Pinpointing Source of Sustained High Casing Head Pressure (HCHP) for Well Integrity Restoration: A Case Study of a Well in the Niger Delta

Abstract

Maintaining the integrity of oil and gas wells is of utmost importance. This requires regular monitoring to ensure the barrier envelop is maintained. Sustained pressure in the casing infers a compromised barrier envelop. It poses a serious threat to the well integrity and if not addressed could lead to increased risk of pressure transmission and fluid leakage through the concentric tubulars. The key objective is the ability to accurately pinpoint the source of the pressure. Modern technologies using through-tubing logging systems are more accurate for leak detection. If the leak is not accurately detected, the sustained high casing head pressure persists and could lead to undesired outcomes even after the repairs. Here, the high accuracy Sonic-Noise Log (SNL-HPT) was deployed through slickline. Data acquisition process involved both shut-in and flowing modes. The shut-in mode required the well to be stable while RIH SNL-HPT tools on slickline for data acquisition. While in the bleed off mode, the well was being produced during data acquisition. A surface choke manifold and flowback tank were rigged-up for flow control. In this paper the results of well Unut-4 Sonic Noise Log- High Pressure and Temperature (SNL-HPT) surveys are presented. The objective was to investigate the source of A annulus pressure in this well. The data was successfully acquired in memory via slickline up to a depth of 10,000ftah using both shut-in and bleed off (flowing) modes. The shut-in mode required the well to be stable while RIH SNL-HPT tools on slickline for data acquisition. While in the bleed off mode, the well was being produced during data acquisition. The acquired data was successfully downloaded and interpreted for the source of leak. The SNL-HPT interpreted data indicated that the High CHP was caused by communication observed through leaks at depth 9,751ft (the dual packer). The spectral noise logging located the active leak source and verified the integrity of cement barriers while the High temperature logging quantified the leak rate using temperature modelling. This paper would detail the history of the well, planning, design and execution of the successful logging including the interpreted results. Sonic Noise Log is a simple technology to deploy for accurate leak source determination. In all the instances this was deployed, acquired and interpreted data was good enough for a decision making on the forward plan. The results of this logging led to the early injection of the well in the rig sequence and well was subsequently worked over. Integrity was restored with further deferment of production averted.