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Global warming is one of the most significant issues the world is facing. Capturing carbon dioxide from the atmosphere or industrial processes and storing it in geological formations (carbon capture and storage, CCS) can help counteract climate change. Nevertheless, the interaction between well barrier elements such as cement, casing, tubulars, packers, and valves can lead to possible leakages. To accomplish successful carbon dioxide sequestration, injecting the carbon dioxide in its supercritical state is necessary. The supercritical carbon dioxide can corrode steel and elastomers and react with the calcium compounds in the cement, dissolving them and forming calcium carbonate and bicarbonate in the process. This carbonation can lead to channels forming on the cement-to-rock interface or cracking due to the carbonate precipitation, resulting in a loss of well integrity. This study focusses on finding ways that enable the continuous monitoring of cement integrity, under in-situ conditions, in a lab setup. The construction of an autoclave, capable of withstanding supercritical conditions of carbon dioxide, facilitates the in-situ monitoring. This autoclave also makes CT-scans of the pressurized sample possible, as well as acoustic measurements, using state-of-the-art piezo elements. The first tests will establish a baseline using neat Class G Portland cement to verify the design and sensors. The set up consists of a rock core in the middle of the autoclave surrounded by a cement sheath. A prepared channel in the center of the core expedites the distribution of the carbon dioxide. Once the ability of the sensors to monitor the integrity is verified, different cement compositions and their interaction with supercritical carbon dioxide can be studied. The experimental setup and the procedure discussed here closely simulate the downhole condition. Hence, the results obtained using this setup and procedure is representative of what could be observed downhole. The direction is not to remove the sample from the autoclave for analysis, as is the current industry practice, but to measure cement integrity under in-situ conditions over an extended period of time. Digitalization is powering the in-situ analysis in these tests. The first two tests of this study, using the afore mentioned autoclave, investigated the carbonation behaviour of two Class G Portland cement slurrys, one with a low and one with a high slurry-density. The low-density slurry showed extensive degradation and even the high-density slurry showed carbonation, but only close to the sandstone core. The results from this study can lead to the prevention of leakage of carbon dioxide to the environment and other formations, which defeats the purpose of carbon dioxide sequestration. These results should improve the economics of these wells as well as the health, safety, and environmental aspects.

Well integrity is one of the main issues during all life cycles of the well and if any barrier element fails and compromise the integrity of well, remedial strategy may have to be performed to restore the safety and economics of the well. Cement is conventionally used as the isolation material in remedial and primary jobs. However, due to several inherent limitations in cement characteristics, such as cement shrinkage or poor cement slurry compatibility with downhole fluids, it is not always the best solution. Besides, cement slurry is a particle laden fluid which prevents it penetrating in to tight cracks/pathways to ensure isolation during remedial treatments. This project illustrates the effort to develop a customized polymer system as cement alternative addressing several challenges posed by conventional materials and experimental studies are designed to evaluate its characteristics such as rheology, injectivity and mechanical properties. Furthermore, the compatibility of these systems with drilling fluids contamination and shrinkage behaviour upon cure are evaluated. Afterward, based on the results of measurements, the limitations of each system are determined and the best formulation is optimized. The results of experiments prove that beside the appropriate rheological properties, the system provides excellent mechanical properties and much lower shrinkage rate upon cure compared to cement. The system withstands and maintains its properties after being contaminated with considerable volume of downhole fluids such as drilling fluids and hydrocarbons and mechanical properties such as compressive strength is not much affected by contamination. The unique characteristics of customized sealing system as cement alternative could provide benefits to industry by solving several current challenges in achieving secure isolation. Particularly due its ability to penetrate in to tight cracks, this system affords an effective method to mitigate sustained casing pressure or as a remedial solution for casing leakages which cannot be achieved easily by conventional methods.

The main objective of this research is to predict the proper bit/reamer size ratio based on the rock strength weakening zone around the wellbore. Nowadays, the Reaming While Drilling (RWD) technology is gaining more and more acceptance in the petroleum industry by means of reducing drilling time and Non-Productive Time (NPT), which results in significant cost saving. The importance of this research is analyzing scenarios in which RWD would add benefit to the operation, given that the reaming process is often fraught with much inefficiency. Thus, through the process of estimation optimum reamer/size ratio, by coupling three key parameters in geo mechanics: thermo-poro-elastic, a model of rock strength is developed to analytically assess how rock strength distribution changes around the wellbores and in particular below the reamer in drilling environments. An analytical model of thermoporoelastic is used with published data (for rock properties usage purposes) in order to develop a model of rock strength below the reamer to show in how far some specific rock could be a good candidate for reamer usage. This in turn allows finding proper candidates for effective RWD applications and also can assist to determine the maximum reamer/bit size ratio for certain rock characteristics in order to optimize the drilling system. From the analysis performed, which was carried considering two different groups in terms of formation permeability, it is be conclusive that for low-permeable formation the size of reamer is function of exposure time of wellbore after making pilot hole while the reamer size for enlargement operation through the permeable formation due to fast diffusion rate is not a time dependent parameter.

One of the objectives of the Long-Term Pavement Performance Specific Pavement Studies (SPS)-1 experiment was to examine the effects of climatic regions and various design factors on the performance of flexible pavements. In a research study sponsored by FHWA’s Long-Term Pavement Performance program, the impacts of climatic regions, drainage, and the thickness of asphalt concrete layers on the functional and structural performance of the flexible pavement test sections of the SPS-1 experiment were analyzed. Functional performance was analyzed on the basis of ride quality [determined by using the international roughness index (IRI) and safety (rut depth)]. Structural performance was analyzed on the basis of alligator, transverse, and longitudinal cracking and rut depth. For each SPS-1 test section, functional performance was represented by the remaining functional period (RFP), and structural performance was represented by the remaining structural period (RSP). Both metrics, the RFP and the RSP, were developed in this study to rate the performance of flexible, rigid, and composite pavement sections. This paper presents and discusses the results of the analyses of the performance of the SPS-1 test sections. It is shown that, as expected, pavement performance is a function of the climatic region. Wet–freeze regions had a significant impact on pavement performance in terms of the IRI, rut depth, and cracking, and drainable bases were found to be more effective in the wet–freeze region than in the wet–no-freeze, dry–freeze, and dry–no-freeze regions.

Existing systems for rating pavement condition are primarily based on current pavement conditions, distresses, or both. These systems do not account for the pavement's deterioration rates. For instance, two pavement sections rated fair this year may or may not have similar ratings next year. A balanced and comprehensive system for rating pavement condition should be based on the pavement's conditions, distresses, and deterioration rates. In a research study sponsored by FHWA, dual systems of rating pavement condition were developed on the basis of the pavement's functional and structural aspects and rates of deterioration. These rating systems account for current and future pavement conditions and distresses. Therefore, the systems provide more accurate information to decision makers about management of the pavement network while being simple enough for communication with legislators and the general public. The functional rating is based on ride quality (international roughness index) and safety (skid resistance and rutting) and is expressed by the remaining functional period (RFP). The structural rating is based on cracking, faulting, and rutting and is expressed by the remaining structural period (RSP). The RFP is defined by the shortest time in years between now and the year when one of the conditions reaches its threshold value. Similarly, the RSP is the shortest period in years between now and when a threshold is reached. The main advantage of the RFP and RSP is that both are proportional to the elapsed time. Their values decrease by 1 year for each calendar year.

Non-point source pollution from agricultural lands is a significant contributor of sediment pollution in United States lakes and streams. Therefore, quantifying the impact of individual field management strategies at the watershed-scale provides valuable information to watershed managers and conservation agencies to enhance decision-making. In this study, four methods employing some of the most cited models in field and watershed scale analysis were compared to find a practical yet accurate method for evaluating field management strategies at the watershed outlet. The models used in this study including field-scale model (the Revised Universal Soil Loss Equation 2 - RUSLE2), spatially explicit overland sediment delivery models (SEDMOD), and a watershed-scale model (Soil and Water Assessment Tool - SWAT). These models were used to develop four modeling strategies (methods) for the River Raisin watershed: Method 1) predefined field-scale subbasin and reach layers were used in SWAT model; Method 2) subbasin-scale sediment delivery ratio was employed; Method 3) results obtained from the field-scale RUSLE2 model were incorporated as point source inputs to the SWAT watershed model; and Method 4) a hybrid solution combining analyses from the RUSLE2, SEDMOD, and SWAT models. Method 4 was selected as the most accurate among the studied methods. In addition, the effectiveness of six best management practices (BMPs) in terms of the water quality improvement and associated cost were assessed. Economic analysis was performed using Method 4, and producer requested prices for BMPs were compared with prices defined by the Environmental Quality Incentives Program (EQIP). On a per unit area basis, producers requested higher prices than EQIP in four out of six BMP categories. Meanwhile, the true cost of sediment reduction at the field and watershed scales was greater than EQIP in five of six BMP categories according to producer requested prices.

Many watershed model interfaces have been developed in recent years for predicting field-scale sediment loads. They share the goal of providing data for decisions aimed at improving watershed health and the effectiveness of water quality conservation efforts. The objectives of this study were to: 1) compare three watershed-scale models (Soil and Water Assessment Tool (SWAT), Field_SWAT, and the High Impact Targeting (HIT) model) against calibrated field-scale model (RUSLE2) in estimating sediment yield from 41 randomly selected agricultural fields within the River Raisin watershed; 2) evaluate the statistical significance among models; 3) assess the watershed models' capabilities in identifying areas of concern at the field level; 4) evaluate the reliability of the watershed-scale models for field-scale analysis. The SWAT model produced the most similar estimates to RUSLE2 by providing the closest median and the lowest absolute error in sediment yield predictions, while the HIT model estimates were the worst. Concerning statistically significant differences between models, SWAT was the only model found to be not significantly different from the calibrated RUSLE2 at α = 0.05. Meanwhile, all models were incapable of identifying priorities areas similar to the RUSLE2 model. Overall, SWAT provided the most correct estimates (51%) within the uncertainty bounds of RUSLE2 and is the most reliable among the studied models, while HIT is the least reliable. The results of this study suggest caution should be exercised when using watershed-scale models for field level decision-making, while field specific data is of paramount importance.

Integrated planning unveils insight into a large project and all its bottlenecks for every discipline. In order to optimize utilization of facilities, optimize scheduling and its subsequent operations, an integrated planning tool was developed especially for large scale and complex shale resource projects. The best option to come up with a suitable planning tool for such projects was found to be an Agent Based Model (ABM). Flexible definition of the individual components of the model, which comprises the subsurface, surface data, and the physical representation of wells, pipelines and equipment, allows effective strategy testing of various scenarios. With the chosen approach, results could be obtained fast and also numerous variations of the original development strategy could be tested and included. It can be shown that through optimization of facilities and optimized scheduling for an asset, economical benefits can be found effectively. It tremendously reduces the time for strategy testing of conventional approaches and also updates due to new development strategies as new information is available. Scheduling and an analysis of various drilling strategies allow a further reduction of economics. It can be concluded that this approach allows more effective testing of strategies for large assets, which involves cross-functional decision making. It allows effective communication and immediately shows possible shortcomings of any strategy which otherwise would be overlooked with any other approach that does not involve everything from the resource itself, to the production system, contractual conditions as well as a representation of the actual field operations.

The publication generally and briefly describes what circumstances governed the petroleum industry and the connected regulatory organizations before the Macondo blowout. The paper shortly describes utilized classic containment and control efforts such as actuation attempts of the BOP, top kill with junk shot, relief wells. The publication's main focus is to describe and graphically present in detail the Cofferdam, the Riser Insertion Tube Tool, Top Hat, Capping Stack and choke and kill line collection method which were utilized to seal off the flow of hydrocarbons at the Macondo blowout. An extended literature review has been completed to fully cover and understand the technologies which were utilized and newly developed in the efforts to stop the outflow and abrogate the accident. The assessment of critical properties, problems are also presented next to the description of the specific source control technology. The blowout has triggered efforts never seen before both in short- and long-term not only from the side of affected regulatory and company side but industry wide. Short-term, the main effort was to contain the blowout as soon as possible, long-term it triggered strong determination from companies, and connected businesses to create proper contingency planning, containment technologies and strategies also through newly established consortiums. The non-profit oriented consortiums, containment systems and established HSE regulations need to be maintained properly even in a low oil price environment, so deeper understanding, recurrent inspection of the development ways of containment technologies in offshore environment can be crucial for sustaining the high HSE standards. The paper also aims to summarize knowledge to be able to make proper decisions in case of deepwater projects.

Coring in unconventional reservoirs with typical unconsolidated formations has introduced additional challenges requiring more innovative concepts to be developed. These requirements, economic issues of unconventional reservoirs, and also issues of conventional coring particularly in regard to excessive trip times incurred have recently led to widespread attention to wireline continuous coring (WCC) modified from mining industry to petroleum industry applications. This coring method has contributed to coring deep formations, long core sections, multiple zones, jam prone formations, exploration zones or areas with unknown core points. Currently, WCC is suffering from several drawbacks while some recent attempts have been made to remove them. In this accordance, this work is missioned to remove some existing defects by adding some innovative concepts to be applied to the ordinary WCC. Therefore, a more efficient continuous coring method is aimed which includes enhanced coring key performance indicators. Therefore, several identified challenges of WCC are considered to be removed or alleviated by innovative concepts to be added. The challenges consist of un-flushed inner tube while run in hole, limited retrievable core size, in-situ/pressure coring hazards (i.e. safety issues, complex sealing, etc.), slick line issues (rig time, torque, rupture, etc.), untimely and inefficient decision making while coring/drilling, non-optimized coring/drilling and tripping induced core damage in WCC. In order to address these issues, as novelty measures, first an inner tube flushing system is proposed for flushing inner tubes prior to commencing coring. Second, casing drilling coring is recommended in order to obtain larger core sizes contributing to improved core analysis. Third, in-situ downhole measurement and sampling systems are proposed to measure properties of in-situ fluids in order to complete or replace pressure/in-situ coring systems and ensure safety. Fourth, an innovative mode conversion system is proposed to mitigate slick line issues. Fifth, a less complex logging while coring system has also been proposed in special cases to enhance and expedite real time decision making process in regard to proceeding to core cutting or not. Sixth, an innovative mode conversion system contributing to partial elimination of wireline jobs will also be proposed to substitute slick line/ wireline retrievals. Seventh, optimum tripping schedules have been characterized as crucial to match formation rock and fluid properties and type of WCC applied and also to prevent coring induced damage.

Historically Reaming While Drilling (RWD) operations have been restricted to softer formations. The objective in this study is to create a thermoporoelastic model of Mechanical Specific Energy (MSE) for RWD in order to shed important new light on the decision process how to use RWD for a specific formation as well as a recommendation for reamer-pilot size ratio.The analytical approach developed in this paper calculates thermoporoelastic coupled time-dependent stress, pore pressure and temperature variations for an inclined borehole that is drilled through permeable or impermeable formation and which is subjected to far field three dimensional in-situ stresses. Apparent rock strength of the rock in Depth of Cut (DOC) zone beneath the reamer can be determined by using Mohr-Coulomb theory. By using Apparent Rock Strength (ARS) the analytical Mechanical Specific Energy (MSE) can be estimated afterwards. This parameter can be used as a key decision to determine whether a specific formation is a good candidate for RWD or not.A proper combination of pilot and reamer is absolutely critical to optimize bottom hole assembly (BHA) performance and durability. For many years, a trial-and-error technique has been employed by the drilling industry to determine advantages or drawbacks of reamer in the BHA and the optimum reamer-to-pilot-size ratio and bit characteristic for drilling, which requires a significant investment of time and money.The comparison of reamer's MSE, to destroy rock around the wellbore, with bit's MSE, to destroy rock at the bottom of the hole, shows how efficiently reamer can drill rock around the wellbore in certain formation, and in some other formations the drawbacks are outweigh of its advantages. This in turn makes it possible to determine proper formation characteristics to employ reamer in the BHA and also the maximum reamer/bit size ratio for certain rock characteristics in order to support efficient drilling operations.Considering that so fare in the market there is no evidence of a specific model to predict rock strength bellow the reamers, this research and study show its degree of novelty since it propose a model to fill this gap, which can in the future and after tuning be used as a reference application in the petroleum industry for decision making and project cost analysis. Validation in different environments is still to be concluded as a next step in this research.

The influence of parameters of a thermo-mechanical rolling process on corrosion properties of materials 316L and Alloy 825 was studied by means of the DL-EPR-method and a conventional corrosion test. Prior to polarization measurements, optimization of the DL-EPR-method was conducted. SEM was used to characterize microstructure and type of attack before and after corrosion testing. A strong correlation between annual corrosion rates and DL-EPR-test results was obtained. Due to the low tendency of both alloys to form corrosion-promoting precipitates, the applicable range of process parameters for both alloys is large and the fabrication process in general is not critical.

Nickel-based alloy 625 was investigated by means of a conventional corrosion test (Streicher-test according to ASTM G28A [1]) and an electrochemical potentiokinetic reactivation test (according to ASTM G108 [1], with some modifications). Susceptibility to intergranular corrosion after various heat treatments was examined by using both test methods and the results were compared. Dependent on the type of heat treatment applied, both methods showed partially different results. Possibilities and limitations of replacing Streicher-test with EPR-test are pointed out and commentated. In conclusion, the EPR-test presents itself as a promising and quick investigation technique for detecting susceptibility to intergranular corrosion in nickel-based alloys.

Pre-salt layers has long-term exploration and production possibilities, however the properties of such layers are highly challenging for exploration (i.e. these carbonate layers are highly abrasive, located deeper than 5000 m, have generally low permeability) and production (i.e. pre-salt layers are located in harsh oceanic conditions, hundreds of km offshore). These conditions mean increased exploration technological and economic difficulties. One of the partial solutions to decrease costs is to reduce the drilling operations time. Rate of penetration (ROP) has a significant effect on the overall drilling time, driving ROP modeling and optimization to be a viable solution for reducing drilling operations time in such environment. Several mathematical ROP models were developed in the last five decades in the petroleum industry, departing from rather simple but less reliable R-W-N (drilling-rate, weight-on-bit and rotary-speed) equations until the arrival to a comprehensive and complex approach: Bourgoyne and Young ROP Model (BYM) which was first published in 1974. The paper explains the equation, how it is applied in terms of ROP modeling, identifies the main drilling parameters driving each sub-functions, and introduces how they were developed. The paper base itself on the sub-functions of the equation, explains the normalization factors which have significant influence on the model, and also introduces simulations which aim to understand the approach by applying the equation in a pre-salt layer case study. Knowing that, the original publication was introduced in 1974, this paper also aims to identify rooms for improvement and/or alternate the sub-functions to match actual field data better than with the originally given drillability coefficient recommended boundaries stated in the first publication. This is accomplished through a real-world practical application of this ROP model in a pre-salt layer. The paper also assesses the limitation in terms of the applicability of this complex model for ROP analysis and optimization in such carbonate layers.

Pre-salt basins and its exploration have become more and more frequently mentioned over the years, not just for their potential reserves, but for the implicit challenges in terms of general operations (downstream and upstream) to be faced in order to make these fields effectively commercially viable. Several research efforts aimed at to addressing these related barriers, but still in the drilling optimization and efficiency discipline, as a known challenge, a considerably low drillability is experienced when drilling throughout the pre-salt carbonates itself. A lot of already known rate of penetration (ROP) modeling and Specific Energy (SE) studies have been developed and improved during the past 50 years, helping in post- and pre-operations analysis, allowing simulations and tendency estimations, enabling a better understanding of possible parameters and design combinations for operations optimization and efficiency enhancement. Pre-run tests may be a very important tool together with consequent interpretation and re-usage of the results to help in boosting optimization in operations. Thus, the main focus of this paper is to address a reverse engineering by evaluating specific well data and information, identifying gaps to boost rate of penetration for a pre-salt well case study, based on a drilling mechanics analysis proposing a new analysis methodology, by playing-back through a reverse engineering procedure the drill-rate test curves, exemplifying its impact in analysis with a more dynamic and real-time focus.

Optimizing operational efficiencies in unconventional resource developments is one of the key success drivers for improved economics. In this work, an approach for exactly that problem is presented, designed for a field development scenario in Germany. Starting with a model that captures all key parameters which are influencing a development program such as the gas market and prize scenarios, political situation, environmental regulations, logistical requirements, etc., it immediately turns out that the highly complex model has to be significantly simplified and a sub-model with clear and precise boundary conditions has to be generated. This sub-model is tuned to problems of particular interest, considering technological parameters such as the impact of various state of the art drilling technologies or different fracturing methodologies on the entire development program. It is possible to identify interrelations of various procedures and allows estimating project costs. Operational scenarios can also efficiently be tested, and validated and the financial key parameters of different scenarios can be compared. Moreover, short- and long-term benefits and drawbacks of various solutions can be assessed and optimized. Also, limitations of System Dynamics for that kind of simulation are pointed out, and it is shown how to solve the problem with an Agent Based Modeling approach.

Summary This work identifies a mechanism that could be responsible for substantial gas invasion into a cemented column after placement. A model is developed to predict the risk for gas invasion and to aid in the design of a cement job suggesting a "tail" and a delayed "lead" slurry. The model provides the absolute theoretical migration height when cement properties and formation parameters are known. The work accounts for the calculation of the hydrostatic pressure drop, for the estimation of the inflow rates resulting from shrinkage and filtration, and for the description of the bubble-rise process. A sensitivity study on important design and well parameters is included.

One of the major challenges in the drilling industry is the quick detection of problems that can occur during drilling a deep well due to high cost implications. These problems can occur for various reasons and can exhibit varying symptoms, which make them difficult to identify or prevent automatically. Visual Analytics has emerged as an alternative approach for data analysis. It combines both the computational power of computers and the experience of domain experts to analyze and gain insights into large data. This paper describes a procedure for analyzing and identifying drilling problem using Visual Analytics techniques. It provides results of an elaborated analysis of sensor measurement datasets that contain “Stuck Pipes” situations - one of the most common drilling problems. Statistical features are calculated from the dataset using the sliding window method. We show how visual analysis by means of linked scatter plots enable relating the problem patterns to the computed features and can hence help in identifying “Stuck Pipes” problems.

During the last decades, non-conventional solutions for more economical well bore drilling have been investigated. Big research efforts and budgets have been spent on alternative drilling methods; such as laser drilling or jet assisted drilling. Simplified assumptions predicted a big future for such technologies. However, to get a better and more realistic picture of the feasibility of such unconventional ways to drill rock, the ability to apply them in field scale applications needs to be questioned. In this paper a holistic energy approach to evaluate drilling alternatives is proposed. To evaluate the energy balance of the drilling system the amount of energy generated, e.g by the rig at surface, needs to be put in comparison with all system energy consumption to lead to an effective energy available to destroy rock at the bottom of the hole. To test this concept a small scale laboratory setup is used to compare different drilling methods under similar conditions. This paper presents a systematic approach using an energy concept to compare alternative drilling methods on a laboratory scale. In this first approach laser assisted spallation and conventional drilling were compared. As a by-product, also the optimum mode for spallation drilling, continuous versus pulse wave, will be presented.

Drilling fluids are subjected to cyclic pressure and temperature loads when circulated in the wellbore. However, little information exists about quantitative changes of fluid viscosities during long-term circulation. Therefore the effects of temperature/ pressure cycles on viscosity reduction/ regaining for different Xanthan products - dissolved in pure solutions and in drilling mud - and for Bentonite fluids are evaluated in a laboratory study. To model these cyclic temperature/pressure loads a new HPHT cyclic load test has been developed and the impact of temperature and time dependent viscosity on hydraulics calculations is evaluated quantitatively. First, the ability of Xanthan and Bentonite fluids to break and reestablish viscosity under cyclic temperature and pressure loads was evaluated. Furthermore it was investigated whether fluids are able to build up original viscosity after applying cyclic temperature and pressure loads. This effect is defined as viscosity degradation per load cycle which could be quantified as part of this work. Bentonite, in contrast to Xanthan fluids, however has a different, more complex and stronger time and temperature dependent viscosity behavior when cyclic loads are applied. For the investigated fluids a significant impact of time dependent behavior under cyclic temperature and pressure loads on hydraulics modeling is shown. By performing the new test procedures it is possible to quantitatively determine cyclic viscosity degradation. When using these findings, the accuracy of hydraulic modeling and nozzle optimization can be improved. Better predictions of critical viscosity breakdowns and additive requirements to maintain fluid viscosity can be done.

Abstract This work discusses the major factors affecting the pressure drop in the cemented annulus which are filtration from the wellbore into permeable layers, shrinkage of the slurry due to hydration, and changes in the rheological properties of the slurry. A model for determining wellbore pressures in cement slurry columns is presented. It accounts for the depth-dependent or placement history dependent behavior of the gel strength evolution. Experiments conducted in the laboratory demonstrate that static gel strength development is a function of temperature, pressure and shear rate. Results show that large differences in wellbore pressures can be obtained when the depth-dependent characteristics of gel strength are neglected in wellbore pressure loss calculations. Introduction The main purpose of cementing oil wells is to maintain proper hydraulic isolation among the various permeable layers. The integrity of the cemented annulus is compromised when formation fluids are allowed to enter the annulus. As the cement sets, its ability to transmit hydrostatic pressure diminishes. Fluid loss from the slurry to a permeable layer can lead to volume reduction, and, if the reduction is not compensated for, the cement pore pressure declines. As the cement gel strength develops, it becomes harder for any volume reduction to be compensated for, and therefore, volumetric shrinkage and the continuation of fluid loss to permeable layers may lead to a cement pore pressure decline (Chenevert and Jin, 1989). When the hydrostatic pressure of the slurry falls below the formation pressure, gas can enter the cement matrix. A more comprehensive discussion dealing with the problem of gas migration/invasion during oil well cementing was given by Beirute and Cheung (1989) and Sutton and Ravi (1989). Predicting the pressure behavior of cement slurries is an important task during well cementing. Several pressure drop predictive models have been presented. The basic model which accounts for gel strength development and filtrate loss was introduced by Sabins et al. (1982), and later by Sutton and Ravi (1989), and Beirute and Cheung (1989). Chenevert and Jin (1989) developed a more detailed pressure drop model to account for the gelation properties of the slurry, and the downward movement of the column due to shrinkage and fluid loss. In the Chenevert and Jin model the wall shear stress of a slurry element is determined as a function of gel strength and displacement and it is used instead of the static gel strength to calculate wellbore pressures. Recently, Daccord et al. (1991) expanded the Chenevert and Jin model to include the mass conservation of the slurry. The Daccord et al. model calculates density changes in the slurry as a function of compressibility, chemical shrinkage and fluid loss. In this paper, an improved model for predicting wellbore pressure is presented in which the depth-dependent or placement history - dependent behavior of gel strength development is included. P. 407^

This paper presents the results of laboratory static and dynamic tests on casing-cement-rock systems exposed to axial loads under ambient conditions. A new testing method has been developed. The casing-cement-rock system mostly fails due to tension and shear stresses. In various applications such as HPHT, deep-water, (steam) injection or geothermal wells, the cement-casing bond is exposed to cyclic thermomechanical loads resulting in casing elongation, contraction, expansion and subsequently in cyclic radial and axial stresses at the cement-casing-rock system. Cement is a brittle material which can fail when subjected to repeated application of stresses lesser in magnitude than the statically determined strength. A novel atmospheric test cell has been designed and constructed. In order to achieve the fatigue limits of the cement-casing bond, a set of testing procedures has been established. Several tests are conducted to evaluate de-bonding. The focus on de-bonding is achieved by allowing the casing to move through the test while preventing any cement movement. Thus, when a force is applied in the axial z-direction - either the casing is pulled out (tension) or pushed down (compression) - the casing has enough space to move in both directions. The advantage of this testing method is that different stress ratios can be applied during the test.