By using the advanced perforation flow laboratory (APFL), the depth of penetration performance of shaped charges can be measured at downhole conditions to confirm whether or not the formation penetration will exceed the depth of formation damage attributable to drilling. In tubing-conveyed perforating, HNS explosive shaped charges have historically been used in elevated temperature environments. The option of using deeper penetrating, but less heat-resistant, HMX explosive shaped charges is possible in the Hejre field wells in the North Sea because the depth to the reservoir interval to be perforated is within the reach of coiled tubing. This process requires less time for the perforating guns to tolerate elevated temperatures, and coiled tubing provides a means of circulating cooling fluid, further increasing the charge lifespan. Based on conservative run times for deploying guns on coiled tubing (estimated to be 4 to 6 hours from surface), there will be sufficient time to position the guns at depth before detonation, and sufficient time to retrieve the gun string from the wellbore in the event of a misfire.
All perforation flow lab tests in the APFL were run at Hejre pressures, with overburden stress at 17,500 psi and pore pressure at 14,600 psi; several tests were run at the reservoir temperature of 160°C (320°F). Aligned with American Petroleum Institute Recommended Practice 19B Section 4 (2006), the APFL tests were conducted to closely match the expected conditions in the Hejre field, requiring minimal scaling of the results.
Tests in the APFL comparing the different explosive powder charges showed a nearly 50% increase in formation-analog target penetration using the HMX charge vs. the HNS charge. This depth of penetration increase improves the prospect of penetrating the estimated drilling damage zone to vastly improve production and the effectiveness of further stimulation. This paper discusses the methodology, obstacles encountered and means of addressing them, and the test program results.
Before the construction and development of testing equipment to shoot a shaped charge at elevated temperatures and high pressures, extrapolations had to be used to predict perforator performance with a higher level of uncertainty.