The computations tabulated in the paper in question were based on a model in which radial stress becomes equal to vertical stress 3 in. away from the borehole; this is believed to be a good approximation and assumes that energy at distances larger than 3 in. is a function of vertical stresses only. As the exact function that will describe the stress between mud, mud-cake, and the formation is not known, a model must be used. Tuman agrees that the effective stress function to be used in the calculation of the curved rays should be of the form suggested by Geertsma; another form of this function is suggested that includes the thermal stresses also.

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