Design of low-field NMR real time mud log device

We propose a construction of a low-field NMR mud log device. This apparatus can collect mud logging data in real time, which includes central control unit, data transceiver with wifi, a signal processor board, power amplifier, de-coupler, preamplifier and Q-Switch (See Fig.1). The central controller that is connected to the data transceiver via wifi is utilized to control the whole system and process the logging data. In this way, this system sends and receives data and commands. The data transceiver with wifi acts as a bridge between the central control unit and signal processor board, and is connected to the signal processor board via USB. The signal processor board consists of Digital Signal Processor (DSP), Field Programmable Gate Array (FPGA), Direst-digital Synthesizer (DDS) and Analog-to-Digital Converter (ADC) [1] . It does not only generate all the timing and control signals required by power amplifier, de-coupler, preamplifier and Q-Switch, but also converts the analog echo signal to digital signal and processes the digitized echo signal. Power amplifier with Class-B architecture was designed to satisfy the 300W power requirement of NMR logging tool antenna. The power of power amplifier can be up to 300W, and the frequency can be up to 30MHz. An active de-coupler was designed based on high voltage MOSFETs with very small input capacitance controlled by digital part. Its main function is to isolate preamplifier from antenna during transmission and to assist the dumping of energy stored in antenna using an auxiliary Q-switch. Q-switch based on high power MOSFETs was designed to reduce the recovery time of antenna.
This device was employed to test drilling mud samples with various oil content, as shown in Fig. 2. It demonstrates the feasibility of testing crude oil and its proportion in drilling mud well with this device.