Voltage on casing for improved well cement quality

Cementing is an essential part of well construction. After drilling an interval of the subsurface, a steel casing pipe is inserted into the borehole and is cemented in place. The cement is thereafter left to harden, to provide mechanical stability and to prevent leakage. Cement is also used to seal wells that are no longer in use. We rely on these cement barriers to protect towards leakage from active and abandoned wells in a long-term perspective. The accuracy with which cement can be pumped and placed in the well, and the quality with which it bonds to its surroundings, is thus of utmost importance to minimize the environmental footprint of oil and gas activities. In the present project, we have studied how to manipulate well cement by applying an electric voltage on the casing. The goal has been to "force" the cement to bond or flow in a specific way inside or outside the casing pipe in wells. Theoretically, this should be possible due to the charged nature of cement particles. Such concepts of manipulating charged slurry constituents had already been applied in other industries, e.g. civil engineering, mining, and food processing. Electric manipulation of well cement is, however, a new idea. The project has been executed during the period 2017-2020, in collaboration between SINTEF, NTNU, Université du Maine (France) and cement experts from the French company Curistec. A series of experiments has been performed to shed light over the fundamental processes of cement manipulation with electric voltage. Both voltage alterations of flowing cement slurries and effects observable after cement hardening under various voltage conditions have been studied. Detailed microscopy investigations have been made to study the interfaces between cement and cathode/anode, and a series of mechanical push-out tests have been made to measure the bonding strength between cement and steel. Our results show that voltage is a promising way to secure tighter cement sheaths in wells. Both cement chemistry, particle packing, porosity and bonding strength was proven to be manipulated by voltage. The work resulted in 8 peer reviewed papers, 11 conference presentations, 7 popular scientific efforts and 1 patentable idea has been identified. Little was known at the project writing stage on how/if this could represent a cost-efficient method for optimizing cement job quality, cement-casing bonding and thereby long-term well integrity. This was the knowledge gap we set out to close in this project. We have performed a series of experiments that clarifies fundamental aspects of e-field manipulation of cement slurries. The project thus established a scientific basis for evaluating whether the concept is viable and whether more application-oriented research efforts should be undertaken in the future. More specifically, during the project we have studied how voltage applied to steel casing affects shear bond strength between the casing and a cement. A series of different voltages, exposure times have been tested. We used push-out tests to measure the bond-strength. Our results show that cement-steel bond strength is affected by potential. It also shows that the application of potential changes particle packing in the vicinity of cathode and anode and also mineralogical composition close to electrodes. The project resulted in 7 papers published in peer-reviewed journals and peer reviewed conference proceedings. Four of them is already published and the remaining three have either been accepted for publication or are under publishing. One patent application is under consideration. The results have been presented at 6 conference and via 3 popular-scientific channels in order to disseminate project findings to a broader public.

Prosjektet er det første som har sett på hvordan elektrisk spenning kan brukes til å manipulere sementheft i brønner. Både eksperimenter og numerisk modellering er utført i perioden 2017-2020 for å studere dette. Arbeidet har blitt utført av SINTEF, NTNU, Université du Maine og Curistec. Hovedresultatet fra prosjektet er at elektrisk spenning er en lovende metode for å manipulere sementkjemi, -porøsitet og mekanisk heft i brønner. Prosjektet har utviklet kunnskap relevant for petroleumsindustrien som også er anvendbar på andre områder hvor sement brukes f.eks. bygningsindustri. Prosjektet har resultert i 8 fagfellevurderte artikler og 1 patentsøknad er under vurdering. Prosjektresultater er presentert på 11 konferanser, og 7 populærvitenskapelige formidlingstiltak er utført. Til sammen 3 prosjekter er (in)direkte spin-offs fra prosjektet. I perioden har 1 PostDoc og 1 MSc student blitt utdannet i prosjektet, begge fra NTNU.

The goal of this project is to reduce the environmental footprint of oil and gas activities. This will be done by studying how to minimize leakage along the interface between cement and steel casing pipe in wells by improving cement placement and the cement-steel bonding quality. The project, which has an experimental focus, will study how cement slurry flow and solidification can be optimized by applying specially-designed voltages to the casing during cementing operations. It is hypothesized that phenomena, such as electrophoresis, dielectrophoresis and electrohydrodynamic effects, can be exploited to improve cement placement and bonding to steel. Cement hardening and flow experiments will be performed to understand the effect of AC and DC electric fields in the annulus. The bond quality will be monitored during and after solidification using microscopic and tomographic characterization techniques, and will subsequently be measured by mechanical testing. Theoretical work will support the design of the experiments and the interpretation of the experimental results.