Perforating Through Casing Strings To Remediate Annulus Gas Leak
Authors: Carpenter Chris 
Published: February 2015

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 166729, ’Perforating for Squeeze Through Four Casing Strings To Remediate Annulus Gas-Leak Problem,’ by Mohamed El-Sayed Ibrahim, SPE, Ahmed Khalifa Al-Neaimi, SPE, Mohamed Abdelsalam Hassane, SPE, Abdul Salam Mohamed Al-Mansoori, SPE, Shanof Mohamed, SPE, and Omar Al-Mutwali, SPE, ADMA-OPCO, and Alan Salsman, SPE, Schlumberger, prepared for the 2013 SPE/IADC Middle East Drilling Technology Conference and Exhibition, Dubai, UAE, 7-9 October. The paper has not been peer reviewed.

ADMA-OPCO had integrity problems in one of its gas wells, and abandonment was the only option available to restore the integrity of the offshore multiwell jacket and revive adjacent wells. Integrity problems included oil/gas bubbles observed on the seabed around the conductor pipe and high sustained pressures in the outer cemented casing annuli. Because the leak was determined to be located outside the casing, the perforation of several intervals was required. Some of the intervals were perforated through three casing strings, and the rest through four strings of casing, before being squeeze cemented.

Background

The example well, designed as a 7-in.- monobore gas-production well (see Fig. 1), was due for abandonment. The surface leaks in the different casing annuli had to be resolved before proper abandonment could occur. It was clear from the prejob analysis that cement-squeezing operations would be required at different depths through three and four casing annuli. Techniques for exposing these annuli for remediation included underreaming with a milling tool, abrasive jetting, and perforating. Underreaming would have been a very costly operation, and abrasive jetting is not reliable to penetrate through more than one casing string; therefore, perforating was chosen as the method for accessing the required annulus.

Perforating through four strings of casing is not typical, and many questions were raised concerning the reliability of this technique and how its effectiveness would be measured. With the need to access up to four different annuli, conventional circulation and pressure-testing techniques could not confirm that all casings had been penetrated. Modeling and testing were performed to improve confidence in this technique.

Perforating Gun and Charge Selection

Modeling. A 4.-in. gun was selected for carrying a premium deep-penetration charge in the 7-in. liner. Two charge options were available for this: a 5-shots/ft (spf) 72°-phase version carrying 38.8-g HMX (a nitroamine high explosive) perforation charges and a 12-spf 45°-phase version carrying 22-g HMX charges. The model was set up with the casing and other well parameters and run with various perforation-charge/gun combinations.

The modeling results show that all charges in all phases will penetrate the four casing sizes; however, the outermost- casing entry-hole size with the 12-spf gun is very small, ranging from 0.16 to 0.09 in.

Laboratory Testing. There was concern over the modeling results because the casing entry-hole prediction is not considered accurate beyond two casing strings; therefore, to improve confidence in the results, a series of tests was conducted in the laboratory. The laboratory tests were set up to simulate offset casing, and each phase of the perforating gun was tested with the same types of charges that would be used in the field.