                Program CWELL - Overview
                ------------------------

CWELL is a crosswell modeling program for two-and-one-half
dimensional layered acoustic media.  Traveltime, amplitude
and phase of acoustic waves are calculated using ray theory.  
The program uses the shooting method of ray tracing and
interpolates to find the above quantities at the precise
receiver locations.  In this respect it is different from
CSHOT1, which uses a two-point ray tracing approach.

In CWELL, the receivers are located inside a well.  (In CSHOT1 
the receivers are confined to the uppermost layer.)  The sources
may also be located in a well, or they may be given general
locations anywhere within the model.  Both source and receiver
wells may be curved (they are splined by the program).

Direct waves, reflections, head waves and multiples can be calculated.

In order to produce wiggle traces, CWELL must be run in conjunction
with CSHOT2 (see the CSHOT documentation).

CWELL accesses a number of input parameter files:
(1) file PARAM1
(2) a model file
(3) a plot colors file
(4) a receiver well file
(5) a source well file (downhole shooting)
(6) a source locations file (general shooting)

The precise format of the input parameter files is developed
in the demos.

The output generated by CWELL may be any or all of the following:
(1) model/ray plot
(2) listing
(3) time data (input to CSHOT2 to produce wiggle traces)

