Downhole Instrumentation Research Articles

Magnetic Design and Electromagnetic Field Simulation of Downhole Turbine Generator

With the increasing difficulty of oil and gas resources exploration and the increase of drilling operations in complex geological environments, the challenges faced by oil drilling operations are also increasing. With the continuous improvement of the intelligence of MWD/LWD drilling technology and downhole instruments, the demand for electric energy is also increasing. In order to ensure the normal operation of the equipment and the accurate acquisition of data, this paper designs a new type of external rotor downhole turbine generator, and designs the structure and parameters of the turbine generator. Finally, Ansoft Maxwell software is used to simulate and analyze the electromagnetic field of the generator. The results show that the induced electromotive force and load current waveform obtained by electromagnetic field simulation analysis have good sinusoidality. At the rated speed of 2500rpm, the effective value of the output line voltage of the turbine generator is about 49.1V, the effective value of the line current is about 10.99A, and the output power is about 841.17W, which meets the design requirements. The research has certain guiding significance for practical engineering.

Simulation study of drilling fluid cooling in long horizontal wells based on phase change heat absorption

ABSTRACT The shale gas resources found in deep formations are abundant and represent a crucial area for current and future shale gas development. However, as shale gas exploration and development intensify in China, an increasing number of high-temperature formations are being encountered during drilling, presenting significant challenges to drilling engineering and severely constraining the development of deep shale gas exploration. In this study, the stability of PCM (phase change material) combined with drilling fluid as a coolant was discussed, and the influence of PCM on wellbore temperature field in drilling fluid was considered. A calculation model of temperature field of drilling fluid containing PCM was established, the cooling characteristics of PCM under the influence of different parameters were simulated, and the cooling effect of PCM integrated with drilling fluid on ultra-deep and high-temperature Wells was analyzed. The investigated PCM has a phase change temperature range of 120 ~ 130°C and a latent heat of 264.15 ~ 265.53 kJ/kg. Our results showed that the cooling impact of PCM exhibits an upward trend as the quantity of PCM utilized increases. Assuming the drilling temperature limit is 135°C, after adding 5% PCM to the drilling fluid, the drilling length of the horizontal section increased by approximately 500 m. With 15% PCM added, the horizontal section could be extended by about 1000 m. We conducted a simulation analysis on a well in southern Sichuan, and found that adding 12% PCM had the best cooling effect, reducing the bottom hole temperature by 12.3°C and extending the horizontal section by 700 m. Compared with conventional drilling fluid cooling methods, incorporating PCM as cooling agents within the drilling fluids provided better cooling effects. It effectively addressed the problem of excessive bottom-hole temperatures in deep wells, extended the drilling length of horizontal sections, and prolonged the service life of downhole instruments. Our research lays the groundwork for the future investigation of cooling techniques for high-temperature deep well drilling fluids.

Thermal Management System of Vapor Compression for Downhole Instrument

Abstract As the depth of oil and gas exploration increases, downhole electronics face the threat of high-temperature failure. At present, passive cooling technology has the problem of short working time, while active cooling technology has low energy utilization. This paper presents a thermal management system of vapor compression with a combination of active and passive cooling. The system uses insulation materials to isolate the high-temperature environment, thermally conductive silicone grease to strengthen the heat exchange in the evaporator, and vapor compression refrigeration cycles to absorb internal heat. The coefficient of performance (COP), exergy destruction and exergy efficiency of octane, nonane, and cyclohexane as refrigerants were examined, and the effects of different insulation materials on refrigeration performance were studied from both theoretical and numerical perspectives. The results showed that cyclohexane exhibited the best cooling capacity with a COP of 1.296 and a exergy efficiency of 49.21%. The thermal management system cooling performance is optimal when the insulation material is a vacuum flask, with an effective cooling capacity of 121.7 W.

Development of autonomous downhole vibration measuring equipment

Background. Drilling vibrations may cause damage to the bit and early failure of downhole instruments. The main approach to solving this problem consists in measuring downhole vibrations while drilling by adding sensors near the bit in to the bottom hole assembly (BHA). When drilling vibrations are registered, measures are taken to avoid their reaching the critical values. If necessary the drilling stoops and the section is worked out to avoid accidents due to the high critical values. Not always drilling companies add such sensors to the BHA due to high price of the equipment. Constant problems with vibrations while drilling, require the creation of domestic low-cost autonomous equipment for measuring downhole vibrations and transmitting respective signals to the surface.Aim. To develop domestic low-cost autonomous downhole vibration measuring equipment.Materials and methods. Analysis of the experimental studies on drilling vibrations. Development technical solution such as domestic low-cost autonomous equipment for measuring downhole vibrations.Results. The problem of drilling vibrations can be controlled by downhole measuring equipment located in the vicinity of the bit. The device under development is presented in the article.Conclusion. In order to achieve maximum economic efficiency and avoid the costs of eliminating the consequences of vibrations, domestic low-cost autonomous downhole vibration measuring equipment should be developed to register torsional and longitudinal vibrations.

Numerical Simulation and Field Test Research on Vibration Reduction of PDC Cutting of Pebbled Sandstone under Composite Impact Load

Downhole vibrations caused by rock breaking when drilling through pebbled sandstone formations negatively affect the rate of penetration (ROP) and the safety of downhole tools. Therefore, it is of great significance to study the cutting characteristics of pebbled sandstone and find a method of reducing the drilling vibrations of pebbled sandstone formations. Based on the DEM (discrete element method), a simulation model of pebbled sandstone considering the random filling of high-strength gravels was established by using the random polygon distribution method. The influence of gravel content on the strength parameters and the breaking state of the pebbled sandstone samples was analyzed. Additionally, a DEM model of PDC cutting rocks loaded by a spring–mass system was established, and the Stribeck effect of contact friction between the PDC cutter and the rock was analyzed. The periodic vibration and the stick–slip phenomenon of the cutting system during the drilling process were presented by this model. The model was employed to simulate and explore the influence of composite impact load on stick–slip vibration during PDC cutting of pebbled sandstone. The simulation results showed that the composite impact load had a more obvious effect on mitigating the vibration of PDC cutting of pebbled sandstone under the condition of a higher horizontal impact amplitude coefficient (qh = 40%). Based on the simulation results, a composite impactor with a large impact angle α = 70° was selected to conduct the field tests in the pebbled sandstone formation of Well T1. The results showed that, compared to conventional drilling, the average WOB (weight on bit) of the section drilled with the composite impactor decreased by 57.13%, the standard deviation of the WOB decreased by 57.29%, and the average ROP increased by 98.31%. The employing of composite impactors in pebbled sandstone formations can significantly reduce drilling vibration, improve ROP, and protect bits and downhole instruments.

The Utilization of Ultrasound for Improving Oil Recovery and Formation Damage Remediation in Petroleum Reservoirs: Review of Most Recent Researches

The ultrasound method is a low-cost, environmentally safe technology that may be utilized in the petroleum industry to boost oil recovery from the underground reservoir via enhanced oil recovery or well stimulation campaigns. The method uses a downhole instrument to propagate waves into the formation, enhancing oil recovery and/or removing formation damage around the wellbore that has caused oil flow constraints. Ultrasonic technology has piqued the interest of the petroleum industry, and as a result, research efforts are ongoing to fill up the gaps in its application. This paper discusses the most recent research on the investigation of ultrasound’s applicability in underground petroleum reservoirs for improved oil recovery and formation damage remediation. New study areas and scopes were identified, and future investigations were proposed.

Transdisciplinary Application of Functional Materials in Petroleum Engineering

Currently, transdisciplinary integration has become increasingly close, and has gradually become the source of innovation. At the same time, petroleum engineering technologies demand more new technologies like functional materials and electronic information technologies. In order to effectively promote technological innovation and development of the petroleum engineering, it is important to continuously monitor, analyze and evaluate the latest development of the technologies outside of the oil and gas industry. This paper combines qualitative analysis of onsite demands, application cases, technical characteristics, and quantitative analysis of literature metrology, patent evaluation, technology maturity, to evaluate the application prospects of densified wood, liquid metal and poly (thioctic acid) in the field of petroleum engineering, and specific transdisciplinary suggestions are put forward. It is recommended to carry out pre-research work for the potential application of functional materials in the petroleum engineering, and it is expected to introduce new materials for downhole tools, new antennas for downhole instruments, extend long-term effectiveness of downhole plugging, and improve drilling efficiency.

Load torque analysis and compensation device design for low power drilling fluid continuous wave generator

As an advanced downhole instrument in drilling engineering, drilling fluid continuous wave generator (DFCWG) has great application prospects. The large load torque is one of the key problems that hinder the development of DFCWG. In this paper, based on the design theory of rotary valve and finite element method, the structure of rotary valve is designed and the load torque characteristics is analyzed and points out that the load torque has strong alternating characteristics. It is pointed out that the load torque has the characteristics of strong alternating. According to the characteristics of the load torque, the "fluid-magnetic" collaborative compensation method is proposed. The load compensation turbine and magnetic compensation device are used to compensate the DC and AC components of the load torque respectively, and the load compensation device is designed. The rationality of the design of the load compensation device is verified by simulation. Finally, the comprehensive compensation effect is analyzed by the finite element method. According to the analysis results, the "fluid-magnetic" collaborative compensation method can effectively reduce the load torque. The research results can provide technical support for DFCWG design.

Working mechanism and experimental study of electromagnetic measurement while drilling systems based on a relay station

ABSTRACTElectromagnetic measurement while drilling systems transmit downhole data via an information channel composed of a drill string and formation; the formation has a strong attenuation effect on the signal. Signal attenuation during electromagnetic wave transmission through the formation limits the well depth at which this technique can be applied. This paper discusses several commonly used methods to improve the depth at which electromagnetic measurement while drilling applications can be conducted, including turbine power supplies, adaptive power outputs and transmitting antenna extensions. Based on both theory and practice, the characteristics of these methods are analysed, and a relay station‐infused electromagnetic measurement while drilling system is proposed. The relay station‐infused electromagnetic measurement while drilling system consists of a downhole instrument assembly, a relay station and a ground receiver assembly. The repeater receives the electromagnetic wave signal from the underground transmitter and, after amplification, decoding and other processing, re‐encodes the signal and forwards it to the ground receiver at different frequencies, so as to increase the underground electromagnetic wave signal relay transmission. The design of the relay station module is introduced in detail, and the influencing factors and rules of signal transmission are analysed. Signal transmission experiments show that the electromagnetic measurement while drilling system based on a relay station can reliably represent the relay of signals and can thus be used in deeper wells.

Simulating a Controlled CO2 Release Experiment in a Shallow Fault Zone in Western Australia

Geological and dynamic modelling studies are routinely performed to design and interpret field test experiments. These studies help with the planning of well location, well operations and monitoring strategies, as well as with a range of different test activities. After the test, the new interpretations of the experiment observations are then integrated with previous knowledge and reconciled with the assumption that was first tested. Often, the results of a test are significantly different from what was anticipated (hence the purpose of testing). In this work, we examine such an example and put in perspective the impact of the first modelling study on the interpretation of the test. The CSIRO In-Situ Laboratory Project (In-Situ Lab) is located at the eastern edge of the South West Hub CCS Flagship project (SW Hub) in Western Australia, which has been identified as a potential area for commercial-scale CO2 storage. A first test at the In-situ Lab has evaluated the ability to monitor and detect unwanted leakage of CO2 from a storage complex in the shallow subsurface. The In-Situ Lab is also collocated within a major fault zone. Prior to a controlled-release test, a numerical simulation study was undertaken to inform the optimal location for a monitoring well, the vertical location of the downhole instrumentation, and to ensure breakthrough of CO2 occurred within the project timeframe. Based on the likely extent of the CO2 plume for an injection volume of 40 tonnes, the observation well ISL OB-1 was located at 7 m from the injection well to maximise the likelihood the CO2 plume would be intersected. The CO2 plume was predicted to migrate vertically for at least 20 m above the injection interval. Due to the resolution of the existing seismic and limited well data, large uncertainty existed regarding the detailed fault zone geometry, and, more specifically, how disaggregation and drag has impacted the contiguity and slope of lithostratigraphic layers within the fault zone. In other words, it was not clear to what extent the relatively low-permeability paleosols would form baffles for the migration of CO2. Also, it was not known whether sub-seismic faults, if present, would act as vertical barriers or conduits to CO2 migration. During a controlled-release test, 38 tonnes of gaseous CO2 were injected in February 2019, and the gas was monitored by a wide range of downhole and surface monitoring technologies. A higher than expected bottomhole pressure was observed. CO2 reached the ISL OB-1 monitoring well after approximately 1.5 days. Observations suggest that the fault zone did not alter the CO2 migration along bedding at the scale and depth of the controlled release experiment. No vertical CO2 migration was detected beyond the perforated injection interval. The injectivity was lower than predicted from core measurements and prior modelling. Also, contrary to prior model predictions, the plume did not migrate vertically across the paleosol overlying the injection interval. Post-injection reservoir simulations calibrated to the observed pressure and CO2 distribution data confirm that (1) a vertical segregation exists just above the injection interval, and (2) local overpressure are due to a combination of wellbore damage, mud invasion at the injection well and, to a lesser extent, reservoir compartmentalisation.

Research and application of logging technology for annulus fluid production profile in highly deviated wells

In view of the low success rate of logging in annulus fluid production profile in domestic oil fields, the relationship between instrument string and well deviation is carried out Requirements of downhole instruments for annular testing construction in highly deviated wells; The lifting and lowering technology of well entry instruments in highly deviated wells has been systematically studied. After field application, the logging technology has been updated and improved. By using large diameter cable, flexibly connecting and splitting instruments, reducing the outer diameter of instruments, configuring automatic direction finder, enhancing the umbrella collecting strength and other improvements in technology and construction methods, the problem of difficulty in measuring the logging data of liquid production profile in the annulus of highly inclined pumping wells is well solved, and the demand of dynamic monitoring of highly inclined wells in oil fields is met.

Design and Analysis of a While-Drilling Energy-Harvesting Device Based on Piezoelectric Effect

A while-drilling energy harvesting device is designed in this paper to recovery energy along with the longitudinal vibration of the drill pipes, aiming to serve as a continuous power supply for downhole instruments during the drilling procedure. Radial size of the energy harvesting device is determined through the drilling engineering field experience and geological survey reports. A piezoelectric coupling model based on the selected piezoelectric material was established via COMSOL Multiphysics numerical simulation. The forced vibration was analyzed to determine the piezoelectric patch length range and their best installation positions. Modal analysis and frequency response research indicate that the natural frequency of the piezoelectric cantilever beam increased monotonously with the increase of the piezoelectric patch’ thickness before reaching an inflection point. Moreover, the simulation results imply that the peak voltage of the harvested energy varied in a regional manner with the increase of the piezoelectric patches. When the thickness of the piezoelectric patches was 1.2–1.4 mm, the designed device gained the best energy harvest performance with a peak voltage of 15–40 V. Works in this paper provide theoretical support and design reference for the application of the piezoelectric material in the drilling field.

Field Measurements Validate Transient Annular Pressure Buildup Model

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 199561, “Validation of Transient Annular Pressure Buildup (APB) Model Predictions With Field Measurements in an Offshore Well and Characterization of Uncertainty Bounds,” by Rahul Pai, Anamika Gupta, and Udaya B. Sathuvalli, Blade Energy Partners, et al., prepared for the 2020 IADC/SPE International Drilling Conference and Exhibition, Galveston, Texas, 3-5 March. The paper has not been peer reviewed. The average geothermal gradient in the subject deepwater field in Nigeria is 4.37°C/100 m, nearly twice the gradient in most fields. As a result, the magnitude of the expected annular pressure buildup (APB) during steady-state production is large enough to threaten well integrity. Therefore, an insulating packer fluid (IPF) was used in Annulus A to reduce heat transfer to the outer annuli and to regulate the APB within acceptable values. The complete paper reports the results of a study that compares the temperature and pressure measurements from these wells with model predictions. Introduction Though APB has been studied by well designers for decades, the use of downhole measurements to study APB has been somewhat limited. Previous uses of downhole instrumentation to study APB phenomena principally have centered on monitoring the magnitude of the APB and managing the risk. None, as far as the authors are aware, use the results gathered from downhole measurements to verify the results of the models that routinely are used in the design of the wellbore tubulars and APB-mitigation technologies. Notwithstanding the wealth of literature on the subject of APB, several crucial and fundamental questions remain unanswered. Chief among these are: What is the accuracy of thermal-model temperature predictions during various well operations? How do temperature uncertainties influence APB predictions? When APB magnitudes are large enough to require installation of APB mitigation devices? How do the mitigation devices perform over the life of the well? The complete paper seeks to address these questions through an examination of downhole pressure and temperature measurements and a parallel analysis of model predictions. Furthermore, field data and model predictions are juxtaposed, sources of uncertainties in the measurement data and model inputs are considered, and overall uncertainties in the APB predictions (i.e., model estimates) are characterized.

Pagoda-Shaped Triboelectric Nanogenerator With High Reliability for Harvesting Vibration Energy and Measuring Vibration Frequency in Downhole

Drill string vibration is very critical to the drilling technology, which needs to be measured in real-time. This paper proposes a highly reliable pagoda-shaped triboelectric nanogenerator which can measure the downhole vibration frequency in self-powered model and harvest the downhole vibration energy to try to power other downhole instruments based on the Chinese pagoda. The designed pagoda-shaped triboelectric nanogenerator has seven layers, and charges are generated by floating contacts of two adjacent layers pasted with PMMA and Kapton, respectively. The sensing tests show that the measurement range is 0 to 5 Hz, the measurement error is less than 5%, and the minimum output signal amplitude difference is about 28 V while the maximum is about 155 V, which shows a higher signal-to-noise ratio. In addition, the pagoda-shaped triboelectric nanogenerator with seven layers can still work normally when the number of undamaged layers are two or more, which shows a higher reliability. The output power tests show that the maximum power is about 4090 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> W when all layers of the pagoda-shaped triboelectric nanogenerator are connected in series with a 470 k ohm resistance and the vibration frequency is about 3 Hz. Compared with the traditional downhole drill string measurement method, the multilayer structure of the pagoda-shaped triboelectric nanogenerator makes it has higher reliability, higher output power, and saves the radial dimension space, which are very suitable for actual drilling requirements of working conditions.

Incorporating electromagnetic measurements into drilling systems with a relay station

Electromagnetic measurement while drilling (EM-MWD) systems transmit downhole data by emitting electromagnetic waves into the formation, thereby carrying the emitted data to a surface antenna; however, these electromagnetic waves are attenuated when transmitted into the formation. To further extend depth capabilities, Extended-Range EM-MWD systems have been developed. Expanding on this approach, this paper introduces an EM-MWD system that incorporates a relay station within ultra-deep wells; our proposed system consists of a downhole instrument assembly, a relay station and a ground receiver assembly. After decoding a received signal, the relay station amplifies, filters and recodes the signal; then, the relay station emits the augmented signal. Through numerical simulations, as presented in this paper, propagation characteristics of electromagnetic waves in heterogeneous and stratified strata show that when the resistivity of the upper formation and the lower formation is kept constant, the voltage of the ground receiving signal first increases and then decreases with the increased resistivity of the interlayer. Similarly, when the resistivity of the upper stratum and interlayer is kept constant, the voltage of the ground receiving signal first increases and then decreases with the increased resistivity of the lower stratum. This paper also presents the design schemes, the technology used to process the insulation gap, and the power-saving technology to increase the lifetime of the downhole instruments. Furthermore, the working principle of the relay station is described. Moreover, by analysing the electric and magnetic excitation methods, under the same conditions, signal attenuation is fast and the signal strength obtained on the ground is low when magnetic excitation is used. Therefore, an electric excitation method is adopted for implementing the relay station. To conclude, suggestions as to reasonable locations of the relay station and reception and decoding of the ground signal are provided.

Technology Focus: Well Integrity (January 2020)

Technology Focus Fiber-optic technologies—distributed temperature sensing (DTS) and distributed acoustic sensing (DAS)—have been experiencing an increasing number of applications in the oil and gas industry as monitoring systems. In the area of well integrity, both technologies have been used in combination to monitor and evaluate qualitatively the cement placement and integrity in wells. An interesting technical article showing how these two technologies are used to monitor cement integrity in an actual well is selected as recommended additional reading. Ongoing research studies are also investigating casing deformation and downhole detection of hydro-carbon leakage. The use of these two technologies seems to have a very promising future when considering well-control situations. One potential application of DTS and DAS technologies is being evaluated now at Louisiana State University (LSU) as a part of a 3-year research project currently under way under the auspices of a grant by the Gulf Research Program to investigate the gas-in-riser issue. A 5,000-ft actual well at LSU was recompleted recently and instrumented with DTS and DAS for continuous monitoring information along the well and downhole gauges to record pressure and temperature at four different depths. These instruments were clamped to the outside of the production tubing installed inside the experimental well. A gas-injection line also was run into the well to displace nitrogen to simulate gas-in-riser situations. The data gathered by the downhole instruments are expected to shed light on well-control attributes such as gas velocity and distribution, two-phase-flow patterns, and gas breakout from solution in nonaqueous drilling fluid inside the marine riser. The viability of generating distributed pressure profiles from DTS and DAS data collected in the experiments also will be investigated. Undoubtedly, the research findings will help detect gas-in-riser situations earlier and monitor deepwater managed-pressure drilling operations that may allow for a controlled amount of gas inside the riser. Recommended additional reading at OnePetro: www.onepetro.org. SPE/IADC 194553 Evolving Well-Control Procedures With Managed-Pressure Drilling on Floaters by Andre Alonso Fernandes, Petrobras, et al. SPE/IADC 194145 Well-Control Incident in the North Sea as Interpreted With Advanced Gas-Influx Modeling by Jan Ole Skogestad, SINTEF, et al. SPE 195678 Real-Time Well-Integrity Monitoring Using Fiber-Optic Distributed Acoustic Sensing by T. Raab, GFZ German Research Centre for Geosciences, et al.

Modeling and Analysis of the Load Torque Acting on the Drilling Fluid Continuous Wave Generator

Drilling fluid continuous wave(DFCW) generator is an advanced downhole instrument and has broad application prospects. The load torque acting on the DFCW generator has a great impact on the performance on the DFCW generator, and there is a lack of theory describing the load torque because of the irregularity of the rotary valve. In this paper, the drilling fluid flow area is divided into the curve flow area, the radial flow area and the axial flow area. The flow area of each part is divided into several meshes based on finite element theory, then the load torque acting on each part is calculated based on the fluid momentum conservation theory. The theoretical model is verified by combining the simulation and the experiment, and the effects of the discharge and the axial gap on the load torque are analyzed. The research results show that:(1) the theoretical model can be used to determine the load torque, (2) the amplitude of the load torque reduces as the gap decreases and increases rapidly as the discharge increases. The results can provide the theoretical guidance for the structure design of the rotary valve and the control system design of the drilling fluid continuous wave generator.

The method of regular temperature labels in measuring phase flow rates in low-flow horizontal wells

This article presents the results of experimental studies of the applicability and range of consumption parameters of the heat tag method for solving practical problems in a horizontal well where an induction heater was used as a heat source. The research was carried out on the certified thermohydrodynamic stand of BSU and in the laboratory of thermometry. The results of the study showed that the method can be applied in a single-phase and two-phase stratified flow with an error of no more than 8%. It was found that the shape and type of the source of the artificial thermoanomaly does not affect the results of measuring local flow rates with an output of the total flow rate. The results of the work defined threshold flow rate (100 m3/day water or light oil for a column of diameter D = 4 ½ꞌꞌ) using an inductor of limited power (P ≈ 1 kW), as well as the requirements to configuration of downhole instruments, providing the possibility of estimating the interval of the phase costs in marginal horizontal wells. The motion front and the evolution of the heat mark along the length of the stand for a stratified horizontal (sub-horizontal) flow consisting of hydraulic oil and process water are demonstrated.

Analysis and modeling of thermoelectric power generation in oil wells: A potential power supply for downhole instruments using in-situ geothermal energy

With the increasing development of smart well technology in the oil and gas industry, there is a need for robust and reliable downhole power supply in order to provide stable power for downhole sensors and control tools. Usually, the produced fluid from the reservoir carries abundant thermal energy, which can be converted to electric power with thermoelectric technology. To realize in-situ power generation in the downhole environment, the design of downhole segmented concentric cylindrical thermoelectric generators (CCTEGs) with a cold fluid is proposed. A mathematical model for downhole thermoelectric generation is presented, which considers the heat transfer in the interior of thermoelectric element and from surrounding formation. The power performance in an oil well with 50% of water cut is investigated by using an engineering equation solver program. Numerical results show that about 800 W of power output could be obtained with 200 m length of segmented CCTEG, which is enough to provide power for typical downhole applications. The length of the segmented CCTEG and the injection rate of cold fluid dominantly affect the power output. The power consumption requirement for downhole applications in different operation periods could be met by simply adjust the injection rate of cold fluid.

Foundational Experiences and Recent Advances in Long-Term Deep-Ocean Borehole Observatories for Hydrologic, Geodetic, and Seismic Monitoring

AbstractFor nearly three decades, various phases of the scientific Ocean Drilling Programs have deployed sealed-hole observatories in deep-ocean boreholes for long-term subseafloor monitoring to address a range of hydrologic and geodynamic objectives. We summarize the scientific motivation for these observatories and review some important early results from those installed in young oceanic crust and subduction zones. We also summarize the evolution of the borehole observatory designs and associated instrumentation, from simple single-interval installations with autonomous low-rate temperature and pressure monitoring to recent multiple-zone installations with sophisticated downhole instrument packages connected to seafloor cabled networks that provide power and high-rate, real-time data access. We emphasize recent advances, illustrated with example data drawn mainly from transects of borehole observatories offshore Japan and Cascadia. These examples illustrate the value of borehole observatory data in resolving a wide range of crustal geodynamic responses from long periods of gradual geodetic change and accumulation of stress to episodes of rapid deformation associated with both seafloor spreading and subduction processes.