Successful Recovery of Well Integrity Before Rig Entry Using Reversible Cross Linker Solution in the Balingian Basin
Authors: Karim Nurul. A. , Chua Hing. L. , Mokhtar Mohd. K. Mohd , Choi Yee. X. , Barat Junnyaruin. , Saleh Nur. E. , Amran Amierul. , Yap Yin. H. 
Published: May 2024

Abstract
Sustained production annulus pressure is one of the common well integrity issues experienced in aging production wells. This type of annular pressure is known as "sustained" because it is long-lasting and cannot be reduced by bleeding off the pressure. Sustained annular pressure poses a threat to well barrier reliability and overall well integrity management. Therefore, it is important to monitor sustained annular pressure trend to understand the potential risk it presents.
Well X is located in shallow offshore terrain in the Balingian Basin. This well was completed as a Dual String Oil Producer with 3-1/2″ × 2-7/8″ tubing inside a 9-5/8″ production casing in year 1994. This well showed a sustained annulus pressure on the A-annulus (CHP) identified during Annulus Pressure Diagnostic (APD). Part of the requirement before rig entry was for the A-annulus pressure to be reduced to below 100 psi CHP.
A Leak Point Survey was conducted and there were 2 leaks found at Long String at depth of 1,560 ft BTHF and depth of 7,271 ft BTHF. All other accessories in the well showed good integrity during the survey. With the findings of the leak points, it was discovered that there was communication between Long String and Production Casing.
A plug was set inside Long String at depth of 7,095 ft BTHF which was located above the Production Packer to isolate any source of pressure that might cause the sustained annulus pressure. No improvement was shown despite hundreds of 1% KCl being pumped to fill up both Long String and Production Casing to bring down the annulus pressure. A-annulus pressure kept building up over time even after the pressure was bled off.
Production Packer Integrity Test was then performed and it was discovered that the Production Packer was also leaking which explained the reason why hundreds of barrels of 1% KCl pumped to A-annulus were not able to keep the pressure down due to the loss of liquid level in the annulus over time.
Multiple attempts were made to cure the Production Packer leak by pumping Calcium Carbonate slurry but CHP remained above the 100 psi maximum pressure intended. Since no development was observed on the well A-annulus pressure, the operation team decided to kill the respective sand formation that might be the source of sustained annulus pressure in well X to reduce CHP as the last resort.
Reversible Crosslinker Solution was pumped to the Short String due to its direct access to sand formation. This pumping operation successfully reduced the CHP to maintain at 50 psi and well integrity was recovered. The Reversible Crosslinker has become the primary solution to the well X integrity problems since the high annulus pressure could not be reduced despite the well being pumped with brine and calcium carbonate slurry in multiple pumping stages before. Reversible Crosslinker was chosen as the solution to restore the well integrity due to its better rigidity as compared to Calcium Carbonate slurry, its ability to control setting time and its ability to be reversed using hydrochloric acid.
The objective of this paper is to describe the successful application of reversible crosslinker in recovering well integrity before rig entry. This paper will also discuss the pros and cons of using reversible crosslinker as compared to brine (1% KCl) and conventional calcium carbonate slurry to reduce annulus pressure.