Nuclear well logging data acquistion system and method

Abstract

A computer-based system and method for acquisition of nuclear well logging data, including downhole generation of energy and time spectral information. For acquiring energy spectrum data, a downhole multi-parameter analyzer is provided including a pulse height analyzer and memory. The analyzer converts each gamma ray pulse height into a digital code by peak detection, level and pulse pile-up discrimination, sample-and-hold, and analog-digital conversion. The digital code includes the address of a unique memory location or channel corresponding to the energy of the particular gamma ray. After a preselected time interval the memory channels collectively contain counts for each incremental energy band in the desired energy spectrum. The memory may then be interrogated by the downhole CPU for presentation of a gamma ray emission versus energy level plot. For acquiring temporal spectrum data, the multi-parameter analyzer also includes a memory address generator. The generator repeatedly produces a numerical sequence of memory address codes corresponding to a sequence of adjacent time windows relative to a reference start time, whereby the windows collectively comprise the time interval of the desired spectrum. Each time a gamma ray pulse is detected, the memory address generated at that time addresses a corresponding memory location and increments the count value resident therein. At conclusion of the time spectrum interval of interest the memory locations may be interrogated by the CPU and presented visually as a gamma ray emission count versus time plot.