Hole Section Research Articles

First Hydraulic Stimulation in Fractured Geothermal Reservoir in Pohang PX-2 Well

The first hydraulic stimulation for enhanced geothermal system (EGS) development in Korea had been conducted in the PX-2 well of 4,348 m depth in Pohang EGS site from January 29th to February 20th, 2016. Treatment histories of injection rate, wellhead pressure and corresponding induced microseismicity data were obtained from the stimulation test upon 140 m long open hole section at the well bottom. Wellhead pressure was up to 89MPa and considerable level of flow rate was attempted up to 47 L/sec. Microseismicity observation showed a trend of lager and more frequent seismicity occurrence in shut-in phase than in injection phase. The injectivity index during the stimulation periods had increased as 2.7 times in January 30th at the wellhead pressure of 73MPa. Postulating the existence of a major fracture zone intersecting the open hole section, the transmissivity and the corresponding equivalent aperture of the fracture were evaluated. Required breakdown pressures by hydrofracturing and hydroshearing mechanisms were estimated based on the various scenarios on the in-situ stress condition, major fracture zone orientation and shear failure criteria.

A new anti-slough drilling fluid study and application

Currently the BIOCAT drilling fluid system adopted in oil field results in wellbore collapsing frequently, borehole enlargement rate over 100%. In order to settle these problems, the Impermeable anti-collapsing inhibitive Polymer Drilling Fluids System is developed by optimizing the inhibitors with high anti-collapsing inhibitive instead of BIOCAT inhibitor, adding impermeable agent SMT3, sealing materials such as graphite, calcium carbonate, etc. Laboratory experiments results show that the developed drilling fluid system has stronger inhibitive and anti-collapse capacity. The swelling increment decreases by over 10% and recovery rate increases by 60%-70%, also, it can efficiently prolong the borehole wall stable period by over 100%. 24 wells applications with the Impermeable anti-collapsing inhibitive Polymer Drilling Fluids System achieved good results, comparing to adjacent wells with BIOCAT drilling fluid system, wellbore collapsing decreasing significantly and borehole diameter enlargement of unstable hole section in wells decreased from 100% to 10%, well drilling time decreased by 15%, drilling cost decreased by 10%. It shows that the developed Impermeable anti-collapsing inhibitive Polymer Drilling Fluids System KPAM-NH4PAN can provide strong and long-term inhibition, close to oil-based drilling fluid. so it is suggested that it be used in subsequent drilling operations to enhance the wellbore stability in an oilfield.

Clay minerals in sediments of the hydrothermally active southern trough in the Guaymas Basin (Gulf of California)

The results of the study of clay mineral alterations in Upper Pleistocene sediments of the southern trough in the Guaymas Basin (Gulf of California) due to the influence of hydrothermal solutions and heat produced by sill intrusions are discussed. Core samples from DSDP Holes 477 and 477A were taken for the analysis of clay minerals. Application of the method of modeling X-ray diffraction patterns of oriented specimens of the finely dispersed particles made it possible to establish the phase composition of clay minerals, determine their structural parameters, and obtain reliable quantitative estimates of their contents in natural mixtures. The modeling data allowed us to characterize reliably the transformation of clay minerals in sediments of the hydrothermally active southern trough in the Guaymas Basin. In Upper Pleistocene sandy–clayey sediments of the southern trough, changes in the composition of clay minerals occurred under the influence of a long-living hydrothermal system. Its lower part (interval 170.0–257.5 m) with maximum temperatures (~300°C) was marked by the formation of chlorite. Terrigenous clay minerals are not preserved here. Saponite appears at a depth of 248 m in the chlorite formation zone. Higher in the sedimentary section, the interval 146–170 m is also barren of terrigenous clay minerals. Sediments of this interval yielded two newly formed clay minerals (chlorite and illite), which were formed at lower temperatures (above 180°C and below 300°C, approximately up to ~250°C), while the relatively low-temperature upper part (110–146 m) of the hydrothermal system (from ~140°C to ~180°C) includes the mixture of terrigenous and newly formed clay minerals. Terrigenous illite is preserved here. Illitization of the mixed-layer illite–smectite was subjected to illitization. The terrigenous montmorillonite disappeared, and chlorite–smectite with 5–10% of smectite layers were formed. In the upper interval (down to approximately 110 mbsf), the composition of terrigenous clay minerals remains unchanged. They are composed of the predominant mixed-layer illite–smectite and montmorillonite, the subordinate illite, mixed-layer chlorite–smectite with 5% of smectite layers, mixed-layer kaolinite–smectite with 30% of smectite layers, and kaolinite. This composition of clay minerals changed under the influence of sill intrusions into the sedimentary cover at 58–105 m in the section of Hole 477. The most significant changes are noted in the 8-m-thick member above the sill at 50–58 m. The upper part of this interval is barren of the terrigenous mixed-layer illite–smectite, which is replaced by the newly formed trioctahedral smectite (saponite). At the same time, the terrigenous dioctahedral smectite (montmorillonite) is preserved. The composition of terrigenous clay minerals remains unchanged at the top of the unit underlying the sill base.

Donor and double-donor transitions of the carbon vacancy related EH6∕7 deep level in 4H-SiC

Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH6∕7 deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH6 and 1.48 eV and 1.66 eV for EH7. The electron emission peaks of EH7 completely overlap while the emission peaks of EH6 occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σp0(T) in p-type samples reveal a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σn(T) and σp(T) differ strongly due to the donor like nature of the deep levels and while all σn(T) have a negative temperature dependence, the σp(T) appear to be temperature independent. Average values at the DLTS measurement temperature (∼600 K) are σn2+(T) ≈ 1 × 10−14 cm2, σn+(T) ≈ 1 × 10−14 cm2, and σp0(T) ≈ 9 × 10−18 cm2 for EH6 and σn2+(T) ≈ 2 × 10−14 cm2, σn+(T) ≈ 2 × 10−14 cm2, σp0(T) ≈ 1 × 10−20 cm2 for EH7. Since EH7 has already been identified as a donor transition of the carbon vacancy, we propose that the EH6∕7 center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites.

A Theory of Alternative Methods for Measurements of Absorption Cross Section and Antenna Radiation Efficiency Using Nested and Contiguous Reverberation Chambers

Average ACS can be measured in a reverberation chamber; however, the existing technique determines a value that includes the effects of the radiation efficiencies of the antennas used in the measurement. Correcting for these necessitates further complex measurements. Here, we present the theory of an alternative measurement methodology using two nested or contiguous reverberation chambers which is free from errors caused by the radiation efficiencies of the antennas. The new method is based on the theoretical average transmission cross sections (TCS) of circular holes in a metal plate between the two chambers. In fact, the method can be viewed as an accurate transfer calibration measurement between TCS and ACS that is independent of both the chamber and antenna characteristics. Further, since the existing method of measuring ACS includes the effects of the radiation efficiencies of the antennas, a comparison of the ACS of a reference object, measured using both the existing and new methods, also provides an alternative method of determining radiation antenna efficiency. Measurement uncertainties for both alternative measurement methods—ACS and antenna radiation efficiency—are also derived.

Technology Focus: Wellbore Tubulars (June 2016)

Technology Focus Today’s economic situation within our industry has been harsh, harder than any downturn I have witnessed during my 44 years in the industry. However, it has provided the environment to influence positively the forging, application, field trialing, and acceptance of innovative technologies within our industry. Recent oil-industry technical publications are filled with a wide variety of applications of models, tools, and techniques being developed and applied to the drilling, completion, intervention, and even wellbore-abandonment arenas, allowing us to be more efficient by driving costly nonproductive time out of our operations. While the development of innovative technologies is critical, their correct and cost-effective application is even more important. No matter how good, technically impressive, or even innovative a technology is, if its application is not operationally practical as well as cost-efficient, then in the end it is just a cute widget. The papers within this Wellbore Tubulars section focus on delivering efficiencies to us, converting nonproductive time into new dollars for the bottom line. These papers span the application of A 1000-m steerable drilling liner directionally drilled in through an unstable shale in the åsgard/ Midgard field in the Norwegian North Sea after multiple attempts to drill and case this same hole section failed. A subsea completion string that would provide efficient hydraulics during fracturing operations while ensuring mechanical and pressure integrity. This high-pressure/high-temperature system was developed to be the answer to extreme completion challenges within multiple deepwater Gulf of Mexico projects within the Jack and St. Malo field reservoirs. A drilling software that delivers operational surveillance in real time, assisting in the avoidance of stuck pipe and with application within a variety of drilling environments. The proposed software was tested with historical data sets from 36 stuck-pipe incidents in the Eagle Ford, Utica, Permian, and Gulf of Mexico. The paper contains discussion of case histories in several shale horizontal unconventional wells. The extended-reading references selected further explore various applications and evaluation techniques spanning tubular-application areas from completion intervention to casing remediation to drilling-challenge mitigation. These include case-history references to assist readers in expanding the applications knowledge within their wellbore-tubulars toolbox. We all strive to deliver quality well construction, production, intervention, and abandonment to our industry. During the evaluation of the writings to be included within these few short pages encapsulating the extensive base of information published that surrounds the application of wellbore tubulars, I was struck by the quality and diversity of information available. Therefore, the reader is encouraged to search further within the industry’s technical-paper and article archives in the OnePetro online library (www. onepetro.org) to explore additional aspects of wellbore tubulars and the tools and techniques that are currently available to responsibly apply and critique their applicability. JPT Recommended additional reading at OnePetro: www.onepetro.org. SPE 175878 Steerable Drilling Liner Matches the Industry’s Common Theme Regarding Cost-Optimization Approaches and Minimizing Geomechanics-Related Challenges—Technology Overview, Applications, and Limitations by Wael El Sherbeny, Baker Hughes, et al. SPE 168271 Tubing-Retrievable Surface- Controlled Subsurface-Safety-Valve Floating-Flapper Remediation by B. Gary, Halliburton, et al. SPE/IADC 178780 Solid-Expandable Solution To Qualify Existing Nonsour- Service Production Casing by Jesus D. Contreras, ConocoPhillips, et al.

New Rotary Shouldered Connection Expands Capability of ERD Operation

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE/IADC 168049, “New Rotary Shouldered Connection Expands the Capability of World-Record ERD Operation,” by S.R. Sanford, SPE, and M.W. Walker, SPE, ExxonMobil; and J.N. Brock, M.J. Jellison, SPE, and A. Muradov, SPE, NOV Grant Prideco, prepared for the 2014 SPE/IADC Drilling Conference and Exhibition, Fort Worth, Texas, USA, 4–6 March. The paper has not been peer reviewed. Eight of the world’s 10 longest wells have been drilled by ExxonMobil as operator of the Sakhalin-1 project in Russia. Components and drilling tools involved in the well design are evaluated and redesigned throughout the program to maximize penetration rate and reduce flat time. Drillstring-torque capacity was recognized as a limiter for increasing penetration rate and for reaching total measured depth capability. The operator consequently sought an alternative drillpipe connection with higher torque capacity. Introduction The Sakhalin-1 project comprises the Chayvo, Odoptu, and Arkutun Dagi fields off the east coast of Sakhalin Island, Russian Federation (Fig. 1). Development drilling at the Chayvo field started in 2003 with extended-reach wells drilled from an onshore location with the Yastreb drilling rig. In 2005, further development drilling commenced from the offshore Orlan platform site. Subsequently, in 2008, the Yastreb rig was moved approximately 75 km north to the Odoptu onshore wellsite and drilled nine extended-reach-drilling (ERD) wells as part of the initial-stage development of Odoptu. During the Odoptu campaign, it was determined that a higher-torque 5?-in. drillpipe connection with good runnability was needed. Following the Odoptu campaign, the Yastreb rig was moved back to the Chayvo onshore wellsite in 2011 for further development and infill drilling of the Chayvo reservoirs. Limiter Identification During the first drilling campaign at Chayvo, available topdrive torque limited drilling performance in the long production hole section (>3000 m). Installation of a new topdrive capable of continuous torque in excess of 90,000 lbf-ft at 140 rev/min eliminated this limiter. During the subsequent Odoptu drilling campaign, the 5?-in. drillpipe connection was identified as a new limiter affecting rate of penetration (ROP) and torque operating margin in the production hole section.

Managed-Pressure-Drilling Technology Delivers Challenging HP/HT Drilling Campaign

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 175479, “MPD Technology Used To Deliver Challenging HP/HT Drilling Campaign,” by Robert Graham, Martin Geddes, Tim Harris, Dominic Flaherty, Nigel Shuttleworth, Bruce McEwan, Noor Nordin, Michael Cadd, John O’Grady, and Pete French, Shell, and Richard Sandell and Stuart Jeffries, Blade Energy Partners, prepared for the 2015 SPE Offshore Europe Conference and Exhibition, Aberdeen, 8–11 September. The paper has not been peer reviewed. The Shearwater field is a deep, high-pressure/high-temperature (HP/HT) reservoir located in the UK Central Graben of the North Sea. A high level of reservoir depletion (greater than 8,000 psi) has resulted in significant changes to the drilling envelope that has added complexity to the drilling practices required to exploit the remaining reserves successfully. Managed-pressure-drilling (MPD) technology was implemented in conjunction with drill-in liner and wellbore-strengthening technologies to successfully deliver the first well in a redevelopment campaign and prove the techniques required to prolong field life. Shearwater Overview Shearwater is an HP/HT gas/condensate field discovered in 1988. Primary production is from the Fulmar, a sandstone reservoir with virgin pressure of 15,400 psi and temperatures greater than 360°F. The field came on stream in 2001. The large field-pressure depletion resulted in compaction at the Fulmar formation level and led to mechanical failure of the production liners because of shear deformation. A drilling campaign to restore Fulmar production was initiated in 2013. The primary plan was to abandon the existing reservoir sections of the wells and perform shallow sidetracks from the 20-in. casing. A 16-in. hole was planned to the top of the Tor formation (above the pressure ramp), and a 12¼-in. hole was to be drilled into the top of the Cromer Knoll formation. 10×10¾-in. casing would be set across this hole section, and an 8½-in.-hole section would be drilled to just above the top of the Kimmeridge shale formation. A 7?-in. drill-in-liner system would then be used in conjunction with MPD and wellbore- strengthening material to drill into the top of the Fulmar reservoir. The reservoir was planned to be drilled with a 6½-in. hole size opened out to 7½ in., and the reservoir would be completed with a 7×5-in. production liner. The MPD objectives by hole section are discussed in detail in the complete paper. MPD was planned as an enabling technology because of the tight fracture-pressure/ pore-pressure wellbore- stability window. Fig. 1 illustrates the planned wellbore configuration and the expected pressure profiles.

Spherical polytropic balls cannot mimic black holes

The so-called black hole shadow is a dark region which is expected to appear in a fine image of optical observation of black holes. It is essentially an absorption cross section of black hole, and the boundary of shadow is determined by unstable circular orbits of photons (UCOP). If there exists a compact object possessing UCOP but no black hole horizon, it can provide us with the same shadow image with black holes, and a detection of shadow image cannot be a direct evidence of black hole existence. Then, this paper examine whether or not such compact objects can exist under some suitable conditions. We investigate thoroughly the static spherical polytropic ball of perfect fluid with single polytrope index, and then investigate a representative example of the piecewise polytropic ball. Our result is that the spherical polytropic ball which we have investigated cannot possess UCOP, if the sound speed at center is subluminal (slower-than-light). This means that, if the polytrope treated in this paper is a good model of stellar matter in compact objects, the detection of shadow image is regarded as a good evidence of black hole existence. As a by-product, we have found the upper bound of the mass-to-radius radio (M/R) of polytropic ball with single index, M/R < 0.281, under the subluminal-sound-speed condition.

RONIN Is an Essential Transcriptional Regulator of Genes Required for Mitochondrial Function in the Developing Retina.

A fundamental principle governing organ size and function is the fine balance between cell proliferation and cell differentiation. Here, we identify RONIN (THAP11) as a key transcriptional regulator of retinal progenitor cell (RPC) proliferation. RPC-specific loss of Ronin results in a phenotype strikingly similar to that resulting from the G1- to S-phase arrest and photoreceptor degeneration observed in the Cyclin D1 null mutants. However, we determined that, rather than regulating canonical cell-cycle genes, RONIN regulates a cohort of mitochondrial genes including components of the electron transport chain (ETC), which have been recently implicated as direct regulators of the cell cycle. Coincidentally, with premature cell-cycle exit, Ronin mutants exhibited deficient ETC activity, reduced ATP levels, and increased oxidative stress that we ascribe to specific loss of subunits within complexes I, III, and IV. These data implicate RONIN as a positive regulator of mitochondrial gene expression that coordinates mitochondrial activity and cell-cycle progression.

APPLICATION OF COMBINED DIE-CASTING PROCESS IN THE MANUFACTURE OF ALUMINUM WIRE FOR WAVEGUIDE SOLDERING

The study covers technical and technological features of a scheme for wire production from casting aluminum alloys designed for waveguide soldering using combined continuous non-ferrous metal die-casting. Dependencies were found that necessary and sufficient for the design of equipment structural elements and process modes ensuring conditions for a stable process of continuous molten metal feeding into the pass of the laboratory plant rotary crystallizer, metal solidification and extrusion into a die hole, the same as per Conform process. The cross section of a batcher hole for feeding molten metal into the crystallizer wheel pass was calculated. Conditions for ∅3 mm workpiece manufacturing at a laboratory continuous die-casting plant were described, with its subsequent processing to finite size by section rolling and drawing combined with intermediate annealing. A pilot batch of round and square wire made of AK12C10 and AK12C15 alloys in the amount of 3 kg was manufactured under this scheme and transferred to JSC «ISS» named after Academician M.F. Reshetnev for industrial tests in waveguide soldering.

Initiation and propagation of fracture shearing during hydraulic stimulation in enhanced geothermal system

This paper develops a generic model to estimate the location of shearing onset, the required pressure, and the overall shearing growth direction during the hydraulic stimulation in Enhanced Geothermal System, for which massive volume of fluid is injected into the fractured rockmass through a long open hole section. General studies on the effects of the stress condition on the shearing initiation and propagation captured some basic features related to the observed induced seismicity. Upward growth of shearing prevails for most stress conditions and a dense fluid favors downward shearing. Performed case studies demonstrate the developed method is potentially applicable to provide first order assessment of shearing initiation and propagation during hydraulic stimulation in a fractured EGS reservoir.

Microseismic reflection imaging and its application to the Basel geothermal reservoir

We have developed a new approach for reflection seismic imaging using microseismic waveform data. We took the specific character of microseismic downhole data into account and were able to image regions in the direct vicinity or inside of a seismically active zone. We used a directional migration method that reduced imaging artifacts caused by the low aperture of the data, but required estimation of the wavefield polarization. We also used hodogram analysis to identify parts of data that provided reliable polarization estimates. Only these parts were then used for imaging, whereas the rest of the data are excluded. The approach was successfully applied to microseismic waveforms recorded during and after the stimulation of the enhanced geothermal system in Basel, Switzerland. This data set included more than 2000 events recorded at five sparsely distributed borehole sensors. The reflection images revealed a distinct network of reflectors in the vicinity of the open hole section within the injection well. The results were compared with the injection borehole ultrasonic image revealing a quite good agreement. Combined analysis of imaged reflectors, event locations, and event focal mechanisms indicated that the approach resolved mostly aseismic highly permeable fluid pathways, whereas most of the seismicity occurred in the second-order fractures.

Numerical investigation of steady suction control of flow around a circular cylinder

This paper numerically investigates the effectiveness of the control of steady suction on a stationary circular cylinder with several isolated suction holes on the surface at a subcritical Reynolds number. The control effectiveness as a function of the azimuthal position, spanwise spacing and suction flow rate of the suction holes on the control of the aerodynamic forces on the cylinder and the suppression of alternate vortex shedding are taken into account. The study of the azimuthal location of the suction holes indicates that azimuthal angles of θ=90° and 270°, which are close to the separation point, provide the most substantial decreases in the aerodynamic forces. When restricted to the most effective azimuthal angle, a remarkable control effectiveness can be achieved when the axial spacing between two neighboring suction holes is less than a minimum value even under a small suction momentum coefficient. However, if the axial spacing exceeds the minimum spacing, the control effectiveness will not be saturated even under a very large suction momentum coefficient. Thus, the cause of the effective aerodynamic force control is suggested to be a result of obvious three-dimensional phenomenon in the near wake, which is characterized by the generation of a convergent flow between two neighboring suction hole sections and a stronger, larger three-dimensional vortex pair adjacent to the convergent flow. It has been suggested that this strongly three-dimensional flow pattern is induced by the strong interaction between two neighboring but counter-rotating three-dimensional vortices separately produced by two neighboring suction holes. Moreover, the effects of such three-dimensional flow patterns are investigated in detail based on variations in the flow field and sectional aerodynamic forces in different cross sections. Finally, the upper limit of the axial spacing between two neighboring suction holes to form such a three-dimensional flow pattern is suggested to be between 0.75D and 1.5D when the suction flow rate exceeds a certain value.

Friction Coefficient Prediction Method for Extended-Reach Well Based on Grey Prediction

Torque and drag prediction is very crucial in the design and drilling of extended-reach well, which has relation to the success or failure of drilling, while the torque and drag prediction result is greatly affected by the value of friction coefficient. Firstly, using the modified 3D soft-string calculation model, the friction coefficient of upper wellbore section was obtained. Then referring the related mathematical methods of system theory, on the basis of the friction coefficient of upper hole section, the friction coefficient prediction model for impending drilling well segment was established based on grey prediction, the prediction results show the error of friction coefficient and hook load is less than 10%. The method could satisfy the engineering requirement, which provides a theoretical guidance for real-time supervision on torque and drag in the drilling of extended-reach well.

Performance Evaluation of Lightweight Oilwell Cements

Drilling through depleted zones and weak formation can prove troublesome since the fracture resistance reduces from its normal boundary [1]. To successfully drill a hole section requires the selection of a low density cement slurry to prevent loss circulation while not exceeding the fracture resistance of the formations exposed. Large number of loss circulation will greatly impact the drilling cost and rig time. This research is focusing on the performance studies of lightweight oilwell cements using foam and cenosphere as the lightweight agents. All tests were conducted according to API Recommended Practice 10B-2. Three performance tests have been conducted such as density test, free water test and compressive strength test. The comparison was made at different percentage of lightweight agents e.g. 10, 20, 30 and 40 percent by weight of cement (%BWOC) respectively. The findings show the performances of formulated foam cement and cenosphere cement are within API limit. However, foam cement can reduce the density of set cement in about 8% greater than the cenosphere cement.

Evidence for an iron-hydrogen complex in p-type silicon

Interactions of hydrogen with iron have been studied in Fe contaminated p-type Czochralski silicon using capacitance-voltage profiling and deep level transient spectroscopy (DLTS). Hydrogen has been introduced into the samples from a silicon nitride layer grown by plasma enhanced chemical vapor deposition. After annealing of the Schottky diodes on Si:Fe + H samples under reverse bias in the temperature range of 90–120 °C, a trap has been observed in the DLTS spectra which we have assigned to a Fe-H complex. The trap is only observed when a high concentration of hydrogen is present in the near surface region. The trap concentration is higher in samples with a higher concentration of single interstitial Fe atoms. The defect has a deep donor level at Ev + 0.31 eV. Direct measurements of capture cross section of holes have shown that the capture cross section is not temperature dependent and its value is 5.2 × 10−17 cm2. It is found from an isochronal annealing study that the Fe-H complex is not very stable and can be eliminated completely by annealing for 30 min at 125 °C.

Scattering by regular black holes: Planar massless scalar waves impinging upon a Bardeen black hole

Singularities are common features of general relativity black holes. However, within general relativity, one can construct black holes that present no singularities. These regular black hole solutions can be achieved by, for instance, relaxing one of the energy conditions on the stress energy tensor sourcing the black hole. Some regular black hole solutions were found in the context of non-linear electrodynamics, the Bardeen black hole being the first one proposed. In this paper, we consider a planar massless scalar wave scattered by a Bardeen black hole. We compare the scattering cross section computed using a partial-wave description with the classical geodesic scattering of a stream of null geodesics, as well as with the semi-classical glory approximation. We obtain that, for some values of the corresponding black hole charge, the scattering cross section of a Bardeen black hole has a similar interference pattern of a Reissner-Nordstr\"om black hole.

Digital Reamer Enhances Drilling Efficiency, Economics, and Safety

Technology Update Expandable reamers were developed to improve efficiencies and reduce risk while drilling through problematic formations in deep water and other offshore wells, where wellbore stability is a major challenge. Lean-profile well designs have been implemented to enable operators to drill faster and more efficiently, with better well control and less material, within a narrow pressure window between formation fracture and shale collapse. Using this concept, the well is drilled using the smallest possible hole sections and minimum clearances between casing strings. This allows access to the reservoir with a larger-diameter hole to increase production flow rate or access to additional reserves that otherwise would be unreachable because of their extreme depth. Lean-profile wells require rotary steerable systems to create smooth wellbores, and expandable reamers to manage equivalent circulating densities (ECDs) and maintain wellbore stability while enlarging the hole under the casing sufficiently to allow reliable cementing. The first concentric expandable reamers were ball-activated. Once expanded, they could not be closed without stopping circulation. The second iteration was modified so that the reamer could be deactivated to allow circulation after reaming for better hole cleaning. The advantages of the concentric expandable reamer over its mechanical-arm predecessors included the attainment of a larger borehole size that could accommodate larger bottomhole assembly (BHA) components, flexibility in pilot bit selection, higher flow rates, and the ability to ream a previously drilled hole or to back ream a hole after drilling. The advances in underreaming technology expanded its application to the point at which it is now used on a high percentage of development wells. The most common application is shoe-to-shoe underreaming to enlarge the clearance for easier tripping and casing running. However, there are drawbacks to traditional expandable underreaming systems. Activation cannot be confirmed. Additionally, the placement of the reamer at 100 to 300 ft above the bit means that the equivalent portion of the hole, known as a rathole, cannot be enlarged without a dedicated trip that typically requires 1 to 2 days of rig time at a daily cost ranging from USD 1 million to USD 2 million.

Measurement of hole damage characteristics in the glass fibre reinforced plastic composite using digital image correlation technique

Characterization of the strain behaviour around the matrix and fibre holes in unidirectional glas fibre reinforced plastic composite laminates was carried out. The longitudinal and transverse strain fields around holes machined in tensile laminate specimen were determined by measurement of full‐field strain distributions during tensile loads using the digital image correlation (DIC) technique. From these measurements, the strain concentration around the holes and strain gradient along the hole section were quantitatively determined and the strain fields during the failure evolvement process could be characterized. It was revealed that the longitudinal strain concentration of the matrix hole was relatively greater than that of the fiber hole, while the compressive transverse strain near the fiber hole was slightly larger than that near the matrix hole. Furthermore, it was found that the normalized peak strains, εyy / ε∞, for both matrix and fiber holes were increased with increasing applied stress and that the strain for the fiber hole was slightly lower than that for the matrix hole. The subsequent failure processes for glas fibre reinforced plastic composite (GFRP) UD (uni‐directional) composite specimen with a hole could be visualized and monitored by acquiring digital image correlation images.