Abstract: Well Seismic Optimization for Field Development, a Case History in Saudi Arabia

ALFARAJ, MOHAMMED, MICHAEL FERGUSON, and AHMED ALMOUSA

Well seismic profiling plays a major role complementing the interpretation of seismic data. Here, to help interpret a giant 3D seismic survey, a well-seismic program was designed to meet three objectives: to confirm correct picking of a reservoir top, to identify multiples, and to substantiate the presence of small-throw faults seen on 3D seismic. For the latter, a single-offset acquisition was decided, where the optimum source distance was inferred by elastic modeling using geologic information in that field. The ambiguity of the reservoir top on 3D seismic is attributed mainly to low contrast in acoustic impedance and multiple interference.

Since quite a few wells were planned to be surveyed with well seismic, a field experiment was first conducted at one of the wells in order to ensure optimum acquisition. Two issues were addressed: 1) the source to use, and 2) the number of casing strings that would still allow recording of good-quality data. Comparing results from different sources, a vibrator was decided for offset acquisition, and an air gun for zero-offset. As for recording beyond casing, it was found that data could still be acquired up to three casing strings without a great loss of signal quality.

Analysis of data revealed that the reservoir zone on 3D seismic was heavily contaminated with multiples, thus obscuring the reservoir top, which was later correctly identified by relying on well seismic. Unlike 3D seismic, offset well seismic did not show any faults, therefore advocating the likelihood of those being absent in that locality.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria