Borehole Fluid Research Articles

C/O Logging by Using the Associated Alpha Particle Method: Proof of Principle

The possibility of using a fast neutron beam with the associated alpha particle (AAP) technique in conjunction with a specially designed probe for carbon-to-oxygen (C/O) nuclear well logging was investigated. Measurements were performed to show the influence of borehole fluid, iron casing, and the cement around the casing in the C/O analysis. Tests were conducted by using fast neutron activation analysis (FNAA), as the conventional approach for C/O measurements in well logging and by using AAP. Analyzed samples were made from quartz sand and graphite powder mixed in different C/O ratios characteristic for the oil-containing formations. Diesel fuel was used as a simulant of the borehole fluid. Monte Carlo (MC) simulations were conducted and the results were compared with the experimental data. In both tests, the linear relation between the measured and real C/O ratios was obtained, but when the FNAA was used, the linear relation was significantly influenced mainly by the presence of the borehole fluid. Contrary to FNAA, the AAP technique resulted in a significant reduction of the background signal coming from the borehole fluid.

Study on the Influence of Borehole Heat Capacity on Deep Coaxial Borehole Heat Exchanger

Based on a semi-analytical model established previously for heat transfer in coaxial borehole heat exchangers, the influences of the heat capacities of different parts of the borehole (fluid, pipes and grout) on the performance of deep coaxial borehole heat exchanger (DCBHE) are analyzed. The results are as follows: the heat transfer performance of DCBHE will be underestimated if the heat capacities of different parts of the borehole are ignored; the influences of the heat capacities of different parts of the borehole on the performance of DCBHE are more obvious in the early stage, and gradually weaken with the increasing of time; among the heat capacities of different parts of the borehole, the influence of the fluid heat capacity on the performance of DCBHE is the greatest, and the influence of the pipe heat capacities is the least. Under the working condition studied in this paper, the results obtained with considering the heat capacities of different parts of the borehole are compared to ones ignoring heat capacities of selected elements. It was found that ignoring the fluid heat capacity led to a 0.29 °C lower estimated outlet fluid temperature after 60 h. Omitting the heat capacities of pipes and grout gave 0.03 °C and 0.13 °C lower outlet fluid temperatures after 60 h, respectively. The larger the borehole radius, the greater the influence of borehole heat capacity. The geothermal gradient has little effect on the influence of borehole heat capacity on the performance of DCBHE. The results show that the heat capacities of different parts of the borehole have important effects on the performance of DCBHE, especially in the early stage and for a large borehole radius.

Rhodothermus bifroesti sp. nov., a thermophilic bacterium isolated from the basaltic subsurface of the volcanic island Surtsey.

Novel thermophilic heterotrophic bacteria were isolated from the subsurface of the volcanic island Surtsey off the south coast of Iceland. The strains were isolated from tephra core and borehole fluid samples collected below 70 m depth. The Gram-negative bacteria were rod-shaped (0.3-0.4 µm wide, 1.5-7 µm long), aerobic, non-sporulating and non-motile. Optimal growth was observed at 70 °C, at pH 7-7.5 and with 1% NaCl. Phylogenetic analysis identified the strains as members of the genus Rhodothermus. The type strain, ISCAR-7401T, was genetically distinct from its closest relatives Rhodothermus marinus DSM 4252T and Rhodothermus profundi PRI 2902T based on 16S rRNA gene sequence similarity (95.81 and 96.01%, respectively), genomic average nucleotide identity (73.73 and 72.61%, respectively) and digital DNA-DNA hybridization (17.6 and 16.9%, respectively). The major fatty acids of ISCAR-7401T were iso-C17:0, anteiso-C15:0, anteiso-C17:0 and iso-C15:0 (>10 %). The major isoprenoid quinone was MK-7 while phosphatidylethanolamine, diphosphatidylglycerol, an unidentified aminophospholipid and a phospholipid were the predominant polar lipid components. Based on comparative chemotaxonomic, genomic and phylogenetic analyses, we propose that the isolated strain represents a novel species of the genus Rhodothermus with the name Rhodothermus bifroesti sp. nov. The type strain is ISCAR-7401T (=DSM 112103T=CIP 111906T).

Estimation method for layered ground thermal conductivity using genetic algorithm based on a 2-D heat transfer model

Estimation of ground thermal conductivity plays an important role in design of borehole heat exchanger (BHE) for ground source heat pump (GSHP) systems, and the ground is usually heterogeneous with layered thermal properties. Therefore, this study presented a novel estimation method for layered ground thermal conductivity by using distributed thermal response test (DTRT) and genetic algorithm. Firstly, a comprehensive new 2-D heat transfer model for coaxial BHE was built to simulate borehole fluid temperature profiles, it revealed that the distribution of ground thermal conductivity showed a significant influence on outlet temperature and temperature profiles. Then, based on the built model, the vertical distribution of ground thermal conductivity was estimated through DTRT data by using the genetic algorithm. It was found that the DTRT data at 2 h was effective to estimate the layered ground thermal conductivity by using the new 2-D heat transfer model. Furthermore, the estimated distribution of ground thermal conductivity was almost independent of numbers or thickness of sub-layer, and the largest difference in distributions of ground thermal conductivity among different layer thickness was less than 0.3 W/(m·K). Also, the estimation convergence showed independence with layer thickness, converged results could be obtained after 10 iterations for different layer conditions.

3-D Electromagnetic Modeling Explains Apparent-Velocity Increase in Crosshole GPR Data-Borehole Fluid Effect Correction Method Enables to Incorporating High-Angle Traveltime Data

For high-resolution crosshole ground-penetrating radar (GPR) tomography, a wide-range of ray path angles are required, including transmitter-receiver pairs with high-angles. However, artifacts have been observed in the inverted GPR tomograms when high-angle data were incorporated in ray-based inversion (RBI) tomography due to not well-understood increasing apparent velocities for increasing ray-angles. To reduce these artifacts, it is common practice to limit the angular aperture to a threshold between 30° and 50°, which reduces the spatial resolution. We apply 3-D finite-difference time-domain GPR modeling including borehole fluid and resistive loaded finite-length antenna (FLA) models to study the increase of apparent velocity with increasing ray path angle. This study shows that the strong refraction of the electromagnetic waves at the borehole interface between water and subsurface is one of the reasons for these not well-understood phenomena. We introduce a novel borehole-fluid effect correction (BFEC) that relocates the transmitter and receiver positions to the location, where the refraction is occurring to remove any influence of the borehole such that the remaining traveltimes can be inverted using an RBI. BFEC improves the estimated apparent-velocity (relative permittivity) values and enables the incorporation of wide-angle ray paths resulting in more accurate tomograms. We verify the BFEC with a simple layered subsurface model and a realistic synthetic model. By applying curved-ray RBI without and with the BFEC, the subsurface structures are reconstructed with more details for the BFEC data and the average relative error model reduced from 13% to below 8% for the high-resolution inhomogeneous model.

A method of monitoring gas saturation in carbon dioxide injection heavy oil reservoirs by pulsed neutron logging technology

A method is proposed to characterize the fast neutron scattering cross-section (σf) quantitatively by the combination of inelastic gamma rays and captured gamma rays, so as to realize the gas saturation evaluation of CO2-injected heavy oil reservoirs based on the three-detector pulsed neutron logging technology. Factors influencing of the evaluation effect of this method are analyzed and the effectiveness of this method is verified by a simulation example. By using the Monte Carlo simulation method and the physical model of bulk-volume rock, the relationship between σf and CO2 saturation is studied, and the saturation interpretation model is established. The influences of formation temperature and pressure, heavy oil density, borehole fluid and reservoir methane content on the evaluation results of CO2 saturation are analyzed. The results show that the characterization of σf by the combination of secondary gamma information can eliminate the influence of formation lithology, borehole fluid and methane content are the main factors affecting the quantitative monitoring of CO2 saturation, and the effects of formation temperature and pressure and heavy oil density are negligible. The simulation example verified the feasibility of the method for evaluating the CO2 saturation of CO2-injected heavy oil reservoirs.

Characteristics of the interface acoustoelectric conversion waveform in fluid-filled boreholes

When acoustic waves meet the side wall media in a fluid-filled borehole, the electromagnetic field at the borehole interface between the formation and borehole fluid called the interface acoustoelectric conversion wave signal is converted. The propagation of the refracted P wave, refracted S wave, Stoneley wave, and other borehole-mode waves in the fluid-filled borehole generates accompanying electromagnetic wave signals corresponding to various borehole-mode waves, called accompanying acoustoelectric conversion wave signals. In this study, we examined the interface acoustoelectric conversion wave. First, we numerically simulated the acoustoelectric wave fields in fluid-filled boreholes using a method of real axis integration and analyzed the effects of the borehole radius, porosity, and pore fluid salinity on the interface acoustoelectric conversion waves. The arrival time of the interface acoustoelectric conversion wave increased as the borehole radius increased, and the amplitude of the interface acoustoelectric conversion wave increased as the porosity increased and decreased as the pore fluid salinity increased. Using the self-developed acoustoelectric effect logging tool, we conducted an actual downhole test in a sand shale well in northern China and observed the interface and accompanying acoustoelectric conversion waves. The observations followed the acoustoelectric effect logging theory. Further, to characterize the interface acoustoelectric conversion wave, we calculated its arrival time using a method of long-short time window energy ratio and calculated its energy by taking the summation of squares of the waveform amplitude in a window, respectively. The arrival time approximated to the time in which the acoustic wave propagated from the radiating surface of the acoustic radiator to the side wall interface, and the energy was consistent with the energy ratio of the accompanying conversion Stoneley wave to the acoustic Stoneley wave. The energy curve of the interface acoustoelectric conversion wave and conventional logging curves were highly correlated. The interface acoustoelectric conversion wave in acoustoelectric logging signals can provide a new reference for evaluating the formation parameters associated with open-hole wells.

Spatial and Temporal Constraints on the Composition of Microbial Communities in Subsurface Boreholes of the Edgar Experimental Mine.

ABSTRACTThe deep biosphere hosts uniquely adapted microorganisms overcoming geochemical extremes at significant depths within the crust of the Earth. Attention is required to understand the near subsurface and its continuity with surface systems, where numerous novel microbial members with unique physiological modifications remain to be identified. This surface-subsurface relationship raises key questions about networking of surface hydrology, geochemistry affecting near-subsurface microbial composition, and resiliency of subsurface ecosystems. Here, we apply molecular and geochemical approaches to determine temporal microbial composition and environmental conditions of filtered borehole fluid from the Edgar Experimental Mine (∼150 m below the surface) in Idaho Springs, CO. Samples were collected over a 4-year collection period from expandable packers deployed to accumulate fluid in previously drilled boreholes located centimeters to meters apart, revealing temporal evolution of borehole microbiology. Meteoric groundwater feeding boreholes demonstrated variable recharge rates likely due to a complex and undefined fracture system within the host rock. 16S rRNA gene analysis determined that unique microbial communities occupy the four boreholes examined. Two boreholes yielded sequences revealing the presence of Desulfosporosinus, Candidatus Nitrotoga, and Chelatococcus associated with endemic subsurface communities. Two other boreholes presented sequences related to nonsubsurface-originating microbiota. High concentration of sulfate along with detected sulfur reducing and oxidizing microorganisms suggests that sulfur related metabolic strategies are prominent within these near-subsurface boreholes. Overall, results indicate that microbial community composition in the near-subsurface is highly dynamic at very fine spatial scales (<20 cm) within fluid-rock equilibrated boreholes, which additionally supports the role of a relationship for surface geochemical processes infiltrating and influencing subsurface environments.IMPORTANCE The Edgar Experimental Mine, Idaho Springs, CO, provides inexpensive and open access to borehole investigations for subsurface microbiology studies. Understanding how microbial processes in the near subsurface are connected to surface hydrological influences is lacking. Investigating microbial communities of subsurface mine boreholes provides evidence of how geochemical processes are linked to biogeochemical processes within each borehole and the geochemical connectedness and mobility of surface influences. This study details microbial community composition and fluid geochemistry over spatial and temporal scales from boreholes within the Edgar Mine. These findings are relevant to biogeochemistry of near-surface mines, caves, and other voids across planetary terrestrial systems. In addition, this work can lead to understanding how microbial communities relate to both fluid-rock equilibration, and geochemical influences may enhance our understanding of subsurface molecular biological tools that aid mining economic practices to reflect biological signals for lucrative veins in the near subsurface.

Magnitude and nucleation time of the 2017 Pohang Earthquake point to its predictable artificial triggering

A damaging Mw5.5 earthquake occurred at Pohang, South Korea, in 2017, after stimulating an enhanced geothermal system by borehole fluid injections. The earthquake was likely triggered by these operations. Current approaches for predicting maximum induced earthquake magnitude ({M}_{max }) consider the volume of the injected fluid as the main controlling factor. However, these approaches are unsuccessful in predicting earthquakes, such as the Pohang one. Here we analyse the case histories of induced earthquakes, and find that {M}_{max } scales with the logarithm of the elapsed time from the beginning of the fluid injection to the earthquake occurrence. This is also the case for the Pohang Earthquake. Its significant probability was predictable. These results validate an alternative to predicting {M}_{max }. It is to monitor the exceedance probability of an assumed {M}_{max } in real time by monitoring the seismogenic index, a quantity that characterizes the intensity of the fluid-induced seismicity per unit injected volume.

Basalt-Hosted Microbial Communities in the Subsurface of the Young Volcanic Island of Surtsey, Iceland.

The island of Surtsey was formed in 1963–1967 on the offshore Icelandic volcanic rift zone. It offers a unique opportunity to study the subsurface biosphere in newly formed oceanic crust and an associated hydrothermal-seawater system, whose maximum temperature is currently above 120°C at about 100m below surface. Here, we present new insights into the diversity, distribution, and abundance of microorganisms in the subsurface of the island, 50years after its creation. Samples, including basaltic tuff drill cores and associated fluids acquired at successive depths as well as surface fumes from fumaroles, were collected during expedition 5059 of the International Continental Scientific Drilling Program specifically designed to collect microbiological samples. Results of this microbial survey are investigated with 16S rRNA gene amplicon sequencing and scanning electron microscopy. To distinguish endemic microbial taxa of subsurface rocks from potential contaminants present in the drilling fluid, we use both methodological and computational strategies. Our 16S rRNA gene analysis results expose diverse and distinct microbial communities in the drill cores and the borehole fluid samples, which harbor thermophiles in high abundance. Whereas some taxonomic lineages detected across these habitats remain uncharacterized (e.g., Acetothermiia, Ammonifexales), our results highlight potential residents of the subsurface that could be identified at lower taxonomic rank such as Thermaerobacter, BRH-c8a (Desulfallas-Sporotomaculum), Thioalkalimicrobium, and Sulfurospirillum. Microscopy images reveal possible biotic structures attached to the basaltic substrate. Finally, microbial colonization of the newly formed basaltic crust and the metabolic potential are discussed on the basis of the data.

The mechanical responses in monopole acoustic LWD and their relation with the output voltage waveform

Abstract Acoustic logging while drilling (LWD), characterised by simultaneous drilling and logging, is widely used to obtain the elastic parameters of the formation around the borehole. Most published monopole acoustic LWD simulation waveforms are routinely presented as pressure. However, these pressure waveforms disagree with the voltage waveforms recorded in the experiments. Here, to find out the reason of the inconsistent of these two waveforms, both the piezoelectric effect of the transducer and the propagation of the acoustic wave are integrally calculated with the finite-element method, obtaining the voltage waveform as well as the mechanical waveforms. The quantitative comparisons between the mechanical waveforms and the voltage waveform show that the output voltage cannot represent the pressure signal, but a combination of multiple mechanical signals. Based on the piezoelectric equation and the structure of the piezoelectric transducer used in this paper, we formulate the output voltage in terms of the four mechanical quantities, i.e. the radial strain and axial stress of the transducer as well as the acoustic pressure and the radial displacement of the borehole fluid. Furthermore, the contributions of these four mechanical quantities to different wave groups are explored. Finally, the waveforms comparisons after drill collar grooving reveal that the displacement waveform before and after grooving should also be displayed when evaluating the grooving effect instead of only the pressure waveform as in previous studies.

Crack geometry of serpentinized peridotites inferred from onboard ultrasonic data from the Oman Drilling Project

To assess the geometry of cracks in highly altered peridotites, we analyzed the ultrasonic velocity of serpentinized dunites and harzburgites collected by the Oman Drilling Project (Holes BA1B, 3A, and 4A). First, we estimated the hydrated fraction from grain density to obtain the porosity-free matrix velocity, which indicated complete serpentinization at shallow depths and decreasing hydration at greater depths. We assume that the difference between the solid matrix and measured onboard ultrasonic velocity is attributed to cracks with a spheroidal shape in the samples. Application of the effective medium theory to onboard data, such as P-wave velocity and porosity, indicates that the average pore aspect ratio is mostly between 0.1 and 0.01, and crack density varies from 0.58 to 0.02. We found a positive relationship between aspect ratio and hydrated fraction, suggesting a change in crack shape related to dissolution–precipitation processes during hydration. The relatively high aspect ratio and hence high fluid flux at shallow depths are also consistent with the onboard resistivity data and present-day hydration processes inferred from the borehole fluid chemistry. The inversion of ultrasonic data provides a series of elastic moduli that can be used to make a rough approximation of Poisson's ratio from the onboard data, which is a key physical property for interpreting geophysical observations in the oceanic lithosphere.

Determining the composition of an object based on its hyperspectral image

The article presents results of the development and research of a hyperspectral imaging spectrometer for analyzing borehole fluids in real operating conditions in the spectral range from 0.35 microns to 2.1 microns. A mathematical model and an algorithm for identifying the borehole fluid by composition and percentage content based on the results of hyperspectral image analysis are developed.

Rock mechanics and wellbore stability of deep shale during drilling and completion processes

The seepage coupling effect between the borehole rock mass and borehole fluid and the effective stress field distribution around the wellbore are obviously different under different working conditions of drilling, fracturing and completion, which affect the stability of horizontal borehole of shale gas reservoir. The physical, chemical, and mechanical properties of the shale in Longmaxi formations in a block of China immersed with different working fluids were tested experimentally. Combined with the experimental data, a theoretical model was established to evaluate and analyze the wellbore stability of Longmaxi formations shale under different working conditions of drilling, fracturing and completion. The results show that the shale of the Longmaxi Formation is a typical hard and brittle shale, the bedrock is dense, with high mechanical strength and weak hydration and expansion ability. The immersion effect of different working fluids has little influence on the expansion and mechanical properties of shale bedrock. However, the mechanical strength of shale with relatively developed bedding fractures is low, and the immersion effect of different drilling fluid further weakens the mechanical strength, resulting in obvious anisotropy of mechanical strength of underground rock. The coupling effect of seepage between wellbore and formation has obvious influence on the dynamic distribution of borehole pore pressure and wellbore stability under different working conditions. The effective fluid column pressure at the bottom of the hole is the highest during the fracturing process, which leads to the increase of pore pressure near the wellbore, and then to the increase of collapse pressure around the borehole wall. The equivalent density of collapse pressure rises to the maximum of 1.93 g/cm3, and the wellbore stability is the worst in the fracturing process. The wellbore stability is secondary in the drilling process, and the wellbore stability is good when drilling along the direction of the maximum horizontal principal stress, and the equivalent density of collapse pressure is 1.69 g/cm3. During the completion process, the formation fluid flows into the wellbore, the pore pressure in the borehole is relieved, and the equivalent density of the collapse pressure is reduced to approximately 1.35 g/cm3, the wellbore stability is the best and open hole completion can be attempted in the horizontal well section. The results provide a certain theoretical reference for the selection of the drilling and completion schemes in shale formation.

Analysis of thermal response tests on boreholes with controlled inlet temperature versus controlled heat input rate

Thermal response tests (TRT) are performed on borehole heat exchangers to estimate design properties needed when the boreholes are coupled to heat pumps. In conventional TRTs the heat injection or extraction rate from an external heater or heat pump is controlled to be nearly constant. More recently some investigators have conducted TRTs while controlling the inlet fluid temperature to be nearly constant. This paper develops computationally efficient heat transfer models that match measured transient temperature curves throughout the entire duration for both types of tests. The models include variable heat rates, thermal storage of the borehole fluid and the different properties between the grout and ground. The models are combined with parameter estimation methods and applied to both types of data sets from the same borehole. An uncertainty analysis indicates the models estimate ground thermal conductivity and borehole thermal resistance with approximately the same uncertainty for both types of tests.

First order born scattering away from a fluid-filled borehole

In this paper we solve the forward scattering problem in the first order Born approximation as it applies to the multipole borehole acoustic measurement configuration. This configuration consists of a multipole source and an array of multipole receivers, both deployed on a mandrel (The tool), and where the latter is axially offset from the former by a certain distance. The tool is deployed in a fluid-filled borehole, penetrating the earth formations. Assuming an arbitrary elastodynamic scatterer away from the fluid-filled borehole, we derive explicit expressions for the far-field scattered wavefield in the borehole fluid. In principle, these expressions could be used as a fast forward operator in the development of a full waveform inversion technique. Subsequently, to further our understanding, we derive analytical expressions for the borehole fluid scattered pressure at ‘small’ source-receiver offsets, and where the scatterer is represented by a Heaviside step change in elastodynamic formation properties, having an arbitrary orientation relative to the borehole axis. Our expressions apply to tools having a multipole source and receiver of order n. Such a source/receiver consists of 2n sources/receivers, located on the circumference of the tool and azimuthally separated from one another by π/n radians. All sources may be fired with equal polarity or adjacent sources may be fired with alternate polarity. In the latter case we compare our analytical solution with 3-D finite difference simulations. We do this for the practically relevant dipole (n = 1) and quadrupole (n = 2) excitation, for the (specular) PP, SVSV and SHSH borehole acoustic scattered pressure contributions. We obtain excellent results as long as the elastodynamic contrast between scatterer and embedding is small (<30%).

Identifying Fracture-Filling Material in Oil-Based Mud with Dielectric Borehole Imaging

Natural fractures maintain a significant role in many hydrocarbon plays, in both conventional and unconventional reservoirs. In exploration and development scenarios, specific fracture properties, such as orientation and density, are important. However, more critical is their internal architecture: are the fractures open to fluid flow or filled with minerals? Borehole microresistivity imaging tools are widely used to determine these fracture characteristics. In wells drilled with water-based muds, open fractures are filled with conductive borehole fluid that enables distinguishing open, water-filled fractures from resistive, mineral-filled fractures and the surrounding rock. However, many wells today are drilled with oil-based muds. In this case, mineral-filled fractures and oil-based-mud-filled fractures are equally highly resistive and cannot be directly distinguished using resistivity images only. The latest-generation wireline oil-based-mud microresistivity imagers operate in the megahertz frequency range, radiating the electrical current capacitively through the nonconductive mud column and delivering photorealistic borehole images. Both electrical conductivity and dielectric permittivity components constitute the measured signal, from which button standoff, formation resistivity, and dielectric permittivity are inverted. Our example case shows highly resistive, high-angle fractures from the resistivity images with their orientation and density. The standoff image determines if the mud column penetrates the fracture plane, showing an apparently high standoff compared with the surrounding rock. If the standoff appears high in the fracture plane, the fracture is classified as open to fluid flow. However, are these fractures indeed fully dilated and open, or are they filled with different materials—are they partially mineralized with calcite and partially open, filled with mud? To further determine the fracture fill and susceptibility to fluid flow, a new workflow employs the material dependency of the relative dielectric permittivity. The relative permittivity is estimated as a function of resistivity and frequency pixel by pixel on the resistivity image. The estimate formula is based on several hundred laboratory measurements on core plugs with different fluid saturations and salinities. The resulting borehole image enables distinguishing materials in the volume of investigation, where low values correspond to mud-dominated oil in open fracture planes, medium values correspond to rock-forming minerals, and high values are attributed to shales and other clay-rich rocks. Fracture planes filled with patches of both low- and medium-permittivity values are classified as partially open.

Studies on a Piezoelectric Cylindrical Transducer for Borehole Dipole Acoustic Measurements

In this article, a novel design of a piezoelectric dipole transducer is proposed for formation acoustic velocity measurement in the vicinity of a borehole with a frequency range of 0.4–6 kHz. The transducer which actuates a cylindrical shell to generate a pure dipole mode wave by using multiple piezoelectric bender bars is analyzed theoretically and simulated numerically by using the finite element method (FEM). Moreover, the transducer is fabricated and tested to compare with the numerical simulation results, which shows that the test and simulation results are in good agreement. Finally, compared with numerical simulation results of the traditional dipole transducer, it is shown that the proposed dipole transducer has higher transmitting sensitivities than commonly used ones, especially in low frequency responses. This work lays a foundation for the new development of the transducer in borehole dipole acoustic shear wave measurements. Especially, in a slow formation where the shear wave velocity is lower than that of compressional wave in the borehole fluid, the transducer could be used for highly efficient shear wave velocity measurements.

Calculation of winding temperature of a submersible motor

The article is devoted to the issue of control and regulation of the high-quality operation of a submersible motor with a long overhaul period. There are some complications of operating the electric submersible pump. One of them is the thermal interaction of the borehole fluid and components and parts of the electric submersible pump that leads to failure and repair. It is necessary to conduct research in the field of physical and hydrodynamic calculations to determine the effect of heat exposure. The article reveals one of the approaches to solving the problem of thermal interaction between a well and the electric submersible pump. We describe calculations of the winding temperature of a submersible electric motor for specific conditions in a particular well, including different modes of fluid flow, different loads of the submersible motor, and different concentrations of oil in water. The development of the described technique will allow creating special software aimed at determining the areas with the highest temperature of the motor winding, taking into account various parameters that affect the heat transfer process.

Indirect determination of shear wave velocity in slow formations using full-wave sonic logging technique

Abstract This article presents a case study concerning a seismic characterization project. Full-wave sonic logging was used to characterize the shallow compressional wave and shear wave velocity profiles in the site. Anomalous values of the Poisson’s ratio derived from the velocity profiles suggested that the boreholes might have traversed slow formations (i.e. with shear wave velocity smaller than the borehole fluid compressional wave velocity or “mud-wave speed”) and that conventional processing of the sonic logs might have misinterpreted the direct arrivals of fluid acoustic waves as arrivals caused by shear wave propagation in the rock. Consequently, the shear wave velocity profiles provided by the contractor were considered to be unreliable by the project team. To address these problems, a non-conventional determination of the shear wave velocity was implemented, based on the relationship between the Poisson’s ratio of the rock formation and the shape of the first train of sonic waves which arrived to the receivers in the sonic probe. The relationship was determined based on several hundreds of finite element simulations of the acoustic wave propagation in boreholes with the same diameter as used in the perforations. The present article describes how this non-conventional approach was developed and implemented to obtain the shear wave velocity profiles from the raw sonic logs. The approach allows an extension of the range of applicability of full-wave sonic logging to determination of shear wave velocity profiles in formations with low compressional wave velocities. The method could be used to obtain shear wave velocity profiles where compressional wave velocity is as low as slightly larger than the mud-wave speed. A sample sonic log in Log ASCII Standard (LAS) format is provided as supplementary material to this paper via Mendeley Data, together with the FORTRAN source code used to process the log following the approach described in this study.