Abstract: A process for signal matching. The process is general and can be applied to matching signals of arbitrary dimension. To implement the process, a suitable discretized description of the two signals to be matched is defined. Such descriptions can be the local signal extrema or any other qualitative signal significant points of interest or features. Allowable feature matches and values for matches are defined, and determined for all potential matches. Matches are confined to the features within defined matching windows and are mapped for each significant point. Within a defined similarity disparity window, a neighborhood of potentially interacting matches are evaluated. Matches within a neighborhood contribute to the decision about the appropriate match for each significant point to determine a composite similarity weighted best value match for each point. Mapping is piecewise continuous. The two signals are matched with disparities therebetween resolved and removed responsive to the best match values.

Abstract: In accordance with an illustrative embodiment of the invention, a technique is set forth for determining a displacement between two or more well logs separately derived from investigating devices passed through a borehole. More particularly, displacements are determined for a number of levels through use of a suitable correlation function compensated for various adverse effects. The displacements for a selected number of levels are analyzed to determine average displacements at representative levels. The average displacements and representative levels are analyzed to determine intermediate levels and corresponding distributed displacements for distributing large changes in displacements. Application of these distributed displacements at the intermediate levels minimizes changes in the nature of the logs that would be caused by abrupt application of large changes in displacements to the logs at one depth level to align the logs.

Abstract: A method of computer generating a subsurface characteristic model which is substantially consistent with readings taken in a well with the well logging device. A set of actual measurement values which represent readings taken over a given depth interval of the well is derived. An initial trial model of the subsurface characteristic under investigation is then selected. The model includes discretely-boundaried beds, the location of boundaries being based on subsurface characteristic data. A simulated measurement value at a particular depth level is generated by applying the approximate response characteristic of the logging device to the model. The simulated measurement value at the particular depth level is compared to the actual measurement value at that depth level and the model is then modified in accordance with the comparison.

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: 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 simulated measurement value at a particular depth level is generated by applying the approximate response characteristic of the logging device to the model. The simulated measurement value at the particular depth level is compared to the actual measurement value at that depth level and an error value is generated as a function of the comparison. The model is then modified in accordance with the error value, the modification being performed over a depth interval which includes the model beds within a preselected span from the particular depth level.

Abstract: In accordance with an illustrative embodiment of the invention, a technique is set forth for determining the depth match between two or more well logs derived from separate passes through a borehole. More particularly, first assumption depth displacement values are determined for a number of depth levels through use of a suitable correlation function. The first assumption depth displacement values for a selected number of depth levels are then analyzed to determine more accurate depth displacement values, which ultimately are used to depth-align the logs.

Abstract: An electrical well logging apparatus of the spherical focusing type is suspended in a borehole drilled into an earth formation and is utilized to provide information regarding the thickness of the mudcake formed on the borehole wall.