A new‐generation multilevel receiver downhole seismic data acquisition system with embedded digital signal processor

Abstract

A new-generation multilevel receiver downhole seismic data acquisition system with embedded digital signal processor and delta-sigma ADCs (analog-to-digital converters) has been developed. A novel real-time data acquisition and processing methodology is introduced and implemented on the DSP (digital signal processing) chip. Multichannel signals from up to five three-component depth levels are parallel-digitized by ADCs in a free-running manner. Multichannel signals are collected through DMA (direct memory access) transfer and then reconstructed in a parallel manner downhole to meet the requirements of decimating from a high sampling rate to different lower rates, synchronizing the free-running signatures with the seismic source, filtering out unwanted frequencies for improving S/N ratio and constructing software antialiasing filters. These multifunctions are achieved simultaneously by a one-time FIR (finite impulse response) operation between raw signals and corresponding predesigned FIR structures. Coupled DC offsets of each channel are separately filtered out by adaptive DC removals. This new algorithm leads to significant reduction of logging time and the acquisition of high-quality data for downhole seismic surveys such as VSPs (vertical seismic profiles). The algorithm can also be easily applied to other data acquisition systems. To date, this system has successfully acquired over 100 surveys worldwide.