The Experts below are selected from a list of 2616 Experts worldwide ranked by ideXlab platform
Nafi M Toksoz - One of the best experts on this subject based on the ideXlab platform.
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elimination of lwd Logging While Drilling tool modes using seismoelectric data
Communications in Computational Physics, 2009Co-Authors: Xin Zhan, Daniel R Burns, Nafi M ToksozAbstract:Borehole acoustic Logging-While-Drilling (LWD) for formation evaluation has become an indispensable part of hydrocarbon reservoir assessment (Tang et al., 2002; Citta et al., 2004; Esmersoy et al., 2005). However, the detection of acoustic formation arrivalsover tool mode contamination has been a challenging problem in acoustic LWD technology. This is because the tool mode contamination in LWD is more severe than in wireline tools in most geological environments (Tang et al., 2002; Huang, 2003). In this paper we propose a new method for separating tool waves from formation acoustic waves in acoustic LWD. This method is to measure the seismoelectric signal excited by the LWD acoustic waves. The acoustic waves propagating along the borehole or in the formation can induce electric fields. The generated electric field is localized around the wave pulses and carried along the borehole at the formation acoustic wave velocity. The LWD tool waves which propagate along the rigid tool rim can not excite any electric signal. This is due to the effectively grounding of the drill string during the LWD process makes it impossible to accumulate any excess charge at the conductive tool – borehole fluid interface. Therefore, there should be no contribution by the tool modes to the recorded seismoelectric signals. In this study, we designed the laboratory experiments to collect simulated LWD monopole and dipole acoustic and seismoelectric signals in a borehole in sandstone. By analyzing the acoustic and electric signals, we can observe the difference between them, which are the mainly tool modes and noise. 1 In this paper, acoustic LWD measurement or signal is composed of formation acoustic waves (modes or arrivals) which are the waves propagating along the formation and tool waves (modes) which are waves propagating along the tool. 2 Seismoelectric signal refers to the electric field induced by seismic (acoustic) waves.
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experimental studies of monopole dipole and quadrupole acoustic Logging While Drilling lwd with scaled borehole models
Geophysics, 2008Co-Authors: Nafi M Toksoz, Daniel R BurnsAbstract:We develop a 1:12 scale model Logging-While-Drilling (LWD) acoustic tool for laboratory measurements in borehole models to investigate the effects of tool wave modes on our ability to determine formation velocities in acoustic LWD. The scaled tool is comprised of three sections: (1) the source section, consisting of four transducers mounted on the tool body that can generate monopole, dipole, and quadrupole waves; (2) the receiver section, consisting of six sets of receivers, each containing two transducers mounted on opposite sides of the tool center line; and (3) the connector section, a threaded steel cylinder that connects the source and receiver sections tightly to simulate an LWD tool. We use four borehole models to simulate fast and slow isotropic and anisotropic formations. The slow-formation models are constructed of synthetic material ( Lucite® for the isotropic case and Phenolite® for the anisotropic case). The fast-formation models are made from natural rock samples (sandstone for the isotropi...
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a finite element analysis of the effects of tool eccentricity on wave dispersion properties in borehole acoustic Logging While Drilling
Seg Technical Program Expanded Abstracts, 2004Co-Authors: Yibing Zheng, Xiaojun Huang, Nafi M ToksozAbstract:Summary A finite element approach is applied to study the acoustic dispersion properties of guide waves inside boreholes with off-centered tools in acoustic Logging While Drilling (LWD). Both soft and hard formation cases are studied with focus on phase velocity dispersions of monopole, dipole and quadrupole modes. When the Logging tool is off-centered, the dispersion curve of the Stoneley mode shifts to the lower phase velocity. MeanWhile, the dipole dispersion curve splits into two curves with different phase velocities, as does the quadrupole mode. The splitting and shifting of the dipole mode is greater than those of the quadrupole mode. These new observations are important in accurately interpreting acoustic LWD data.
William E Preeg - One of the best experts on this subject based on the ideXlab platform.
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inversion based interpretation of Logging While Drilling gamma ray spectroscopy measurements
Geophysics, 2016Co-Authors: Oyinkansola Ajayi, Carlos Torresverdin, William E PreegAbstract:ABSTRACTNeutron-induced spectroscopy measurements are commonly used to quantify in situ elemental compositions of rocks from the processing of measured gamma-ray energy spectra. However, geometric effects on the measured spectroscopy logs, such as thin beds, dipping beds, and deviated well trajectories, can cause shoulder-bed averaging that compromises the assessment of the true layer elemental composition. We have developed an inversion-based interpretation method to evaluate layer elemental compositions from spectroscopy measurements acquired with a commercial 14-MeV pulsed-neutron Logging-While-Drilling spectroscopy tool. The algorithm is based on a new spectroscopy fast-forward simulation technique, and it estimates layer-by-layer elemental relative yields, weight concentrations, and their uncertainties. Calculations are performed with inelastic and capture gamma-ray spectroscopy measurements that arose from high- and low-energy neutron interactions, respectively. This strategy provides two sets of da...
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2d inversion based interpretation of Logging While Drilling thermal neutron and gamma ray time decays
Geophysics, 2015Co-Authors: Edwin Ortega, Carlos Torresverdin, William E PreegAbstract:ABSTRACTIdentification and petrophysical evaluation of thinly bedded formations with borehole resistivity measurements can be problematic due to the large volume of investigation of the measurements. Logging-While-Drilling (LWD) Sigma logs can overcome this difficulty because Sigma measurements have a smaller volume of investigation. Sigma is the macroscopic absorption nuclear cross section of a material that quantifies the material’s ability to absorb thermal neutrons. The contrast in Sigma between salty formation water and hydrocarbons makes Sigma logs useful for resistivity-independent estimation of water saturation. We assumed LWD Sigma measurements acquired with one near thermal-neutron detector (near), one short-spaced gamma-ray detector (SSn), and one long-spaced gamma-ray detector (LSn). Separation of multidetector Sigma logs may indicate the presence of mud-filtrate invasion in the case of thick formations. However, Sigma measurements acquired in thinly bedded formations are affected not only by ...
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1D radial inversion of multidetector Logging-While-Drilling Sigma measurements
Geophysics, 2014Co-Authors: Edwin Ortega, William E Preeg, Carlos Torres-verdín, Jeffrey MilesAbstract:ABSTRACTSigma measurements are useful in formation evaluation because they can be used to calculate water saturation independently of resistivity. One of the most advantageous features of the Logging-While-Drilling (LWD) Sigma tool under study is the use of three detectors to measure time decays from which three Sigmas are calculated: one near thermal-neutron detector, one short-spaced gamma-ray detector, and one long-spaced gamma-ray detector. Each detector has a different volume of investigation. Analogous to array resistivity logs, the multidetector Sigma logs, also called multi-depth of investigation Sigma logs, can indicate the presence of invasion and can be used to estimate true formation Sigma. However, the efficacy of the multidetector Sigma interpretation is conditioned by a high-Sigma contrast between invasion and virgin zones. We used a nonlinear gradient-based fast inversion method that uses the measured three-detector time decays and a reference value for invasion-zone Sigma to estimate the ...
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rapid forward modeling of multidetector Logging While Drilling sigma measurements
Geophysics, 2014Co-Authors: Edwin Ortega, Carlos Torresverdin, William E PreegAbstract:ABSTRACTMultidetector Logging-While-Drilling (LWD) Sigma was introduced to the oil industry to measure neutron absorption cross section (Sigma) and radial length of invasion in shallow-invaded formations. Sigma quantifies the ability of a material to absorb thermal neutrons and is calculated from the late time portion of the time decay of thermal neutrons or gamma rays generated from thermal-neutron absorption. The assessment of invasion is made possible with the combination of a thermal-neutron detector and two gamma-ray detectors with different source-detector spacings. However, the interpretation of LWD Sigma logs is often affected by several environmental and/or geometric effects that can mask the formation response. A fast numerical simulation method embedded with inversion-based techniques can be used to estimate intrinsic formation Sigma from borehole measurements affected by shoulder-bed, invasion, and/or environmental effects. We developed a fast and accurate method to numerically simulate LWD mu...
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inversion based petrophysical interpretation of Logging While Drilling nuclear and resistivity measurements
Geophysics, 2013Co-Authors: Olabode Ijasan, Carlos Torresverdin, William E PreegAbstract:ABSTRACTInterpretation of borehole measurements acquired in high-angle (HA) and horizontal (HZ) wells is challenging due to the significant influence of well trajectory and bed geometrical effects. Experience shows that accurate integrated interpretation of well logs acquired in HA/HZ wells requires explicit consideration of 3D measurement physics. The most reliable alternative for interpretation of well logs in HA/HZ wells is with inversion techniques that correct measurements for shoulder-bed, undulating well trajectory, and bed geometrical effects While taking advantage of high data resolution. We discovered an efficient layer-based inversion workflow for combined, quantitative petrophysical and compositional interpretation of Logging-While-Drilling sector-based nuclear (density, neutron porosity, photoelectric factor, gamma ray) and array propagation resistivity measurements acquired in HA/HZ wells. A challenging synthetic benchmark example confirmed improved formation evaluation with the layer-based ...
M. Nafi Toksöz - One of the best experts on this subject based on the ideXlab platform.
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Higher Order Modes In Acoustic Logging While Drilling
Seg Technical Program Expanded Abstracts, 2020Co-Authors: M. Nafi ToksözAbstract:Summary In multipole acoustic Logging While Drilling (LWD), the fundamental modes dominate recorded waveforms. Higher order modes may also appear and complicate the processing of LWD data. In dipole LWD measurements, the dipole tool mode is often not well separated from the flexural mode. This makes the shear wave measurement more difficult. We conducted theoretical and numerical analysis on dipole LWD Logging responses. We found that hexapole mode may be present in the dipole waveforms. Laboratory dipole data show the presence of hexapole mode, which asymptotes to the formation shear wave velocity. This observation supports our conclusion. We may make use of these higher order modes for accurate determination of formation shear wave velocity.
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An Experimental Study Of Seismoelectric Signals In Logging While Drilling
2020Co-Authors: Xin Zhan, M. Nafi ToksözAbstract:Acoustic Logging While Drilling (LWD) may be complicated because of contamination by waves propagating along the drill collar (the tool waves). In this paper we propose a new method for separating tool waves from the true formation acoustic arrivals in borehole acoustic LWD. The method utilizes the seismoelectric signal induced by the acoustic wave at the fluid-formation boundary. The basis for seismoelectric conversion is the electric double layer (EDL) that exists in most rock-water systems. EDL does not exist at the tool (conductor) water interface. Therefore, there should be no seismoelectric signals due to tool modes. In this paper, borehole monopole and dipole LWD acoustic and seismoelectric phenomena are investigated with laboratory measurements. The main thrust of the paper is the utilization of the difference between acoustic and seismoelectric signals, to eliminate the tool waves and enhance the formation acoustic signals in acoustic LWD.
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Effects of tool eccentricity on wave dispersion properties in borehole acoustic Logging While Drilling
2020Co-Authors: Yibing Zheng, M. Nafi ToksözAbstract:In this paper, a finite element approach is applied to study the dispersion properties of non-leaky acoustic waves inside boreholes with off-centered LWD (Logging While Drilling) tools. Both soft and hard formation cases are studied with focus on phase velocity dispersions of Stoneley, dipole and quadrupole modes. When an LWD tool is off-centered, the dispersion curve of the Stoneley mode shifts to the lower phase velocity compared with that of a centered-tool condition. MeanWhile, the dipole dispersion curve splits into two curves with different phase velocities. This splitting phenomenon is also observed with the quadrupole mode. The splitting and shifting of the dipole mode are greater than those of the quadrupole mode. These new observations are important for interpreting acoustic LWD data accurately.
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An Experimental Study of Seismoelectric Signals In Logging While Drilling And Filtering Out of Tool Waves
Seg Technical Program Expanded Abstracts, 2020Co-Authors: Xin Zhan, M. Nafi ToksözAbstract:Acoustic Logging While Drilling (LWD) may be complicated because of contamination of waves propagating along the drill collar (the tool waves). In this paper we propose a new method for separating tool waves from the true formation acoustic arrivals in borehole acoustic LWD. The method utilizes the seismoelectric signal induced by the acoustic wave at the fluid-formation boundary. The basis for seismoelectric conversion is the electric double layer (EDL) that exists in most rock-water systems. EDL does not exist at the tool (conductor) water interface. Therefore, there should be no seismoelectric signals due to tool modes. In this paper, borehole monopole and dipole LWD acoustic and seismoelectric phenomena are investigated with laboratory measurements. The main thrust of the paper is the utilization of the acoustic and seismoelectric signals to filter out the tool waves and enhance the formation acoustic signals in LWD.
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Analysis of the Acoustic Wavefields Excited by the Logging-While-Drilling (LWD) Tool
Geosystem Engineering, 2003Co-Authors: Joongmoo Byun, M. Nafi ToksözAbstract:ABSTRACTS Synthetic seismograms recorded with a Logging-While-Drilling (LWD) tool in the presence of slow formation are computed by the discrete wavenumber method. Monopole, dipole, and quadrupole Logging tools are simulated with a source center frequency of 4 kHz. The modes in the responses are identified and characterized with time and frequency semblance plots. Numerical results show that, to obtain the formation shear velocity, we need to correct the peak velocities of the multipole modes in the semblance plots by using analytical dispersion curves.
Carlos Torresverdin - One of the best experts on this subject based on the ideXlab platform.
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fast inversion of Logging While Drilling resistivity measurements acquired in multiple wells
Geophysics, 2017Co-Authors: Shaaban A Bakr, David Pardo, Carlos TorresverdinAbstract:ABSTRACTWe have developed a new method for the fast inversion of borehole resistivity measurements acquired in multiple wells using Logging-While-Drilling instruments. There are two key novel contributions. First, we approximate general 3D transversely isotropic (TI) formations with a sequence of several “stitched” 1D planarly layered TI sections. This allows us to approximate the solution of rather complex 3D formations using only 1.5D simulations. Second, the developed method supports the simultaneous inversion of measurements acquired in different neighboring wells and/or with different Logging instruments. Numerical experiments performed with realistic 3D synthetic formations confirm the flexibility of the method and the reliability of the inversion products. The method yields relative errors of less than 5% on the model space, and it enables the interpretation of resistivity measurements acquired in multiple wells (e.g., an exploratory, an offset, and a geosteering well) and with any combination of c...
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inversion based interpretation of Logging While Drilling gamma ray spectroscopy measurements
Geophysics, 2016Co-Authors: Oyinkansola Ajayi, Carlos Torresverdin, William E PreegAbstract:ABSTRACTNeutron-induced spectroscopy measurements are commonly used to quantify in situ elemental compositions of rocks from the processing of measured gamma-ray energy spectra. However, geometric effects on the measured spectroscopy logs, such as thin beds, dipping beds, and deviated well trajectories, can cause shoulder-bed averaging that compromises the assessment of the true layer elemental composition. We have developed an inversion-based interpretation method to evaluate layer elemental compositions from spectroscopy measurements acquired with a commercial 14-MeV pulsed-neutron Logging-While-Drilling spectroscopy tool. The algorithm is based on a new spectroscopy fast-forward simulation technique, and it estimates layer-by-layer elemental relative yields, weight concentrations, and their uncertainties. Calculations are performed with inelastic and capture gamma-ray spectroscopy measurements that arose from high- and low-energy neutron interactions, respectively. This strategy provides two sets of da...
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2d inversion based interpretation of Logging While Drilling thermal neutron and gamma ray time decays
Geophysics, 2015Co-Authors: Edwin Ortega, Carlos Torresverdin, William E PreegAbstract:ABSTRACTIdentification and petrophysical evaluation of thinly bedded formations with borehole resistivity measurements can be problematic due to the large volume of investigation of the measurements. Logging-While-Drilling (LWD) Sigma logs can overcome this difficulty because Sigma measurements have a smaller volume of investigation. Sigma is the macroscopic absorption nuclear cross section of a material that quantifies the material’s ability to absorb thermal neutrons. The contrast in Sigma between salty formation water and hydrocarbons makes Sigma logs useful for resistivity-independent estimation of water saturation. We assumed LWD Sigma measurements acquired with one near thermal-neutron detector (near), one short-spaced gamma-ray detector (SSn), and one long-spaced gamma-ray detector (LSn). Separation of multidetector Sigma logs may indicate the presence of mud-filtrate invasion in the case of thick formations. However, Sigma measurements acquired in thinly bedded formations are affected not only by ...
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rapid forward modeling of multidetector Logging While Drilling sigma measurements
Geophysics, 2014Co-Authors: Edwin Ortega, Carlos Torresverdin, William E PreegAbstract:ABSTRACTMultidetector Logging-While-Drilling (LWD) Sigma was introduced to the oil industry to measure neutron absorption cross section (Sigma) and radial length of invasion in shallow-invaded formations. Sigma quantifies the ability of a material to absorb thermal neutrons and is calculated from the late time portion of the time decay of thermal neutrons or gamma rays generated from thermal-neutron absorption. The assessment of invasion is made possible with the combination of a thermal-neutron detector and two gamma-ray detectors with different source-detector spacings. However, the interpretation of LWD Sigma logs is often affected by several environmental and/or geometric effects that can mask the formation response. A fast numerical simulation method embedded with inversion-based techniques can be used to estimate intrinsic formation Sigma from borehole measurements affected by shoulder-bed, invasion, and/or environmental effects. We developed a fast and accurate method to numerically simulate LWD mu...
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inversion based petrophysical interpretation of Logging While Drilling nuclear and resistivity measurements
Geophysics, 2013Co-Authors: Olabode Ijasan, Carlos Torresverdin, William E PreegAbstract:ABSTRACTInterpretation of borehole measurements acquired in high-angle (HA) and horizontal (HZ) wells is challenging due to the significant influence of well trajectory and bed geometrical effects. Experience shows that accurate integrated interpretation of well logs acquired in HA/HZ wells requires explicit consideration of 3D measurement physics. The most reliable alternative for interpretation of well logs in HA/HZ wells is with inversion techniques that correct measurements for shoulder-bed, undulating well trajectory, and bed geometrical effects While taking advantage of high data resolution. We discovered an efficient layer-based inversion workflow for combined, quantitative petrophysical and compositional interpretation of Logging-While-Drilling sector-based nuclear (density, neutron porosity, photoelectric factor, gamma ray) and array propagation resistivity measurements acquired in HA/HZ wells. A challenging synthetic benchmark example confirmed improved formation evaluation with the layer-based ...
Dzevat Omeragic - One of the best experts on this subject based on the ideXlab platform.
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High-Fidelity Real-Time Imaging With Electromagnetic Logging-While-Drilling Measurements
IEEE Transactions on Computational Imaging, 2017Co-Authors: Michael Thiel, Dzevat OmeragicAbstract:A pixel-based inversion approach is introduced for interpretation of deep directional resistivity Logging-While-Drilling electromagnetic measurements. It can be used for real-time reservoir mapping While Drilling to accurately place the well with respect to reservoir boundaries and fluid contacts as well as for reservoir characterization in high angle and horizontal wells. The methodology is based on the Gauss-Newton approach, using an adaptive l1-norm regularization and a robust error term to determine the 1-D formation anisotropic resistivity profile and local formation dip. The new inversion allows high-resolution imaging of the subsurface resistivity distributions and consistent integration of measurements of different depth of investigation. To further enhance the robustness and accuracy of the subsurface images, a fast approximate 2-D inversion is developed, which uses approximate modeling based on locally 1-D models, resulting in reservoir images of improved accuracy and consistency in mildly 2-D and 3-D scenarios. The inversion's ability to generate a stable robust but detailed resistivity image of the formation near the wellbore is proven on synthetic and field data.
