This paper illustrates a specific perforation technique using Coiled Tubing with an abrasive jetting tool in a highly deviated HP/HT gas well suffering severe drilling formation damage and describes how this technique bypassed the damage and increased the efficiency of acid stimulation, allowing the well to flow as expected.
Occasionally, while drilling carbonate (Khuff) gas wells in Saudi Arabia fluid losses encountered are which often leads to stuck drill pipe. Hence, a specific mud system designed with loss circulating materials (LCM) including calcium carbonate chips, graphite, and fibers is used to stop losses and reduce the risk of stuck pipe. However, the design side of this mud system creates a high near wellbore damage with very low acid solubility.
The abrasive jetting tool was selected as the perforating method because slots cut with sand slurry generate clear passage across the formation bypassing any formation damage. The slots through the casing, cement and formation were created by pumping nitrified sand slurry. Nitrogen was used for the first time in Khuff gas wells along with an orienting tool in order to increase the slot cutting efficiency and obtain deeper penetration to bypass the formation damage and allowing the acid to reach the virgin reservoir. Real-time depth correlation and differential pressure measured across the abrasive jetting nozzles were also used for the first time.
In contrast to wells drilled with the same type drilling mud but perforated with different methods, this well showed a noticeable increase in wellhead pressure during the abrasive slotting procedure. The follow up acid stimulation performed at average pump rates and pressures for a non-damaged Khuff-C gas wells.
Slot cutting design and execution, acid stimulation treatment, and well performance will be discussed to evaluate the abrasive perforation and demonstrate the advantages of generating clean and deep tunnels.