Spectral Noise Log to Confirm Source of Sustained Casing Pressure

Abstract

Sustained casing pressure (SCP) or annulus pressure is one of the most critical issues in well integrity. Among over 2000 existing wells in Pertamina Hulu Mahakam (PHM), around 330 wells (16.5%) have SCP problems. The problems vary from the simplest one with pressure in only one annulus, to the more complicated one with multi-annulus problem and interconnected pressure between annulus. Possible causes of SCP are identified, such as leak from tubing and/or casing due to aging wells, non-sealing packer, or poor cement condition with micro-channeling. Several remedial methods and technology are available to overcome the issue, but due to the high variation of SCP problems in PHM, each well problem and its mitigation must be defined case-by-case.

Common practice in industry, well intervention operations shall be done to withstand any SCP issue where it could increase OPEX of the company. Hence, we need future solutions to minimize or avoid such SCP existence.

In order to support future solutions, the first mitigation method is to confirm the source of pressure. Noise Log is a technology developed to detect flow in the annulus by running a sound-sensitive hydrophone to record down hole noise. Minimum two log runs are needed to have a representative result. The first run is in shut-in condition with all annulus valve closed, and the second run is performed while bleeding off the problematic annulus. The differential pressure caused by bleed off process creates flow from source of pressure up to the surface, and the flow will produce noise that will be recorded by the hydrophone. The noise reading is then combined with temperature profile and supported by reservoir data to confirm the depth and source of pressure (gas, oil or water).

During trial, several wells with varied annulus problems are chosen as candidates for Noise Log and showing a conclusive result of the depth and source of the pressure. The result and interpretation then shall be considered when planning future campaign to mitigate the SCP problems.