Study Of Data Process And Interpretation For Pulsed Neutron Spectra Logging

Pulsed neutron logging is the most effective logging to determine the reservoir remaining oil saturation in cased holes. The logging tools introduced from foreign companies, such as RST,RMT,PND-S,RPM,TMDL and PNN, have the advantages of abundant information and high precision. But the cost of logging is enormous and it can't be applied widely, and it is unfavorable to the development of our domestic pulsed neutron spectrum logging technology, too. The domestic pulsed neutron logging tools have the defects of single logging model, therefore it is important to carry out researches on a new-type pulsed neutron spectral logging tool and the corresponding interpretation methods.Pulsed neutron spectral tool(PNST) is a new kind of logging tool, which integrates all the present main pulse neutron logging methods in one. The tool's models are as carbon/oxygen spectral logging mode (C/O), pulsed neutron capture logging mode (PNC), and pulsed neutron-neutron logging mode (PNN).According to the tool characteristics, a few studies are accomplished as follows: the features of the main pulsed neutron logging tools at home and aboard are compared and described, then the significance of researching and developing full spectral logging tools is indicated. The nucleus physics theory of the pulsed neutron logging, the basic theory of C/O logging, neutron lifetime logging and PNN logging are systematically studied; determining H and Fe peak position in capture spectrum is the key to correct spectrum shift, therefore the method of seeking Fe peak position in the capture spectrum is improved. By using fast fourier transform to determine thermal neutron life for the pulsed neutron-neutron logging, the value of neutron lifetime is not be affected by background and thermal neutron count rate, thus can improve accuracy of the formation capture cross section. For cutting the abnormal values in measured spectra, a method of 53H given by Tukey is adopted, and after that these points are compensated. For the disadvantage of large statistics presented in radioactivity logging, the Savitzky-Golay filter method is advised, the filter method can give the smoothness without resolution loss, furthermore, it can choose data width and fit polynomial order. As for quantitative interpretation of remaining oil saturation, this paper presents a method to estimate shale content and porosity for the well without OH logging data, shale content can be calculated from formation capture cross section measured through pulsed neutron full spectral logging, and porosity from ratio of the near capture count rate to the far detector's. The key of quantitative interpretation of neutron life logging is to precisely determine capture cross section of every component in formation, in this paper, a method is advanced to determine shale capture cross section by using that the oil line is equal to water line at shale interval. According to the theory of fast neutron slowing down, a means of qualitatively identifying gas-bearing zone by C/O logging data is also given first.By using the software of data process and interpretation developed by this research to process logging data, as well as comparing them with the data from open hole logging and production performance, the interpretation results can effectively reflect the change of reservoir remaining oil saturation, and find potential oil zone and identify gas-bearing formation.