For through-tubing perforating operations, it is important to consider jobs with temperatures above 360°F (182°C) at depths of approximately 15,000 ft. In this instance, the wireline conveyance time approaches 1.5 hours, which begins nearing the HMX thermal limit. This may require a switch to a higher-rated explosive, such as HNS, but unfortunately, this comes with an accompanying 20% loss of charge performance.
To guide perforating operations for these conditions, an experimental test-firing program was conducted to determine the performance of a 2.0-in. diameter HMX perforating system using 7.0-g shaped charges as a function of well temperature from 360–440°F (182–227°C). A novel two-step heating ramp was used to "thermally equate" perforating gun tests with shooting fixture tests. This experimental technique was necessary because of the large difference in thermal mass between the gun, which had a relatively small thermal mass, versus a shooting fixture whose mass was much larger for safety reasons.
The two-step heating-ramp tests showed that the temperature inside the perforating gun was still climbing toward the external well temperature even after the simulated 1.5-hr conveyance time. Temperature differences between the external gun surface and a charge located inside the gun ranged from 12–25°F (7–14°C). This thermal delay experienced by the gun worked to the advantage of HMX exposure, as the decomposition reaction for the explosive was also delayed. Taking the thermal delay into account, an upper temperature limit was established when perforating gas wells with the 7.0-g HMX-shaped charges inside 2.0-in. OD perforating guns. In addition, penetration performance for the HMX charge at various temperature levels was generated and then compared to baseline performance data that had been generated at ambient temperature.
The outcome of the test program provided guidelines for: (1) how far 2.0-in. HMX charges can be thermally pushed when perforating gas wells and still undergo proper ballistic functioning, (2) performance degradation of the 7.0-g charge as a function of temperature, and (3) recommendations for when to switch to higher thermally rated systems.