Borehole Sonic Logs Research Articles

On the cause of 1/f‐power spectral scaling in borehole sonic logs

Borehole logs provide in situ information about the scaling of fluctuations in the elastic properties of rock. A surprising finding has been the widespread 1/fβ‐type (0.5 < β < 1.5) scaling of borehole sonic log power spectra, yielding no clear correlation with geological age, type or history, raising questions about the reliability and origin of these findings. Ubiquitous fractures, for example, have been evoked as the most likely explanation of these results. Firstly, we show that the smoothing effects of the logging tool must be taken into account in order to obtain reliable values of β. We then investigate the scaling properties of lithology only in perfectly exposed metamorphic rock, by explicitly excluding fractures. We find clear 1/f scaling for reconstructed velocity data based solely on lithological variations. Although fractures are certainly important in contributing to 1/f fluctuations in borehole logs, intrinsic geology may also play a significant role.

Acoustic spectrum analysis of borehole sonic logs for engineering properties and fracture characterisation: a case history : Yearsley, E N; Crowder, R E Proc 1990 Annual Symposium on Geology and Geotechnical Engineering, Instrumentation and Computer Applications, Pocatello, 4–6 April 1990P25.1–25.14. Publ Pocatello: Idaho State University, 1990

Acoustic spectrum analysis of borehole sonic logs for engineering properties and fracture characterisation: a case history : Yearsley, E N; Crowder, R E Proc 1990 Annual Symposium on Geology and Geotechnical Engineering, Instrumentation and Computer Applications, Pocatello, 4–6 April 1990P25.1–25.14. Publ Pocatello: Idaho State University, 1990

Acoustic Velocities in Petroleum Oils

Summary Results of laboratory experiments on acoustic-wave velocities in oils showthat the measured acoustic velocities are strong functions of both temperatureand pressure. The experimental results are discussed in light of existingliquid-state theories and models to interpret and understand theacoustic-velocity behaviors of oils. Correlations are made between acousticvelocity and temperature, pressure, API gravity, and molecular weight. Empirical equations are established to calculate acoustic velocities in oilswith known API gravities. Various applications or potential applications of theexperimental results are also discussed. Introduction With the rapid developments in seismic and well logging technologies, detailed studies on hydrocarbon resrvoirs are getting more attention. In recentyears, seismic borehole-to-borehole tomography, 3D seismic reservoir imaging, seismic delineation of reservoir fluid saturations, seismic evaluation andcharacterization of hydrocarbon reservoirs, seismic monitoring of productionand EOR processes in time, and detailed borehole sonic logging have all begunto emerge. These technologies will become routine in the near future. Usingthese new methods and interpreting their results, however, require that weunderstand the acoustic properties of reservoir fluids and rocks. Unfortunately, the importance of the acoustic properties of reservoir liquidshas not yet been recognized; i.e., there are very few experimental data onacoustic velocities in crude oils and no systematic studies. Therefore, themain purpose of this paper is to provide acoustic-wave-velocity information ondifferent oils. We measured acoustic velocities at the ultrasonic frequency of 800,000cycles/sec [800 kHz] in eight dead oils and two refined petroleum hydrocarbonswith gravity ranging from 5 to 62°API [1.037 to 0.73 g/cm3]. We alsomeasured acoustic velocities in a live or gas-saturated oil. The experimentalresults show that all velocities in oils strongly depend on temperature andpressure and that dissolved gases substantially reduce the acoustic velocitiesin live oils. In this paper, we briefly describe the experimental method and theproperties of the oil samples used in the experiments, and we show theexperimental results of acoustic velocities in dead and live oils. Tounderstand and interpret the acoustic-velocity behaviors of the oils better, wediscuss various liquid-state theories and models and the relationship betweenacoustic velocities and PVT measurements. We correlate acoustic velocities indead oils with temperature, pressure, API gravities, and molecular weights ofthe oils and establish empirical equations to calculate or to estimate acousticvelocities in oils if the API gravities are known. Finally, we discusspotential applications of our velocity results in both geophysical andpetroleum engineering aspects and present conclusions from this study. Experiments For the experiments, we used the pulse transmission method with an apparatusconsisting of a pulse generator/receiver, a digital oscilloscope, two acoustictransducers, and a pressure vessel. Electrical pulses generated by the pulsegenerator/receiver were sent to the emitting piezoelectric transducer, whichconverts electrical energy into mechanical vibrations. After traveling throughthe fluid sample, the ultrasonic waves were converted back to electricalsignals by the receiving transducer and recorded by the digital oscilloscope. Travel times of the ultrasonic waves through the oil sample were measured witha precision of 0.05 µsec. Ultrasonic velocities were calculated by v(p, T)=L(p, T)/?t(p, T), whereL(p, T)=distance between the two transducers corrected forpressure and temperature and ?t(p, T)=travel time of theultrasonic waves, which is a function of pressure and temperature. Temperatures were controlled by a heating coil and a temperature controllerand were measured by two thermocouples connected to a digital meter. Theaccuracy of the temperature measurements was about 1°F [0.5°C]. Pressures inthe experiments were controlled by an automatic fluid pump and were readthrough a digital pressure gauge with an accuracy of about 10 psi [0.07Mpa].

Advanced Seismic Techniques For Delineation of Petroleum Reservoirs

Introduction Seismic inversion yields synthetic sonic logs from seismic reflection data recorded at ground surface. Synthetic sonic logs are similar to, and have most of the properties of, long source-receiver borehole sonic logs. They provide a new area/or application of seismic digital process technology. The synthetics have been found to be particularly useful for the delineation of petroleum reservoirs, including the extent, thickness and porosity of the reservoir rocks. In a typical survey, field data, obtained from seismic line profiles across reservoirs, yield a sequence of synthetic sonic logs. Continuous vertical cross sections which display colour-coded transit time units can be interpreted in terms of lithology and porosity within the limits of interpretation of the single sonic curve and the resolution of the method. Sonic velocity changes are related to porosity and, by establishing the velocity of the matrix rock, the porosity within it can be estimated from synthetic sonic logs. Applications include optimizing development drilling patterns to obtain maximum production, the design of secondary recovery programs, the positioning of injection wells and the location of offshore drilling platforms to ensure maximum recovery. Introduction Delineation and definition of a known new petroleum reservoir is generally the responsibility of the production engineer or geologist, who must rely on a few well logs to make his determination. The advantages of the superb vertical resolution of the logs are offset by poor horizontal sampling; well logs can be obtained only by first drilling expensive boreholes, which are therefore usually spaced at rather wide intervals. The field was probably discovered with the reflection seismograph, which provides excellent horizontal sampling, but poor vertical resolution. Also, the conventional seismograph merely maps stratigraphic boundaries and pro- vides little or no confirmation about the actual rock units. Hence, it is of little help in determining reservoir properties. As a result, the development, geologist prefers to rely on samples and well logs, as they yield the desired degree of resolution and type of information. At the borehole location, both well logs and seismic traces sample the same geological column. In fact, a seismic reflection trace is merely a transform of the sonic and density information on borehole logs. For years, geophysicists have computed synthetic seismograms from sonic and density logs. A well constructed synthetic seismogram will match a field-recorded seismogram very closely, and aids in correlating seismograph information to borehole geology at the tie point. The reverse process, of computing a synthetic sonic log from a seismic trace, is also theoretically possible, but it has not worked well in the past, because of a difference "in quality of source signals. A sonic log is a relatively pure signal, recorded directly from the rock at the level of investigation. A seismic reflection signal, generated at the ground surface, must travel down through the· earth to the level of investigation and back again. In transit, it is often contaminated by external noise, distorted by wave pro" pagation phenomena, and part of it may be lost or attenuated in the transmission.

Diagenesis of Marine Sands to Tight Gas Sands: Effects on Acoustic and Hydraulic Properties: ABSTRACT

Figure The primary stages of diagenesis of marine sands usually increase total grain contact area, increase the number of contacts, decrease porosity, and increase pore network tortuosity. These microstructural factors strongly affect the continuum acoustic and hydraulic properties of the sands. To better understand diagenetic effects on these properties, compressional and shear wave velocities, Vp and Vs, and their specific attenuation, Qp-1 and Qs-1, were measured in an unconsolidated quartz sand (Ottawa sand, porosity ^approx 35%), a quartzarenite sandstone (St. Peter sandstone, porosity ^approx 22%), and a lithic-quartz arenite (Spirit River tight gas sand, porosity ^approx 5%). Measurements were made under effective press res, Pe, up to 350 bars as a continuous function of partial gas saturation, at frequencies from 10 to 15,000 Hz, and from 150 to 500 kHz. Experimental results are explained with relations derived from contact and packing theories. Results suggest that Vp/Vs and Qp-1/Qs-1 may be used to distinguish between gas and consolidation effects in reflection seismology and borehole sonic logs. Gas permeability was also measured in Spirit River tight gas sands from the Alberta Deep Basin as a function of effective pressure and partial gas saturation. These values are compared with known values for quartz sands and sandstones, and the results are examined with simple pore network models. While porosity decreases by a factor 7 from Ottawa sand to Spirit River sandstone, gas permeability drops by as much as 8 orders of magnitude. Gas permeability in all granular sedimentary materials, especially the tight sands, is a strong function of clay content, partial gas saturation, and effective pressure. End_of_Article - Last_Page 963------------

Synthetic Sonic Logs for Delineation of Petroleum Reservoirs: ABSTRACT

A recent development in digital process technology yields synthetic sonic logs from seismic reflection data recorded at the ground surface. Synthetic sonic logs are similar to, and have most of the properties of, long source-receiver borehole sonic logs. The synthetics have been found to be particularly useful for the delineation of petroleum reservoirs, including the extent, thickness, and porosity of the reservoir rocks. In a typical survey, field data, obtained from seismic line profiles across reservoirs, yield a sequence of synthetic sonic logs. Continuous vertical cross sections which display color-coded transit time units can be interpreted in terms of lithology, porosity, and related subsurface information, within the limits of interpretation of the single sonic curve and the resolution of the method. Applications include the optimization of development drilling patterns to obtain maximum production, the design of secondary recovery programs and the positioning of injection wells, and the location of offshore drilling platforms to ensure maximum recovery. End_of_Article - Last_Page 949------------