United States has an estimated 327 billion barrels of oil in existing production fields that remain in place even after primary and secondary recovery techniques have been employed. High resolution borehole-to-borehole seismic tomography can provide the information needed to locate these unproduced regions through the identification of subtle geologic anomalies and can be used to assess the progress of certain production strategies. However, advances in both data acquisition hardware and data processing are required before high resolution images are practicable between oil well boreholes separated by several thousand feet. This project involves the research and development of an innovative fluid coupled seismic source design that overcomes many of the disadvantages of existing piezoelectric seismic sources. The new source has a lower operating frequency capability approaching 5.0Hz, is efficient, is more suitable for borehole applications, and is expected to operate at borehole temperatures approaching 200øC. Phase I of this project will prove the feasibility of the borehole piezoelectric seismic source through a laboratory and field study aimed at defining the piezoelectric source transducer performance characteristics through free field acoustic and borehole-to-borehole seismic measurements. Of specific interest are the source transmission properties such as (1) usable bandwidth, (2) source behavior over this band, and (3) the pilot wave front to be used in correlation of the source. This borehole piezoelectric source will be characterized for efficient high duty-cycle sweep excitations. Its pilot signal characteristics will be suitably defined so that it can be properly correlated to produce a high quality Klauder wavelet Anticipated Results/Potential Commercial Applications as described by the awardee: The p fluid-coupled seismic source will provide improved low frequency capabilities enabling operation of the source in less cooperative geologies where seismic velocities are less than 10,M feet per second. Improvements in the source operating temperature capabilities will enable practical operation in enhanced oil recovery applications. Accurate definition of the source pilot wavelet addresses a great need for borehole sources that can be correlated to produce a high quality Klauder wavelet. This source definition will allow precise correlation of sweep excitations resulting in (1) system dynamic range improvements of at least 40 dB and (2) practical diffraction tomography pmg of resultant data sets. These seismic source innovations, when combined with borehole tube wave suppression techniques and future innovations in seismic detectors, will ultimately improve system dynamic range, allowing propagation and detection of kilohertz seismic signals in a variety of geologies.
