Abstract:An offsef panel display of seismic data has been developed to locate shallow drilling hazards. The offset panel displays six sets of common offset, single channel data taken from a conventional marine seimic survey. The single channel profiles are displayed below one another and arranged vertically by offset and horizontall by common depth point. This arrangement causes effects due to nearsurface geologic changes to generate geometric patterns that are different from patterns due to changes in seismic source or receiver. Both reflection and refraction data are usedin the display. Reflection data of the near trace or offset are at the top of the display and indicate the presence of acoustic boundaries. Refractions observed on distant traces are sensitive to changes in the near surface. They allow properties of acoustic layers to be determined through their alteration of transit times and amplitudes. A shallow-gas drilling hazard is a low-velocity zone at a depth less than about 700 meter. A seismic reflection from that zone will have a high amplitude. Refractions which transit the zone will be delayed because of low velocity and attenuated because of transmission loss. The offset panel allows correlation of a high amplitude reflection on a near trace with delayed refraction breaks on distant traces thus identifying the hazards. Refractions penetrate to depths of perhaps one fifth of the maximum source to receiver distance depending upon the subsurface velocity distribution. Typical marine seismic surveys with maximum source to receiver offsets of 2700 m permit positive identification of hazards to a depth of about 500 m along the seismic line. The identification of shallow-gas drilling hazards on the offset panel display of conventional data is less subjective than on displays of high resolution hazard surveys because the identification is based on both high amplitude reflection and delayed refraction. The offset panel may be used to indicate the possible need of a hazard survey. Hazards indicated by the offset panel may be mapped in greater detail by a hazard survey. The offset panel display of conventional data can add significantly to the interpretation of shallow-gas drilling hazards.
引用本文:
T. K. 富尔顿, 俞寿朋. 用炮检距汇集图确定浅层钻井危险区[J]. 石油地球物理勘探, 1982, 17(1): 45-54.
Thomas K. Fulton. Offset panel locates shallow drilling hazards. OGP, 1982, 17(1): 45-54.