Abstract
The placement of multiple fractures in deep horizontal wells is more difficult than that in shallow formations due to HTHP conditions. This paper presents the latest advances in hydra-jet acid fracturing for solving problems in the process of deep well acid fracturing. Basic researches and application evaluations were conducted to overcome down-hole conditions. Special schedule was designed delicately to lower the cracking pressure. The jet velocity was increased more than 800ft/sec to enhance the penetration efficiency. Acid pad fluid also was jetted to the target point for 15 minutes to erode carbonate rock, which leads to lower the rock strength. An explanation how to execute process has been included in details. The different procedures of treatment in shallow and deep reservoir were also discussed.
A novel hydra-jet acid fracturing job was performed with great success on two horizontal wells in an ultra deep carbonate reservoir in China. Seven separated acid fractures were placed along horizontal section from 19,816.3∼21,056.4ft in one well and a large total acid volume of 21,824.5ft3. After acid fracturing, the well produced naturally high rate of 251∼314STB/D. The other well is completed with un-cemented liners and the deepest treatment was applied at the TVD of 20,999.1ft. Four separated fractures were achieved along the 656.17ft lateral section. The pump pressure was controlled in the scope of predicted value (Below 10,000psi).
The main finding is that the hydra-jet acid fracturing has two mechanisms. The first is the hydraulic dynamic sealing effect and the second is the reduction of the time of acid-rock reaction to extend the effective distance. An addition, hydra-jet acid fracturing method proved the effectiveness of delivering acid fractures in the ultra deep horizontal wells.
