Well deviation

In this particular geometry, the wells are not confined to a single plane. Instead, they deviate gradually form the vertical plane that contains both wells at the near surface. We have taken this effect into account following this two-steps procedure:

• Find the true 3-D distances between sources and receivers.
• Assume that one well is vertical (for example, the source well) and locate the receivers at the corresponding real distances and real depths in the other well. This is equivalent to locate the origin of the coordinates to measure the distances always at the source well.

When correcting for the well deviation in this way, true source-receiver separations are used in the inversion. The relative position of the two wells after considering the deviation is shown in Figure 10. To use the true distances, it is necessary to move the receivers positions horizontally in the deviated well. This is way the receiver positions in Figure  look like horizontally smeared. The selection of the vertical well used as a reference to measure the relative deviations is irrelevant if we assume that the model is 1-D. In 2-D somewhat different distorsions may occur depending on which well is chosen as a reference.

 

deviation
Figure 10 Positions of the source and receiver wells after considering their relative deviations. Each dot represents a source or a receiver position (left and right respectively). Note that the density of sources is larger at the middle of the surveyed area than in the extremes.