Crosswell seismic reflection/diffraction tomography: A reservoir characterization application

Autor: Wafik B. Beydoun, M. Ali C. Tura, Robert J. Greaves
Rok vydání: 1994
Předmět:
Zdroj: GEOPHYSICS. 59:351-361
ISSN: 1942-2156
0016-8033
Popis: A crosswell seismic experiment at the San Emidio oil field in Bakersfield, California, is carried out to evaluate crosswell reflection/diffraction tomography and image the interwell region to locate a possible pinchout zone. In this experiment, the two wells used are 2500 ft (762 m) apart, and the zone to be imaged is 11 000 ft (3350 m) to 13 000 ft (3960 m) deep. With the considered distances, this experiment forms the first large scale reservoir characterization application of crosswell reflection/diffraction tomography. A subset of the intended data, formed of two common receiver gathers and one common shot gather, was collected at the San Emidio oil field. The crosswell data display a wide variety of wave modes including tube waves, singly and multiply reflected/diffracted waves, and refracted waves. The data are processed using frequency filters, median filters, and spatial muting filters to enhance the reflected/diffracted energy. A 2-D layered velocity model with gradients is built using zero‐offset VSPs and full‐waveform acoustic logs from the two wells. This model is used to generate synthetic finite‐difference data for the field data acquisition geometry. The synthetic data are processed and imaged using the elastic ray‐Born 𝓁2-migration/inversion (ERBMI) method. A smooth 2-D velocity model incorporating only gradients and a few layers is used as a background model for the imaging. Considering the limited data acquisition geometry, synthetic data images compare favorably with the initial velocity model. With the encouraging results obtained from synthetic data, the ERBMI method, with the smooth background velocity model is used next to image the processed field data. Images obtained from the crosswell data show a good match with the reflected field in the zero‐offset VSPs and with migrated surface seismic data. From the interpretation of these images, the potential of this crosswell seismic method for answering questions regarding reservoir continuity and existence of pinchout zones can be seen.
Databáze: OpenAIRE
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