Field Pilot P&A Using Bentonite

Publieke samenvatting / Public summary

Durable and cost-efficient solutions for annular sealing and well plugging can save billions of predicted well abandonment costs and would strongly contribute to the economic competitiveness of all sustainable geo energy options exploiting the deep subsurface. In recent years ductile natural downhole materials such as clays (bentonites) or evaporates (rock salt or squeezing salts) have been identified as promising solution to provide a reliable alternative well sealing and plugging option, also for deep applications below 1500m. Unlike cement, the conventional sealing material of choice, natural downhole material like bentonite is ductile, self-healing, chemically stable under (acidic) downhole conditions and is considered more cost-efficient. The R&D Program Natural Formation Sealing has investigated the functional bentonite sealing performance in the light of the P&A application for geo energy wells starting with feasibility studies (TRL2) up to full-scale rig-test in 2020 (TRL5). The logical next step is to conduct a P&A field trial (TRL6) before operators can perform necessary qualification and pilot testing of this sealing technology as final demonstration to the regulator(s).

A field trial is extremely difficult to organize for obvious reasons such as timing, costs or liability arrangements. Therefore, the consortium is very pleased to have the opportunity to conduct a research field trial in a typical Dutch onshore gas well (owned by NAM/Shell). This well is scheduled for abandonment and, after abandonment is finished, the project will install bentonite plugs at relevant depth of ca. 2000m and test the plug properties with respect to Dutch Mining Law requirements. Being part of an existing P&A operation, the project can deploy available permits, equipment and staff, which strongly reduce the costs of the field test compared to a stand-alone field test. Based on the detailed planning provided in this proposal, a priority candidate well in the Groningen area has been selected according to test requirements and the P&A plans of NAM. The overall goal of the project is to create a downhole field lab” at ~2000 meters to conduct the essential testing with hydrostatic pressure, real downhole fluids and elevated temperature to validate the sealing performance of bentonite as barrier material for well sealing and plugging at operational conditions.

Korte omschrijving
Key activities of this project will comprise: - Small and/or large-scale experiments specifically dedicated to de-risk the execution of the field trial, based on latest details of the exact well design and how the well will be left by NAM (e.g. top of cement and fluid type in the well) - Validation of placement concepts, including coating options or wireline concepts, to ensure good plug performance - The final verification of a test and monitoring concept for the downhole sealing test based on the detailed preparation and planning provided in this proposal - The actual conduction of the field trial: placement, pressure testing of the plug including retrieving an aliquot for inspection in the lab - Microscopic and petrophysical evaluation of the retrieved sample martial in the lab to confirm the sealing properties of the placed, hydrated bentonite plug - To validate numerical models for bentonite plug performance prediction - Communication to other national and international research groups, companies, policy makers and stakeholders to facilitate a near-future application of the technology.

The presented approach including the development of dedicated placement technologies for bentonite placement below 1500m is unique in the world. The major project result is a downhole placed and tested bentonite plug with a verified performance under actual hydrostatic and chemical conditions in relevant operational environments of ~2000m depths (TRL 6). This is the essential and ultimate step to provide the knowledge to develop a new, innovative sealing and placement product for deep wellbores before the operators can apply this technology as real P&A plug or actual zonal isolation in pilot projects (TRL 7-9). Bentonite well sealing could become a key element to lower costs, increase safety and reduce the environmental footprint of well sealing, re-use and abandonment, and is thus actually crucial for all sustainable geo energy technologies making use of the deep subsurface. Overall, the method could be a game-changing technology providing long term zonal isolation performance and economic abandonment procedures at the same time which would strongly facility the energy transition by making sustainable geo energy application more efficient.