Stratum density measuring while drilling instrument based on deuterium-tritium accelerator neutron source

Abstract

The invention provides a stratum density measuring while drilling instrument based on a deuterium-tritium accelerator neutron source. The stratum density measuring while drilling instrument is used for measuring the density of a stratum around a well hole in the well drilling process, and meanwhile can measure the neutron porosity. According to the stratum density measuring while drilling instrument, a U-shaped groove is formed in one side of a drill collar, a fast neutron monitoring detector and a neutron generator are arranged inside a neutron generator module compression resistance cylinder, a neutron shielding body, a first thermal neutron detector, a neutron shielding body, a second thermal neutron detector, a gamma ray shielding body, a gamma detector and a control processing circuit are sequentially installed inside a detector installation skeleton from top to bottom, and the neutron generator module compression resistance cylinder and the detector installation skeleton are connected and fixed into the U-shaped groove through a coupling connector. The stratum density measuring while drilling instrument adopts the deuterium-tritium accelerator neutron source for measuring the stratum density, a chemical gamma radioactive source is prevented from being used, damage to people and environment is eliminated, and the measuring precision is effectively improved by monitoring the neutron yield in real time.

Description

technical field [0001] The invention relates to the technical field of oil drilling and well logging, in particular to the density logging while drilling technology. Specifically, it is a measurement-while-drilling instrument based on the formation density of a deuterium-tritium accelerator neutron source. Background technique [0002] 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. [0003] Currently known density measuring devices, one is to use a radioisotope source (for example, 137 Cs or 60 Co) emit gamma rays, and then use two gamma ray detectors at different source distances to measure the gamma rays scattered by the formation Compton, and calculate the density value of the formation acc...

AI Technical Summary

Problems solved by technology

[0004] The density logging tool using chemical gamma radiation sources has the following disadvantages: because the radioisotope source uses the gamma rays released during the isotope decay process, and in order to meet the measurement accuracy, the source intensity of the isotope source is high and the half-life is long , so the source of the radioisotope produces intense radioactivity

However, the gamma detector count rate is 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 sub-detectors to correct for the effect of fast neutron transport on the gamma count rate, but the measurement accuracy is lower

[0006] 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 contamination, the fast neutrons released by it with an energy of 14 MeV are After release, 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. Therefore, relative to the chemical gamma source, the position of the gamma ray is not fixed, and changes with the influence of the formation while dynamic changes

According to the well-known principle of neutron porosity logging, although the epithermal neutron detector is more sensitive to neutron attenuation, the count rate it can measure is lower than that of thermal neutron. If it is used to count the gamma detector Calibration will result in low accuracy of the measurement results of deuterium-tritium neutron density while drilling

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