Sonic Logging Tools Research Articles

Azimuthal evaluation of formations near borehole: Numerical simulations and field examples

Azimuthal evaluation of formation properties near borehole is an important research direction of well logging technology, and we develop an innovative 3D sonic logging tool for that purpose. Except conventional measurements of monopole and dipole, this tool is added into an azimuthal transmitter station and a set of azimuthal receiver stations, all of which consist of eight piezoelectric vibrators in circumference to excite or acquire sonic waves. Our numerical simulation results show it can detect the heterogeneity of formations by using the measurement mode of azimuthal transmission and azimuthal reception that two types of P-wave with different velocities are found in the waveforms from some azimuths, but only one P-wave exists in other azimuths. Even two types of S-waves in one waveform are discovered when the formations are very hard. Similar phenomena for both P- and S-waves are also observed in field examples.

Prediction of the Shear Wave Velocity from Compressional Wave Velocity for Gachsaran Formation

Shear and compressional wave velocities, coupled with other petrophysical data, are very important for hydrocarbon reservoir characterization. In situ shear wave velocity (Vs) is measured by some sonic logging tools. Shear velocity coupled with compressional velocity is vitally important in determining geomechanical parameters, identifying the lithology, mud weight design, hydraulic fracturing, geophysical studies such as VSP, etc. In this paper, a correlation between compressional and shear wave velocity is obtained for Gachsaran formation in Maroon oil field. Real data were used to examine the accuracy of the prediction equation. Moreover, the genetic algorithm was used to obtain the optimal value for constants of the suggested equation. Furthermore, artificial neural network was used to inspect the reliability of this method. These investigations verify the notion that the suggested equation could be considered as an efficient, fast, and cost-effective method for predicting Vs from Vp.

Investigation of low-frequency broadband dipole transducer driving by PMN-PT transverse shear mode

A low-frequency broadband dipole transducer with a standard dipole directivity pattern is a crucial factor in the research and development of a sonic logging tool. A new dipole transducer design based on cylindrical shell oscillating is proposed in this paper, in which transverse shear polarization PMN-PT crystal stacks are used to provide a driving force to excite a cylindrical-shell oscillation to generate dipole acoustic field. The resonant frequency of the transducer is decided by the dimensions of crystal stacks. Piezoelectric coefficient d 15 of the PMN-PT crystals can reached 7000 pC/N, which means there is enormous potential in high power transducer design; Several ceramic plates are connected in a series to reduce the resonant frequency of the exciting source and increase the driving amplitude at the same time so as to enhance the radiation power further; several stacks of different sizes are connected in a parallel to broaden the bandwidth. Finite element method is adopted to optimize the structure of transducer. According to the optimized results, a prototype is produced and then tested in anechoic tank. Test results show that the transmitting response is larger than traditional dipole transducer and the directivity pattern is better in the operating frequency range.

Eliminating the azimuth ambiguity in single-well imaging using 3C sonic data

The shortcomings of conventional single-well sonic imaging are the inefficiency in eliminating azimuth ambiguity of the reflector outside boreholes. To resolve this problem, we proposed that 3C data of the reflection echoes be migrated simultaneously. The quantitative expressions of the received 3C data were first derived. The direct correlations between the polarity of the 3C data and the reflector azimuth were analyzed. It was revealed that the reflector positions can be fully identified by the associated echoes consisting of the transverse and axial components of wavefields. And an improved single-well imaging procedure using axial displacement component in addition to transverse components was thus developed. Numerical examples were evaluated for validation of the imaging method. According to the numerical results, the image intensity of the reflectors was effectively enhanced whereas the artificial mirrors of the reflectors were greatly weakened. It was suggested that a sonic logging tool with the 3C receivers be necessary for the image of reflectors without azimuth ambiguity.

Numerical simulations of dipole sonic responses in a liquid-filled trough with arc-shaped section

To test the running performance of a sonic logging tool, it is an effective way to place the tool in a water-filled trough and record the sonic responses for an integrated check of the transducers in laboratory. Hence it is necessary to investigate the wave propagation in such a non-symmetric structure. In this study, we present the numerical modeling results of dipole sonic responses in a trough with arc-shaped section. A 3D cylindrical finite difference code as well as the irregular free-surface conditions is implemented. It is revealed that the flexural mode in a trough is evidently slower than that in a cylindrical pipe with same sizes. The flexural velocity decreases with the increasing gap angle of the trough. Moreover, the trough structure shows strong elastic anisotropy. The in-line responses (XX and YY) of the logging tool are difference in phases and amplitudes. The amplitudes of both cross-line responses (XY and YX), which reflect the level of anisotropy, become greater as the gap angle increas...

Analyses on mode waves of acoustic logging while drilling in transversely isotropic formations

We investigated the phase-velocity dispersion and excitation intensity features of the Stoneley,flexural,and screw waves,respectively,for acoustic logging-while-drilling(LWD)in vertical wells surrounded by transversely isotropic formations.The sensitivity coefficients of those modes with respect to all elastic parameters are evaluated.And the comparisons between the LWD and conventional wireline logging are present.It is revealed that the monopole Stoneley waves at low frequencies can be applied for the inversion of the horizontal shear modulus(c66) using the LWD data because that parameter governs the velocities of low-frequency Stoneley modes.The propagation velocities of flexural modes do not tend to the shear velocities in the whole frequency range in a slow formation.The flexural-wave velocities,however,have a nearlylinear relation with the shear velocities in higher frequencies(e.g.,at 6kHz).Thus we can indirectly estimate the shear velocity using a dipole sonic logging tool even in a slow formation.Similar to the wireline logging,the screw modes excited by aquadrupole can also be used for the effective measurement of shear velocity.

Pre-injection Baseline Data Collection to Establish Existing Wellbore Leakage Properties

Poor wellbore integrity is a risk in CO2 storage that must be evaluated at any geologic sequestration site. The conditions of five wells from two fields in Wyoming were studied to better understand pre-injection leakage potential in existing wells. Ultrasonic and sonic logging tools mapped the condition of the casing and cement in each well. Permeability testing outside the casing was conducted using two different dynamic testing tools making point and vertical interference test measurements Permeability was also measured through laboratory testing of cased-hole sidewall cores. The results of laboratory measurements were generally in the microdarcy-to-nanodarcy range and indicate that the well cements have not degraded from exposure to the formation brines. The results of vertical interference tests when compared to lab measurements imply interfaces between casing and cement or cement and formation are more significant with respect to leakage than the quality of the cement at the tested location.

Finite difference modelling of dipole acoustic logs in a poroelastic formation with anisotropic permeability

SUMMARY Sedimentary rocks can exhibit strong permeability anisotropy due to layering, pre-stresses and the presence of aligned microcracks or fractures. In this paper, we develop a modified cylindrical finite-difference algorithm to simulate the borehole acoustic wavefield in a saturated poroelastic medium with transverse isotropy of permeability and tortuosity. A linear interpolation process is proposed to guarantee the leapfrog finite difference scheme for the generalized dynamic equations and Darcy’s law for anisotropic porous media. First, the modified algorithm is validated by comparison against the analytical solution when the borehole axis is parallel to the symmetry axis of the formation. The same algorithm is then used to numerically model the dipole acoustic log in a borehole with its axis being arbitrarily deviated from the symmetry axis of transverse isotropy. The simulation results show that the amplitudes of flexural modes vary with the dipole orientation because the permeability tensor of the formation is dependent on the wellbore azimuth. It is revealed that the attenuation of the flexural wave increases approximately linearly with the radial permeability component in the direction of the transmitting dipole. Particularly, when the borehole axis is perpendicular to the symmetry axis of the formation, it is possible to estimate the anisotropy of permeability by evaluating attenuation of the flexural wave using a cross-dipole sonic logging tool according to the results of sensitivity analyses. Finally, the dipole sonic logs in a deviated borehole surrounded by a stratified porous formation are modelled using the proposed finite difference code. Numerical results show that the arrivals and amplitudes of transmitted flexural modes near the layer interface are sensitive to the wellbore inclination.

Constraints on the Permeability Structure of Alluvial Aquifers From the Poro-Elastic Inversion of Multifrequency P-Wave Sonic Velocity Logs

We have explored the possibility of obtaining first-order permeability estimates for saturated alluvial sediments based on the poro-elastic interpretation of the P-wave velocity dispersion inferred from sonic logs. Modern sonic logging tools designed for environmental and engineering applications allow one for P-wave velocity measurements at multiple emitter frequencies over a bandwidth covering 5 to 10 octaves. Methodological considerations indicate that, for saturated unconsolidated sediments in the silt to sand range and typical emitter frequencies ranging from approximately 1 to 30 kHz, the observable velocity dispersion should be sufficiently pronounced to allow one for reliable first-order estimations of the permeability structure. The corresponding predictions have been tested on and verified for a borehole penetrating a typical surficial alluvial aquifer. In addition to multifrequency sonic logs, a comprehensive suite of nuclear and electrical logs, an S-wave log, a litholog, and a limited number laboratory measurements of the permeability from retrieved core material were also available. This complementary information was found to be essential for parameterizing the poro-elastic inversion procedure and for assessing the uncertainty and internal consistency of corresponding permeability estimates. Our results indicate that the thus obtained permeability estimates are largely consistent with those expected based on the corresponding granulometric characteristics, as well as with the available evidence form laboratory measurements. These findings are also consistent with evidence from ocean acoustics, which indicate that, over a frequency range of several orders-of-magnitude, the classical theory of poro-elasticity is generally capable of explaining the observed P-wave velocity dispersion in medium- to fine-grained seabed sediments.

Acoustic modeling for designing sonic logging tools

Formation acoustic properties such as velocity and attenuation provide useful information regarding rock type and formation fluid. Sonic logging is one of the principal measurements to evaluate the presence of hydrocarbons in the well and to enable an efficient and safe production of oil. Unfortunately the sonic measurement is affected by the tool itself. Suppressing or attenuating the tool wave, which propagates along the logging tool and is received by the sensors, is directly related to the accuracy of the answer products. In order to improve the measurement quality and to increase the efficiency of logging operations, the structure of sonic logging tools must be well understood. A sonic tool with known effects is decidedly more complex and acoustic modeling incorporating the tool structure details is becoming essential to better sonic tool design. The methodology of numerical modeling used to predict the response of a sonic tool is to be presented.

Simulating Sonic Scanner responses in an interactive Web‐based High Performance Computing environment

Sonic Scanner logging tool collects a wealth of data about the geological formation. The drawback of this is that we are now discovering new features on the acoustic logs that have never been observed before; only rigorous modeling can help properly interpret the data. Invariably, it is difficult to learn quickly how to run a modeling code, set the parameters properly, and be able to detect possible errors in the input. In addition, complex modeling requires high power computing resources, which are not always easily accessible the user. To address these problems we developed a multi‐tier Web‐based log modeling environment where the Sonic Scanner simulator is easily accessible from the common Web browser. The user builds the model in an intuitive AJAX‐like interface and submits the simulation to a remote High Performance Cluster. The computed waveforms are played back in the browser using Scalable Vector Graphics in a variety of customizable displays. The Web application is easily available to any user with an Internet access. In addition, a programmatically accessible Web service is available to application developers who desire to build their own interpretation applications using the Sonic Scanner simulator engine.

Application of multipole array sonic logging to acid hydralic fracturing

Multipole array sonic logging tools have widely been employed in Chinese oilfields in recent years. We have developed a software package for rock mechanical analysis with multipole array sonic logs. This advanced data processing method and software have been applied to the Tahe oilfield in Northern West China to provide guidance to acid hydraulic fracturing design and evaluation. In this paper, we present the field examples of such data processing and applications to demonstrate the validity and advantages of our method and software package.

日本発の技術開発のトレンドと事例

Sonic Scanner has been recently introduced to the market. This is the first 3D sonic logging tool developed in Japan. It measures sound slowness(1/velocity) of P and S wave along well axis, around well bore and away from well bore. There are many applications including drilling related applications. One example is “damaged zone” identification. Sonic Scanner is the latest example of logging tool developed in Japan, and there was a history to achieve such advanced tool development. It's been 70 years since the first electrical log was run in Japan, and it's been 50 years since logging service was brought into Japan. Schlumberger opened Engineering and Manufacturing center facility in Sagamihara 20 years ago, and started tool development. The reason Schlumberger opened such center in Japan was to capture Japanese leading technology and manufacturing quality and apply to oil field. One of the examples is color printer for oil field use, which was 20 years ahead of consumer market. The trend to capture leading edge“enabling” technologies to apply them to increase efficiency of oil field development will continue. To do that, we need to work with such technology providers that may be another strong industry in Japan or Academic community.

In-situ stress dependence of wave velocities in reservoir and overburden rocks

Seismic waves propagate through a stressed earth. Sonic waves recorded by a borehole sonic logging tool propagate in the near-well environment—which is also stressed, albeit under different stress conditions than the untouched formation far away. Cores excavated from within the earth undergo stress release, and are then reloaded in the laboratory—but hardly ever to the complete, fully anisotropic in-situ state of stress and pore pressure. Based on this, we easily recognize that stress sensitivity affects our ability to compare and correlate geophysical and petrophysical measurements of wave velocities. On the other hand, it also provides an avenue to extract information about rock stresses. As an example, the presence of abnormally low velocities in seismic or log data is evidence of high pore pressure.

Finite‐difference modeling of viscoelastic materials with quality factors of arbitrary magnitude

To minimize acoustic noise, designers of sonic logging tools often consider coatings of viscoelastic materials with very high attenuation properties. Efficient finite‐difference modeling of viscoelastic materials is a topic of current research. To model viscoelastic materials in the time domain through finite differences efficiently, one needs to replace the time convolution, which enters in the stress–strain relations, by a set of first‐order differential equations. This procedure is equivalent to computing a rational approximation of a certain form to the frequency‐dependent complex modulus of viscoelasticity. Known schemes for computing such approximations are designed to treat materials with low attenuation, such as underground formations, but fail to produce accurate or even physically meaningful results for highly attenuative materials. We propose a novel scheme that allows one to construct, for a given frequency range, a uniformly optimal rational approximation for the most widely used model of materials with constant quality (Q‐) factors of arbitrary magnitude. We present the proof of convergence and demonstrate it on numerical finite‐difference examples. These examples also demonstrate the effective transparency of a simple tool modeled as a pipe of highly viscoelastic material. For frequency‐dependent quality factors we present a modified numerical scheme to compute a nearly optimal rational approximation of the viscoelastic modulus.

Method and system for calibrating acoustic receivers in borehole logging tools

Monopole and quadrupole contamination on dipole measurements is one of the main problems for sonic logging tools that employ arrays of acoustic receivers to measure a borehole’s dipole mode. The amplitude and phase mismatch of the array of sensors in acoustic logging tools plays an important role in the quality of dipole measurements. Acoustic receivers often have different sensitivities, and different sensitivities to the same wave field result in a greater possibility of no dipole contamination. Even similarly or identically manufactured receivers tend to report different amplitudes and time measurements (i.e., amplitude and phase mismatch). In practice, the no-dipole modes are removed by making the measurements at different azimuth and extracting the dipole mode from those that reject the other contaminating modes. Therefore, to improve rock formation slowness estimation and downhole modal computation, it is necessary to calibrate acoustic logging tools by detecting and correcting the amplitude and phase mismatch of the individual sensors mounted in the logging tools. A method and system for calibrating acoustic receiver arrays mounted in a downhole logging tool and the factors that affect their sensitivity are discussed in this paper.

Azimuthal anisotropy using shear dipole sonic: insights from the AIG 10 well, Corinth Rift Laboratory

Abstract Within the Corinth Rift Laboratory, dipole sonic data have been acquired in the AIG 10 well between depths 711 and 1004 m during three passes of a sonic logging tool at three different borehole fluid pressures. Specific sections of the well reveal clear characteristics of either moderate-to-large azimuthal anisotropy (9–25%) below the Aigion Fault, e.g., 779–784 and 809–816 m, with a fast-shear azimuth directed 105°, or homogeneous isotropic medium (i.e., 735–753 m) between the casing shoe and the fault. The presence of the fault is coincident with the identification of lower velocities over an interval of approximately 12–14 m. Analysis of the data reveals that the formation is not acoustically stress-sensitive to the 3 MPa differential pressure applied. Interpretation of the sonic data with complementary image logs suggests the anisotropy is due to intrinsic fractures and bedding, and the fast-shear direction 105° is consistent with the regional maximum horizontal stress. To cite this article: R. Prioul et al., C. R. Geoscience 336 (2004).

Modeling of borehole Stoneley waves in the presence of skin effects

An important aspect of oil production from a geological formation is the process of flow into a well penetrating the formation. Recent laboratory experiments indicate that well-inflow can be significantly reduced by a skin effect caused by the presence of a thin layer of low permeability around the wellbore. This impairment layer is drilling induced and differs from the mudcake that is usually encountered when logging a well. Whereas a mudcake may have built up on the borehole wall during drilling, the drawdown pressure often removes it when oil is produced from the well. In contrast with such a temporary mudcake, the impairment layer is believed to form a permanent flow impedance throughout the lifetime of a well unless extensive cleaning measures are taken. A simple poro-elastic model is constructed to investigate the propagation of Stoneley waves in a borehole with a thin impairment layer. If the impairment layer affects Stoneley wave propagation, it may be possible to acoustically detect this layer with sonic logging tools. Using realistic values for the impairment flow impedance, model calculations for a typical sandstone reservoir of 20% porosity indicate that the impairment layer changes the dispersion characteristics of borehole Stoneley waves. The magnitude of these changes increases with increasing mobility of the reservoir pore fluid.

A three-dimensional finite difference code for the modeling of sonic logging tools

This paper presents a numerical program for the simulation of elastic wave propagation and scattering in three-dimensional (3-D) cylindrical coordinates based on the first-order velocity-stress finite-difference scheme on staggered grids. Both Liao’s and Lindman’s absorbing boundary conditions are implemented for the exterior boundaries to efficiently truncate the computation domain for elongated 3-D well logging problems. Symmetric and anti-symmetric boundaries in azimuthal and axial directions are also implemented in the code to further reduce the size of the problem. Included for the first time with this code are very large and complex geometrical structures such as the whole slotted sleeve housing of a sonic well-logging tool which typically involves hundreds of millions of unknowns. The calculation for such a large problem only takes a couple of days on a four-processor SGI Power Challenge machine. Different types of slotted sleeve models are studied for sonic logging tools. Simulation results show that different slotted sleeves vary widely in delaying and attenuating the pipe waves which travel along the tool housing. A new slotted sleeve structure with three horizontal slot sections for every vertical slot period is proposed for better performance. A dipole source is found to produce much cleaner waveforms than a monopole source.

Application of theoretically derived rock physics relationships for clastic rocks to log data from the Wilmington Field, CA

Relationships between porosity and shear modulus are applied to logs recorded in the Miocene Upper Terminal formation of the Wilmington Field, CA. to predict porosity from shear‐wave velocity data recorded through casing using a dipole sonic logging tool. A relationship based on a modified Hashin‐Shtrikman lower bound, appropriate for the unconsolidated nature of the formation, allows determination of porosity from the shear modulus. The results are similar to those obtained using standard log analysis in sands. Standard logs predict higher porosities in smectite‐bearing wackes because of the inclusion in the standard analysis of bound water or micro‐porosity in the clays which is not included in the porosity value derived from the shear‐wave velocity.