Noise Logging Application for Well Integrity Evaluation: A Case Study in Peninsular Malaysia

Abstract

Field-X was first discovered in 1979, comprising of saturated oil reservoirs with several shallower non-associated gas reservoirs. Field-X is currently producing from several oil producers. X8 well was recently drilled, completed, and produce from A and B reservoirs. However, 5 months later, the oil rate has been reduced by half with gas oil ratio (GOR) increased up to 5 times. Consequently, the well had to be shut-in due to reservoir management plan (RMP) violation. X9 well was drilled and completed, but 5 years later the well started experiencing the sustained production casing pressure (PCP) and was forced to shut-in in the following year with the locked-in potential of both A and B reservoirs. To diagnose the root cause of high GOR (HGOR) in X8 well and sustained PCP in X9 well, the Spectral Noise Log (SNL) was deployed. The main advantage of utilizing SNL is its capability of detecting fluid movement behind tubing and casing. High differential pressure creates lots of fluid movement, which generates higher noise amplitude. Meanwhile, smaller pores or leaks generate higher frequency noise that can be easily picked up by SNL. SNL tool was run in flowing condition for X8 well and the results indicated the HGOR zones were mainly contributed by the shallower B05 sand which was flowing through the leaked 4-1/2″ liner packer. Temperature deflections also indicated that the liner packer seal was leaking and B05 reservoir was contributing to the production. The liner packer leak and B05 reservoir flow would not have been detected by conventional production logging tools as the flow was happening beyond the tubing and casing. For X9 well, SNL was run in the wellbore whilst pumping water via annulus, through the leaks and flowing back up the tubing. Three tubing leaks were successfully detected from the SNL run, whereas previous conventional noise log only managed to detect 2 leaks. It is possible that the third small leak was very small, hence the conventional tool was unable to detect it. X8 well successfully back online with 8.4% rate increase than last production with GOR reduced back to initial GOR and X9 well successfully back online as per last production rate. The liner packers which are not permanent barriers for reservoir isolation and allocation can be validated, moreover, verifying that tubing leakage is mainly contributed by tubing joints, which can be used as the main input in tubing materials selection in the future. Well integrity issues can cause significant loss of production, oil spill or worst case, even loss of lives. Proper selection in data acquisition tools helps to accurately diagnose well integrity issues that can be swiftly addressed. In the low oil price environment, skimming down on data acquisition costs may not uncover the true underlying well issues or reservoir issues, but might jeopardize future projects to be undertaken in years to come.