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Analysis of Greenzyme® in Oilfield Recovery: Biological enzyme treatment to remove blockage. Oil Well WeiZhou 11-4-A3 Off Shore April 30, 2003, CNOOC (China) Limited Zhanjiang Branch Drilling of this well started in 1992. Drilling was completed at a well depth of 1217 m on August 31. Well completion started on January 3, 1994 and ended on January 5th. Production started on January 6, 1994. The production situation was initially good. The initial submersible electric pump discharge amount was 100 m3/d with oil production of 148 m3/d and zero water content. As the water content increased, the oil production dropped gradually. The oil production had dropped to 49 m3/d, the fluid generation rate had dropped to 200 m3/d, and the water content was 76%. This indicates the wellbore of the oil well had been blocked, hindering the flow of oil and water. BASIC WELL DATA Well No.: WZ11-4-A3 Well type: Producing well Substrate hole No.: 2# Complete drilling well depth: 1217 m Complete drill stratum position: Xiayang formation Artificial well bottom: 1180 m Maximum well inclination: 45°/826.0-872.0 m Current Production Zone: Jiaowei formation II Well completion method: Filled with gravel STIMULATION OBJECTIVE   Inject Greenzyme® to remove blocking in order to lower the water content, stabilize oil and control water, and increase the crude oil production. Based on calculations from experience, this well should use 15 barrels (15x0.2=3 m3) Greenzyme®. Since this well has a high water content, the recommended concentration is 8% Greenzyme® solution, prepared using the formation water. The temperature of the injected solution should be higher than 50°C. The treatment process has the following requirements: a) Injection method: Squeeze reversely from the casing to directly enter the reservoir. b) Pumping rate: 0.5-1.2 m3/min. This can be determined based on pumping pressures encountered on-site. c) Pumping pressure: Lower than 20 MPa d) Injection procedure: - First, mix 15 barrels of Greenzyme® solution into 37 m3 formation water to prepare 40 m3 of 8%   Greenzyme® solution. - It is important to keep the temperature above 50°C. - Use a pump to inject the solution into the stratum, followed by pumping 18 m3 diesel fuel to close the   well. - It is necessary to close the well 4 days before resuming production RESULTS AND ANALYSIS Production was resumed at 4 PM on April 4 after the Wei 11-4-A3 well had been closed for 90 h. After the well was opened, the total fluid production rate rose continuously. Three days later, the fluid production rate rose from 200 m3 per day to about 430 m3 per day. The oil production rose from 49 m3 per day to 76 m3 per day, and the water content changed from 76% to about 82%. This situation has now been stable for almost one month. Many data points have stayed on the same levels. This means that blockage in the oil layer has been completely removed. Currently, the fluid production rate exceeds the capability of the pump (300 m3/d). The fluid flow capability of the formation is very sufficient. Although the water content has increased (by 6%), the experiment was still very successful. It has proved that Greenzyme® is the best choice for removing blockage in oil wells. GuiLin Engineering Institute conducted unblocking using Greenzyme® on the A3 well from March 31 to April 4, 2003. After the unblocking operation was conducted, the fluid generating rate reached 430 m3/d. The daily oil production was 77.8 m3/d. The water content was 81.9%. Before the unblocking operation, the amount of fluid generated daily was 200 m3/d. The daily oil production was 48.9 m3/d, and the water content was 75.6%. After the unblocking operation, the fluid amount increased by 230 m3/d, the oil production increased by 29 m3/d, and the water content increased by 6%. Although the water content increased after the unblocking operation, the fluid amount doubled. The unblocking effect was very good. Also, the fluid amount held at a stable level. The cumulative increase in oil production up to the end of August, 2005 was 0.9x104 m3/d. This technology was successfully applied to unblocking the WeiZhou 11-4 oilfield. Zhonghai Petroleum (China) Co., Ltd. Production Department Zhanjiang Branch, August 31, 2005
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