Geopolymers, being inorganic polymers created from rock sources, were evaluated as an alternative to Portland cement. To evaluate their usability, some properties of a selected geopolymer were measured and compared with those from a neat class G Portland cement. The geopolymeric slurries showed a non-Newtonian viscosity behavior with a measurable, albeit low, yield stress. The pumpability measurements using atmospheric and pressurized consistometer showed an adequate set profile for both the geopolymer and cement sample. Static fluid loss test shows that the geopolymeric slurries experienced a lower fluid loss compared to that of the Portland cement. The shrinkage factor for the geopolymers was reduced (expanded) as the downhole temperature was ramped up. The shrinkage of the Portland cement sample proceeded only with a lower rate. Tensile strength of the geopolymers was approximately 5% of their compressive strength; however, this value for Portland cement was approximately 10% of its compressive strength. Finally, shear bond strength of geopolymers would benefit from improvement.
The objective of plug and abandonment of wells can be described as Љrestoring the cap rockЉ. In that respect, the long-term integrity of the plugging material is crucial. I.e. it is important that the plugging material can resist downhole chemicals and otherwise withstand downhole conditions. In this paper, we have performed ageing tests with cement samples at relevant downhole conditions to determine the long-term integrity of well cement as plugging material. Portland cement samples with and without silica flour as additive have been separately exposed to crude oil, brine and H 2 S (in brine) at 100°C and 500 bar for 1, 3, 6 and 12 months. The long-term integrity of the samples was determined by measuring changes in weight, volume, mechanical strength and permeability, as well as physical appearance.It is seen from the results that the addition of a pozzolan such as silica has a significant impact on the long-term integrity of Portland cement, especially in a corrosive environment such as H 2 S. All the samples were affected by most of the different chemical environments, but the cement samples without silica were considerably more affected than the samples with silica as additive. Furthermore, the exposure to H 2 S in brine resulted in the formation of an unexpected white deposit, which precipitated both inside and outside the samples.
The cement height requirements for primary cement jobs, or annulus cement, are stated as absolute values in some parts of the world. For example the Norsok Standard, D-010, "Well integrity in drilling and well operations" states that one cement barrier is either 50 meters when verified by displacement calculations, or 30 meters when verified by bonding logs. The requirements do not distinguish between reservoirs with high pressure/ temperature- and reservoirs with typical low pressure/termperature conditions. A numerical method has been developed which considers the current or future well conditions as part of the cement evaluation process. This numerical approach is an additional tool in the decision making process and does not replace existing verification practices. The time to run the analysis has also been an issue to address, since existing tools in the industry (FEM-analysis etc.) can be quite time consuming to run. Additionaly it is also possible to perform analysis up-front the operations and various pre-defined cement length intervals can be compared to the requirements or other upper acceptable cases. Offshore well cases from the Norwegian Continental Shelf have been used as basis in the development and demonstration of the method. The numerical model is based on monophase or multiphase Darcy flow calculations through the cement sheath involving uncertainties like cement permeability, reservoir pressure in the eternal perspective etc. The model allows a parametric analysis in a reasonable computation time and building of a well case library making the process efficient in an industrial comparison perspective. The method is an ‘engineering approach' taking place in the decision making process of well integrity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.