鄂尔多斯盆地陇东地区长9油层组古盐度特征及其地质意义

利用黏土矿物X衍射分析和微量元素分析结果，采用Couch公式和Adams公式对鄂尔多斯盆地陇东地区长9油层组沉积期湖盆古盐度进行恢复，确定由于受到成岩作用影响，由Couch公式计算出的古盐度值比实际值低，而由Adams公式计算结果反映的水体古盐度性质更可靠。研究表明:①鄂尔多斯盆地长9油层组沉积期湖盆水体具微咸水-半咸水性质，盐度从北东、北西及西南3个方向往湖盆中央呈逐渐升高，晚期的盐度低于早期盐度，反映湖平面上升的湖进过程。盐度高值区为相对闭塞的湖湾和湖盆中心的半深湖区。平面上，古盐度向河流入注湖盆的河口方向降低。由古盐度变化为古地理恢复提供了依据；②湖泊水体盐度与储层关系密切，较高盐度的水体有利于早成岩阶段绿泥石环边胶结和浊沸石的形成，前者有利于原生粒间孔隙的保存，后者更容易被溶蚀而形成丰富的次生溶孔。

Paleosalinity of Chang 9 Reservoir in Longdong Area,Ordos Basin and Its Geological Significance

On the basis of clay mineral X-ray diffraction analysis and trace element analysis, the lake basin paleosalinity of the deposition of Chang 9 reservoir in Longdong area, Ordos Basin has been recovered according to Couch formula and Adams formula. We discover that they are affected by diagenesis, the value of the paleosalinity which calculate by the Couch formula is lower than the actual value, and Adams formula calculation results reflect the nature of the ancient body of water salinity is more reliable. Studies have shown that, the lake water of Ordos Basin is brackish during the Chang 9 deposition period. Paleosalinity was gradually increased from northeast, northwest and southwest to the central lake basin. The salinity of the late Chang 9 deposition period is lower than the early that reflect the transgressive lake level rise. The salinity high value area was relatively isolated bays or lake centers which belongs half deep lake. The paleosalinity gradually decrease from the lake center to the river estuary direction. The variation of paleosalinity provides a foundation for restoring  the ancient geography. The reservoir is closely to lake water salinity, and high salinity water is conducive to the formation of early diagenetic stage chlorite ring edge cement and laumontite. The chlorite ring edge cement formatted in early diagenetic stage is favourable for  intergranular porosity preservation. The laumontite is more likely to be dissolved and formed abundant secondary dissolved pores.