Uniwell Borehole Seismic Data on Tube Wave Noise Abatement
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Abstract:
The sensitivity to oil-water fluid-substitution events of Uniwell sourcing and sensing seismic waves in the same borehole is degraded by tubewave noise generated by the source. To assess some abatement measures, a ten-level clamped vector-motion sensor string was ganged with a high-frequency or a low-frequency seismic source to record data on tubewave noise levels.Keywords:
Seismic Noise
Vertical seismic profile
Summary A deep exploration well was drilled down to 5300 m on the top of a surface fold in the mountainous Zagros in order to encounter a deep anticline at the top of Permian reservoir formation expected in the area. Due to poor surface seismic, geological and practical considerations were used for locating the well. The structural interpretation was refined during the drilling operation, using: well logs, borehole resistivity imaging, geological data, a 2D surface seismic and an intermediate VSP recorded using a three component (3C) sensor tool implemented with a Relative Bearing / Roll angle sensor. The VSP data was processed before drilling the deep interval 5300m to 6130m Total Depth (TD), with the intention to predict any reflection below the intermediate 5300m drilled depth. Next, the whole borehole data was further analyzed after reaching TD. The main focus was on independent extraction of dip/azimuth information from oriented 3C VSP data and from borehole wall resistivity measurements. The highly folded structure encountered by the well and the absence of high energy seismic reflectors with substantial lateral extension detected by the VSP are coherent with the blurred results on the 2D surface seismic section in the well vicinity.
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Anticline
Scientific drilling
Reflection
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This note describes a vertical borehole geophone array which can be used in slim boreholes. The array was designed as part of a research program in Sweden to study the potential of seismic crosshole techniques for mapping cracks and fracture zones in crystalline rock. The design meets not only the constraints imposed by the slim boreholes (diameter 56 mm) available in Sweden for crosshole surveys, but also the desire to make array recordings with three component locked geophones. The use of vertical arrays in boreholes has been discussed by Galperin (1974).
Geophone
Vertical seismic profile
Seismic array
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Borehole seismology is the highest resolution geophysical imaging technique available to the oil and gas industry for characterization and monitoring of oil and gas reservoirs. However, the industry's ability to economically do high resolution 3D imaging of deep and complex gas reservoirs using borehole seismology is currently frustrated by the lack of the acquisition technology necessary to record the large volumes of the high frequency, high signal-to-noise-ratio borehole seismic data needed to do 3D imaging. This proposal takes direct aim at this shortcoming. P/GSI is developing a 400 level 3C clamped downhole seismic receiver array for borehole seismic 3D imaging. This array will remove the acquisition barrier to record the necessary volumes of data to do high resolution 3D VSP or 3D cross well seismic imaging. 3D VSP and long range Cross-Well Seismology (CWS) are two of the borehole seismic techniques that will allow the Gas industry to take the next step in their quest for higher resolution images of the gas reservoirs. Today only a fraction of the original Oil or Gas in place is produced when reservoirs are considered depleted. This is primarily due to our lack of understanding of the detailed compartmentalization of the oil and gas reservoirs. The 400 level 3C borehole seismic receiver array will allow for economic use of 3D borehole seismic imaging for reservoir characterization and monitoring. By using 3C surface seismic or 3C borehole seismic sources the 400 level receiver array will furthermore facilitate 9C reservoir imaging. The 9C borehole seismic data will provide P, SH and SV information for imaging of the complex deep gas reservoirs and allow quantitative prediction of the rock and the fluid types. The data quality and the data volumes from a 400 level 3C array will allow us to develop the data processing technology necessary for high resolution reservoir imaging.
Geophysical Imaging
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A bstract An exact formulation for borehole coupling, which is valid for all frequencies and all azimuthally symmetric and non‐symmetric components, is presented. The borehole effects on downhole seismic measurements are studied in detail as functions of frequency, angle of incidence and polarization of an incident wave as well as geophone orientation. We found that correction for the borehole effect on downhole measurements should be made for frequencies above 500 Hz in a hard formation. In a soft formation, if the angle of incidence is well away from the resonance angle for SV incidence, no borehole correction is needed for frequencies below 300 Hz, while for frequencies above 300 Hz, the borehole can cause severe problems in downhole measurements. The borehole can also significantly alter the particle motion direction which implies that horizontal component rotation from data itself is unreliable for experiments with frequencies above 1 kHz in the hard formation and around 500 Hz in the soft formation.
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Borehole geophysics is essential for exploration, assessment, and production of Earth's resources, in addition to carrying out fundamental studies on the Earth itself. Borehole-based technology encompasses activities ranging from coring to measurements such as logging, VSP, crosswell profiling, and passive seismic monitoring. Each of these disciplines has grown into an established branch of borehole geophysics. The idea behind all these measurements has been to obtain useful information about the geological environment that helps evaluate subsurface zones of interest.
Coring
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Profiling (computer programming)
Geophysical prospecting
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Velocity measurements in shallow sediments from ground surface to approximately 370 to 400 feet bgs were collected by Redpath Geophysics using impulsive S- and P-wave seismic sources (Redpath 2007). Measurements below this depth within basalt and sedimentary interbeds were made by UTA between October and December 2006 using the T-Rex vibratory seismic source in each of the three boreholes. Results of these measurements including seismic records, wave-arrival identifications and interpreted velocity profiles are presented in the following six volumes: I. P-Wave Measurements in Borehole C4993 II. P-Wave Measurements in Borehole C4996 III. P-Wave Measurements in Borehole C4997 IV. S-Wave Measurements in Borehole C4993 V. S-Wave Measurements in Borehole C4996 VI. S-Wave Measurements in Borehole C4997 In this volume (V), all S-wave measurements are presented that were performed in Borehole C4996 at the WTP with T-Rex as the seismic source and the Lawrence Berkeley National Laboratory (LBNL) 3-D wireline geophone as the at-depth borehole receiver.
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Geophone
P wave
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The U.S. Dept. of Energy funded Frio Brine Pilot provided an opportunity to test borehole seismic monitoring techniques in a saline formation in southeast Texas. A relatively small amount of CO{sub 2} was injected (about 1600 tons) into a thin injection interval (about 6 m thick at 1500 m depth). Designed tests included time-lapse vertical seismic profile (VSP) and crosswell surveys which investigated the detectability of CO{sub 2} with surface-to-borehole and borehole-to-borehole measurement.
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