Jin, Fu (CNPC Research Institute of Petroleum Exploration and Development & CNPC Drilling Research Institute) | Xi, Wang (CNPC Research Institute of Petroleum Exploration and Development & CNPC Drilling Research Institute) | Shunyuan, Zhang (CNPC Drilling Research Institute)
Located in south of Eastern Venezuela Basin, Orinoco Oilfield is the unique huge ultra-tight oilfield that has not been developed by scale in the world. The high-density tight oil is known for its high content of acids, heavy metals and asphaltenes with a viscosity of 1000-10000mPa·s. ML Block whose OOIP is 178*108bbl is situated in east of the oilfield, while cluster horizontal well drilling and cold production technologies are still under research there.
Based on precise geological researches numerical simulation was carried out to optimize cold production of ultra-tight oil with foamy oil flow patterns in horizontal wells, including optimization of well placement, well spacing and horizontal section length. The near-bit geo-steering drilling technology was applied on adjacent wells to test its performance, while an experiment was conducted with PVT apparatuses to examine the effect of pressure decline rates on foamy oil flow. A long core pressure depletion test was accomplished to reveal the effect of foamy oil flow on recovery factors.
Three-dimension cluster horizontal well drilling and completion technologies shall be applied to develop ultra-tight oil reservoirs in huge loose sandstones, with the near-bit geo-steering drilling technology that controls landing points and horizontal sections in real time, keeping the bit move ahead along the lower boundary of the reservoir. Therefore, recovery rates may be dramatically improved due to the gravity drainage of ultra-tight oil. The most appropriate spacing of horizontal wells (500-600m) and horizontal section length (800-1200m) were determined to achieve the maximum recovery rate. The experiment proves that the recovery rate improves as the formation permeability increases, which means the "worm hole" contributes to heavy oil extraction. Boreholes with relatively large diameters, extensive perforated holes and slotted liners may be used to complete wells. In order to take the most advantages of the foamy oil flow mechanism high displacement ESPs shall be used with the selected thinner squeezed at the bottom, otherwise PC pumps with the thinner added at the wellhead are recommended.
Cold production technologies applied in ML Block save the overall production cost by 15.2%, improving the ultimate recovery rate by 8.6%. The foamy oil flow theory is improved, while it is the first time to integrate foamy oil flow production technologies with cluster horizontal well drilling technologies and near-bit geo-steering drilling technologies. As a result, the overall production rate of tight oil was greatly improved and the average production life of wells was extended.