While-drilling controllable source density logging device

Abstract

The invention relates to a while-drilling controllable source density logging device, which comprises an independent while-drilling controllable neutron source and a while-drilling density detection system. A radioactive source is a while-drilling controllable neutron source independent bin and comprises a while-drilling controllable source body, a neutron tube compressive cylinder and a shield, and the neutron source is mounted in the neutron tube compressive cylinder; the while-drilling density detection system comprises a detector body, a near-source-distance detector, a thermal neutron detector, a far-source-distance detector, a central processing circuit and an ultrasonic hole diameter measurer; and the central processing circuit comprises a microprocessor, a signal amplification, shaping and screening circuit, a storage, an interface circuit, a bus driver and a bus. The while-drilling controllable source is mounted in the neutron tube compressive cylinder and the while-drilling controllable source body, the independent while-drilling controllable neutron source is formed, during high-voltage powering-on, high-energy fast neutrons are stimulated, in the process that the fast neutrons penetrate through a stratum, gamma rays are attenuated, and attenuation of the gamma rays also mainly depends on the density of electrons constituting the stratum.

Description

technical field [0001] The invention relates to a downhole device of a radioactive measuring instrument in the field of logging-while-drilling instruments, in particular to a density logging device based on a controllable source while drilling. [0002] Background technique: [0003] In the field of measurement while drilling in the drilling industry, the density logging tool is used to measure the density of the formation in real time during the drilling process, so as to effectively calculate the porosity of the formation, identify oil and gas layers, and calculate the oil storage capacity of the formation. [0004] Currently known density measurement devices, one is to use a radioactive isotope source (for example, 137Cs or 60Co) to emit gamma rays, and then use two gamma ray detectors at different source distances to measure the gamma rays scattered by the formation Compton. For horse rays, the density value of the formation is calculated according to the count rate of a ...

AI Technical Summary

Problems solved by technology

[0005] The LWD density logging tool using chemical gamma radiation sources has the following disadvantages: Since the radioisotope source uses the gamma rays released during the isotope decay process, in order to meet the measurement accuracy, the isotope source is required to have a higher source strength and a shorter half-life. long, so the source of the radioisotope produces intense radioactivity

However, the gamma detector count rate will be affected by the transport of fast neutrons in the formation, so in order to reduce the influence of fast neutrons, a gamma detector and an epithermal neutron detector are used in the instrument, using the epithermal neutron detectors to correct for the effect of fast neutron transport on the gamma count rate, but with lower measurement accuracy

[0007] The instrument for measuring formation density using a deuterium-tritium neutron source has the following disadvantages: First, although the use of a controllable deuterium-tritium reaction accelerator neutron source can solve the problem of radioactive source pollution, the energy released by it is 14MeV fast neutrons, After being released, it will be transmitted in the formation, and gamma rays will not be released until inelastic scattering occurs with the atomic nuclei in the formation. changes dynamically so that the gamma detector response is a function of formation density

According to the well-known principle of neutron porosity logging, although epithermal neutron detectors are more sensitive to neutron attenuation, their measurable count rate is lower than that of thermal neutrons. The correction of the detector count will have the problem of low accuracy of the density measurement result

Secondly, the deuterium-tritium reaction accelerator has a certain working life, generally hundreds of hours. As the use time increases, the output of neutrons released by it will decrease, thereby causing the reduction of gamma ray count rate, and further Affects the accuracy of density measurements

Images