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With the increase in shale oil and gas activity and complexity, companies deploy new solutions to safely and efficiently drill, complete, and produce wells in unconventional plays. These include Oil Country Tubular Goods (OCTG) connections, which must withstand installation, stimulation, and production loads specific to this application. Industry available standards provide manufacturers and operators a framework for quality founded on best practices and testing. In some instances, existing testing protocols may not be adequate (e.g. insufficient or overconservative) to assess connections’ performance for this application. For this reason, the American Petroleum Institute established an expert working group to develop Technical Report 5SF (TR 5SF) intended to evaluate casing connections performance in multi-fractured horizontal wells. The objective of this paper is to present a set of verified testing protocols applicable to casing connections used in the most common shale plays, complementing the existing body of knowledge. We discuss testing elements and parameters tailored to the conditions of various shale plays. Based on the operations planned for the life of a well, the testing procedure is adjusted to resemble the expected conditions and loads in the correct order. This includes make-up, high-cycle fatigue associated with the casing string installation, thread compound degradation under temperature and time, and mechanical load cycles generated by stimulation. Specimen sealability is confirmed under production loads, after which failure testing is performed. Some of the inputs to build the testing protocol are: maximum internal pressure, axial load, dogleg severity, number of cycles, temperature, and fluid type. Since connections play a crucial role in the integrity of a well, a testing procedure to ensure their performance is shown. Testing protocols for Multi-fractured Horizontal Wells (MFHW) applied to two connection types are presented, highlighting how tailored testing protocols and robust engineering improve product reliability and well integrity assurance. We compile a set of testing inputs for the most relevant shale plays worldwide, together with the testing elements, sequence, and acceptance criteria. This should help end users validate and benchmark products’ performance while improving industry knowledge of connections capabilities.

Oilfield cements are a key element in well construction, during the operational phase of a well, and after its abandonment. Evaluating and understanding cement properties is crucial, since these properties are used in various engineering designs and calculations. In many scenarios, these properties are assumed constant with time, but an increasing number of studies have shown how properties change with time, temperature, and pressure. This work presents experiments run on API Class G cement mixed with and without additives and cured at 25 °C, 50 °C, and 75 °C, and constant pressure over a total of approximately two years. The influence of time, temperature, and additives on the performance of these cements is evaluated, and destructive and non-destructive testing methods are used to develop correlations to assess cement mechanical properties and to understand the development of porosity and its influence on cement performance. We applied NMR for the non-destructive evaluation of porosity, pore size distribution, cement water saturation, and curing of cement.

Bradenhead pressure, or sustained casing pressure, is pressure build up in the annular space between the surface casing and the next smaller diameter casing string within the wellhead. The objective of the test pad was to determine if increasing the physical flexibility of cement and rotating the casing string to increase displacement efficiency would help improve the cement bond to casing, decrease cement channeling, and help eliminate future bradenhead pressure accumulation. A twelve well pad housed three different cement slurries: four latex-type jobs, four resin jobs, and four foam jobs. A rotating cement head was used to enable mud circulation, dropping plugs, and rotating the string of casing during the cementing process on two of the four wells of each slurry type. For the production casing string, a threaded and coupled connection with a wedge thread profile was used to withstand the high torque experienced during rotation operations. Results were determined by evaluating pre- and post-stimulation logs along with continued bradenhead pressure monitoring. According to the outcomes from this test pad, recommendations were made on cementing practices within the Denver-Julesburg (DJ) Basin, based on regional gas-oil ratios (GOR). This interdisciplinary work determined whether the deployment of advanced cement slurries and casing rotation would help eliminate a potential health, safety, and environment (HSE) risk and help improve well integrity as related to bradenhead pressure.

Wellbore cement is used as a mechanical and hydraulic barrier in order to support casing and to prevent vertical and horizontal fluid migration, making wellbore cementing jobs one of the most important operations in thermal recovery projects. Drilling high quality wells requires the use of high-performance drilling muds that can support and protect the wellbore during the drilling process. Drilling mud will create an internal and external filter cake to protect the well during drilling. Although the external filter cake is usually removed before or during cementing jobs, the internal filter cake remains in the near-wellbore formation throughout the life of the well. This directly influences the wellbore overall heat transfer coefficient. As thermal well design relies on maximizing the heat delivered to the reservoir, minimizing heat losses to top formations while also protecting casing and cement layers is mandatory. This paper presents a unique experimental investigation of thermal cycle behavior of cement with focus on surface casing cementing. A more accurate assessment of overall heat transfer coefficients, directing efforts towards increasing the efficiency and understanding of thermal well design has been also performed in order to better understand the induced thermal loads on cements under complex scenarios. Thermal mixing laws have been used to determine the approximate impact of drilling fluid invasion and filter cake formation within rocks’ pores on overall heat transfer coefficients. In an experimental approach it was noticed that applying temperature cycles to fresh cements (curing time less than 21 days) will lead to mechanical strengthening of the casing-cement-system, enhancing well integrity, whereas old cemented wells will lose strength.

Research and development drives success in shale plays throughout the world, enabling operators to deploy new drilling, completions, and production technologies to reach more reservoir area and extend the life of production wells. This work demonstrates the development, validation, and deployment of an extreme torque casing connection addressing technical challenges of tubulars in unconventionals. Throughout the well lifetime, Oil Country Tubular Goods (OCTG) experience various loads during the installation, stimulation, and production phases. Some of the challenges experienced during the stimulation and production phases relate to internal and external pressure resistance, sealability, corrosion and cracking, erosion, and wear. Furthermore, with the increase in lateral length and the more demanding well geometries, the OCTG capabilities related to high cycle fatigue, connection runability, and torque limits become more important to safely and efficiently reach the total depth of the well and ensure integrity throughout well life. Another scenario in which the torque limit of an OCTG connection is important is rotating while cementing, a practice undertaken to mitigate sustained casing pressure, improve well integrity, and completion efficiency. We present the key elements in the development of a casing connection that overcomes these challenges and the decision process leading to a prototype. To prove the design concept, a fit-for-purpose testing protocol was adopted to validate its performance, replicating the installation, stimulation, and production phases under the expected loads. Once validated, a pilot involving casing installation, rotation while cementing and stimulation was completed in two wells, and its outcomes will be discussed in this work. This novel casing extreme torque connection, designed to overcome the application challenges, enables the installation of casing in longer laterals, together with the improvement of well integrity through rotation while cementing. The performance of the product, tested through a special procedure while ensuring reliability, was confirmed by the case study from the Niobrara shale. A new connection considering the challenges of wells in unconventional plays must account for several aspects from design to installation. We show the process, from the design stage and validation, leading to successful field deployment.

Cement is a key element for successful drilling and completing of a well. From oil and gas wells to geothermal applications, cement is a major material ensuring zonal isolation. With an increase in global energy needs and an expected uptick in drilling and plugging and abandonment activities, evaluating and understanding cement properties is crucial, since these properties are used in various engineering designs and calculations. The objective of this paper is to present how Nuclear Magnetic Resonance (NMR) can be used to understand the cement hydration process and the development of key properties such as strength and porosity. NMR applications for cement include determination of porosity, water interactions, identification of hydration stages and C-S-H gel development with curing time. Since water is present in all cement slurries, NMR can potentially help to understand microstructural changes in cement during curing. Data from more than 600 cement specimens cured for more than a year are compiled. Standard cement properties such as UCS (unconfined compressive strength) are compared with NMR responses. In this paper, we document cement hydration and porosity changes through NMR measurements in samples with five different recipes. Our study also confirms a strong correlation between NMR response and cement strength.

Geothermal energy has been used by mankind since ancient times. Given the limited geographical distribution of the most favorable resources, exploration efforts have more recently focused on unconventional geothermal systems targeting greater depths to reach sufficient temperatures. In these systems, geothermal well performance relies on efficient heat transfer between the working fluid, which is pumped from surface, and the underground rock. Most of the wells designed for such environments require that the casing strings used throughout the well construction process be cemented in place. The overall heat transfer around the wellbore may be optimized through accurate selection of cement recipes. This paper presents the application of a three-phase analytical model to estimate the cement thermal properties. The results show that cement recipes can be designed to enhance or minimize heat transfer around wellbore, extending the application of geothermal exploitation.

The process of making drill pipe connections is not only crucial in drill string integrity but also in assessing rigfloor safety. Almost 15% of recorded incidents in US onshore rigs occur due to improper make-up/tripping process as reported by IADC in 2015. Even with advances in pipe handling systems, human factors greatly influence the likelihood of errors which can lead to accidents. Training on simulators is a proven solution for innovation. The crew can better understand the rig equipment and prepare for potential risks. While drilling simulators exist for all aspects of drilling operations, a simulator for making drill pipe connections through human factor assessment is critically needed. This paper presents three unique approaches in building and using this much needed tool. One approach works like a visual interactive interface where the user can click and drag the rig components over to the rig floor and make a connection in a step-by-step manner. This enables a thorough understanding of the process and highlights errors if tasks are not performed sequentially. Another approach looks at the driller's screen where the user can control all the rig floor operations. This is a more realistic approach for a user who is well versed in the make-up process. The system works in real time and features a risk-meter that evaluates the process safety. The third approach is an automated interface for making connections. Before initiating the process, the user can choose among the different pipe handling systems, dope to be applied and rig crew assignments for the job. Different rig crews have combinations of experience, operational awareness and physical strength as attributes. The process begins with an animation of the make up process alongside a log of the process and description. Riskmeter and the option to pause-start are also features of this interface. These novel drilling simulators can play a crucial role in understanding and assessing the make up process on a rig floor. The simulators developed can be used for training new, and more experienced crews. The crew can be trained on the correct operational procedures, and create a profile evaluating the competency of the user. Since it features a safety meter that rates the ongoing process based on the handling system and crew selected, a comparative study was done and WAR (Weighted Assessment of Risk) was defined. The rig crew competency was analysed using these parameters. The tool could also be used for rig crew profiling and job assignments to improve safety and efficiency of tripping operations.

Well cements are an important aspect of wellbore integrity and recent investigations focus on describing the cement lifetime using, when possible, nondestructive tests like ultrasonic measurements. However, the original API and ASTM testing standards were based on destructive mechanical testing of cements, leading to the decision to investigate the backward and forward compatibility between ultrasonic measurements and mechanical testing, which makes the subject of this work. Ultrasonic cement measurement became a very popular method to assess the mechanical properties of the cement in a nondestructive manner. Since various measurement systems exist on the market, the development of an accurate reference data base that can be used to calibrate such measurements becomes very important. Two major systems have therefore been compared: the ultrasonic compressive strength, using the ultrasonic pulse velocity (UPV) principle, and the unconfined compressive strength (UCS), using the standard testing frame according to API and ASTM standards. The tests have been performed at different curing times, using both devices, on API Class G cements with bentonite and other additives. This paper presents the results of over 200 experiments that have displayed a different UPV response as a function of the additive content. Cement specific UPV versus UCS correlations were established. Thereby, a new level of accuracy was reached. Moreover, it was observed that after a given curing time, depending on the additive and its concentration, the UPV response is not as sensitive as the results yielded by the UCS method. The outcomes are an important step forward to improve and understand the wellbore integrity.

Centrifugal pumps are widely used in the industry, especially in the oil and gas sector for fluids transport. Classically, these are designed to transfer single phase fluids (e.g., water) at high flow rates and relatively low pressures when compared with other pump types. As part of their constructive feature, centrifugal pumps rely on seals to prevent air entrapment into the rotor during its normal operation. Although this is a constructive feature, water should pass through the pump inlet even when the inlet manifold is damaged. Modern pumps are integrated in pumping units which consist of a drive (normally electric motor), a transmission (when needed), an electronic package (for monitoring and control), and the pump itself. The unit also has intake and outlet manifolds equipped with valves. Modern systems also include electronic components to measure and monitor pump working parameters such as pressure, temperature, etc. Equipment monitoring devices (vibration sensors, microphones) are installed on modern pumping units to help users evaluate the state of the machinery and detect deviations from the normal working condition. This paper addresses the influence of air-water two-phase mixture on the characteristic curve of a centrifugal pump; pump vibration in operation at various flow rates under these conditions; the possibilities of using the results of experimental investigations in the numerical simulations for design and training purposes, and the possibility of using vibration and sound analysis to detect changes in the equipment working condition. Conclusions show that vibration analysis provides accurate information about the pump’s functional state and the pumping process. Moreover, the acoustic emission also enables the evaluation of the pump status, but needs further improvements to better capture and isolate the usable sounds from the environment.

Well cements are an important aspect of wellbore integrity and recent investigations focus on describing the cement lifetime using, when possible, non-destructive tests like ultrasonic measurements. However, the original API and ASTM testing standards were based on destructive mechanical testing of cements, leading to the decision to investigate the backward and forward compatibility between ultrasonic measurements and mechanical testing, which makes the subject of this work. Ultrasonic cement measurement became a very popular method to assess the mechanical properties of the cement in a non-destructive manner. Since various measurement systems exist on the market, the development of an accurate reference data base that can be used to calibrate such measurements becomes very important. Two major systems have therefore been compared: the ultrasonic compressive strength, using the ultrasonic pulse velocity (UPV) principle, and the unconfined compressive strength (UCS), using the standard testing frame according to API and ASTM standards. The tests have been performed at different curing times, using both devices, on class G API cements with bentonite and other additives. This paper presents the results of over two hundred experiments that have displayed a different UPV response as a function of the additive content. These allow us to expand the existing UPV vs. UCS correlations. Moreover, it was observed that after a given curing time, depending on the additive and its concentration, the UPV response is not as sensitive as the results yielded by the UCS method. The outcomes are an important step forward to improve and understand the wellbore integrity.

Various authors have pointed out the importance of cement mixing process and its effect on cement properties. From all cement properties, two are extremely important: the mechanical cement strength (unconfined compressive strength or UCS) and the rheology. The first is critically impacting the well integrity whereas the latter is affecting the pumping ability and displacement in the well, which will also have effects on the well integrity. A previously performed literature survey has pointed out that mixing energy alone may not be sufficient to describe the cement slurry changes, and inferred that shear rate can also impact the final cement properties, such as thickening time or cement strength. Starting from the existing investigations, our goal is to quantify the source of maximum energy input during a conventional cement job and estimate its effect on final cement properties. This paper is showing theoretical and experimental investigations on selected API cements with respect to their properties as a function of mixing energy. The first part of the paper is focusing on the estimation of mixing energy in different section of the cement pathway to the annulus. The second part will show some experimental results and the new way ahead, based on our findings.

Well integrity is becoming a subject of increasing interest with current developments in technical, political and social aspects echoing over the oil and gas industry. Both onshore and offshore activities are strongly constrained by the operator's ability to provide solid facts regarding their well integrity over the life of the well. As a result of new technologies, the life of the well has increased, generating new questions about novel integrity tiers. This paper presents the new cement repository that is currently under development at OU. The concept is to create a physical storage unit as well as a cement database to hold cement samples for a minimum of 5 years after well spud. All information will be stocked on a custom-made database, whereas the cement samples will be kept in a special "cement bank" - holding the cement samples under constant in-situ pressure. The cement samples can be taken during normal cementation jobs at the well site, transported using a "for purpose" developed mobile autoclave system and stored in the special units that will be built at OU. Additional samples (reference units) will be manufactured at the OU Well Integrity Laboratory. The paper will demonstrate that in case of any wellbore integrity issues, wellbore owners will have immediate access to accurate cement properties that can be used to perform numerical studies on the wellbore cement situation.

Drilling high quality wells requires the use of high-performance drilling muds that can support and protect the wellbore during the drilling process. Drilling mud will create an internal and external filter cake to protect the well during drilling. Although the external filter cake is usually removed before or during cementing jobs, the internal filter cake remains in the near-wellbore formation throughout the life of the well. As thermal well design relies on maximizing the heat delivered to the reservoir, minimizing heat losses to top formations while also protecting casing and cement layers is mandatory. A literature review shows that the effects of temperature on drilling fluids or cements have been intensively investigated. For example, high temperature generates a decrease of rheological properties of drilling muds, as well as increasing fluid loss. When heat transfer estimations are required, the drilling mud properties are not important, unless a thick filter cake is considered. This is why laboratory investigations on filter cake thermal capacity and conduction, together with theoretical estimations of the effect of filter cake on the wellbore heat transfer process make the subject of this paper. For this, the overall heat transfer coefficient has been revisited and additional effects of cement layers and filter cake have been incorporated. The results show that conventional water base muds can reduce the heat transfer from and to the wellbore. Two mud samples have been tested and an increase of the thermal conductivity with temperature is observed. Adding barite to the drilling mud will increase the thermal diffusivity of the filter cake. The thermal diffusivity of the drilling mud is higher than that of its produced filter cake, but can change the heat distribution in the well and the cement temperature levels. Such effects, together with cement layer conductivity and size are usually neglected in conventional heat transfer models and a reassessment of conventional models while considering such parameters is presented in this work.

Thermal wells (observation, productions or abandoned) are highly susceptible to leaks due to cement degradation resulting from thermo-chemical-mechanical loads. Therefore, successful application of thermal processes requires a close look at well integrity assessment and prediction for long periods of time. During the life of the well, the casing-cement-rock system is experiencing a cumulative damage which can, for instance, explain the sustained casing pressure that appears after years of good well integrity. Our industry is striving to implement the highest well integrity standards during the field development and beyond. Deficiencies in well construction and well abandonment are the most common causes of defects inside the composite system of rock, cement and casing. These defects can be measured using standard wellbore measurement tools, and some solutions exist to cure them. Long time exposure of the well to several loads may change the well response due to parameter degradation, with typical loading mechanisms being related to chemical and mechanical interactions. A large number of studies have been conducted to investigate chemical and thermal degradation process of Portland cement systems. The degradation process is very complex and is affected by temperature, pressure, chemistry of the products and time. A literature review of various investigations on well degradation processes shows that most of the experiments are time limited, and therefore the well integrity is limited to the frame in which we can extrapolate the results. This paper will point out the future need for research to improve the prediction of well integrity. The results of the work show that the major unknowns are long-term properties of the downhole environment like casing, cement, and the interaction between casing-cement-formation. Some preliminary laboratory testing also point out the importance of specific cement testing, beyond those recommended by various regulations and recommended practices. As an example, a theoretical demonstration of why fully cemented casing strings may additionally damage the cement sheath during heating and cooling cycles is provided in this paper, pointing out a novel testing procedure.

In various parts of the world, heavy oil projects use high temperatures in order to support the oil production. Most of these projects are still on-going after several years of high temperature well exposure, while others have been suspended due to operational and environmental issues. The well integrity time span should extend itself beyond the field estimated operational date. These wells (observation, productions or abandoned) are highly susceptible to leaks due to cement degradation resulting from thermo-chemical-mechanical loads. Therefore, successful further development of heavy oil reservoirs requires a closer look at the assessment of well integrity and its prediction for extensive periods of time. During the life of the well, the casing-cement-rock system is experiencing, as a secondary problem, a cumulative damage. This could explain the sustained casing pressure that appears after years of good well integrity. Long time exposure of the well to several loads as well as cyclic load changes may affect the well response due to a rather unexplored degradation of the mechanical, chemical and thermal parameters. In this case, the typical loading mechanisms are thermal, associated with superimposed chemical and mechanical loads. A large number of studies has been conducted to investigate the very complex chemical degradation process of Portland cement systems, which is influenced by temperature, pressure, chemical reactions and their products and, more important, time. A literature review of various investigations on well degradation processes has shown that most of the experiments are time-constrained, and therefore the well integrity is limited to the interval in which results extrapolation is possible. Cement retrogression has also been investigated and research led to recommendations of adding silica flour to the Portland cement. The least investigated aspects of the cements are their cyclic resistance to variable loads. This paper will critically analyze the various existing well integrity concepts and point out the future need for research to improve the prediction of well integrity. The results of the work show that the major unknowns are long term properties of the downhole environment like casing, cement, and the interaction between casing-cement-formation. Moreover, a simple, yet attention-grabbing experimental investigation has been carried out on several cement samples with different properties by simulating the cement layer associated to the surface casing of a well exposed to temperature variations. Due to the shallow depths, the cementing of the surface casing may yield specific well integrity issues generated by low slurry density requirements, original low temperature environment, high fluid-formation temperature differences, all leading to potential problems related to health, safety and environmental standards worldwide (e.g. aquifers damage, operational risk, etc.).

Steam injection is a known Enhanced Oil Recovery technique with application in heavy oil exploitation. The process is generating a rather high amount of carbon dioxide (CO2) that according to the current climate regulatory initiatives should be reduced. CO2 injection to enhance heavy oil production is a known technique for such reservoirs. The technology of capturing CO2 has evolved today up to a point where it can also be applied to steam generators. This work starts with a comprehensive review of most recent steam generator developments and their possibility of subsequently capturing CO2. Co-generation concepts will also be investigated and their potential to generate steam and CO2 for heavy oil enhanced recovery will be evaluated. The thermal properties of CO2 are well known, and its critical state poses challenges in many injection applications. This low-cost completion is proposing a parallel injection of steam through tubing and CO2 through annular space. While injecting CO2 in a steam-heated well, the elevated temperature keeps the carbon dioxide gas away from its critical state. The gas will cool down the upper part of the well, especially the surface casing, avoiding cement damage and well integrity breaches. This paper describes an economical completion technique that replaces the expensive thermal packer with a new budget-friendly design. This novel setup allows free tubing expansion and protects casing against high temperature through continuous gas circulation in the annulus. It also enables the simultaneously injection of combustion gases from steam generators or other gas supply. In this manner, substantial CO2 credit could be saved by operators while cutting completion expenses and environmental hazards at the same time.