Source Radiation Patterns In Cased Boreholes

Source radiation from open and cased boreholes are well documented. The effect of an unbonded casing on the radiation patterns of volume, radial stress and axial stress sources in a borehole has received less attention and is modeled and analyzed here in the context of performing single well imaging. Radiation patterns were evaluated using a global matrix approach and wavenumber integration. 'While a borehole with a bonded casing has a single propagating mode at low frequencies, the stoneley mode, the borehole with unbonded casing has three propagating modes. Of the two additional modes that are due to the unbonded casing, one is present mainly in the cross-section of the casing and has a phase speed close to the speed of longitudinal waves in steeL Because of its large phase speed (~ 5400 m/s), this mode radiates into almost all formations and influences the radiation pattern of all source types. Test data and the predicted radiation patterns were used to identify the annulus material behind the casing.Massachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation Consortiu

Shear-Wave Tomographic Images Of An Oil Reservoir At MIT's Michigan Test Site

We conducted a P- and S-wave crosswell survey with Conoco's orbital vibrator source and three-component receivers at M.LT.'s Michigan Test Site. The receiver and source wells bracket a known oil reservoir. Applying a nonlinear crosswell traveltime tomography method, we reconstruct the velocity structures in the oil reservoir using P- and S-wave data separately. The P-wave tomogram shows a similar image to the one by Matarese (1993), and it does not present much velocity variations in the oil producing zone. However, the S-wave tomogram clearly shows the image of the reservoir zone, which is characterized with low velocities in a pinnacle reef. The S-wave velocities in the reservoir are about 20% lower than those of the surrounding carbonates.Massachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation Consortiu

Elastic waves push organic fluids from reservoir rock

Elastic waves have been observed to increase productivity of oil wells, although the reason for the vibratory mobilization of the residual organic fluids has remained unclear. Residual oil is entrapped as ganglia in pore constrictions because of resisting capillary forces. An external pressure gradient exceeding an ‘‘unplugging’’ threshold is needed to carry the ganglia through. The vibrations help overcome this resistance by adding an oscillatory inertial forcing to the external gradient; when the vibratory forcing acts along the gradient and the threshold is exceeded, instant ‘‘unplugging’’ occurs. The mobilization effect is proportional to the amplitude and inversely proportional to the frequency of vibrations. We observe this dependence in a laboratory experiment, in which residual saturation is created in a glass micromodel, and mobilization of the dyed organic ganglia is monitored using digital photography.We also directly demonstrate the release of an entrapped ganglion by vibrations in a computational fluid-dynamics simulation

Some observations of P n spectra from the New Madrid earthquake of February 2, 1962

Master of ScienceGeologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/115519/1/39015003275354.pd

Calibration and Testing of Sonic Stimulation Technologies

In conjunction with Baker Atlas Inc. Michigan Technological University devised a system capable of recording the earth motion and pressure due to downhole and surface seismic sources. The essential elements of the system are 1) a borehole test site that will remain constant and is available all the time and for any length of time, 2) a downhole sonde that will itself remain constant and, because of its downhole digitization feature, does not require the wireline or surface recording components to remain constant, and 3) a set of procedures that ensures that the amplitude and frequency parameters of a wide range of sources can be compared with confidence. This system was used to record four seismic sources, three downhole sources and one surface source. A single activation of each of the downhole sources was not seen on time traces above the ambient noise, however, one sweep of the surface source, a small vertical vibrator, was easily seen in a time trace. One of the downhole sources was seen by means of a spike in its spectrum and a second downhole source was clearly seen after correlation and stacking. The surface vibrator produced a peak to peak particle motion signal of approximately 4.5 X 10-5 cm/sec and a peak to peak pressure of approx. 2.5 X 10-7 microPascals at a depth of 1,485 ft. Theoretical advances were made with our partner, Dr. I. Beresnev at Iowa State University. A theory has been developed to account for the behavior of oil ganglia trapped in pore throats, and their ultimate release through the additional incremental pressure associated with sonic stimulation

Crosswell seismic amplitude-versus-angle studies at a Niagaran reef

A high-resolution crosswell seismic data set was collected over a Silurian Niagaran reef in Michigan\u27s lower peninsula. The survey was optimized for both reflection imaging purposes and the gathering of a wide range of incidence angles. With this we can do a highly detailed interpretation using the post stack migrated data, and utilizing the prestack data for AVA (amplitude variation with angle) analyses. With the wide range of incidence angles and by comparing AVA observations with model predictions we can better determine and map the various litho-facies and fluid distributions within a carbonate reef oil reservoir. In addition to the extremely high resolution of the crosswell images, reflections are obtained from boundaries that have near-zero reflectivity at small angles of incidence because of the large reflectivity that occurs near the critical angle. This has implications in allowing operators of carbonate reef oil reservoirs to better image the interior structure of the reservoirs and to identify those areas that may still contain amounts of oil after initial production. © 2005 Society of Exploration Geophysicists

Crosswell seismic imaging of acoustic and shear impedance in a Michigan reef

Acoustic and shear impedance images, obtained from deterministic simultaneous inversion of a high-resolution crosswell seismic survey, were used to obtain the internal structure of Niagaran reef in Michigan. The crosswell seismic survey was conducted using two monitor wells external to the reef. These wells had depths that extended beyond the depth of the reef, and imaging used reflections from above and beneath the reef, resulting in the best seismic images of any Niagaran pinnacle reef obtained to date. The top of the reservoir can be clearly distinguished, as well as its lateral extent or dipping edges. Reflection events internal to the reef are evident; some are fairly continuous across the reef and others are discontinuous. © 2010 Society of Exploration Geophysicists

Numerical modeling of ambient-noise seismic interferometry

This numerical modeling study examines the use of seismic interferometry to retrieve weak seismic reflections from background noise, a form of passive monitoring. Assuming we seek reflections from deep noise sources, representing either teleseismic events or local events as expected in a field of active injection, the factors that influence the quality of the retrieved reflections from interferometry include geophone interval, geophone depth, and effect of shallow noise sources. Using model data, geophone interval showed no significant effect on the reflection quality, but buried geophones produce ghost reflections, suggesting that shallow geophones might be optimal. However, using the combination of buried hydrophones and geophones should be able to cancel the ghosting effects. Shallow noise sources produce a destructive effect on the reflections from deeper noise sources and damage the resulting image

Crosswell seismic imaging and inversion of a michigan reef from above and from beneath

Summary: A high-resolution crosswell seismic survey was conducted using two monitor wells located external to a Silurian (Niagaran) reef, at Springdale field in northern Michigan. These wells extended to much greater depths than the reef, and imaging was conducted both from above and from beneath the reef. The resulting seismic images provide the best views of any Niagaran pinnacle reef obtained to date. The tops of the reservoir can be clearly distinguished, and its lateral extent or dipping edges can be observed along the profile. Reflection events internal to the reef are evident; some of them are fairly continuous across the reef and others are discontinuous. Inversion of the seismic data indicates which events represent zones of higher porosity and which are lower porosity or anhydrite-plugged. The full stacked images include angles that are beyond critical for many of the interfaces, and some reflections are visible only for a small range of angles, presumably near their critical angle. Strong apparent attenuation of signals occurs when seismic ray paths pass through the upper part of the Springdale reservoir; this may be due to intrinsic attenuation and/or scattering of events due to the locally strongly varying gas saturation and extremely low fluid pressures. The seismic images obtained, and interpretations of them, as assisted by inversion, provide additional insight into the internal geometry of this reef and provide data that should be useful for reservoir management