Cementing Irregular Wellbore Geometries

Drilling for oil consists of drilling holes underground to reach the oil/gas reservoirs. The rock formation near the drilled hole reacts to the changes in pressure due to the drilling. Such interaction may cause hole collapse, formation fracturing and unwanted fluid loss. In order to protect and stabilize the formation, steel pipes known as casing are cemented in place in the wellbore. Cement is pumped outside the casing from the bottom of the hole to seal the different regions being drilled from each other. This is to avoid flow in the region between the casing and the rock wall. This is normally done several times at different depths in an oil well. The cementing operation is of primary importance for to ensure a functioning well. The difficulty in doing a good cementing job lies partially in the geometry of the region. The drilled rock "cylinder" is not always cylinder-shaped, and the pipe is not always in the center of the hole. The cement may thus flow asymmetrically between the pipe and the rock formation, resulting in a poor cement operation. One success factor in obtaining good cementing is understanding the cement flow occurring in real situations. The goal of this project is to improve such understanding by studying the cementing process, and subsequently to develop numerical tools to predict cementing behaviour. The actual shape of the rock wall in the region where the steel pipe is to be cemented can be and is measured by a caliper tool. The project will investigate the fluid flow in irregular annuli based on caliper logs. The effect on the flow of uneven wellbore and pipe being off center will be investigated. The experimental and numerical methodoly used in the project can serve as basis for further optimization studies of displacement in irregular annuli.

Prosjektet har generert unike eksperimentelle og numeriske resultater relatert til væskefortrengning i et ringrom mellom to sylindre, der effekt av en brå geometrisk endring har vært et spesielt fokusområde. Enkelte av de eksperimentelle resultatene fra prosjektet har allerede vært brukt av et serviceselskap til å validere egen utvikling av ny simuleringsmetodikk. Bedre verktøy for å planlegge og designe sementeringsoperasjoner vil kunne bidra til å øke kvaliteten på primærsementeringsoperasjoner og redusere behovet for uønskede og kostbare reparasjoner. Prosjektdeltakerne har utviklet nye eksperimentelle metoder og oppsett for å studere væskestrømning i eksentriske og mulig irregulære ringrom, og vi har også bygget simuleringskompetanse for å studere samme fenomen numerisk. Dette kommer andre pågående og fremtidige prosjekter til gode. Prosjektet har også vært viktig for å øke internasjonalt samarbeid med ledende akademisk institusjon i Canada.

The primary objective of this project is to develop a methodology for planning cementing operations of wellbores with irregular geometries. To achieve this we plan to address the following secondary objectives: Improved experimental knowledge basis: develop unique physical experimental setup using irregular wellbore geometries based on 3D caliper logs and 3D printing and perform experiments, Improved 3D numerical modeling: develop and asses methodology for 3D numerical modeling of displacement process during cementing using open software code and general commercially available software framework, Improved work flow: develop and improve the workflow for planning cementing jobs of wellbores with irregular geometries. A successful cementing operation depends on an efficient displacement of the drilling fluid and maintaining pressures within critical limits. In order to plan the cementing operation properly, the physics of the displacement process must be understood and resulting tools and principles used for evaluation of the displacement efficiency have to be properly validated. Furthermore the actual status of the well including possible irregularities in the well geometry like wash out need to be taken into account in addition to actual pressure, temperature, drilling fluid properties and hole condition (cuttings, filtercake, ..). Planning a cementing job includes making decisions related to mud conditioning, selection and placement of centralizers, properties and volumes of washer, spacers and cement, pump rates and casing movement via reciprocation and rotation. The immediate result of this project will be better methods for planning cementing jobs for irregular wellbore geometries. The long term results will be more efficient cementing operations and improved zonal isolation contributing to improved recovery.