Relative Dip Research Articles

S-58-2: CUFFLESS WEARABLE 24-HOUR BLOOD PRESSURE MONIT ORING VERSUS STANDARD AMBULATORY MONITORING

Objective: Cuffless wearable blood pressure (BP) monitors have great potential in assessing 24-hour BP without user disturbance for weeks and months. However, it is uncertain whether these devices can accurately track BP changes during usual daily activities and sleep as with standard 24-hour ambulatory BP monitoring (ABPM). We assessed daytime and nighttime BP using a commercially available cuffless wearable BP device versus classic ABPM. Design and method: We included 45 individuals (age 58 ± 14 years [mean ± SD], 33% female, 80% hypertensive) in two centres (Perth, Australia; Athens, Greece). Participants used a cuffless wearable BP monitor (Aktiia, Switzerland) continuously for 7–10 days and 24-hour ABPM (MicroLife WatchBP O3, Switzerland) on the first and the last day of cuffless BP monitoring. Daily 24-hour, daytime, and nighttime BP values were averaged across the total study days for the cuffless device and across the two ABPM days. Results: The cuffless device reported higher systolic BP for 24-hours by 6.8 mmHg, 95%CI [3.7, 9.7], daytime by 3.8 mmHg [1.0, 6.7], and nighttime by 17.5 mmHg [13.6, 21.4] (all p < 0.01). Cuffless 24-hour diastolic BP was comparable with ABPM (difference 1.2 mmHg, 95%CI [-1.0, 3.5]), as was daytime diastolic BP (-0.8 mmHg [-3.0, 1.3]) (both p. < 27). However, the cuffless device reported higher nighttime diastolic BP by 9.2 mmHg, 95%CI [6.3, 12.2] (p < 0.001). Nighttime dip as measured by the cuffless device, namely systolic BP (-5.1 mmHg, 95%CI [-13.7, 3.6]) and diastolic BP (-3.8 mmHg [-11.6, 4.2]) were substantially less than ABPM (systolic BP dip: -18.0 mmHg [-35.5, -1.2]; diastolic BP dip: -13.8 mmHg [-27.2, -0.8]). The cuffless device identified 44 nighttime non-dippers (defined as a relative dip < 10%) for systolic BP and 42 non-dippers for diastolic BP, compared to 10 non-dippers for both systolic and diastolic BP as identified by ABPM (both comparisons p < 0.001). Conclusions: The Aktiia cuffless wearable BP device considerably overestimated average systolic BP compared to classic ABPM and was unable to adequately track diurnal BP variation.

Abstract 088: Comparison Of 24-hour Blood Pressure Tracking Between A Commercially Available Cuffless Wearable Device And Standard Ambulatory Monitoring

Introduction: Cuffless blood pressure (BP) monitoring offers great potential in assessing 24-hour BP without user disturbance. Despite the myriad of commercially available cuffless BP devices, it is uncertain whether these devices can accurately track BP changes during usual daily activities and sleep as with standard 24-hour ambulatory BP monitoring (ABPM). Hypothesis: A commercially available cuffless wearable BP device, previously demonstrated to have good accuracy for seated BP, can track 24-hour BP changes as well as standard ABPM. Methods: We included 45 individuals (36 hypertensive, 15 female, age 58±14 years [mean±SD]) in two centres (Perth, Australia; Athens, Greece). Participants used a cuffless wearable BP device (Aktiia, Switzerland) continuously for 7-10 days and 24-hour ABPM (MicroLife WatchBP O3, Switzerland) on the first and the last day of cuffless BP monitoring. Daily 24-hour, daytime, and nighttime BP values were averaged across the total study days for the cuffless device and across the two ABPM days. Results: Compared to ABPM, the cuffless device reported higher 24-hour systolic BP (SBP) by 6.8 mmHg, 95% CI [3.7, 9.7], higher daytime SBP by 3.8 mmHg [1.0, 6.7], and higher nighttime SBP by 17.5 mmHg [13.6, 21.4] (all p≤0.01). Cuffless 24-hour diastolic BP (DBP) was comparable with ABPM (difference 1.2 mmHg, 95% CI [-1.0, 3.5]), as was daytime DBP (difference -0.8 mmHg, [-3.0, 1.3]) (both p≥0.27), but nighttime DBP was higher by 9.2 mmHg, [6.3, 12.2] (p<0.001). Nighttime dip in SBP (-5.1 mmHg, 95% CI [-13.7, 3.6]) and DBP (-3.8 mmHg, [-11.6, 4.2]) as measured by the cuffless device were substantially less than ABPM (SBP dip: -18.0 mmHg, [-35.5, -1.2]; DBP dip: -13.8 mmHg, [-27.2, -0.8]). The cuffless device identified 44 nighttime non-dippers (defined as a relative dip < 10%) for SBP and 42 non-dippers for DBP, compared to 10 non-dippers for both SBP and DBP as identified by ABPM (both comparisons p<0.001). Conclusions: A commercially available cuffless wearable BP device was unable to adequately track diurnal BP variation and considerably overestimated average SBP over 24 hours as compared to standard ABPM.

Open-Angle Glaucomatous Optic Neuropathy Is Related to Dips Rather Than Increases in the Mean Arterial Pressure Over 24-H.

Mean arterial pressure (MAP) drives ocular perfusion. Excessive 24-h MAP variability relates to glaucoma, however, whether this is due to dips or increases in the blood pressure (BP) is undocumented. We investigated the association of open-angle glaucoma (OAG) in relation to the 5 largest MAP dips/increases over 24-h, henceforth called dips/blips. In the Maracaibo Aging Study (MAS), 93 participants aged ≥40 y (women, 87.1%; mean age, 61.9 y) underwent baseline ophthalmological and 24-h ambulatory BP monitoring assessments. OAG was the presence of optic nerve damage and visual field defects. Statistical methods included logistic regression and the generalized R2 statistic. For replication, 48 OAG cases at the Leuven Glaucoma Clinic were matched with 48 controls recruited from Flemish population. In the MAS, 26 participants had OAG. OAG compared to non-OAG participants experienced longer and deeper dips (116.5 vs. 102.7 minutes; to 60.3 vs. 66.6 mm Hg; -21.0 vs. -18.0 mm Hg absolute or 0.79 vs. 0.81 relative dip compared to the preceding reading). The adjusted odds ratios associated with dip measures ranged from 2.25 (95% confidence interval [CI], 1.31-4.85; P = 0.009) to 3.39 (95% CI, 1.36-8.46; P = 0.008). On top of covariables and 24-MAP level/variability, the dip measures increased the model performance (P ≤ 0.025). Blips did not associate with OAG. The case-control study replicated the MAS observations. Dips rather than increases in the 24-h MAP level were associated with increased risk for OAG. An ophthalmological examination combined with 24-h BP monitoring might be precautious steps required in normotensive and hypertensive patients at risk of OAG.

Logging-while-drilling formation dip interpretation based on long short-term memory

Azimuth gamma logging while drilling (LWD) is one of the important technologies of geosteering but the information of real-time data transmission is limited and the interpretation is difficult. This study proposes a method of applying artificial intelligence in the LWD data interpretation to enhance the accuracy and efficiency of real-time data processing. By examining formation response characteristics of azimuth gamma ray (GR) curve, the preliminary formation change position is detected based on wavelet transform modulus maxima (WTMM) method, then the dynamic threshold is determined, and a set of contour points describing the formation boundary is obtained. The classification recognition model based on the long short-term memory (LSTM) is designed to judge the true or false of stratum information described by the contour point set to enhance the accuracy of formation identification. Finally, relative dip angle is calculated by nonlinear least square method. Interpretation of azimuth gamma data and application of real-time data processing while drilling show that the method proposed can effectively and accurately determine the formation changes, improve the accuracy of formation dip interpretation, and meet the needs of real-time LWD geosteering.

First LWD Co-Located Antenna Sensors for Real-Time Anisotropy and Dip Angle Determination, Yielding Better Look-Ahead Detection

Electromagnetic (EM) resistivity tools measure the electrical properties of downhole formations that are critical in determining the hydrocarbon saturation of a reservoir. In complex and heterogeneous reservoirs, both horizontal and vertical formation resistivities are required to obtain an accurate hydrocarbon saturation. For decades, wireline multicomponent induction type measurements have provided reliable determination of formation anisotropy, structural dip, and dip azimuth in wells with any orientation relative to the bedding planes. Logging-while-drilling (LWD) multi-array propagation resistivity tools have also demonstrated similar capability in deviated wells where the relative dip angle is between 45° and 90°. However, measuring anisotropy and dip in wells with a low relative dip angle still poses difficulties for LWD propagation resistivity systems because of the antenna structures employed. This paper describes the development of a new LWD EM sensor equipped with an innovative, co-located, tilted antenna structure. The tool, along with a unique processing scheme, enables the determination of horizontal and vertical resistivity as well as the dip angle and the azimuth of the formation based on an assumption of transversely isotropic (TI) formation models (Graciet and Shen, 1998) while drilling in real time. The co-located sensor design is capable of acquiring multicomponent signals that are sensitive to formation anisotropy and structural dip in wells at any orientation. Modeling studies and several field trials have proven that the design concept can detect these formation properties at any arbitrary wellbore deviation. This paper presents test results from the new technology, together with reference measurements from azimuthally compensated LWD and fully triaxial wireline resistivity measurements. A good comparison is observed in these trials, providing an independent verification of the tool performance. The azimuthal measurements of the new sensors allow for determining formation anisotropy and dip at any wellbore deviation (Bittar et al., 2011b; Bittar et al., 2012), as well as providing 360° azimuthal resistivity and geosignals and allowing a three-dimensional (3D) resistivity mapping technique for real-time decisions. Integrating the co-located antennas with deep-reading antennas in a near-bit collar further provides both anisotropy measurements and ultradeep signals very close to the bit and enhances look-ahead detection ranges for LWD applications.

Novel transient multicomponent induction logging method for the determination of dip angle and anisotropy of formation

The relative dip angle and anisotropy of the anisotropic formation are generally determined through an inversion process. We have studied the responses of the novel transient multicomponent induction logging method and find that all of the components measured in the instrument coordinate system have the same decay with time. However, the cross component decays much faster than the coaxial or coplanar components in the formation coordinate system. We adopt an algebraic time-domain method to calculate the dip angle and anisotropy coefficient and thereby avoid the inversion process. The accuracy and applicability of this pseudoinversion method are studied theoretically. Numerical results demonstrate that coaxial, coplanar, and cross components are used to calculate the apparent relative dip angle that yields the exactly true value at very early times and then goes through a transition deviating from the true dip and gradually approaches the true value again at late times. The apparent anisotropy is calculated by the coaxial and coplanar components and is equal to zero at early times and nonzero to the true anisotropy during the transition times. Moreover, by using realistic source dipole moments as well as adding random measurement errors, the practicality of this algebraic method is also investigated. Determination of the relative dip is still stable and valid. Determination of the anisotropy is more easily affected by measurement error and has some application limitations.

Mechanistic 3D finite-difference simulation of borehole spontaneous potential measurements

The quantitative interpretation of borehole spontaneous potential (SP) measurements via Nernst’s equation often relies on limiting assumptions such as shallow mud-filtrate invasion, negligible streaming potentials, and uniform borehole symmetry. To overcome these limitations while honoring the governing physics of coupled mass transport associated with SP phenomena, we have developed a 3D finite-difference algorithm to simulate borehole SP measurements acquired across water-bearing rocks that incorporates electrochemical, membrane, and electrokinetic SP. The algorithm is based on a mechanistic description of nonequilibrium thermodynamics that enables its coupling with a fluid flow simulator to quantify the effects of continuously varying properties within permeable formations due to mud-filtrate invasion. Numerical modeling of SP measurements acquired under complex petrophysical and geometric conditions enables uncertainty quantification in the estimation of formation-water resitivity, location of bed boundaries, or detection of permeable beds while accounting for shoulder-bed effects, borehole deviation, and borehole eccentricity. Our results indicate that for well trajectories with a relative dip of less than 30°, the assumption of perpendicular beds does not entail significant errors in SP-related calculations, thereby reducing CPU time by a factor of at least 1.76. In vertical wells, SP provides the best resolution possible because deviated wells or dipping beds result in more extended and pronounced shoulder-bed effects. Furthermore, electrokinetic effects can be neglected for commonly used pressure overbalance ranges. In cases in which electrokinetic contributions are not negligible, we conclude that they are more significant when the rock permeability is in the two-figure millidarcy range. Finally, the simulation algorithm enables hypothesis testing to determine the origin and conditions under which SP shale-baseline shifts may occur. The latter shifts can signal vertical variations in salt concentration, which are crucial in the estimation of water saturation and detection of aquifer compartments.

Anisotropy interpretation and the coherence research between resistivity and acoustic anisotropy in tight sands

Abstract Aiming at the problem of anisotropy inversion of tight sands, a new method for extracting resistivity anisotropy from array laterolog and micro-resistivity scanning imaging logging is proposed, and also the consistency of electric and acoustic anisotropy is discussed. Array laterolog includes resistivity anisotropy information, but numerical simulation shows that drilling fluid invasion has the greatest influence on the response, followed by the relative dip angle θ and electrical anisotropy coefficient λ. A new inversion method to determine ri, Rxo, Rt and λ is developed with the given θ and initial values of invasion radius ri, flushed zone resistivity Rxo, in-situ formation resistivity Rt. Micro-resistivity image can also be used for describing the resistivity distribution information in different directions, and the electrical characteristics from micro-resistivity log in different azimuths, lateral and vertical, can be compared to extract electric anisotropy information. Directional arrangement of mineral particles in tight sands and fracture development are the intrinsic causes of anisotropy, which in turn brings about anisotropy in resistivity and acoustic velocity, so the resistivity anisotropy and acoustic velocity anisotropy are consistent in trends. Analysis of log data of several wells show that the electrical anisotropy and acoustic anisotropy extracted from array laterolog, micro-resistivity imaging and cross-dipole acoustic logs respectively are consistent in trend and magnitude, proving the inversion method is accurate and the anisotropies of different formation physical parameters caused by the intrinsic structure of tight sand reservoir are consistent. This research provides a new idea for evaluating anisotropy of tight sands.

Forward simulation of array laterolog resistivity in anisotropic formation and its application

A scaling-down experiment system of array laterolog resistivity was developed, and a corresponding formation model was built by 3D finite element numerical method to study the effect of different factors on the logging response quantitatively. The error between the experimental and numerical results was less than 5%, validating the reliability of the numerical simulation method. The single factor analysis of the formation relative dip, resistivity anisotropy and drilling fluid invasion was carried out by numerical simulation method, and the results show that: (1) The increase of relative dip can lead to the increase of formation resistivity, but the increasing value is relatively small, and the values of five array resistivity curves will reverse when the relative dip angle reaches a certain degree. (2) The increase of anisotropy coefficient λ can also cause the formation resistivity to rise, and the resistivity will increase by about 10% when λ increases from 1.0 to 1.5 in vertical wells. (3) Drilling fluid invasion has a more significant effect on the logging response than the former two factors. The order of the five curves will change due to drilling fluid invasion in anisotropic formation and the change rule is contrary to resistivity anisotropy. Taking the logging data of the Yingxi oilfield in the Qaidam Basin as an example, an anisotropic formation model considering drilling fluid invasion was built, and the numerical simulation results from the above methods were basically consistent with the logging data, which verified the accuracy of the method again. The results of this study lay a theoretical foundation for multiple-parameter inversion in anisotropic formation under complex well conditions.

Effect of different stabilizers on dispersion of gold nanoparticles in bismuth borosilicate glass and their intensity dependent nonlinear behaviour

Here, we report the role of different stabilizers (Eu2O3, EuF3 and KSCN) in stabilizing gold nanoparticles (AuNPs) embedded in Bismuth-Borosilicate glasses. The prepared nanocomposites are characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), UV–Visible transmission spectroscopy, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), ellipsometery and Z-scan. From FESEM, it has been observed that the morphology of AuNPs is highly dependent on the type of stabilizer. Also HRTEM confirms the covering of AuNPs by stabilizer that prevents the coagulation of NPs. The localized surface plasmon resonance related transmission dip is observed around 585 nm for glass containing Eu2O3 as a stabilizer. The linear and nonlinear refractive index of the prepared glasses is obtained from ellipsometery and Z-scan measurements, respectively. All the Z-scan measurements have been carried out at different input peak intensities varying from 1.9 to 14.38 GW/cm2. Nonlinear optical studies with open aperture Z-Scan shows the switching between saturable absorption and two photon absorption as the laser intensity is increased. The existence of third order nonlinearity has been detected using closed aperture Z-scan in the prepared glasses.

Study on the Structural Parameters and Response Characteristics of the Tilted Antenna of Directional Electromagnetic Wave Resistivity Measuring Instrument

The directional logging-while-drilling measurements enable to monitor the distance to formation boundaries and their orientation and facilitate proactive well placement, and thus can provide directionality information useful in detecting physical parameters such as bed boundaries, formation dip and formation azimuth, so the oil and gas recovery can be greatly improved. The characteristics of a kind of electromagnetic wave resistivity logging while drilling (LWD) tool with tilted antennas are computed via the magnetic-current-source dyadic Green’s function for horizontally stratified anisotropic media. The current characteristic at the formation interface of the tilted antennas is compared with that of the axial antenna, and how the LWD tool with tilted antennas to detect the formation interface position and orientation is revealed. The amplitude-attenuation and phase-shift characteristics of LWD tool with tilted antennas are analyzed, and how to design the angle of tilted antenna is presented. The relationship between the emitting frequency and emitting-receiving antenna space parameters is expounded, and the emitting-receiving antenna space parameter suitable for different frequencies is presented. The detection characteristic of the electromagnetic wave measuring instrument is studied. For the highly deviated well formation model, the directional response characteristics of the different relative dip angle isotropic and anisotropic formation are numerically simulated and analyzed. The directional response characteristics of the two kinds of coil arrangement (unilateral arrangement and symmetrical arrangement) are analyzed by numerical simulation, and the solution to reduce or eliminate the influence of the directional response of the isotropy on the directional response is obtained. The conclusions obtained by theoretical analysis and numerical simulation provide a guide for the instrument principle research and application.

High-sensitivity nanostructured aluminium ultrathin film sensors with spectral response from ultraviolet to near-infrared

An aluminum ultrathin film with nanohole arrays arranged in a hexagonal lattice is theoretically explored for the sensor application. Two transmission dips, which exhibit high sensitivity to the refractive index (RI) of the cladding layer or substrate, are presented owing to the excitation of surface plasmons at the top and bottom surfaces of the ultrathin metal film. Numerical results show that a sensitivity of 348 nm/RIU, with a figure of merit of 34.8, are obtained, which are tolerated in the existence of aluminum oxidization. By increasing the RI of the substrate, the related transmission dip is obviously red-shifted, which makes the sensors based on the proposed nanostructure work effectively in a broad spectral range from ultraviolet to near-infrared.

Characterizing Fracture Geometry from Borehole Images

The use of borehole image logs in natural-fracture evaluation has traditionally focused on mapping the strikes and dips of the individual fractures that intersect the borehole, estimating their apertures, and from these computing fracture attributes such as fracture density. These fracture attributes are commonly used to build three-dimensional fracture-network models. However, these attributes do not directly constrain an important aspect of these models—fracture geometry—specifically, the size, shape, and rotation of three-dimensional fractures within the model. The published formulas of Ozkaya estimate the radius of circular fractures from the statistics of fracture intersections observed in a borehole image. These formulas are shown to be approximate, only applying to circular fractures with shallow relative dip, and are replaced with exact formulas for elliptical fractures that are valid over the entire range of relative dip. A new statistic is defined, the measured distribution of relative azimuths for fracture-trace midpoints, that is sufficient for estimating both the elongation ratio and the rotation angle of elliptically shaped fractures. As estimation accuracy for this fracture geometry is dependent on the number of observed fracture traces, practical methodologies are provided for computing the uncertainty of these estimates. Finally, since natural fracture size is typically not constant, but follows a distribution such as a power law, solutions are provided for using these same borehole image statistics to estimate the fracture-size distribution. Numerical examples with exponential and Pareto distributions demonstrate that a single parameter of a parametric size distribution can be estimated along with its uncertainty.

An Improved Complex Image Theory for Fast Resistivity Modeling and Its Application to Geosteering

Summary azimuthal resistivity logging-while-drilling (LWD) tools with tilted antennas (Bittar 2002; Li et al. 2005) are widely used in geosteering because of their azimuthal sensitivity and the relatively large depth of investigation compared with other LWD tools such as nuclear, acoustic, or gamma ray measurements. Compared with conventional resistivity tools, azimuthal-resistivity LWD measurements can provide additional information including distance-to-boundary, relative dip angle, and resistivity anisotropy (Li et al. 2014). Because of the computing efficiency requirement, modeling and inversion of azimuthal-resistivity LWD measurements are usually based on a 1D parallel-layer model in practice (Zhong et al. 2008). Clearly, this 1D model assumption is not applicable to some realistic situations such as when the tool is navigating in unparallel-layer formation, or approaching a fault. The 3D full-wave simulations such as finite-difference or finite-element methods can handle the complex cases, but they are generally too slow for real jobs, not to mention the inversion that is based on iterative calls of forward modeling. An approximation method called complex image theory was proposed for geophysical prospecting (Wait 1969; Bannister 1986), and recently was introduced to well logging (Dong and Wang 2011; Wang and Liu 2014). This theory approximates electromagnetic-wave reflection by an interface between local and adjacent beds as signal radiated from a virtual source with a complex distance from the observation point. The complex image theory can be several orders of magnitude more efficient than 3D simulations. However, it also has several limitations: This method only works in resistive beds with conductive shoulders, and the measurement cannot be too close to bed interfaces. Those shortcomings greatly limit this method to more extensive applications. An improved complex image theory is proposed here to tackle the aforementioned difficulties. This improved theory can handle a very short distance from the tool to a bed interface as well as the scenarios in which the source is in a conductive bed instead of a resistive one. One can implement robust inversion schemes on the basis of this method. The effectiveness and efficiency of this method are verified by several numerical examples as well as laboratory tests and field jobs.

Enhanced real-time determination of resistivity anisotropy and dip using multifrequency and multicomponent induction logging

Multicomponent induction (MCI) logging is able to provide a wealth of measurements at multiple subarrays and frequencies that can be used to evaluate complex subsurface formations. Real-time and postprocessing inversion methods have been introduced by various researchers for determining formation resistivity anisotropy (horizontal and vertical resistivity or conductivity), dip, and dip azimuth/strike using MCI measurements. The majority of these methods are based on single-frequency information. We have developed an enhanced real-time method and relevant workflow for determining formation resistivity anisotropy, dip, and dip azimuth using multifrequency MCI information. This enhanced method can be used to improve accuracy in formation evaluation applications, such as reservoir identification, hydrocarbon/water saturation calculation, and geologic and structural interpretation. Enhancements over the present single-frequency data processing include: (1) optimal harmonization of multiple single-frequency inverted logs, (2) robust determination of dip and dip azimuth angle for low-resistivity anisotropy ratios, (3) practical data-quality evaluation that takes into account the effects of formation resistivity, anisotropy ratio, and dip parameters, and (4) a new integrated workflow that can be used to determine formation anisotropy, true dip, and dip azimuth by integrating processed relative dip and azimuth and borehole directional logging data. Finally, all of these data process enhancements have been validated with synthetic data and field log data.

Plasmon‐exciton coupling in neighboring metal nanoparticles and a semiconductor quantum well: Theory

Spectroscopic effects of plasmon‐exciton coupling are studied theoretically for metal nanoparticles and a semiconductor quantum-well located nearby. Resonant polarizability is self-consistently calculated for dipole plasmons supported by nanoparticles and influenced by image dipoles due to exciton polarization of the quantum well. Spectra of elastic scattering and reflection of light are analyzed in conformity with high-quality plasmons of silver nanoparticles and quasi-two-dimensional excitons of AlGaAs/GaAs quantum well. Essential two-peak resonant structure associated with plasmon‐exciton Rabi splitting is found. The related spectral dip is interpreted in terms of excitonic response enhancement by plasmons of nanoparticles.

Fast determination and characterization of formation resistivity anisotropy, dip, and fracture using multicomponent induction data

Multicomponent induction (MCI) logging measurements have been widely used in the past decade for determining formation resistivity anisotropy (horizontal and vertical resistivities: [Formula: see text] and [Formula: see text]), dip, and azimuth. Currently, almost all MCI processing and interpretation algorithms of determining [Formula: see text], [Formula: see text], dip, and azimuth are based on simplified transversely isotropic (TI) formation models. In most geologic environments, formations are layered or laminated, making the TI model a reasonable assumption. Subsurface formations usually contain different types of fractures (natural or drilling-induced), and exhibit azimuthal resistivity anisotropy in the bedding plane, which leads to formation biaxial anisotropy (BA) in the same bedding plane. (This type of media is usually called orthorhombic or orthotropic in mechanical engineering and geomechanics.) Therefore, MCI data processing based on TI models may not be valid in complex BA formations caused by fractures. MCI processing and interpretation methods based on BA formation models are needed for more accurate descriptions of complex anisotropic formations. Fractures significantly affect fluid flow in formations, and therefore the fracture characterization with MCI logging can provide some useful information for oil/gas development and production, especially in unconventional reservoirs. We have developed a fast and practical integrated method of borehole multiarray MCI data processing for effective determination of formation BA anisotropy (or triaxial resistivities: [Formula: see text], [Formula: see text], and [Formula: see text]), dip, and azimuth. The multiple MCI data sets were further applied to fracture evaluation, and they were tested with synthetic and field log data sets. The method has the following components: the inversion algorithm based on the multiple BA models, a fracture identification function for detection of the fracture, and the corresponding approach for estimation of the fracture relative azimuth and dip angle. The application results demonstrated that accurate triaxial formation anisotropy and dip can be obtained based on the BA models compared with the TI processed logs. Furthermore, fractures can be characterized by integrating measurements and processed log data, such as the recovered horizontal resistivities [Formula: see text] and [Formula: see text], vertical resistivity [Formula: see text], and formation dips based on the BA and TI models.

Net-Pay Optimization and Improved Mapping With Look-Around LWD Measurements

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 171856, “Net-Pay Optimization and Improved Reservoir Mapping From Ultradeep Look-Around Logging-While-Drilling Measurements,” by Frank Antonsen, Per Atle Olsen, Stein Ottar Stalheim, Monica Vik Constable, Matthieu Irondelle, Michael Cook, and Trond Rognebakke Bjørstad, Statoil, and Christophe Dupuis, Philippe Marza, Jean Seydoux, Dzevat Omeragic, and Jean-Michel Denichou, Schlumberger, prepared for the 2014 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 10–13 November. The paper has not been peer reviewed. This paper discusses ultradeep directional-resistivity (DDR) logging-while-drilling (LWD) measurements for high-angle and horizontal wells that have been applied recently with success on the Norwegian continental shelf (NCS). The main benefits from the DDR measurements in the license have been to maximize reservoir exposure by active geosteering, optimize well placement above the oil/ water contact (OWC), and increase subsurface understanding. Background More than 50% of all production wells today on the NCS are highly deviated or horizontal. An operator has tested DDR measurements since 2009. This new while-drilling technology, with its increased depth of investigation and ability to interpret multiple boundaries above and below the wellbore, is regarded as a key technology in reaching the ambitious target recovery rate of 70%. Fig. 1 presents the bottomhole-assembly (BHA) architecture for the first DDR LWD tool with depth of investigation in excess of 30 m away from the borehole. The tool architecture consists of a set of subs spaced out on a BHA providing multispacing, multifrequency azimuthal measurements. With these measurements, a multilayer inversion generates a mapping of the resistivity distribution above and below the borehole. Differentiating this technology from standard image logs, the relative dip of the formation layer can be determined not only at the trajectory, but also away from the trajectory. In addition to the 1D (layer-cake) resistivity mapping, the tool provides an orientation of the map perpendicular to the formation-structure planes.

SU‐E‐I‐16: Scan Length Dependency of the Radial Dose Distribution in a Long Polyethylene Cylinder

Purpose:The area‐averaged dose in the central plane of a long cylinder following a CT scan depends upon the radial dose distribution and the length of the scan. The ICRU/TG200 phantom, a polyethylene cylinder 30 cm in diameter and 60 cm long, was the subject of this study. The purpose was to develop an analytic function that could determine the dose for a scan length L at any point in the central plane of this phantom.Methods:Monte Carlo calculations were performed on a simulated ICRU/TG200 phantom under conditions of cylindrically symmetric conditions of irradiation. Thus, the radial dose distribution function must be an even function that accounts for two competing effects: The direct beam makes its weakest contribution at the center while the scatter begins abruptly at the outer radius and grows as the center is approached. The scatter contribution also increases with scan length with the increase approaching its limiting value at the periphery faster than along the central axis. An analytic function was developed that fit the data and possessed these features.Results:Symmetry and continuity dictate a local extremum at the center which is a minimum for the ICRU/TG200 phantom. The relative depth of the minimum decreases as the scan length grows and an absolute maximum can occur between the center and outer edge of the cylinders. As the scan length grows, the relative dip in the center decreases so that for very long scan lengths, the dose profile is relatively flat.Conclusion:An analytic function characterizes the radial and scan length dependency of dose for long cylindrical phantoms. The function can be integrated with the results expressed in closed form. One use for this is to help determine average dose distribution over the central cylinder plane for any scan length.

A novel method for quantitative geosteering using azimuthal gamma-ray logging

A novel method for quantitative geosteering by using azimuthal gamma-ray logging is proposed. Real-time up and bottom gamma-ray logs when a logging tool travels through a boundary surface with different relative dip angles are simulated with the Monte Carlo method. Study results show that response points of up and bottom gamma-ray logs when the logging tool moves towards a highly radioactive formation can be used to predict the relative dip angle, and then the distance from the drilling bit to the boundary surface is calculated.