Design Of Launching Module For NMR Logging Tool While Drilling

As a strategic resource,petroleum is closely related to the development of national economy.Although China’s petroleum logging technology has been successfully applied in some petroleum exploitation,there is still a big gap between it and that of western developed countries.Therefore,improving China’s petroleum logging technology is an important guarantee to enhance China’s oil self-sufficiency and emergency response ability.As a logging method that can provide accurate formation permeability,nuclear magnetic resonance logging（NMR）while drilling（LWD）has become the effective method to measure porosity.In the world,a relatively complete nuclear magnetic logging instrument while drilling has been formed,but the domestic research is still in the primary stage.Unlike Wireline NMR logs,LWD NMR logs have greater volume limitations on the instrument.Funded by the A class leading special project of Chinese Academy of Sciences"Intelligent Guided Drilling Technology Equipment System and related theoretical research"project,this paper has carried out the research on the launch module of LWD NMR logging tool.The main research contents are as follows:1.Master the principle of NMR logging,refer to the design idea of domestic NMR logging instrument and combine with the project requirements,design the launching module of LWD NMR logging instrument,and divide the launching module into launching circuit,main absorption circuit,isolation circuit and soft absorption circuit.2.For the transmitting circuit,adopt the double bridge structure,without the use of transformer to get 2 times the voltage excitation antenna,greatly reduce the volume of the transmitting circuit;For the main absorption circuit,the energy of the antenna is rapidly discharged by changing the world quality factor to reduce the recovery time of the antenna.For the isolation circuit,the isolation protection of the receiving circuit is completed by using back-to-back high-voltage power MOSFET.For the soft absorption circuit,the residual energy of the main absorption circuit is discharged again by reducing the antenna quality factor to ensure the normal operation of the receiving circuit.Aiming at the above four circuits,corresponding driving circuits are designed to achieve reliable driving of power MOSFET while meeting the requirements of temperature resistance and volume.3.Conducted functional tests on each circuit of the transmitting module to complete the design indicators.The installation area of the transmitting module designed in this paper is 22500mm~2,which is near 2 times smaller than that of the transmitting module of the domestic cable-type nuclear magnetic instrument.At the same time,the isolation circuit and soft absorption circuit of the transmitting module are measured on the cable logging instrument of China Oilfield Service,which is consistent with the measured results,which verifies the effectiveness of the design in this paper.