The formation of karst weathering crust is the major phase of the palaeo-karst evolution in the Ordovician limestone in the Ordos Basin.Based on the study of cores,thin sections and well logs from the central and eastern parts of the basin,combined with its specific hydrodynamic characteristics,this article takes the Well SH15 as an example to study the process of karstification.Three zones of weathering crust karst were recognized.They are,from the top to the bottom,vertical vadose zone,horizontal subsurface flow zone and bedrock subcritical flow zone.The process of palaeo-weathering crust karstification was discussed,and a model was established in this paper.The Ordovincian karst limestone is an important reservoir in the region.The characteristics of palaeokarst reservoirs and their governing factors are carefully studied based upon the data of lithofacies,palaeogeography,palaeogeomorphology and so on.Results show that the enrichment of natural gas is related to the development of weathering crust karst in this region.The conclusion is helpful to gas exploration in the Ordos Basin.

在煤矿生产中,经常会遇到水患问题,例如地下富水带、地下岩溶溶洞、积水采空区等。若不及时发现、处理,会对煤矿安全生产与人民生命财产造成严重威胁。瞬变电磁法法对低电阻率地层反应比较敏感,用该方法探测、发现水患问题,为矿井避免遭遇水患威胁提供了有效的手段。

The discrepancy of physical property of Chang 3 reservoir in Heshui area,Ordos basin are researched using physical property,Reservoir petrological,sedimentary microfacies,diagenesis.The result show that Chang 3 reservoir's physical property is low,but partly is relatively high-porosity and permeability.The reasons of the discrepancy is:①The contents of quartz in clastic constituents play a part role,the contents of quartz is higher,the physical property is good,otherwise is bad.②In the distributary channel microfacies sedimentary microfacies,the physical property is relatively good,but sand dam of branch estuary sedimentary microfacies is relatively bad.③The diagenetic stages comprise compaction,kaolinite cementation,chlorite filling,siliceous cementation,damage the physical property of the reservoir.Chlorite graphragm protect the reservoir.The contents of carbonate play an important role,the contents of carbonate is lower,the physical property is good.The contents of carbonate is higher,the physical property is bad.The metasomatism functions and dissolve role is one of the reasons that partly interval is relatively high-porosity and permeability.

Elashan volcanic rocks from late Triassic Elashan Group in southeastern margin of the Qaidam Basin are mainly consisted of a set of medium and acid volcanics combination,including rhyolite and dacite primarily,followed by andesites.The results of the analyses on principal elements,rare-earth elements and trace elements show that Rittman index(δ) of the samples are all below 4,and belongs to calc-alkaline volcanic rocks;the average of SiO2 is 71.95%,most of the samples have a characteristic of low aluminum,alkali content is higher,and that belongs to the sub-alkaline volcanic rocks.The ratios between LREE and HREE are large and negative Eu anomalies are obvious,so they have the typical late rare earth fractionation characteristics of magmatic differentiation.The samples display a characteristic of LREE enrichment.The discriminant diagram of tectonic environment shows its environment is volcanic arc-within plate volcanic region.This feature may reflect this volcanic activity happened in the tectonic environment of Qinling orogenic belt underthrusting to Qaidam block.

The oil sand resources are very abundant in China,and its reserves occupy the fifth level in the world.So it will probably be one of major fields for unconventional oil-gas resources exploration in China.The oil sand resources are found in almost all petroliferous basins,but mainly distributed in four types of basins: the tectonic compressive basins in the west,the rift basins in the east,the transitional basins in the middle and the intermountain basins in the south,among which such seven basins as Junggar,Tarim,Qiangtang,Qaidam,Songliao,Sichuan and Ordos ones have enormous oil-sand resources.They will be major areas of domestic oil sand exploration and development in the future.

根据煤岩层的物性特征,利用测井曲线中的视电阻率、自然伽玛和人工伽玛曲线的异常特征和异常组合规律,主要从以下几个方面论述了如何利用测井曲线进行煤层对比:(1)曲线异常幅度宽度;(2)曲线异常形态;(3)曲线异常组合规律。