Introduction to Permanent Plug and Abandonment of Wells

This open access book offers a timely guide to challenges and current practices to permanently plug and abandon hydrocarbon wells. With a focus on offshore North Sea, it analyzes the process of plug and abandonment of hydrocarbon wells through the establishment of permanent well barriers. It provides the reader with extensive knowledge on the type of barriers, their functioning and verification. It then discusses plug and abandonment methodologies, analyzing different types of permanent plugging materials. Last, it describes some tests for verifying the integrity and functionality of installed permanent barriers. The book offers a comprehensive reference guide to well plugging and abandonment (P&A) and well integrity testing. The book also presents new technologies that have been proposed to be used in plugging and abandoning of wells, which might be game-changing technologies, but they are still in laboratory or testing level. Given its scope, it addresses students and researchers in both academia and industry. It also provides information for engineers who work in petroleum industry and should be familiarized with P&A of hydrocarbon wells to reduce the time of P&A by considering it during well planning and construction

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

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

Effect of Zn2+ and K+ as Retarding Agents on Rock-Based Geopolymers for Downhole Cementing Operations

Geopolymer material has a potential to function alongside Portland Cement as an efficient cementitious material for well cementing and plug and abandonment applications. Geopolymer material requires retarding agents to be displaced into the well while considering the properties required to maintain efficient zonal isolation through superior mechanical properties. Chemical admixtures affect the material structure and can, in some cases, jeopardize material integrity if not engineered properly to suite downhole conditions. The present article shows the effect of Zn2+ and K+ species have as retarding agents on slurry, mechanical, and microstructural properties. The approach has been carried out to obtain a preliminary overview of how retarding agents can behave in mix design slurries where eventually sealing performance was examined. Samples were cured and examined for periods of 1, 3, 7, 14, and 28 days at downhole conditions. The results obtained confirm a retardation effect by the addition of Zn2+ and K+ species and some shortcomings in early strength development due to a poisoning mechanism by Zn2+ species. This phenomenon indicates the formation of Ca-Zn phase that can hinder the nucleation of the geopolymeric gel structure. No significant effects were observed on the microstructural development throughout the curing period. The effect of Zn2+ species was also observed in increasing threshold for hydraulic sealability. It may be concluded that the tested retarding agents require furthermore development to minimize shortcomings in mechanical properties specifically early strength development.publishedVersio

Aging and Temperature Effects on the Performance of Sustainable One-Part Geopolymers Developed for Well-Cementing Applications

This study elucidates the effects of aging and temperature over the performance of one-part “just add water” (JAW) granite-based geopolymers for application in well cementing and well abandonment. Additionally, the investigation delves into the fluid-state and early-age solid-state properties of these geopolymers, with a particular emphasis on their performance after aging. The aging process extended up to 56 days for assessing mechanical properties and up to 28 days for evaluating hydraulic sealability through dedicated tests. The obtained results unveil a nonlinear correlation between the designated temperature and pumping duration. Notably, the issue of fluid loss emerged as a significant concern for these geopolymers. The early-age strength development of the mix design containing zinc demonstrates adherence to industry norms by achieving minimal strength requirements within 24 hours of curing. Zinc plays a pivotal role as a strength enhancer during the initial curing stages of geopolymers, both under ambient conditions and at elevated temperatures (70℃). However, upon extended curing at elevated temperatures, zinc’s impact slightly diminishes compared with the unmodified mix design. After around 30 days of curing, a consecutive reaction occurs in both the unmodified and zinc-modified mix designs. Aging leads to a decline in the material’s hydraulic sealability that was initially established during the early stages of curing.publishedVersio

Characterization of the mud displacement in an enlarged wellbore: An integrated rock-fluid model

Cement-mud displacement plays a crucial role in the sealability of cement sheaths. Irregular geometric features of a wellbore due to washout can have a negative impact on mud and cement mobilization. An unstable interface between two fluids always leads to mud channeling, interfluid mixing, and cement contamination, degrading the cement quality. Many factors, such as mechanical and rheological properties of fluids, annulus geometry, flow pattern, and flow rate, significantly influence the displacement efficiency. This study investigates the characterization of the mud displacement in an irregular horizontal well using a 3D computational fluid dynamics (CFD) model. Mud is displaced in an enlarged wellbore by geopolymer and neat class G cement. The wellbore geometry is developed based on the caliper log data from an unconventional shale well in the Tuscaloosa Marine Shale (TMS) lithology. The effects of pump rate, density difference, and mud contamination are evaluated by numerical simulations. The results present those residual muds mainly exist in the upper annulus of the enlarged section. Geopolymer has a better sealing performance and can resist more water-based mud (WBM) contaminations than neat class G cement. The scenario with a low mud-cement density difference and high cement injection rate results in a high cement volume fraction, mitigating the gas migration.publishedVersio

Design and Early Age Performance of Sustainable One-Part Geopolymers for Well Cementing

One-part geopolymers, known as “just add water” (JAW), alkali-activated formulation is presented in this work. This work reveals the design and development of short-term properties of JAW geopolymers for use in oilwell cementing and well abandonment. Granite-based mix designs normalized with a byproduct slag and a small amount of microsilica as precursors were developed. The solid activator is composed of potassium silicate and potassium hydroxide, which are mixed with the precursors to synthesize the JAW formulation. Zinc oxide is used as a strength booster admixture. The cementing properties of the developed granite-based mix designs were characterized by investigating reaction phases and mechanical properties. Dissolution, heat evolution, pumpability, strength development, and mineralogy are also studied. The results show that a positive correlation among all the given analyses for the final geopolymeric product is quite observable. Zinc oxide is favorable to be added for optimizing the given precursor mix design to enhance the solubility and leads to much higher heat evolutions. Furthermore, it develops early strength up to 16 MPa without any negative effect on the investigated one-part geopolymer slurries.publishedVersio

Bonding Mechanism of Zonal Isolation Materials to Clean and Rusted Casing

In oil and gas and geothermal well construction, a cementitious material is pumped in the wellbore to provide zonal isolation and support the casing during the life cycle of the well. Thus, the cementitious barrier materials must be durable in terms of chemical and mechanical properties and have chemical compatibility with casing pipe. The complex region of casing-cement interface is considered a key parameter to fulfill long-term zonal isolation. This interface must be chemically stable and impermeable to block unwanted formation fluid communication. Shortcomings of conventional Portland cement under operational conditions and increasing sensitivity to its carbon footprint are motivations for a green alternative. Bond strength and sealability of cement with steel surface have been measured previously. But few research works cover surface characterization and morphological analysis of barrier materials and the connected steel surface. This study provides a full picture of selected alternative materials in terms of shear bond strength, hydraulic sealability, and interface morphology analysis of the materials. Materials include API Class G cement, an industrial expansive cement, noncement-based pozzolanic material, geopolymer, and thermosetting resin. Also, clean and rusted steels were considered as a representative for the casing pipe in the field. The samples were prepared under elevated pressure and temperature. The results proved that higher shear bond strength is not an indication of good sealability, and the ingredients used to mix slurries have a critical role in the structure of the interfacial zone between casing and barrier material.publishedVersio

Application of the quemada viscosity model for drilling fluids

A number of different models are used to describe the shear rate dependent viscosity of drilling fluids. Most, such as the Herschel-Bulkley model, have a purely empirical basis. The Quemada model, while still empirical, is based on physical principles. It is based on the notion that structural units develop in the fluid at low shear rates which are then partially broken down as the applied shear rate increases. In the current work, drilling fluid rheological data are fitted to the Herschel-Bulkley and the Quemada model. The development of the Quemada model and the calculation of each model parameter are presented. We show that the Quemada model better fits measurements over a wider range of shear rates than the Herschel-Bulkley model. We describe how to select the parameters of the Quemada model. Knowing the difficulty of obtaining a known shear rate for fluids with yield stresses, we discuss how this can affect the quality of the Quemada model fit. Furthermore, in principle, the Quemada model is not applicable in presence a non-zero yield stress. Therefore, we show how to handle the yield stress using a (very high) zero shear rate viscosity.acceptedVersio

Rheological Compatibility of a Hardening Spacer Fluid and Oil-based Drilling Fluid

In the placement process of the cement slurry, treatment fluids such as the spacer are pumped ahead of the cementitious slurry to minimize the contamination of the slurry by drilling fluid and ensure superior bonding to the casing and formation. The spacer discussed in this work can harden with time and act as a settable spacer. This characteristic can be an advantage for well integrity if some spacer pockets are left in the annulus. Rheological compatibility of different mixtures of the spacer with oil-based drilling fluid (OBDF) has been studied using a rheometer, and the resulting R-factor, which indicates the degree of compatibility between fluids, has been calculated. An increase in the flow curve was observed for the mixture of the fluids. However, based on the R-index, these fluids are compatible with displacement in the wellbore. A nonionic surfactant, typically used in conventional spacers acting as an emulsifier and a water-wetting agent, was used in the hardening spacer design. The results show that the addition of OBDF to hardening spacer containing surfactant can increase viscoelasticity. Hardening spacer containing surfactant can successfully reverse the OBDF emulsion. By performing a small-scale mud displacement experiment, we observed that surfactant can improve the wall cleaning efficiency of the spacer while having minimal impact on the bulk displacement.publishedVersio