Abstract: A method of computer generating a subsurface characteristic model which is substantially consistent with readings taken in a well with a well logging device. A set of actual measurement values which represent readings taken over a given depth interval of a well is derived. An initial trial model of the subsurface characteristic under investigation is then selected. Next, a set of simulated measurement values is generated by applying the approximate response characteristic of the logging device to the discrete trial model. The simulated measurement values are compared with the actual measurement values and an error function is generated in accordance with the comparison, the error function reflecting the comparison taken over a substantial portion of the given depth interval. The model is then modified in a manner which tends to minimize the error function.

Abstract: Disclosed is a machine implemented method of utilizing existing log data from one or more boreholes in a field to find out what zero shift, if any, may be necessary in order to calibrate a log from a borehole in the same field. In one embodiment, the disclosed system utilizes the three porosity logs (neutron, density and sonic) and builds a statistical model of the field by counting the number of occurrences of each combination of the three porosity log measurements and by storing the counts in a three-dimensional cell memory where the three dimensions correspond to the three porosity logs and each cell location is identified by a particular combination of the three porosity measurements.

Abstract: An electrical well logging apparatus of the spherically focusing type is utilized to determine the diameter of a borehole drilled into a formation or the thickness of the mudcake on the borehole wall.

Abstract: An apparatus and method for determining the amount of adsorbed fluid in formations surrounding a borehole. In accordance with the present invention, means are provided for deriving a first quantity which is a function of the dielectric constant of the formations as measured by passing electromagnetic energy of a first frequency through the formations. Means are also provided for deriving a second quantity which is a function of the dielectric constant of the formations as measured by passing electromagnetic energy of a second frequency through the formations. Finally, means are provided for determining the amount of adsorbed fluid in the formations as a function of the difference between the first and second quantities.