| The basic principle of natural gamma Logging is based on the differences in abundance of natural radioactive element in different stratigraphics, and measures directly the gamma-ray intensity on the axis of the well by radiation detectors(NaI crystal). We can identify the geological profile, calculate the Vsh, do the stratigraphic correlation, track the perforation and search for the radioactive minerals.Because the natural radioactivity intensity is always weak, in order to overcome the statistical noise and ensure the sufficient precision, the natural gamma logging tool at home and abroad always use the large NaI crystal as the detector. And its vertical resolution of logs at most is 0.6m, which can not satisfy the needs for oilfield to exploitate and develop the thin and poor reservoir.Therefore, it is a very urgent task for oil exploration and exploitation at Daqing to develop the high-resolution gamma ray logging tool to enhance the vertical resolution to 0.2m,because the thickness of thin-poor layer and untabulated reservoir is low.This paper is based on the principle of natural gamma logging, and determine the appropriate Nal crystal size for the high-resolution natural gamma logging tool through the development of natural gamma ray logging response data simulation and the test data analysis.Through the study of the high resolution screen detector and their response characteristics.we optimize the structure of the high-resolution natural gamma logging tool and improve the response of the thin bed.Through the study of high-resolution natural gamma logs handling technology, this paper introduces wavelet analysis. Compared to traditional least squares moving average, wavelet analysis is more suitable for high-resolution gamma-rays logs at Thin-Poor layer untabulated reservoir.Combined with modern electronic technology, modular and integrated circuits, we succeed in developing a high-resolution natural gamma logging tool.This instrument is produced successfully for the first time in our country and the general technical standard is far beyond domestic level and reach the international quality.The instrument works in a stable and reliable way, and successful completes the testing and evaluating of 8 wells.According to the logging data, we do the second evaluation of the curve. We find that the repeated logging curve is consistent with the main logging curve, both of them have the same amplitude and the repeated errors is low.The formation lithology and petrophysical properties reflected by the logging curve is consistent with the core composition. It can indentify 0.2m reservoir accurately, and has somehow display for 0.1m reservoir. |
