ALBERT

Description: Summary Improved numerical efficiency in simulating wellbore gas-influx behaviors is essential for realizing real-time model-prediction-based gas-influx management in wells equipped with managed-pressure-drilling (MPD) systems. Currently, most solution algorithms for high-fidelitymultiphase-flow models are highly time consuming and are not suitable for real-time decision making and control. In the application of model-predictive controllers (MPCs), long calculation time can lead to large overshoots and low control efficiency. This paper presents a drift-flux-model (DFM)-based gas-influx simulator with a novel numerical scheme for improved computational efficiency. The solution algorithm to a Robertson problem as differential algebraic equations (DAEs) was used as the numerical scheme to solve the control equations of the DFM in this study. The numerical stability and computational efficiency of this numerical scheme and the widely used flux-splitting methods are compared and analyzed. Results show that the Robertson DAE problem approach significantly reduces the total number of arithmetic operations and the computational time compared with the hybrid advection-upstream-splitting method (AUSMV) while maintaining the same prediction accuracy. According to the “Big-O notation” analysis, the Robertson DAE approach shows a lower-order growth of computational complexity, proving its good potential in enhancing numerical efficiency, especially when handling simulations with larger scales. The validation of both the numerical schemes for the solution of the DFM was performed using measured data from a test well drilled with water-based mud (WBM). This study offers a novel numerical solution to the DFM that can significantly reduce the computational time required for gas-kick simulation while maintaining high prediction accuracy. This approach enables the application of high-fidelity two-phase-flow models in model-prediction-based decision making and automated influx management with MPD systems.

Description: Summary Advanced drill-collar connections have been developed with 10 times extended fatigue life compared with the corresponding replaced connections. More than 4,000 advanced connections have been run in North America. Although these connections have demonstrated substantial fatigue-strength improvement in operation, some failures have occurred. Multiple failed connection samples have been retrieved and analyzed for their failure modes and the root causes. In the failure analyses, manufacturing data were reviewed to identify any possible discrepancies between design specifications and manufactured components. The field run data were analyzed for the loading histories of the connections. The downhole fluid properties were also reviewed to identify their possible effects on the connection performances. The bottomhole assemblies (BHAs) were numerically analyzed to determine the loading distributions. The failed connection samples were physically processed and inspected in a metallurgical laboratory. Based on the combined numerical and testing analyses, the conclusions on the failure modes and the root causes were drawn. It was found that the primary failure mode for these connections was fatigue. The root causes for the fatigue failures can be divided into two categories: manufacturing causes and operational causes. Among the manufacturing failure causes, incorrect cold rolling is the primary one. The operation-related failures were mainly caused by overloading. Through failure mode and root-cause analyses, the manufacturing and operational related risks for the advanced drill-collar connections were mitigated accordingly. It therefore greatly improved the quality assurance of the advanced connections.

Description: Summary As part of plug and abandonment (P&A) operations, several acceptance criteria need to be considered by operators to qualify barrier elements. In casing annuli, highly bonded material is occasionally found far above the theoretical top of cement. This paper aims to describe how the highly bonded material can be identified using a combination of ultrasonic logging data, validated with measurements in laboratory experiments using reference cells and how this, in combination with data from the well construction records, can contribute to lowering the costly toll of P&A operations. Ultrasonic and sonic log data were acquired in several wells to assess the bond quality behind multiple casing sizes in an abandonment campaign. Data obtained from pulse-echo and flexural sensors were interactively analyzed with a crossplotting technique to distinguish gas, liquid, barite, cement, and formation in the annular space. Within the methodology used, historical data on each well were considered as an integral part of the analysis. During the original well construction, either water-based mud (WBM) or synthetic oil-based mud (OBM) was used for drilling and cementing operations, and some formation intervals consistently showed high bonding signatures under specific conditions, giving clear evidence of formation creep. Log data from multiple wells confirm that formation behavior is influenced by the type of mud used during well construction. The log data provided information of annulus material with a detailed map of the axial and azimuthal variations of the annulus contents. In some cases, log response showed a clear indication of formation creep, evidenced by a high bond quality around the production casing where cement cannot be present. Based on observations from multiple fields in the Norwegian continental shelf, a crossplot workflow has been designed to distinguish formation from cement as the potential barrier element. NORSOK Standard D-010 (2013) has initial verification acceptance criteria both for annulus cement and creeping formation as a well barrier element, both involving bond logs; however, in the case of creeping formation, it is more stringent stating that “two independent logging measurements/tools shall be applied.” This paper aims to demonstrate how this can be done with confidence using ultrasonic and sonic log data, validated against reference barrier cells (Govil et al. 2020). Logging responses like those gathered during full-scale experiments of reference barrier cells with known defects were observed in multiple wells in the field. Understanding the phenomenon of formation creep and its associated casing bond signature could have a massive impact on P&A operations. With a successful qualification of formation as an annulus barrier, significant cost and time savings can be achieved.

Description: Summary A potential application of optical fiber technologies in the well control domain is to detect the presence of gas and to unfold the gas dynamics inside marine risers (gas-in-riser). Detecting and monitoring gas-in-riser has become more relevant now when considering the application of managed pressure drilling operations in deep and ultradeep waters that may allow for a controlled amount of gas inside the riser. This application of distributed fiber-optic sensing (DFOS) is currently being evaluated at Louisiana State University (LSU) as part of a gas-in-riser research project granted by the National Academies of Sciences, the Gulf Research Program (GRP). Thus, the main objective of this paper is to present and discuss the use of DFOS and downhole pressure sensors to detect and track the gas position inside a full-scale test well during experimental runs conducted at LSU. The other objectives of this work are to show experimental findings of gas migration in the closed test well and to present the adequacy of a mathematical model experimentally validated to match the data obtained in the experimental trials. As a part of this research effort, an existing test well at the LSU Petroleum Engineering Research and Technology Transfer Laboratory (PERTT Lab) was recompleted and instrumented with fiber-optic sensors to continuously collect data along the wellbore and with four pressure and temperature downhole gauges to record those parameters at four discrete depths. A 2⅞-in. tubing string, with its lower end at a depth of 5,026 ft, and a chemical line to inject nitrogen at the bottom of the hole were also installed in the well. Seven experimental runs were performed in this full-scale apparatus using fresh water and nitrogen to calibrate the installed pieces of equipment, to train the crew of researchers to run the tests, to check experimental repeatability, and to obtain experimental results under very controlled conditions because water and nitrogen have well-defined and constant properties. In five runs, the injected gas was circulated out of the well, whereas in two others, the gas was left inside the closed test well to migrate without circulation. This paper presents and discusses the results of four selected runs. The experimental runs showed that fiber-optic information can be used to detect and track the gas position and consequently its velocity inside the marine riser. The fiber-optic data presented a very good agreement with those measured by the four downhole pressure gauges, particularly the gas velocity. The gas migration experiments produced very interesting results. With respect to the mathematical model based on the unsteady-state flow of a two-phase mixture, the simulated results produced a remarkable agreement with the fiber-optic, surface acquisition system and the downhole pressure sensors data gathered from the experimental runs.

Description: Summary The cleanliness of wellbore is a key factor in the drilling speed and quality of an oil field, especially in long horizontal sections of horizontal wells. Therefore, a hydraulic-magnetic rotary hole cleaning tool has been designed that does not rely on the rotary action of the drillpipe and could be used with a downhole motor to improve hole cleaning efficiency. However, the influence of magnet shape on the transmission of magnetic torque has remained unclear, such that the magnetic shaft transmission torque needed to be optimized to ensure efficient tool operation. In this study, magnetic field control equations were established in the region of the permanent magnet and air gap, and the magnetic flux distribution and magnetic torque generated between two magnetic axes in each field were calculated. Also, the influence of various magnetic field parameters on magnetic torque conduction of a strip magnet were compared and analyzed and then confirmed by comparison with experimental results. The results showed that the magnetic torque transmitted by strip magnets varied sinusoidally with magnetic axis deviation angles and that the highest torque was generated in the 12-pole model. However, the rate of increase in magnetic torque with magnet thickness was opposite to that of tile magnets, increasing with increasing magnet thickness. Magnetic torque variation with covered area was specific in the 6-pole model, showing a tendency of increasing and then decreasing. When magnet thickness was 12 mm and magnet coverage area in the effective cross section of the tool was 80%, the highest magnetic torque/unit volume of magnet was generated for achieving economic optimization. The results led to conclusions that, by solving the regional magnetic field, the magnetic torque change characteristics during movement of the magnetic drive mechanism of the hydraulic-magnetic rotary hole cleaning tool were simulated successfully and that these results could be used as an optimization analysis method for the magnetic drive mechanism of such tools.

Description: Summary In this paper we present a methodology to superimpose the American Petroleum Institute (API) uniaxial and triaxial limits on tubular design limits plots (API TR 5C3 2018). Complications caused by a recent change of axis are resolved, producing a practical design limits plot that avoids the horizontal shift of the API vertical limits, which is currently the industry standard. The commonly used slanted ellipse is compared against an adaptation of the circle of plasticity in the form of a horizontal ellipse, showing the convenience of this last one with examples. After the current official collapse formulation was made part of the main body of standard API TR 5C3 (2018), the horizontal axis on the standard industry well tubular design limits plot changed. The present study evaluates this redefinition of the horizontal axis. One consequence of this modification is a difficulty plotting the API tension and compression limits. The API horizontal limits (uniaxial burst and collapse) are found to be independent of load situation, whereas the API vertical design limits (uniaxial tension and compression) are dependent on inside and outside tubular pressures. The approaches used by commercial software and industry publications to solve this challenge are reviewed. A new design methodology is developed to link API uniaxial limits to the triaxial theory. One main objective of the study is to establish a mathematical relationship between API tubular design limits and the von Mises triaxial theory (API TR 5C3 2018). A methodology that allows plotting the API uniaxial force limits on the design limits plot is developed. The study also shows that the results obtained from the industry standard slanted ellipse are identical to those obtained from the horizontal ellipse and circle. One important difference is that the slanted ellipse is based on the zero axial stress datum, whereas the horizontal ellipse/circle uses the neutral axial stress datum. The horizontal ellipse/circle is well suited for calculations involving buckling, compatible with the information used in field operations, and its formulations are less complicated than the tilted ellipse. Therefore, attention is called to the use of the horizontal ellipse/circle in well tubular design.

Description: Summary Fly ash, which is a pozzolan generated as a byproduct from coal-powered plants, is the most used extender in the design of lightweight cement. However, the coal-powered plants are phasing out due to global-warming concerns. There is the need to investigate other materials as substitutes to fly ash. Bentonite is a natural pozzolanic material that is abundant in nature. This pozzolanic property is enhanced upon heat treatment; however, this material has never been explored in oil-well cementing in such form. This study compares the performance of 13-ppg heated (dehydroxylated) sodium bentonite and fly-ash cement systems. The raw (commercial) sodium bentonite was dehydroxylated at 1,526°F for 3 hours. Cement slurries were prepared at 13 ppg using the heated sodium bentonite as partial replacements of cement in concentrations of 10 to 50% by weight of blend. Various tests were done at a bottomhole static temperature of 120°F, bottomhole circulating temperature of 110°F, and pressure of 1,000 psi or atmospheric pressure. All the dehydroxylated sodium bentonite systems exhibited high stability, thickening times in the range of 3 to 5 hours, and a minimum 24-hour compressive strength of 600 psi. At a concentration of 40 and 50%, the 24-hour compressive strength was approximately 800 and 787 psi, respectively. This was higher than a 13-ppg fly-ash-based cement designed at 40% cement replacement (580 psi).

Description: Summary As wells in modern operations are getting longer and more complex, assessing the effect of casing wear becomes ever more crucial. Degradation of the tubulars through mechanical wear reduces the pressure capacity significantly. In this paper, we use the finite element method (FEM) to analyze the stress distribution in degraded geometries and to assess reduction in collapse strength. A model for the collapse strength of the casing with a crescent-shaped wear groove is developed and its performance evaluated in relation to experimental data. The model was created by using the Buckingham Pi theorem to make generalized empirical expressions for yield and elastic collapse of tubulars. Finite element analysis (FEA) of 135 geometries was used in the development of the model. The results show that the generalized expressions capture the trends observed in the FEA accurately and match the experimental data from six tubular collapse tests with an average relative difference in collapse pressure of 5.2%.

Description: Summary Hole cleaning is a concern in directional and horizontal well drilling operations where drill cuttings tend to settle in the lower annulus section. Laboratory-scale experiments were performed with different non-Newtonian fluids in a 6.16-m-long, 114.3- × 63.5-mm transparent annulus test section to investigate cuttings transport behavior. This experimental study focused on understanding the cuttings transport mechanism in the annulus section with high-speed imaging technology. The movement of cuttings in the inclined annular section was captured with a high-speed camera at 2,000 frames/sec. Also, cuttings bed movement patterns at different fluid velocities and inner pipe rotations were captured with a digital single-lens reflex video camera. The electrical resistance tomography (ERT) system was used to quantify the cuttings volume fraction in the annulus. Different solid bed heights and cuttings movements were observed based on fluid rheology, fluid velocity, and inner pipe rotation. The mechanistic three-layer cuttings transport model was visualized with the experimental procedure. This study showed that solid bed height is significantly reduced with an increase in the inner pipe rotation. This study also identified that cuttings bed thickness largely depends on fluid rheology and wellbore inclination. The image from the high-speed camera identified a downward trend of some rolling particles in the annulus caused by gravitational force at a low mud velocity. Visual observation from a high-speed camera identified a helical motion of solid particles when the drillpipe is in contact with solid particles and rotating at a higher rev/min. Different cuttings movement patterns such as: rolling, sliding, suspension, helical movement, and downward movement were identified from the visualization of a high-speedcamera.

Description: Summary Two of the most important parameters to monitor during a primary cementing job are the flow rate in and return flow rate measurements. To achieve optimum job results of a primary cementing job, measuring annular return rates and comparing them with simulated data in real time will provide a better understanding of job signatures and result in the best possible top of cement (TOC) estimation prior to running any cement evaluation log or making a decision to continue drilling the next section of the well. The return rate job signature along with the wellhead pressure is essential to understanding the behavior and discrepancies between simulated and acquired surface data. Therefore, to assess the risk of job issues, such as unsuspected washout and lost circulation among others, accurate measurements of the return rate are critical. Historically, the cement job evaluation has been limited by the fact that most drilling rigs do not have an accurate flowmeter installed on the annulus return line, and a simple verification of mud tanks volume vs. pumped volume, as reported by drillers or mud loggers, more often than not results in an unreliable assessment of the volume lost downhole, due to the unfamiliarity with the U-tubing effect and lack of data consolidation from the cement unit (flow rate in) and the rig (flow rate in and flow rate out). In this paper, we will review a solution developed to mitigate the lack of a direct flow-rate measurement by computing and displaying the return rate using either a paddle meter measurement or the derivative over time of the volume observed in the rig tanks.