SHOOTING DIRECTION AND CROSSWELL SEISMIC DATA-ACQUISITION

Four crosswell seismic surveys were acquired in the Glenn Pool Field o f northeastern Oklahoma as part of a multidisciplinary reservoir chara cterization project. The acquisition goal was to generate data suitabl e for tomographic traveltime inversion, Acquisition parameters and sho oting geometry were selected by conducting a parameter test at the sit e. Following the parameter test, the first survey resulted in high qua lity data showing clear first arrivals, low ambient noise, some reflec tion events, and strong source-generated tube waves, The second survey involved a different receiver well and encountered high ambient noise levels. The noise was strong enough to prohibit first-arrival picking for much of the data. On-site analysis of the second survey revealed tube waves emanating from a perforated interval in the receiver well. This well was shut in and was not flowing fluid or gas at the surface, We interpret the source of ambient tube waves as borehole-to-formatio n fluid flow (circulation) associated with the perforations. Since thi s image plane was important for characterization of the reservoir, the survey was reshot (third survey) by reversing sources and receivers i n the two wells. The resulting high-quality data indicates that shooti ng direction can be an important factor in crosswell seismic acquisiti on, This experience influenced acquisition of a previously planned fou rth survey so that the ambient noise problem would be avoided.