南图尔盖盆地Aryskum坳陷钾盐的测井响应特征及其分布

Logging response characteristics and distribution of potash salt in Aryskum Depression,South Turgay Basin

钾盐作为战略资源,在农业、工业等领域具有重要的使用价值。世界大多数固态钾资源发现于大规模的石油勘探过程中,充分利用各种油气地质、地球物理资料开展钾盐勘探对于国家发展尤为重要。位于哈萨克斯坦的南图尔盖盆地地质构造简单、资源勘探潜力较大。文中以南图尔盖盆地Aryskum坳陷为研究区块,基于其沉积地质特点,结合多口井的常规测井资料及前人研究成果,综合分析自然伽马、自然电位、三孔隙度等测井曲线的响应特征,含钾层段具体表现为自然伽马异常高值,并通过无铀伽马曲线等排除铀、钍元素影响,扩径使得中子值偏高,自然电位异常幅度由砂岩层的负异常变化为正异常,电阻率值偏高,密度值介于2.25~2.45 g/cm^(3),声波时差在270~350μs/m范围内。基于含钾层测井曲线特点,利用测井曲线综合识别法、重叠法、交会图法进行研究区钾盐识别。在研究区30余口井中发现有可溶性钾盐层分布,分布在M-Ⅱ-3、M-Ⅱ-2小层底部,其中M-Ⅱ-3层底部为主要钾盐层段,并对各井含钾层段累计厚度进行统计分析。最后,借助地层对比分析含钾层段在横向和纵向上的展布情况,通过等厚图的绘制开展了找钾有利区分析,拓展了测井资料在南图尔盖盆地钾盐勘查中的应用,进而为今后研究区钾盐找矿提供重点方向。

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 2.252.45 g/cm^(3),and the acoustic value ranged between 270350μs/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 1020.361055.85 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.