The Research Pre-Carboniferous Palaeogeomorphology And Paleokarst The West Side Of The Gas Field Of Jingbian In Ordos Basin

Ordos Basin have rich natural gas resources， the Majiagou formation inOrdovician is one of the important beneficial reservoir. The study area is located inthe connection of the Jingbian gas field and Sulige gas field，they are main gasproduction block of the basin. This study integrated analysis and research in takingthe theory of The Sedimentology，Stratigraphy，Petroleum geology and Geochemistryetc as a guideline and using the present materials such as drilling data，logging data，the data of the test gas and the production of dynamic data atc. This artcle carried outstratigraphic classification and correlation and used the impression method and theresidual thickness method to restore the study area palaeogeomorphology. detailedanalysis of the paleokarst features of the study area and draw up of related maps. Andthen discuss the paleokarst and the paleogeomorphological reservoir impact and gasdeposit rules. Main recognize include the following:Firstly，Characteristics of the study area Ordovician marker beds is more clearly，the strata can be correlated，bauxite and tuff are standard stratigraphic interfacelithology. Through drawing up a small layer of stratigraphic thickness maps，reconstruct the strata spatial and temporal distribution of condition. Study area，theoverall performance of the ancient geomorphological features of strata from west toeast，north to south the old to the new distribution is gradually shrinking.Secondly，Compare the pros and cons of the methods of paleogeomorphologicalrecovery such as Geophysical method，an impression of method，residual thicknessmethod and sedimentology method etc. This study mainly use the impression methodcombined with the residual thickness method to recovery the study areapalaeogeomorphology. Palaeogeomorphology of the study area can be divided into ahigh region and slope area，while the slope area can be subdivided on the up slopearea and the down slope zone. That the overall geomorphic characteristics of the studyarea is high in the west low in the east，from north to south，the uneven distribution ofstratigraphic thickness. Thirdly，The study area have good conditions of rich material foundation andmoderate tectonic and climatic for the karst. Therefore，the study area extensivelydeveloped the paleokarst at the top of Ordovician stratum. The dissolution of thestudy area including the supergene karstification and burial karstification two types，Supergene dissolution play a crucial role for the reservoir of formation Ma54.Karstification development is controlled by lithology， sedimentary facies andstructure factors.Fourly，Gas reservoir model of the study area is mainly due to the accumulationpattern of the Palaeogeomorphology and paleokarst control. Ancient monadnock inthe slope area is a favorable area of the gas reservoir，because the dolomite andgypsodolomite in side of monadnock subjected to weathering and leaching is easy toform the solution porosity reservoir; but monadnock in central dolomite dissolutionlevel is poor，is not conducive to the development of the reservoir.