Abstract
An increasing energy demand combined with the natural decline of old field discoveries has forced oil producers to develop and improve returns from existing assets. In Latin America, many major oil companies have been interested in heavy oils. Higher oil prices and improvements to technology allowing recovery factors up to 30% have made these reservoirs more attractive to operators.
In Colombia, heavy oil fields are being developed in the Magdalena Medio area using steam injection as a thermal recovery method. Cyclic steam stimulation (CSS) is used and consists of three stages: injection, soaking, and production. Steam is first injected into a well for a certain amount of time to heat the oil within the surrounding reservoir to a temperature at which it flows. After sufficient steam has been injected, the steam is usually left to "soak" for a predetermined time period. Finally, oil is produced out of the same well. This process can cause high stress in the wellbore because of the high temperatures used and the cyclical nature of dramatic temperature changes. The elevated temperatures can reach up to 350°C (650°F) during thermal cycling, which, in turn, can potentially cause radial fractures or debonding of the cement, thus potentially compromising the zonal isolation.
Achieving zonal isolation within these shallow vertical and horizontal wells (90° and 2, 200 ft measured depth [MD]/1, 396 ft true vertical depth [TVD]) and avoiding water communication between zones are the primary challenges encountered during these projects. This paper presents a successful methodology, lessons learned, and engineering design changes applied during the past three years to more than 200 wells in the Magdalena Medio area.
