Corrosion assessment

TGT’s Well Integrity Platform is being built to address the ever changing oil and gas market and its need for high quality services. Our range of memory logging services addresses the full well lifecycle and provides operators with tool packages to assist in the critical decision making process of well optimisation. Applications include: fluid breakthrough identification, injection and production profiling, stimulation and fracture flow evaluation and formation pressure determination behind multiple casings.

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The short 5" sensor generates short electromagnetic pulses to survey tubing and casing of small diameters up to 5". The length of the sensor defines the minimum detectable size of defects, which is 0.9" for the short one.

The medium 13" sensor is optimised to scan metal barriers of up to 10" in diameter. As this sensor module generates electromagnetic pulses of higher amplitude and longer duration than the short one, it can detect defects in the more distant second and third barriers of 2–10" diameter. The minimum detectable size of defects is 1.8".

The long 19" sensor generates the longest electromagnetic pulses of highest amplitude and detects responses from metal barriers appearing in magnetisation decays at late times. This sensor is designed to scan metal barriers upto 18 5/8” in diameter with a total thickness of up to 2"

Collars, X-nipples and other completion components can be identified directlyin raw time responses. However, metal loss (such as due to corrosion or perforations) cannot be displayed directly, and the data must first be processed using TGT’s proprietary software to simulate the response. A comparison of logging data and the simulated response then reveals metal loss, even behind multiple barriers.

The informative DELTA panel shows differences between simulated and real responses. This panel provides sharp image contrast and shows metal losses in fine detail.

EmPulse is a memory tool and, therefore, can be conveyed on slickline.This feature greatly reduces operating costs allowing the EmPulse to be used as a diagnostic tool to assess well integrity and prevent failures before they occur. The tool is also equipped with a pressure sensor to detect pressure drops due to tubing leaks and with a temperature sensor to detect deviations from the geothermal profile outside the tubing. In addition, the tool can be run in combination with the Spectral Noise Logging (SNL HD) memory tool to detect fluid movements, even behind multiple barriers, providing a unique through-tubing well integrity suite implemented with a slim memory toolstring.

Hardware & software tools

EmPulse Metal Loss Calc


  • Pick up corrosion zones in several barriers independently (up to 4 barriers)
  • Locate and recognize completion elements

Criteria for Candidates Selection

  • Borehole accessibility
  • Pressure test fail
  • Sustainable annulus pressure (SAP)
  • Abnormal increase in Water/Gas production
  • Completion peculiarities susceptible for corrosion impact

Inputs for Candidates Selection

  • Well sketch & zones of interest
  • Maximum borehole temperature and pressure

Inputs for Job Proposals

  • Well sketch & zones of interest

Inputs for Interpretation and Analysis

  • Raw logs (MID)

Example 1

This example shows typical readings of the MID tool in tubing. Tubing collars are clearly seen as blue horizontal lines in the NEAR DELTA panel. Brown areas indicate a weaker receiver coil response than the simulated model and are interpreted as metal loss.

Corrosion is clearly shown in Zone 1 of the TUBING THICKNESS profile: the metal loss at early times represents a tubing hole. A visual inspection conducted at the surface after tubing retrieval confirmed the tool readings and revealed a 4.5-cm hole in the tubing at location.

Example 1-08012015

Example 2

This example illustrates MID logging results in a two-barrier completion. The short-sensor data panel (NEAR DELTA) accurately displayed tubing collars and indicated that the tubing was in good condition. The long-sensor data panel (FAR DELTA) shows casing collars in blue, apparently less distinct because of being farther from the tool. An anomaly detected in Zone 1 indicates corrosion in the 9-5/8” casing.

Additionally, an X-Nipple in Zone 2 was clearly identified as metal loss in the TUBING THICKNESS profile and as horizontal brown and blue bars in the NEAR and FAR DELTA panels. The corroded perforations in the 9-5/8” casing were accurately picked up, as shown in the FAR DELTA panel and the CASING THICKNESS profile.

Example 2-08012015


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