关键词: 南图尔盖盆地, 含钾地层, 常规测井, 曲线异常, 地层对比

Abstract: As a strategic resource, potash salt has an important value in agriculture, industry, and other areas of national interests. Most of the solid potassium resources of the world were discovered in the process of large-scale petroleum exploration. It is particularly important to make full use of various types of petroleum geological and geophysical data in carrying out potash salt exploration. The South Turgay Basin in Kazakhstan has simple geological structure as well as great potential for resource exploration, and we chose the Aryskum Depression of the basin as the study area. Taking into account the sedimentary geological characteristics of the depression, combining with conventional logging data and results obtained in the study area by previous researchers, we performed comprehensive analysis of logging response by examining the abnormal changes in response curves, including natural electric potential curve, natural gamma ray curve, neutron curve, and resistivity curve. The potassium layers have abnormally high GR intensity while the effects of uranium and thorium were eliminated using “uranium free gamma ray” curve. Influenced by drilling fluid, dissolved potash salt causes drill hole to enlarge, which resulted in higher neutron level, slightly higher resistivity, and change of natural electric potential anomaly from negative to positive in sandstone layer. The density value was between 2.25-2.45 g/cm³, and the acoustic value ranged between 270-350 μs/m. These characteristics were used in the comprehensive logging curve analysis, logging curve superposition, and cross-plot analysis to identify potash salts in the study area. Soluble potassium were found in more than 30 wells. They are mainly distributed at depths of 1020.36-1055.85 m. The potassium layers were stable at the bottom of sublayers M-Ⅱ-2 and M-Ⅱ-3, mainly in M-Ⅱ-3. Measurements of the overall thickness of potassium-bearing layers of each well show that the overall thickness does not change significantly over the mostly thin stratum, from 0.76 m to 2.16 m, averaging at 1.23 m. Finally, by analyzing the distribution of potassium layers in the transverse and longitudinal directions by stratigraphic correlation analysis, we obtained the isopach map, which allowed us to delineate the favorable areas for finding potash salt. Thus, we expand the application of logging data to potassium prospecting in the Aryskum Depression and provide future directions for potash exploration. One of the target areas is likely in the northwestern part of the depression. It has good potassium formation, relatively thick potassium salt deposit, favorable evaporation environment, and strong salt formation, making it a potential area for potassium exploration.

Key words: South Turgay Basin, potassium formation, conventional logging, abnormal curve, stratigraphic correlation