Abstract: Single Well Seismic Imaging: Recent Advances and Status
MAJER, E., Lawrence Berkeley National Laboratory, Berkeley, CA; T. DALEY, Lawrence Berkeley National Laboratory, Berkeley, CA; R. GRITTO, Lawrence Berkeley National Laboratory, Berkeley, CA; J. HARRIS, Stanford University, Stanford, CA
Over the last five years as part of DOE's Fossil Energy Program, LBNL in conjunction with industry has been developing and applying methods of extending the penetration of conventional seismic logging from a few meters out to tens if not hundreds of meters. This is accomplished by increasing the distance between the source and the receiver in the well from a few meters up to hundreds of meters, depending upon the desired depth of investigation. This is referred to as single-well seismic imaging, however, as one increases the source receiver distance many problems not encountered in conventional well logging became more severe. In effect, one now is trying to image in a true 3-D sense away from the well, therefore, directionality becomes important of the transmitted as well as the received signals.
This is particularly true when multicomponent sources and/or receivers are used. Also, the frequency range in single-well seismic imaging is much broader (50 Hz to 10 kilohertz) than in sonic logging (2 to 3 kilohertz). Although this can be an advantage, such issues as source generated noise, borehole interaction, tube waves and other sources of noise became more apparent. To address these, as well as other issues, we have been carrying out a series of experiments at a variety of scales and conditions to identify fundamental issues and solutions to advance the practice of single-well imaging. The scales between source and receiver have ranged from a few meters to over 150 meters. The sources used have been piezoelectric sources with frequencies between 1 kilohertz to 10 kilohertz and mechanical orbital sources with frequencies between 50 hertz and 400 hertz. In most cases the objective has been to perform CMP imaging from the borehole by using multiple receivers hung below the source. Both hydrophones and three component locking geophones have been used. The target of most investigations has been vertical or near vertical features away from the borehole. To date the target has been permeable fractures, but it is also possible to image bed boundaries, edges of faults and other structures (salt domes) or any other feature which will cause a reflection back to the borehole.
Presented will be the results of recent surveys and recommendations of use. To date it appears that single-well seismic imaging could be a powerful method, especially if used in a time lapse sense and where high resolution is needed and well spacing is such that crosswell cannot be used. Recent and near future advances in instrumentation will make the method more economical and possibly deployable through the end of tubing. Obvious applications are hydrofracture monitoring, steam/water flooding monitoring, fracture mapping and validation of drilling paths in horizontal drilling applications.
MAJER, E., R. GRITTO, and J. HARRIS
AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California