鄂尔多斯盆地东缘临兴地区上古生界烃源岩特征及其对天然气成藏的控制作用

Characteristics of Upper Paleozoic Source Rocks in Linxing Area,Eastern Margin of Ordos Basin and Their Controlling Effect on Accumulation of Natural Gas

应用测井、录井、岩心等资料确定鄂尔多斯盆地东缘临兴地区上古生界烃源岩展布特征,通过有机质丰度、类型、成熟度指标对烃源岩进行综合评价,并分析了烃源岩条件对气藏形成与分布的控制作用。研究表明,临兴地区上古生界烃源岩为山西组、太原组和本溪组的煤层及暗色泥岩,其中主力烃源岩为煤层。煤层厚度2. 17～31. 01 m,均值18. 91 m;暗色泥岩厚度16. 93～119. 95 m,均值59. 19 m。烃源岩有机质丰度较高,煤的残余有机碳20. 40%～87. 32%,均值62. 15%,暗色泥岩的残余有机碳0. 09%～38. 60%,均值4. 59%;有机质类型以Ⅲ型干酪根为主,含有部分Ⅱ型干酪根;受紫金山岩体侵入的影响,烃源岩成熟度较高,烃源岩镜质体反射率0. 78%～4. 89%,均值1. 23%,主体处于成熟—高成熟阶段。临兴地区生气强度(10. 22～44. 86)×108m3/km2,与邻区神木气田(生气强度(8～33)×108m3/km2)相比,临兴地区的气源条件优于神木气田。平面上,临兴地区内煤层厚度> 11 m,生气强度> 11×108m3/km2的区域为工业气流井主要分布区,且在烃源岩条件较好的区域,其含气性也较高;纵向上,天然气垂向运移距离与煤层厚度和生气强度具有一定的正相关性,表现为随煤层厚度、生气强度增大,天然气垂向运移距离更远。

The distribution characteristics of the Upper Paleozoic source rocks in Linxing area,the eastern margin of Ordos Basin are determined by well logging,mud logging and core data.The source rocks was comprehensively evaluated by means of the abundance,type and maturity indexes of organic matter,and the controlling effect of source rock conditions on the formation and distribution of gas reservoirs was analyzed.The results show that,the Upper Paleozoic source rocks in Linxing area are coal seams and dark mudstones of Shanxi,Taiyuan and Benxi Formations,of which the coal seamsaremain source rocks.The thickness of the coal seams is 2.17~31.01 m,with a mean of 18.91 m.The thickness of the dark mudstones is 16.93~119.95 m,with an average of 59.19 m.The organic matter of source rocks in Linxing area is abundant.The residual organic carbon of the coal seams is 20.40%~87.32%,with a mean of 62.15%,and the residual organic carbon of the dark mudstones is 0.09%~38.60%,with an average of 4.59%.The organic matter of the source rocks in Linxing area is mainly type Ⅲ kerogen,and contains some type Ⅱ kerogen.Affected by the intrusion of the Zijinshan rock mass,the source rocksin Linxing area are of high maturity,their vitrinite reflectance is 0.86%~4.89%,with an average of 1.29%,and their main part is in mature-high maturity stage.The gas generation intensity is(10.20~42.83)×10^8 m ^3/km^2 in Linxing area.Compared with Shenmu gas field(the gas generation intensity is(8~33)×10^8 m^3/km^2),the gas source conditions in Linxing area are better.On the plane,the industrial gas flow wells in Linxing area mainly distribute in the areas where the coal seam thickness is greater than 11 m and the gas generation intensity is greater than 11×10^8 m^3/km^2,and the gas content is also higher in the areas with better source rock conditions.Vertically,there is positive correlation between vertical migration distance of natural gas and coal seam thickness and gas generation intensity,that is,with the increase of coal seam thickness and gas generation intensity,the vertical migration distance of natural gas is longer.