利用自然伽马测井计算准噶尔盆地沉积层生热率及其热流贡献

沉积层放射性生热的热流贡献（沉积层热流）是沉积盆地大地热流的重要组成部分，能够有效促进中国西部“冷”盆深层-超深层烃源岩的增温和热演化.本文利用不同的自然伽马（GR）-生热率（A）经验关系式分别计算了准噶尔盆地不同构造单元16口钻孔共6120个沉积层生热率，通过与实测生热率的统计对比，确定了适用于研究区的GR-A经验关系，建立了准噶尔盆地地层生热率柱，据此计算了研究区沉积层热流贡献，并以盆参2井为例定量分析了沉积层热流的增温效应.结果表明，准噶尔盆地沉积层平均生热率为1.179±0.339 μW·m^-3，总体上随着时代变老，沉积层生热率呈现出递减趋势.准噶尔盆地沉积层热流平均为7.9±4.9 mW·m^-2，约占地壳热流的29.2%和大地热流的19.6%，区域上与盆地沉积层厚度大体一致，表现为中央坳陷最高，北天山山前冲断带变化较大，陆梁隆起和西部隆起次之，东部隆起和乌伦古坳陷最低.沉积层热流能够有效增高深层—超深层烃源层受热温度，促进有机质热演化，如在考虑和忽略沉积层生热的两种情况下计算的盆参2井下侏罗统三工河组烃源岩底部（5300 m）温度差异最大为7.3 ℃，这显然对于地温梯度小、主体油气藏埋深大的准噶尔盆地油气资源评价和勘探目标优选具有重要意义.

Heat production rate and heat flow contribution of the sedimentary formation in Junggar Basin,northwest China

As an important part of the terrestrial heat flow, radioactive heat flow production of sedimentary formation can warm the deep and ultra-deep source rocks and promote their maturity evolution effectively in the‘cold’basins in western China which are characterized by low geothermal gradient and low terrestrial heat flow. 6,120 heat production rates of sedimentary formation in 16 boreholes among six tectonic units in Junggar Basin were acquired using different empirical relationships between natural gamma ray (GR) and heat production rate (A). By comparison with the measured heat production rates, the applicable GR-A empirical relationship to the study area was determined. Then, the heat production rate columns of the sedimentary formation in Junggar Basin were established and the heat flow contribution of the sediments was calculated. Finally, as an example, its warming effect of Well Pc2 was calculated quantitatively. The results showed that the average heat production rate of the sediments in Junggar Basin was 1.179±0.339 μW·m^-3 and it decreased gradually as the formation age became older. The Quaternary formation was with the maximum heat production rate while the Carboniferous formation minimum. The average heat flow contribution of the sediments was 7.9±4.9 mW·m^-2, which was approximately 29.2% of average crustal heat flow and 19.6% of average terrestrial heat flow. The heat flow contribution of sediments was consistent with the thickness of sediments and showed the following characteristics. (1)Relatively high heat flow contribution of sediments was confined to the Central Depression. (2) Southern Depression varied dramatically on heat flow contribution of the sediments. (3)The Luliang Uplift and Western Uplift were characterized by lower heat flow contribution of the sediments. (4) The lowest heat flow of sediments occurred in the Eastern Uplift and Wulungu Depression. The heat flow contribution of sediments can warm effectively the deep and ultra-deep source rocks in Junggar Basin and promote maturity evolution of the organic matter. For example, the temperature in the bottom of J₁s source rock (5300 m) in Well Pc2 was 7.3 ℃ higher in the condition of considering the heat production of sediments. Obviously, it was very significant to the hydrocarbon resource evaluation and exploration targets optimization in Junggar Basin which was characterized by low geothermal gradient and deep reservoirs.