陕北三叠纪煤田最大古地温与焦油产率关系

Relationship between Maximum Paleotemperature and Tar Yield of Triassic Coalfield in Northern Shaanxi

煤田地质勘探过程中主要测定现今地温特征,对于煤层形成时的古地温和地温梯度研究较少。为了研究三叠纪煤田煤层形成时的热演化特点,基于煤炭勘查资料和样品测试结果,利用深成变质作用地质温度计,恢复煤层形成时的最大古地温。由于煤田地质勘查数据缺乏典型镜质体反射率剖面,利用距离较近典型油井的镜质体反射率剖面数据,通过典型镜质体反射率剖面平移法,恢复地层最大剥蚀厚度。分析了焦油产率与古地温、古地温梯度之间的关系,探讨了古地温和古地温梯度对焦油产率的影响。研究结果显示:(1)古地温99.37℃~125.17℃,平均值115.62℃,古地温梯度3.63℃/(100 m),古地温高于现今地温,古地温梯度高于现今地温梯度;(2)焦油产率由研究区中部向外逐渐减小,整体上随着古地温的升高,焦油产率逐渐增加;(3)古地温大于110℃后,随着古地温升高,局部区域焦油产率呈现下降趋势。

In the process of coal geological exploration,the present geothermal characteristics are mainly measured,paleotemperature and the geothermal gradient during the formation of coal seam is rarely studied.In order to study the characteristics of thermal evolution during the formation of coal seam in the Triassic coalfield,based on the coal exploration data and sample test results,plutonic metamorphic geothermograph is used to restore the maximum paleotemperature during the formation of coal seam,Due to the lack of typical vitrinite reflectance profile in coal field geological exploration data,using the vitrinite reflectance profile data of typical oil wells which close to research area,the maximum denudation thickness of strata is restored by the translation method of typical vitrinite reflectance profile.The relation between tar yield and paleothermal gradient and paleothermal gradient is analyzed,and the influence of paleothermal gradient on tar yield is discussed.The results show that:(1)the paleogeothermal temperature ranges from 99.37℃to 125.17 C,the average value is 115.62℃,the paleogeothermal gradient is 3.63 C/(100 m),the paleogeothermal temperature was higher than the present earth temperature,the paleogeothermal gradient is higher than the present geothermal gradient;(2)the tar yield gradually decreased outward from the middle of the study area,and as a whole,the tar yield gradually increased with the increase of paleotemperature;(3)when the palaeoground temperature is greater than 110 C,the tar yield in some areas shows a decreasing trend with the increase of palaeoground temperature.