The Karst Paleomorphology Of Majiagou Formation In Sulige East Area And Yu37 Well Area And Its Influence On Reservoirs

The Gas reservoirs in Mawu1-4 subsegment of Ordos Basin which lies inside the top of the Ordovician weathering crust and have experienced long period Weathering,Denudation was developed with the migration of gas from the coal seam in Carboniferous,Upper Paleozoic.The Impression method and the Residual thickness method are used to restore and divided the study area's Palaeogeomorphology with the help of quantitative present basic geological data and many Core observation,Logging,Gas production test datas.Considering that the Palaeogeomorphology of Sulige Gas Field is Karst highland.From north to south,the Three geomorphic units are Ancient-depression,Ancient platform and Ancient highland respectively and their Outcropping strata are Mawu7-Masi,Mawu4-6,and Mawu1-3,the Mawu1-4 subsegment are mainly located in Ancient highland..The distribution of Micro-Palaeogeomorphology is scattered.Compared with the former one,the Yu37 area is mainly located in Karst slope.Paleo-slope land develops best,Paleo-hammock develops fragmentary,Paleo-depression is rare.Palaeogroove is chararistic of arborization,whose distribution direction from west to east is from limb to major.Then examining the reservoir characteristics of Mawu1-4 subsegment in the east of Sulige Gas Field and Yu37 area and discuss the main controlling factor to reservoir,such as Sedimentary microfacies,Diagenesis,Tectonism and Karst Palaeogeomorphology.It's suggested that the Sedimentary environment belongs to Platform evaporative tidal phase during Mawu1-4 subsegment Period.The Anhydrite concretion micrite-fine powder dolomite and the Coarse-powder dolomite or Fine-crystalline dolomite.The type of reservoir space are mainly Gypsum dissolution pore,Intergranular dissolution pores and Intergranular pore.The reservoirs mainly distribute in Mawu1-3 and Mawu1-4.The small Nose structure,in a manner,have influenced the distribution of gas reservoirs and its denudation.The Tectonic fissure have improved the penetrance of rock.In the constructive diagenesis respect,the Dolomitization,Gypsification and dissolution play a important role.In the destructiveness Diagenesis respect,the Mineral filling results in a significant decrease in porosity,of which sparry calcite is the most destructive.Emphasizing on the influence of Karst paleoglandomorphologies on Mawu1-4 subsegment.?The degree of formation denudation is related to the Karst paleoglandomorphology and the Paleostructure.The area where the Inheritant depression develops and the Erosion depression develops is best.?Compared with the Micro-highland and Paleo-Hammock,the coal team is thicker in the place where the Depression and Palaeogroove develop.?Having influenced the karst and the distribution of gas reservoirs.Due to the strong Karstification and adjacent Local hydrocarbon supply center,the gas reservoir offen develop at the place near the Local depression and Palaeogroove.Besides the circular perimeter zone,The Micro-highland with large scale cannot be erosioned anymore.At last,quantificating the Mawul-4 and Mawul-2 favorable area in the Sulige Gas Field and Yu37 area into three part,according to the preservation condition,the transition between Micro-highland and Micro-platform which is adjacent to the Micro-depression area can be divided into the first and the best class in the east of Sulige Gas Field.The place where the Paleo-Hammock develops and near Paleo-depression and Palaeogroove can also be divided into the first and the best class in Yu37 area.