Thru-tubing wellbore cement bond has potential to unlock rigless P&A opportunities, optimising inspection and saving up to £550 million

Project Summary

NZTC supported BHGE to evaluate a technology that delivers cement logging through multiple casing strings, an advancement on existing solutions which can only deliver logging behind one casing or tubular. A means of inspecting the quality and quantity of cement in the annulus behind casing does not currently exist without removing the wellbore tubing. If it were possible to deploy a tool to inspect the casing annulus cement from within the tubing, additional costs could be avoided and the potential for thru-tubing and rigless abandonments could be realised.

The aim was to evaluate a number of potential delivery models and resulted in a four-month feasibility study of BHGE’s nXis multi-nodal, thru-tubing inspection system. nXis is composed of neutron, x(y)-ray, electromagnetic and ultrasonic inspection techniques. This project would provide proof of concept, showing that combining the techniques would allow defect detection and live, in-situ, 3D visualisation of wellbore defects.

Industry value:
By eliminating the requirement to removing tubing, the industry could benefit from significant cost savings by unlocking rigless abandonment opportunities.

This technology has the potential to deliver industry savings between £105-£550million, based on analysis of the anticipated UKCS P&A well count up to 2025, by assuming that between 10-50% of the subsea wells could be inspected to deliver thru-tubing abandonments.

Key results:
The project was successful, proving the concept of multi-modal joint analysis with each logging modality showing unique sensitivity to distinct geometrical and physical characteristics of the well.

Simulations confirmed the challenge and complexity of evaluating cement integrity thru-tubing for plug and abandonment applications.

Lessons learned:
Now that the initial framework has been established, planning for the next phase of the project has begun.

Future activities will include:

1. The design and construction of a test fixture for evaluating the multi-modal, lab-based test articles
2. To build and test pulsed-neutron/gamma-ray/acoustic-based test articles to acquire experimental data for validating and refining simulation models
3. To investigate additional logging modalities with complementary responses
4. To further enhance data fusion capabilities by refining algorithms through the use of acquired and refined synthetic data