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An autonomous system for performing a well operation at a predetermined location in a wellbore comprises a tool string having at least one well tool, a motive device for traversing the wellbore, and a control system adapted to position the tool string near the predetermined location. The control sys

An autonomous system for performing a well operation at a predetermined location in a wellbore comprises a tool string having at least one well tool, a motive device for traversing the wellbore, and a control system adapted to position the tool string near the predetermined location. The control system comprises (i) a sensing system for detecting mass irregularities in the wellbore and (ii) a processor system having a processor with memory for storing at least one well log. The processor acts under programmed instructions to compare sensor signals to the stored well log to determine a tool string position in the wellbore. The control system also contains circuits for controlling the operation of the well tool and the motive device.

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1. An autonomous downhole system for operating a well tool proximate a predetermined location in a wellbore, comprising:a. a tool string having at least one well tool for performing a well operation in the wellbore; b. a motive device in the tool string causing the tool string to traverse the wellbo

1. An autonomous downhole system for operating a well tool proximate a predetermined location in a wellbore, comprising:a. a tool string having at least one well tool for performing a well operation in the wellbore; b. a motive device in the tool string causing the tool string to traverse the wellbore; and c. a control system in the tool string adapted to autonomously position said tool string proximate the predetermined location in the wellbore, wherein the control system comprises: i. a sensing system having at least one sensor for detecting at least one parameter of interest related to the wellbore and generating at least one signal in response thereto; ii. a processor system having a processor with a memory for storing, at the surface, at least one well log therein, said processor acting according to programmed instructions to compare said at least one sensor signal to said at least one stored well log to determine a tool string position in the wellbore, said processor system having circuits adapted to control said well tool and said motive device. 2. The system of claim 1 further comprising a power module providing at least one of (i) electrical power and (ii) hydraulic power, to energize the well tool, the motive device, and the electronics system.3. The system of claim 1 wherein the at least one sensor is chosen from (i) an electromagnetic sensor, (ii) a sonic sensor, (iii) an ultrasonic sensor, and (iv) a gamma ray sensor.4. The system of claim 1 wherein the at least one well log is one of (i) a joint and tally log, (ii) a log of unique mass signatures, and (iii) a gamma ray log.5. The system of claim 1 wherein the at least one parameter of interest is one of (i) the change of an electromagnetic field caused by a mass irregularity in a wellbore, and (ii) a formation gamma ray emission.6. A method for autonomously performing a well operation at a predetermined location in a wellbore, comprising:a. storing, at the surface, at least one well log in a memory of a processor of a control system in a tool string; b. traversing the tool string through the wellbore under autonomous control of the control system; c. sensing at least one parameter of interest in the wellbore and generating a signal related thereto; d. comparing, using a signal comparison technique, said sensed signal to said at least one stored well log to identify the predetermined location in said wellbore; and e. operating a well tool under autonomous control of the control system to perform the well operation at the predetermined location in the wellbore. 7. The method of claim 6 wherein the well log is one of (i) a joint and tally log, (ii) a log of unique mass signatures, and (iii) a gamma ray log.8. The method of claim 6 wherein the signal comparison technique is cross correlation.9. A method for autonomously performing a well operation at a predetermined location in a wellbore, comprising:a. storing in a memory of a processor of a control system in a tool string, at the surface, a first number of mass irregularities to be traversed to reach a predetermined wellbore location; b. traversing the tool string through the wellbore under autonomous control of the control system; c. using a sensor to detect a second number of mass irregularities traversed in the wellbore and generating a signal related thereto; d. comparing said first number with said second number to locate the predetermined wellbore location; and e. operating a well tool to perform the well operation at the predetermined location in the wellbore. 10. The method of claim 9 wherein the sensor is an electromagnetic sensor.11. A method for autonomously performing a well operation at a predetermined location in a wellbore, comprising:a. storing in a memory of a processor of a control system in a tool string, at the surface, a sensor signature for identifying a predetermined mass irregularity related to a predetermined location in a wellbore; b. traversing the tool string through the wellbore under autonomous control of the control system; c. using a sensor to detect at least one mass irregularity traversed in the wellbore and generating a signal related thereto; d. locating said tool at the predetermined location by identifying said predetermined mass irregularity by comparing said sensor signal to said stored signature using a signal comparison technique; and e. operating a well tool to perform the well operation at the predetermined location in the wellbore. 12. The method of claim 11 wherein the sensor is an electromagnetic sensor.13. The method of claim 11 wherein the signal analysis technique is cross correlation.