Method of producing impact point position probability maps for a well

Method of producing impact point position probability maps for a well over a surface S included within a three-dimensional medium and whose location is known with geometrical uncertainties, characterized in that it consists ir:

• defining a fixed, invariant target point chosen a priori on an initial location E0 of the surface S,
• discretizing the surface S with the aid of a grid composed of nodes and of grid cells,
• assigning at least one elementary geometrical uncertainty vector to each node of the grid of the surface S,
• determining a statistically significant number of occurrences of locations of the surface S as a function of the geometrical uncertainties affecting it,
• projecting the target point onto each occurrence of location of the surface so as to deduce a point of impact therefrom,
• transferring the set of impact points onto the location E0 of the surface S by allocating, to each of these points, surface co-ordinates identical to those which it had on the occurrence of location of the surface containing it,
• defining over the surface S a statistical distribution for the set of impact points,
• determining from the statistical distribution a probability density at all points of the surface S, the said density giving the probability that any point of the surface S is a point of impact, and
• mapping over the surface S the probability density as level curves.