High-resolution crosswell seismic experiment With a large interwell spacing in a west Texas carbonate field

摘要

A high-frequency crosswell seismic dataset acquired in a west Texas carbonate field has demonstrated the feasibility of the technique with a large interwell spacing. Two crosswell profiles were acquired with a Well spacing of 1500 ft (460 m) and over a depth interval from 7700 ft (2350 m) to 9600 ft (2930 m) using piezoelectric bender source. The data quality is profile and depth dependent, with the ambient noise level at the receiver position being the most important factor. Noise levels and noise characteristics among three wells were significantly different. Tube waves and gas- and fluid-movement in the borehole are the dominant noise sources found in the data set. Two lithologic properties, attenuation and transmis- sion loss controlled the data quality. Good quality and high frequency ( > 1000 Hz) data were acquired over most of the survey interval which contains massive limestones. However, we could not acquire any useful data within the shale layers. Transmission losses and the effects of the source radiation pattern that occurred at interfaces with large impedance contrasts limited the aperture of the useful data. There were two critical issues encountered during the reflection imaging process: (1) sparse trace spacing and poor coherency of the reflection events in common-source gathers degraded the image in a region near the receiver well; and (2) possible lateral velocity heterogeneity in the medium and limited aperture made it difficult to build an appropriate velocity model for reflection imaging.