Between fires, explosions and pollution, accidental oil and gas spills and their consequences are a major risk in our industry. Wells connect reservoirs to the surface, but also act as impermeable barriers. Cement sheathes play a key role by filling the annulus between the well casings and the rock. That’s why we need to ensure their integrity against pressure, temperature and different types of stress throughout the well’s life, from construction to abandonment. Leveraging our recognized expertise in drilling and completion, we have devised a pioneering approach to assess well integrity and simulate the mechanical behavior of cement sheathes, to ensure safety during all types of operations.
A Well Safety Bulwark
During well construction, cement is introduced into the annulus between the well casing and the surrounding rock. Designed to seal the well and protect the casing from corrosion, this cement sheath is subjected to tensile or shear stresses induced by pressure and thermal loads emanating from the well, which can negatively affect its mechanical integrity.
It is critical to ensure that the cement will be able to withstand the stress created by changes in pressure, temperature and rock deformation throughout the well’s life and after final abandonment. Otherwise the cement sheath’s integrity may be breached, which is what happened on the offshore Elgin-Franklin field.
Yet ensuring sheath integrity is complex, because the problem involves several disciplines and complex issues:
- The first difficulty comes from the need to compute the pre-stress in the cement sheath which is the result of complex hydraulic, chemical, thermal and mechanical interactions during hydration.
- The second is to measure the evolution of relevant hydro-thermo-mechanical (HTM) parameters that affect the transition from hydrostatic pressure after placement to stress with shear components after hardening.
A multidisciplinary, innovative approach
So we launched an R&D program involving multidisciplinary technological collaboration and combining a number of different areas of expertise. Our dedicated drilling fluids and cement lab also played a key role.
That’s how we developed in house modeling capacities (T-CemInt™) and patented laboratory means (STCA™). They are unique in the industry and have been validated by laboratory measurements and a number of project post-mortems:
- The Slurry To Cement Analyzer™ (STCA™) measures cement hydro-thermo-mechanical parameters in the laboratory; the results are extremely reliable. We use unconventional triaxial shear tests to characterize and track the changes in the cement’s properties, from hydration to curing, under in situ pressure and temperature conditions encountered in wells.
- Our proprietary T-CemInt™ software uses the cement’s hydro-thermo-mechanical parameters, as measured by the STCA™ analyzer, to simulate, evaluate and predict the cement sheath’s behavior over time, under temperature and pressure conditions encountered during drilling, production and/or injection. It is a powerful yet still easy-to-use tool. It takes only a few minutes to complete a full study, in an easy-to-interpret format.
A Cutting-Edge Technology Suitable for All Operations
Helped by these unique, trailblazing tools, we can now:
- Determine the cement hydro-thermo-mechanical parameter ranges best suited to the anticipated operating requirements.
- Perform quality control and assurance and fine-tune the most complex cement formulations marketed by oilfield service companies.
We employ this cutting-edge technology to design safe, cost-effective cement sheaths, making operations safer and lowering related costs. We do this for all our operating wells, whether in the deep offshore in Côte d’Ivoire or Bulgaria; for our unconventional resources in Argentina; and in HP/HT environments in the United Kingdom, Egypt and Azerbaijan. We have done it many times. We even posted a world first in Brunei, where two ML-JAM wells were cemented using a 2.48-density, resilient cement.
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