Investigation of the hydraulic integrity of cement plug: Oilwell cementitious materials

The loss of hydraulic integrity in oil and gas wells due to the loss of cement sheath sealability can lead to environmental contamination, annular pressure build-up, and safety threats. In this study, we examine the hydraulic integrity of geopolymers an alternative to cement to be used in well cementing. The hydraulic integrity of geopolymer was compared to conventional API class G and Industrial expansive cement. Down-scaled test specimens representing cement-plug in casing were prepared and tested using an in-house experimental set-up that allows continuous curing and testing of the cementitious materials under undisturbed pressure and temperature conditions. The samples were cured at 90 °C and 172 bar for 7 days after which the hydraulic sealability of the specimens was examined by applying a pressure differential to one end of the specimen and observing the resulting fluid leakage rates on the other end. The leakage rates were then expressed in terms of permeability and microannuli aperture. By injecting nitrogen and water, it was possible to compare the effects of fluid type on the hydraulic sealability of cementitious materials. Lastly, we examined the hypothesis of a linear relationship between plug length and its hydraulic sealability. The results indicate that geopolymer and Industrial expansive cement have higher hydraulic sealability compared to API class G. Geopolymers also have sufficient hydraulic bond strength to perform as much as Industrial expansive cement. The fluid type used in testing does not play a critical role in the loss of hydraulic sealability of cementitious materials. The influence of cement plug length showed varying trends on the hydraulic sealability of the cementitious materials. The results presented in this work help us understand the sealing potential of cementitious materials and the need for standards for performing laboratory-scale hydraulic sealability tests. This can benefit the improvement of cement integrity tests and well abandonment operations.publishedVersio

Experimental Evaluation of the Effect of Temperature on the Mechanical Properties of Setting Materials for Well Integrity

A fundamental understanding of the mechanical properties of zonal isolation materials is important for predicting well integrity during well operation conditions. Conventionally, the mechanical properties of zonal isolation materials are tested at ambient temperature using uniaxial testing. This study examined the mechanical properties of alternative zonal isolation materials such as rock-based geopolymer, thermosetting resin, and an industrial class expansive cement under realistic well conditions by triaxial testing. Mechanical properties such as Young’s modulus, Poisson’s ratio, cohesive strength, friction angle, and compressive strength of these materials at 30 and 90°C were compared. The effect of confining pressure on the mechanical properties of the materials was also examined. The findings of this study show that all selected materials possess compressive strength at 30 and 90°C and that the compressive strength of all the selected materials is strongly impacted by temperature and confining pressure. The Young’s modulus of all the selected materials was unaffected by confining pressure, while only the Young’s modulus of thermosetting resin was sensitive to temperature. The influence of temperature on the Poisson’s ratio varied from one material to another. In addition, when the test temperature increased, the friction angle of neat Class G and geopolymer decreased.publishedVersio

Preparation and characterization of Nanocomposite gels for fracture plugging in chalks

Master's thesis in petroleum EngineeringExcessive water production is a common challenge the oil industry is faced with. The lifting, treatment and disposal of produced water can cause a financial strain on the profitability of a hydrocarbon asset or even shorten the productive life of the asset. These effects are even more severe in fractured reservoirs as they mature. Among the chemical techniques used for controlling excessive water production, nanocomposite gels (NC) are considered as an effective treatment method. The presence of Nano-clay/polymer network in their structure makes them exhibit stronger fracture plugging potential compared to conventional polymer gel treatments. In this contribution, laponite and bentonite NC gels were prepared in deionized and seawater. Their performance was characterised and described. The effect of cations like calcium, and potassium, and also the effect of chalk on laponite dispersions were examined. The performance of various low molecular weight glycols like butyl glycol, butyl diglycol and Polyethylene glycol (PEG) employed as gelation retarders on laponite dispersions were also examined. Finally, core flooding tests were carried out to examine and compare the potential of NC gels as a fracture plugging agent in chalk to laponite gels. The results showed that laponite generally formed better NC gels than bentonite. Laponite clay also dispersed to form weak to highly viscous NC gels with polymers in deionized water depending on its concentration. The presence of cations helped to screen electro-static repulsion between laponite particles resulting in less aging time and stronger laponite gels. PEG can retard laponite gelation reaction, by adsorbing on the clay surface (steric repulsion) resulting in longer aging time to allow the injection of nanocomposite into target zones before its transformation to a rigid gel. Both NC and laponite gels showed potential for plugging fractures and reducing the permeability of water in chalk. However, NC gels showed higher resistance residual factor compared to laponite gels. It is proposed that further work should be done to confirm the performance of nanocomposite gels as an effective fracture plugging agent in chalks and also their superiority to laponite gels