Method of sampling environmental conditions with a self-contained downhole gauge system

DETAILED DESCRIPTION The present invention overcomes the above-noted and other shortcomings of the prior art by providing a novel and improved method for controlling the rate at which a downhole logging tool samples and records a detected condition within a well bore.
The method of the present invention claimed herein controls the sample rate at which conditions within a well bore are sampled by a downhole tool, and the method also determines which samples are to be recorded within the tool.
The sampling and recording are responsive to differences between a predicted value and the actual value of the sampled condition, and the sampling is also responsive to remaining memory and battery capacities.
The method of the present invention includes the steps of (a) initializing a sample counter within the tool to zero; (b) selecting the shortest one of a plurality of sample rate intervals; (c) reading and recording in the tool a first sample of the condition at a first sample time; (d) reading a second sample of the condition at a second sample time in correspondence with the selected sample rate interval; (e) reading a third sample of the condition at a third sample time in correspondence with the selected sample rate interval; (f) computing from the first, second and third samples a prediction value for the n-th sample, where n is an integer not less than 2; (g) reading an n-th sample at an n-th sample time; (h) determining whether each n-th sample is within a predetermined threshold or difference of the predicted value for such n-th sample; (i) recording in the tool the (n-1)-th sample, resetting the sample counter to zero, and repeating steps (f) through (i) commencing with the (n=1)-th sample if the n-th sample is not within the predetermined threshold of the predicted value for the n-th sample; (j) incrementing the sample counter if the n-th sample is within the predetermined threshold of the predicted value; (k) determining whether the sample counter has reached a predetermined maximum count; (1) repeating steps (g) through (l) if the sample counter limit has not been reached; and (m) increasing the sample interval to the next longer one of the plurality of sample rate intervals if the predetermined maximum count has been reached and repeating steps (f) through (m) commencing with the (n-1)-th sample