Researches On Key Technologies Of X-ray Fluorescence Logging

Drilling is an important method in geological survey. It is an economic and direct approach to discovery and validation concealed deposits. Some minerals (such as uranium) have been carrying out large-scale survey with drilling. However, there has been only one traditional way to get the drilling result, and that is the chemical analysis of rock core samples. This traditional approach comes with shortcomings of heavy rock transportation tasks, high costs, large scale projects, and enable to correct the chemical analysis result shall it be untrue, and also long cycle to get the drilling result. The X-ray fluorescence (XRF) logging technology could change the ground geophysical logging from "qualitative" in the past to the contemporary development of "quantitative" stage. XRF logging provides real time in situ exploration data and determines the metal ores'scale, layer thickness and calculates line reservation in the well. Thus, The XRF logging technology greatly improve the drilling efficiency, lower the drilling cost, and shorten the time of getting the drilling results.Based on extensive researches, this paper discusses in details about the theoretical basis of XRF logging, provides in-depth analysis of factors affect the XRF logging. It also discusses key technologies of XRF drilling tube design, high-sensitivity XRF probe design and drilling liquid influence and corrections. Major research contents include:(1) XRF drilling tube design。Based on the technical requirements of XRF logging, designed the mechanical structure of the XRF tube, and conducted stress analysis and strength check to achieve safe and reliable work of the tube in borehole as deep as 1500m, and the detection window closely contact the hole wall.(2) High-sensitivity XRF probe design. Proposed methods to lower the probe materials'absorption of characteristics X-ray from stimulation-source primary ray and target elements; Determined the model of stimulation-source and detector; Conducted theoretical analysis and experimental verification of geometry layout of stimulation-source, core samples and the detector.(3) Drilling fluid influence analysis and correction. Researched the influence of drilling fluid on XRF logging result. Analyzed and experimentally verified the drilling fluid thickness influence on scattering peak counts; Analyzed and experimentally verified the influence of drilling fluid thickness on target element characteristic peak counts; Corrected the drilling fluid influence from the aspects of tube structure and techniques.(4) Field XRF logging tests. Compared results from XRF logging field tests and rock core sample lab analysis results to evaluate XRF logging effectiveness and practicality in the production process of real world geological exploration.The main innovations of this paper are as follows:(1) Developed the XRF tube. The tube is made of aluminum alloy, double sealed with O-shape rubber ring. Structure wise, the detection part is a separate arm (XRF probe), and is attached to the main tube through an electronic-controlled support arm (hole wall-contact device); Driven by a drive, the support arm pushes the main tube and XRF probe to the sides of the well, and maintains a certain pressure to the hole wall to ensure that through the whole XRF logging process, the detection window has close contact with the wall; when logging is done, the support arm is withdrawn, the probe and the main tube closed into each other and become one for easy tube withdraw from the borehole. According to the logging result from both the test well of Chongqing Geological Instrument Factory and the No. ZK702 exploration well of the Lala copper exploration of Sichuan Huili County, the tube had sufficient strength and good sealing; support arm had sufficient strength, rigidity and was not deformed; no matter it was point logging or continuous logging, the detection window contacted with the hole wall well. Tube worked safely and reliably with 1500m well-depth.(2) Developed a highly sensitive XRF probe. To reduce the probe material's X-ray absorption, a detection windows is implemented at where the stimulation-source and the detector are. This detection window's is made of rare metal beryllium, which has high X-ray transmittance. The detection window's exterior has circular-shaped surface which is compression-resistant and wear-resistant, and has good sealing when glued. XRF probe uses high energy resolution, electronic cooling Si-PIN semiconductor detector, radioactive isotope as stimulation source, and the "hypotenuse symmetry stimulate" approach to effectively improve the peak to background ratio of characteristic X-ray detection. Through theoretical analysis and experimental validation, with source sample distance of 8mm and 35 degree angle between stimulate-source surface center line and the detector, the detected peak to background ratio of the characteristic X-ray is18%.(3) Proposed Scattering Internal Standard Method drilling fluid correction model. From aspects of the XRF logging probe itself and techniques, effectively solved the problem of drilling fluid thickness influence on XRF logging result. From aspect of the probe hardware design, made sure to minimize the space between the detection window and hole wall during XRF logging process through the wall-contact device; From aspect of techniques, used Scattering Internal Standard Method drilling fluid correction model to further adjust the influence of drilling fluid with thickness less than a few millimeters on XRF logging result. Experiments show that when drilling fluid changes within a range 0-3mm, peak area of characteristic CuKa series radiation generated by copper layer with 5% copper content relative change was less than 10%.(4) Evaluate XRF logging effectiveness and practicality in the production process of real world geological exploration through field tests. Logging tests of Y422 model XRF logging device were conducted in the test well of Chongqing Geological Instrument Factory and the No. ZK702 exploration well of the Lala copper exploration of Sichuan Huili County. Total of 550.34m logging test were conducted. Among which, continuous logging total depth was 352.25m, and point logging total depth was 192.03m. In ZK702 well, took 0.1% copper content as the boundary grade, copper layer were categorized into 13 grades, copper layer average grade was 0.1156% and its line reserves was 2.9754% m. Compare this result with core samples chemical analysis result, the relative error of the two methods on average grade of ore bed is 12.98%.