Downhole Tools Research Articles

Dynamic Analysis of a Downhole Regulator for Drilling in Interbedded Formations

Summary In this paper, we investigate the effect of a downhole passive regulator [anti-stall tool (AST)] on the dynamics of rotary drilling systems in interbedded formations. Drilling in interbedded formations can significantly affect the vibrational signature of these systems and the associated drilling performance. Hence, models to assess the impact of drilling in such formations are needed. Here, we construct a dynamic model of the drillstring system which incorporates the bit/rock interface laws for the transitional phase of bit motion between rock layers with distinct mechanical properties. In the model, the axial and torsional dynamics of the drillstring systems are coupled by these interface laws and cast in the form of discontinuous (state-dependent) delay differential equations. Next, we include the AST in the dynamic model to enable the assessment of the influence of this downhole tool on drilling performance, in particular in terms of rate-of-penetration (ROP) and drilling efficiency. Furthermore, we also investigate the mechanical specific energy (MSE) and steady-state power losses at the bit (due to frictional torque) for different operational conditions and rock layer thicknesses. The analysis reveals that an increased drilling efficiency and lower MSE are obtained by incorporating the downhole tool in the drillstring, resulting in a higher ROP and a lower frictional contact between the bit and rock in interbedded formations.

MEMS‐based 3‐C borehole gravimeter development

AbstractA micro‐electro‐mechanical‐based 3‐C borehole gravimeter has been developed in China for mineral and hydrocarbon exploration. The 3‐C borehole gravimeter is composed of a three‐axis gravity sensor chip based on a deep silicon etching technique, high‐precision capacitive displacement sensing and weak signal detection circuitry. The gravity‐sensing chip is a silicon‐based integrated spring‐mass block system. Silicon wafer is etched by the micro‐nanofabrication technique to form a high collimation groove. The size of the gravity‐detecting mass block in the sensitive element plays a decisive role in the thermal noise level of the instrument. Deep silicon processing technique can produce a thicker silicon mass block (500 μm), which can obtain a larger mass block in the same area compared with the traditional silicon surface processing technique (10–100 μm). The out diameter of the final tool is 50 mm with 10,000 mGal measurement range, 155°C temperature and 100 MPa pressure rating. Apart from the 3‐C micro‐electro‐mechanical gravity sensor, a 3‐C fluxgate magnetic sensor is also integrated into the downhole tool. This allows us to measure both 3‐C gravity field and 3‐C magnetic field downhole simultaneously and conduct joint inversion of both the downhole 3‐C gravity and 3‐C magnetic data during the data processing stage. The prototype tool was tested in a borehole up to 850 m depth, and the 3‐C gravity sensor inside the tool can measure the vibration of the environment during the stationary measurement downhole. The first test data set shows repeatability near 800 m depth, which verifies the adaptability of the micro‐electro‐mechanical‐based gravimeter to the down instrument environment.

Drilling Heat Maps for Active Temperature Management in Geothermal Wells

Summary Geothermal energy has gained much attention as a promising contributor to the energy transition for its ability to provide a reliable, environmentally friendly source of heat and baseload power. However, drilling high-temperature (HT) reservoirs presents significant technical and economic challenges, including thermally induced damage to bits and downhole (DH) tools, increasing drilling time and cost. This paper introduces drilling heat maps for proactive temperature management in geothermal wells during well planning and real-time drilling operations phases to avoid thermally induced drilling problems. This study uses a transient hydraulic model integrated with a thermal model to predict the bottomhole circulating temperature (BHCT) while drilling geothermal wells. The model is used to generate a large volume (1,000s) of case scenarios to explore the impact of various cooling and other heat management strategies on the BHCT in the Utah FORGE field, used here as an example, covering a wide range of drilling parameters. Results are captured, visualized, and analyzed in convenient heat maps, illustrating the advantages of using such heat maps in geothermal well construction and real-time operations. Model validation with FORGE 16A(78)-32 well data and a west Texas case scenario shows good agreement between the modeling results and experimental data, with a mean absolute percentage error (MAPE) of less than 4%. There is a clear logarithmic relationship between the drilling flow rate and BHCT at a constant mud inlet temperature and a linear relationship between the mud inlet temperature and BHCT at a constant drilling flow rate. Pronounced variation of BHCT in geothermal wells is observed with mud type, mud weight, and mud viscosity. In addition, insulated drillpipe (IDP) technology is found to significantly reduce BHCT (14–44% on average for FORGE scenarios) compared to conventional drillpipe (CDP), particularly in wells with extended measured depth (MD) where other heat management technologies and strategies become less effective. Drilling heat maps can alert drilling engineers to strategies with the highest BHCT-lowering impact, allowing focused technology selection and decision-making regarding optimal temperature management during the geothermal well design phase. In addition, real-time heat maps are valuable for facilitating active temperature management and providing real-time guidance for optimal drilling parameters during daily drilling operations. In general, heat maps can help to avoid drilling problems related to the combination of HT and temperature limitations of DH equipment, which will benefit the safe and cost-efficient development of geothermal resources.

Wireless Monitoring of Downhole Pressure Based on Tubing Transmission

Downhole pressure is an important parameter for evaluating the production status of production wells. A wireless monitoring system was designed for downhole pressure which consists of two parts, i.e., the downhole tool and the wellhead tool. The tubing was used as the information transmission medium between the two parts. The downhole tool includes four pressure sensors, and the measured results will be applied to the tubing in the form of an alternating voltage with a frequency of 2.5 Hz. The amplitude of the alternating voltage output by the downhole tool is related to the magnitude of the downhole pressure. The wellhead tool measures and decodes the signal uploaded through the tubing, and the decoded result will be transmitted to the host computer through the ground cable. The wireless transmission model of downhole pressure in the production well was equivalent to a resistance network. Simulation analysis indicates that the amplitude of the signal received by the wellhead tool is negatively correlated with the downhole depth of the downhole tool and positively correlated with the formation resistivity. The designed wireless monitoring system for downhole pressure was tested in gas-producing wells in southwestern China. The test results verified the stability and reliability of the system for downhole pressure monitoring. It also confirmed that the strength of the received signal at the wellhead is negatively correlated with the downhole depth of the downhole tool for the first time and is not affected by the structure of the wellbore. The wireless monitoring scheme of downhole pressure introduced in this paper can be extended and applied to the monitoring of other downhole parameters such as temperature.

Deep Learning Methods for Improving Electromagnetic Telemetry Signal-to-Noise Ratio

Summary Electromagnetic (EM) telemetry is a cost-competitive method for communication between downhole tools and oilfield surface equipment. However, EM telemetry use is limited to wellsite deployments that result in favorable signal-to-noise ratio (SNR) levels. Increasingly, the EM attenuation brought by deeper wells, conductive service fluids, and conductive formation layers has made it more important to increase EM telemetry SNR. This study explored the ability of various deep learning (DL) methods to improve EM telemetry SNR with data sets composed of mixed synthetic downhole signals and real field noise. The DL models explored were previously proven to achieve state-of-the-art performance with seismic random noise attenuation and speech separation use cases. Furthermore, architectural adjustments that improved model performance with EM telemetry data were targeted. Then, the SNR improvement performance of different design changes was evaluated. Finally, the study targeted improvements that reduced the requirements for deployment hardware, including number of stakes, without sacrificing SNR improvement performance. Optimized models were found to successfully improve SNR in EM telemetry data, outperforming traditional bandpass filter methods and enabling the demodulation of mixtures that were otherwise too noisy to be demodulated.

Derivation of rock's geomechanical parameters while drilling by combining surface drilling data, gamma ray data, and machine learning techniques in carbonate formations

This work presents a field application of an effective and reliable methodology for geomechanical parameters evaluation, using surface logging drilling data (rate of penetration, torque, weight on bit, stand pipe pressure, rotation per minute, flow rates) and well log data (sonic log, bulk density log, gamma ray log) to feed a model characterised by the combination of different machine learning algorithms (multiple linear regression, support vector regression, random forest, artificial neural network, and XGBoost). To expand the range of application to those cases where the downhole tools are not technically feasible or economically viable, a flexible workflow has been developed to derive a Synthetic Gamma Ray (SGR) from X-ray Fluorescence (XRF) analysis performed on cuttings. The methodology, applied to a dataset of 11 wells drilled in the same geological units but in different fields in Kuwait, proves its successful use to derive several geomechanical parameters, among which the results associated with Young’s Modulus, density, and Poisson’s Ratios are here presented.

Reduced Friction and Excellent Anti-Wear Performance of QBe2 Beryllium Bronze against 38CrMoAlA Steel in Pneumatic Downhole Motor under Grease Lubrication

To improve the service life of the newly designed pneumatic downhole motor, a kind of commercially available lithium complex grease was used to help avoid the rapid wear-induced failure of the dynamic seal of pneumatic downhole tools in operation. The investigation on the tribological behaviors of QBe2 beryllium bronze and 38CrMoAlA steel tribo-pairs in pneumatic downhole motor revealed that under lubrication, the instantaneous friction coefficient and wear volume became very low, showing greatly reduced friction and excellent anti-wear performance. Compared with the case without lubrication, the adhesive wear mechanism and ploughing effect of the tribo-pairs were significantly alleviated. Moreover, Cu and Fe were oxidized to form composite oxides between the frictional surface, further improving the lubrication effect between the QBe2 beryllium bronze and 38CrMoAlA steel. Notably, the test could be operated stably for more than 150 h under lubrication, fully reaching the requirement of pneumatic downhole tools under actual drilling conditions. These results provide a solid support for the practical application of the reported pneumatic downhole tools.

Machine Learning Application in Enhancing Drilling Performance

Drilling Oil and Gas wells is an expensive operation, where the cost for drilling a single shallow offshore HP-UHT well may exceed 30 million USD easily. Due to the huge cost involved, companies are eager to accomplish the drilling operations in a minimal time frame, by increasing the drilling rate or rate of penetration (ROP) and reducing the downhole tool failures. The Mechanical Specific Energy (MSE) concept addresses these two drilling performance measures in totality as it provides maximum ROP which can be achieved with the existing drilling system (i.e., Drill Bits, Drilling Tubular, Well Profile, and Mud weight) without causing downhole tool failures. ROP is a function of Weight on Bit, Rotation per Minute, and Flow rate for an existing drilling system, optimization of these parameters results in increased ROP, whereas unharmonious values lead to shock and vibration in drilling assembly. Machine Learning algorithms facilitate this optimization of drilling parameters for enhancing drilling performance, by the development of an accurate ROP prediction and optimization model. The ROP prediction model was developed using Artificial Neural Network and Random Forest, and the optimization model was developed using evolutionary optimization algorithms like particle swarm optimization and genetic algorithms. The result of the optimization model depends upon the accuracy of the ROP prediction model and the upper and lower limits of drilling parameters defined in the optimization model. Machine learning applications in improving the Drilling Performance can be easily quantified in terms of saving days, where one day of operational cost for the company is approximately 0.2 million USD per Offshore – HP-UHT well.

HYDRO-MECHANICAL DRILLING OF WELLS

The solution to the problems of the construction of deep wells is possible when creating downhole tools on a fundamentally new ideological basis, involving physical principles, technical solutions unconventional in the field of drilling equipment. It is important to take into account the energy resources that increase with depth. Following this concept, based on the tasks of geological exploration, a downhole layout has been developed and introduced into the production of drilling wells, with design features and technological capabilities focused on a comprehensive solution to the problems of well wiring. Structurally, the downhole layout aimed at maximizing the potential energy of the working fluid is universal, designed for drilling wells with core sampling of increased diameter (100 mm or more), and with a solid face. In addition to the outer pipe and core receiver, the downhole layout is equipped with diamond drill heads with a stepped matrix, with a separate system of flushing channels, collectively realizing the effect of hydro-mechanical destruction of rocks. By introducing into the composition of the bottom-hole layout, converting the ascending flow into a rotational-ascending one, the problem of removing sludge from under the end of the stepped matrix is effectively solved. Production tests of the downhole layout with core sampling were carried out at the polymetals deposit of Central Kazakhstan, solid face during drilling of groundwater wells in the territory of the Almaty region. According to the results of production tests, it was found that the hydro-mechanical destruction of rocks is especially effective in combination with diamond drill heads with a stepped matrix. The presence of a turbulator-expander in the bottom-hole layout made it possible to significantly increase the amount of incoming sludge of drilled rock in the well sump, especially when drilling wells with a solid face. In comparable geological and technical conditions of drilling wells, serial core sets HQ with a drilling diameter of 95.6 mm had the following indicators: energy consumption – 2.1-2.4 kW / hour, core yield with a diameter of 63 mm – 93%, specific lumpiness of the core – 5-8 pcs / per linear meter of drilling, drilling was carried out at an axial load of 2200-2500 kgf, rotation speed 500-700 rpm. Similar indicators of the downhole layout: energy consumption – 1.2-1.5 kW / hour, core yield – 98-100% with a diameter of 112 mm, specific lumpiness – 2-3 pieces, axial load – 700-900 kgf, rotation speed – 300-400 rpm.

How to Choose the Suitable Steel of Wellhead, Wellbore, and Downhole Tools for Acid Gas Reinjection Flooding

The material selection of injection gas wells in acid gas flooding is the bottleneck of the successful implementation of the technical scheme. Through standard and literature research, the materials of the wellhead, wellbore, and packer for reinjection well in acid gas flooding are preliminarily established, and then the suitable materials are further screened by using the weight-loss and surface characterization method. Finally, a new type of packer is designed to optimize the wellbore material. The results show that 35CrMo (CR = 0.0589 mm/y) steel is used for wellhead materials, 625 alloy steel is selected as the sealing surface, and 625 or 825 alloys (with CR ≤ 0.0055 mm/y) steel is used for wellhead sealing material. The main material of the packer is 718 Alloy (with CR ≤ 0.0021 mm/y). The cost of T95 steel within 20 years (1263 ten thousand yuan) of service is much smaller than that of G3 alloy (1771 ten thousand yuan), but after 30 years of service, its cost is close to that of G3 alloy. A kind of downhole packer for acid gas reinjection is designed. Among them, G3 alloy steel tubing is used between the packer and the relief valve, T95 steel tubing is selected above the packer and below the safety valve, and the packer is set in the G3 steel tubing. The serious pitting corrosion of T95 steel in the liquid phase environment is due to the uneven deposition of FeS and FeCO3 on the steel surface.

Technology Focus: Bits and Bottomhole Assemblies (December 2022)

Drilling-efficiency improvements must guarantee consistent reductions in project cost. The industry continues to pursue this critical requirement through different approaches—rate of penetration (ROP) maximization or cycle-time improvement. Recent advancements in technology, drilling processes, and applications characterization have begun to crystallize the differences and implications of the two methods. Most importantly, these efforts also identify crucial requirements and considerations that must be resolved as the move toward drilling analytics and automation gathers momentum. Considerations and factors that influence project costs must be identified and analyzed from an operational perspective, instead of the usual mechanical evaluations that focus just on ROP. Recent advancements in technology development, field performance trends, and applications characterizations have established the effects and contributions of numerous other factors such as vibrations control, durability, borehole quality, directional challenges, downhole tool life, footage drilled, borehole verticality, and ROP on operational costs. The different factors have peculiar relationships with, and effects on, project costs and must not be analyzed in isolation. Consequently, solutions needed to address risks, failures, opportunities, and associated implications of these factors must be developed holistically. Actionable lookbacks and relational benchmarking that focuses on the “why” and “how” of events rather than the “what” are critical requirements of this process. This systematic and holistic approach promotes cycle-time improvement, with measurable positive effects on operational costs. The methodology ensures that problems are addressed at their source, while certifying relevance and functional compatibility of all drilling-system components. Drilling analytics and automation must improve performance, with clear objectives to further drive down operational costs. To achieve these goals, critical pillars that focus on the holistic-solution approach and fast learning principles must be built. This strategy will promote process efficiency, explainable results, performance consistency, and fast adaptability by project teams. The industry’s commitment to improve drilling efficiency and reduce operational costs is in full gear, yielding positive results, because of the new alignment and focus on cycle-time improvement. Holistic methodologies and solutions needed for this endeavor pose several questions that must be answered because clearer and complete pictures must be drawn for all challenges. Recommended additional reading at OnePetro: www.onepetro.org. SPE 204129 When Slick Is Not Smooth: Bottomhole Assembly Selection and Its Effect on Wellbore Quality by Marc Willerth, Helmerich and Payne, et al. SPE 207423 Novel Motor Adjusts Bend Setting Downhole, Addressing Today’s Directional Drilling Challenges by Rohan D’Souza, NOV, et al. SPE 208541 Optimizing Bottomhole Assembly Design Criteria To Improve Mechanical Performance in Slimhole Drilling Environment by Stephen Fleming, Halliburton, et al.

A New Integrated Downhole Tool for Primary Logging in the Open Hole of Wells in Infiltration-Type Uranium Deposits

A New Integrated Downhole Tool for Primary Logging in the Open Hole of Wells in Infiltration-Type Uranium Deposits

Effect of Fault Slip on the Casing Passability of Horizontal Shale Oil and Gas Wells

Summary Fault slip, a secondary effect of the hydrofracture to extract shale oil and gas, deforms the casing locally and affects downhole tools going through it, hindering the exploitation plan. The casing passability is introduced to evaluate the casing passability for the downhole tool. A simulation model of the fault slip was established to analyze the effect of fault type, slip distance, and fault dip on the casing passability. Meanwhile, the simulation method adopted in this paper was verified by the large-scale physical experiments of the perforated casing subjected to uniform outer pressure. Based on the experimental results and the geometry of fault slip, an empirical formula is proposed for the relationship between casing passability and fault slip. The result shows that the sensitivity of casing passability affected by fault type is ranked from highest to lowest by strike-slip fault, normal fault, and reverse fault. This study provides a reference for determining the available diameter of downhole tools quickly and reduces the cost of exploring wells when downhole tools are obstructed.

Downhole heat management for drilling shallow and ultra-deep high enthalpy geothermal wells

Heat management while drilling high-enthalpy geothermal wells is crucial for successful drilling and commercial energy extraction from hot reservoirs (150+ °C). Accurate modeling of heat transfer between drilling fluids and rock is vital to predict the transient bottom hole circulating temperature (BHCT). This allows downhole tools and drill bits to operate within their temperature limits, thereby preventing premature failure while drilling from high-temperature exposure.In this study into the most effective ways to pro-actively manage downhole temperatures, a validated coupled thermal/hydraulic model is used to simulate the transient behavior of BHCT and the mud temperature profile inside the drill string and the annulus of geothermal wells. The developed model investigates the effectiveness of different heat management techniques for relatively shallow (< 3 km, 10,000 ft TVD) as well as deep (> 6.1 km, 20,000 ft TVD) high enthalpy geothermal wells. Simulation results show that higher drilling flow rates, use of mud coolers/chillers, use of certain fluid types and viscosities, as well as increased hole size can all be used as strategies to reduce the BHCT of shallow geothermal wells effectively. However, the situation changes for deep geothermal wells and/or wells with long geothermal reservoir exposure, with reduced effectiveness of e.g., mud cooling and other generally accepted cooling measures. For such wells, however, the use of an insulated drill pipe (IDP) in combination with drilling flow rate can be used effectively for heat management.As part of the results, correlation maps are presented to provide drilling engineers with a user-friendly tool to quickly gain an understanding of the impact of various downhole cooling strategies for drilling geothermal wells, which in turn can be used to technically and economically justify their selection in the well design and drilling programs.

Technology Focus: Hydraulic Fracturing Modeling (November 2022)

Hydraulic fracture stimulation is proven to be the economic way to develop tight unconventional reservoirs. From an operational perspective, hydraulic stimulation is well established and widely applied to most unconventional plays. There is still room for improvement, however, to increase the efficiency and deepen the understanding of the detailed mechanism in the process. Particularly in the domain of fracture simulation, significant effort has been devoted to enhance model complexity and accuracy. Recent simulation studies have covered sophisticated mechanisms such as hydraulic fractures—natural fracture interaction, proppant transportation and settlement, casing friction, new government equations of fracture propagation, and fracture roughness. Fully coupled fracture modeling work flows with stress variation, solid transportation, and fluid flow become the mainstream, while model complexity and budget tradeoff remains challenging. Interestingly, fracture modeling has been applied beyond hydrocarbon production. New applications include cutting injection, coal-seam-gas production, and recently evolving enhanced geothermal systems (EGS). Both industrial and academic researchers have made progress on EGS by introducing another dimension of complexity in that thermal effects alter hydraulic fracture modeling behavior. With the advancement of powerful measurement techniques in the past decade, the industry has seen novel ways to calibrate fracture models. Other than microseismicity and pumping-schedule history matching, data collected from downhole tools such as distributed temperature and acoustic sensing and fiber-optic sensors have broader applications and show promising results. By leveraging computational power and machine-learning approaches, scaled-up modeling on the field level energizes the study of well interference, the depletion effect, and frac-hit-damage mechanisms. Recommended additional reading at OnePetro: www.onepetro.org SPE 205896 - Offshore Cuttings Reinjection Well-Performance Diagnostics and Fractured Domain Mapping Using Injection Data Analytics and Hydraulic Fracturing Simulation, Verified Through 4D Seismic and Wireline Logging by Franz Marketz, Sakhalin Energy Investment Company, et al. URTeC 2021-5414 - Modeling of Distributed Strain Sensing and Distributed Acoustic Sensing Incorporating Hydraulic and Natural Fractures Interaction by Kildare George Ramos Gurjao, Texas A&amp;M University, et al. URTeC 2021-5526 - Efficient Modeling of Enhanced Geothermal System With 3D Complex Hydraulic and Natural Fractures by Hongbing Xie, Sim Tech, et al.

Corrosion Inhibition Investigation of Small Organic Inhibitor on API5LX60 Steel in 3.5% NaCl Solution with CO2 Saturation

CO2 corrosion has emanated as a significant concern in the oil/gas industry owing to the aging of its oilfields. Thus, corrosion protection is significant for maintaining the integrity and sustainability of pipelines, surface facilities, and downhole tools in the oil/gas sector. The present study evaluates the corrosion inhibitory properties of three oxazolone derivatives in CO2 saturated 3.5 weight% NaCl solution against API5LX60 carbon steel used in certain wells and oil/ gas transportation pipelines. The inhibitory behavior was investigated utilizing gravimetric and electrochemical techniques viz. EIS, PDP, and LPR. Electrochemical and Gravimetric technique results were in congruence. EIS asserts capacitive behavior, and PDP affirms oxazolones as mixed inhibitors. SEM and SEM-EDX confirmed the formation of a protective layer by adsorption. At an optimum inhibitor concentration of 200 ppm, inhibitor I exhibited 91.30% inhibition—linear correlation coefficient R2 value of 0.99 avowed adsorptions via Langmuir Isotherm.

Downhole tools

Downhole tools

Thermal management systems for electronics using in deep downhole environment: A review

During the exploration of underground energy such as oil and gas and the application of geothermal energy, more deep drilling wells are developed. To meet the increasingly multifunctional demand of downhole equipment, many high-temperature sensitive electronics should be integrated and operate under deep downhole environment at the temperature over 200 °C. In this regard, the application of cost-effective thermal management strategies for the electronics is critical to ensuring the stable and reliable operation of downhole tools. This paper presents a review on applicable thermal management systems (TMSs) of electronics operating under deep downhole environment. Firstly, the structural characteristics, thermal performance and applicable restrictions of active and passive thermal management strategies used for downhole devices are detailly discussed. The merits and demerits of various TMS are also summarized. Meanwhile, due to the high heat flux transferred from the external environment, reviews on the thermal insulation shielding are also emphasized. As a result, the thermal management methods are divided into two categories based on the heat sources and heat dissipation terminals. Meanwhile, future developments of various thermal management approaches are discussed, aiming to serve as a reference guide for engineers and promote the progress of the next-generation equipment TMS in downhole environment.

Downhole tools

Downhole tools

Drill string dynamics and experimental study of constant torque and stick-slip reduction drilling tool

Aiming at the problems of large torque fluctuation of drill bit and low weight-on-bit(WOB) transmission efficiency during the drilling process, a novel drilling tool generating constant torque and reducing stick-slip is proposed. For investigating the further dynamics behavior of drill string system, the mathematic models are established based on the new tool output characteristics. Also, compared with field test and application, the drilling tool effects on increasing ROP (rate of penetration) and reducing drill bit wear are verified. The research results show that the peak value of drill bit angular velocity increases gradually with the bigger value of the pre-compression of disk spring system, so as the rotary table inputting speed, during drill bit downward movement. About the drill string influence, the larger the length of drill string, the longer response time is the rotating angular velocity of drill bit. Another one, the shorter the steady time of drill bit angular velocity, the bigger ratio is the stick-slip within one period. This new drilling tool can effectively improve the drill bit force conditions, and reduce the stick-slip stage, which can also profitably increase drilling efficiency and the service life of downhole tools, especially in ultra-deep or long distance horizontal wells.