| Popis: |
The bond between casing and cement placed in the annulus is an important aspect to wellbore construction. Bond is inferred after the cement has cured using acoustic methods well-known in the industry. This evaluation is dependent on the acoustic coupling between the cement and the pipe. If acoustic coupling exists, proper evaluation allows for a subjective assessment of the cement sheath behind casing. However, if the acoustic coupling is weak, non-existent, or has been damaged by operations such as pressure testing or stimulation treatments, the cement may be present but cannot be properly evaluated, leading to ambiguous conclusions and ultimately unnecessary remedial cementing. Enhancements to the casing/cement bond is achieved by use of surfactants, expansion agents, and other chemicals added to the cement slurry and/or spacer. Modification to completion practices is sometimes practiced to prevent bond disturbance. Modifications to the mechanical properties of the cement sheath are also done in an attempt to prevent or limit the permanent deformation to the cement sheath that occurs during these load events. All have varying degrees of success and cost. Attempts to modify the surface of the steel pipe have been practiced for several decades with varying results. The simplest and most effective has been to grit-blast the casing to remove mill varnish, as varnish highly hydrophobic and not conducive to cement bonding. Grit blasting also leaves the surface slightly roughened, which has been proven to improve both shear bond and acoustic transmittance. Coatings have been attempted in the past, usually based on altering the surface roughness by adhering grit using an adhesive. None of the afore-mentioned methods practiced to date have addressed two fundamentals: (1) carbon steel is naturally hydrophobic, and (2) cement and steel do not form a chemical bond. The purpose of this project was to address these short-comings by developing a method to modify the external surface of oil well pipe making it super-hydrophilic, and at the same time attempt to create a chemical bond to cement. Through a collaborative working relationship between this major operator and a small innovative technology company, a successful nano-technology treatment process has been developed and field tested in both unconventional and Deepwater environments. This paper will chronicle the project from concept development to lab proof-of-concept, several field trials, and provide a review of the lessons learned along the way. Comparative cement evaluation logs will be reviewed that show a significant improvement in some cases between the treated pipe and pipe that is either unmodified or grit-blasted. |
