Solvent Stimulation as a Solution for Heavy Oil Production in B Structure Pertamina
Abstract
Producing heavy oil requires more efforts than usual. Low degree of API, High viscosity, and high pour point make producing wells with this oil type quite challenging. B Structure oil in Pertamina has 17-23 API, 10-222 cp viscosity, and 450C pour point. Producing wells in this structure results in either low production rate or water coning. Altering oil characteristic by pumping suitable chemical would be an ideal solution for this problem. However, the efforts that have been made since 2011 could not meet expectation in terms of production gain and decline of water cut.
Laboratory test was performed to find proper chemical that can alter oil characteristics for this structure. Since oil in B structure contains asphaltene and paraffin, the logical thingto do to achieve this goal is to utilize aromatic solvent. Mixture of xylene and diesel as the main ingredients was chosen. Solubility test with oil from B structure showed that the mixture can dissolve its asphaltene and paraffin content. A dose of surfactant, mutual solvent, and potassium chloride are added into the mixture to condition formation. Compatibility test with brine from B Structure was observed, and neither emulsion nor sediment was formed. The mixture’s laboratory tests showed promising result. Stimulation jobs using solvent mixture mentioned above were performed for three wells in B Structure: well B-104, B-122, and B-121. The problem in well B-122 was the same, i.e. sudden increase in water cut after performing well service. In well B-121 case, it lost its production after water shut off activity. B-104 showed significant oil cut in swab job sample but could not be produced due to its heavy oil characteristics. Stimulation was performed using bullhead method with 6 ft penetration into the formation and minimum 120 minutes of soaking time. The best result out of these three treatments is from well B-121. The well’s oil production before treatment was 25 bbls per day and is improved post treatment into 175 bbls/day, with decreasing trend for its water cut. Another improvement also happened in well B-122. Pretreatment oil production for this well was 21 bbls/day and is improved into 76 bbls/day. In B-104 well, which delivered zero production since intervention job, delivered peak oil production of 54 bbls/day. All wells were produced using artificial lift and still have more than 300 m of pump submergence, which means the door for production optimization is wide open.
The success from these stimulation jobs using aromatic solvent provide a solution for heavy oil production in B Structure in Pertamina. Several more wells are already scheduled to receive solvent stimulation treatments. Production monitoring is still on going with production optimization is on the plate. Wells’ lifetime is also closely monitored as well as design optimization for stimulation treatment.
