Comment on Interference Analysis for Anisotropic Formations

Ramey's paper. "Interference Analysis for Anisotropic Formations - A Case History." (Oct. 1975 JPT. Pages 1290–1298)' is excellent and should form the basis for calculations for years to come.There is an interesting point on nonunique solutions that-should be made. Ramey states that "If C were known. data from only two wells arc sufficient. "His previous remarks indicate that multiple solutions are previous remarks indicate that multiple solutions are possible if both observation wells are on the same straight possible if both observation wells are on the same straight line with the injection well.What is not so obvious. however. is that two solutions are possible in the general case when data from two observation wells are used.Consider the case in which the lines containing the wells are at right angles to each other. Then there is a second solution with the same kxx and kyy as the first, but with the angle 0 being the negative of the first. Inspection of Figs. 1 and 2. and consideration of the fact that Points 1.D and 5-E are independent observation points. makes this clear.Ramey's calculation procedure gives just one answer unless the coordinate axes are rotated 900, putting Point 1-D at (–475. 0) and Point 5-E at (0. 475). This interchanges the values of kxx and kyy, leaves kry, kxx. and kyy the same. and gives an angle of 28 deg. P. 1429