 bbl/d) at the maximum design pressure of the water plant. At that point there were more than 40 wells shut in because of disposal limitations. Typical water disposal cost is $0.25/m3 ($0.04/bbl). The cost of drilling additional disposal wells is $500,000 / well and the cost of twining the disposal flow-line is higher at about $ 1 million.
