| The coal bearing formation rich in shale gas and coal-bed methane, which are close, in Hedong coalfield, where contrast of the reservoir forming characteristics between Shale Gas and Coalbed Methane can be studied wel. That can provide theoretical reference for the joint exploration of Shale Gas and CBM. This thesis, making the Shanxi Formation and Taiyuan Formation be as theresearch subject, with the methods of data collection and arrangement, geological field investigation, core observation, experimental test and analysis, studied contrast of the reservoir forming characteristics between shale gas and CBM from five respects: geological background, depositional environment, source rock and reservoir characteristics, accumulation process, reservoir conditions and accumulation mechanism.Hedong coalfield is located in the east margin of Ordos Basin. The east side is a SN-tending lishi fault. Strata bearing coals shows a SN-tending monoclinal structure with rolling folds and a few of faults.Late Paleozoic coal-bearing strata in the study area has a clear structure of cycle, divided into 10 cycle from the bottom up.The thickness of the shale is 1~23m, 1~14.5m, 4~45m and 1~43m respectively in Jici Segment, Xishan Segment, Shangou Segment and Shanxi Formation. The thickness of coal seam of 9# in Taiyuan Formation is 0~7.60 m, and the thickness of coal seam of 5# in Shanxi Formation is 0~6.69 m.The type of organic matter about shale in the study area is mainly of Ⅲ type, with an average Ro being 2.03%, and an average TOC being 2.01%, with a highest content of Clay and a higher content of quartz. The average porosity is 2.82% and microporous and eyelet is the main storagespace. The average permeability is 0.01305 m D. The average gas content is 1.47 m3/t. The Ro of coal seam general y more than 2%. The average porosity is 6.87% and macropore and transitional pore is the main storagespace. The average permeability of coal seam is more than 1 m D in study area. The gas content, with less than 2m3/t in eastern outcrop area, increases with the increase of coal seam buried depth,even more than 18m3/t in west.Shale gas and coalbed methane are unconventional gas of low porosity and permeability. The shale is rich in minerals and lack of organic matter and the coal seam is rich in organic matter and lack of minerals which makes the following differences between Shale gas and coalbed methane:1. Shale with super tight reservoir and mainly micropores and nanopores in pores shows low porosity(The average porosity is 2.82%) and permeability(The average permeability is 0.01305 m D).Coal with dual porosity system composed by pore and fracture has big span in pore size dominant and macropores and transitional pores are dominant. Porosity(The average porosity is 6.87%) and permeability(The average permeability is more than 1m D) in coal are bigger than that in shale.2. The accumulation mechanism of CBM is piston accumulation mechanism with the adsorption state, the free state and the dissolved state, especialy adsorption state is dominant and the maximum adsorption of primary mineable coal bed is 6.90 m3/t. Coalbed methane is adsorbed at the surface of coal after produced, and adsorption gas too much to translate into free state with occurrence in pore and fracture. With the control of temperature and pressure, the adsorption gas, the free gas and the dissolved gas are in the state of dynamic balance. Shale gas consists of the free gas and the adsorption gas which accounts for 20%~80% of the total volume with the influence of temperature and in study pressure and the maximum adsorption of shale is 0.2~0.62 m3/t. In the early days of accumulation, shale gas is adsorbed by organic matter and clay minerals, which is similar to the accumulation mechanism of CBM. As the process of hydrocarbon generation continues, shale gas begins to migrate and accumulate in cracks, which is different to the accumulation mechanism of CBM. |
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