Research On Accumulation Characteristics Of Shale Gas In Lower Cambrian Niutitang Formation In Block 2 Of Fenggang, Guizhou

The geological reserves of shale gas in Guizhou province is 10.48 × 1012 m3, ranked the fourth, which has a good prospect of shale gas exploration and development. The block 2 of Fenggang also has a good shale gas exploration and development prospects which is divided by Ministry of Land and Resources when the second round of domestic public bidding proceeding. It is located in northern Guizhou, where the terrain ups and downs, geomorphic type is complex, and for the oil and gas exploration right blank area. In view of that the geological characteristics research of the lower Cambrian Niutitang Formation shale gas is relatively weak, shale gas geological conditions are not clear, shale gas exploration is still in its infancy and the date which can be used for shale gas resource potential prediction is also very limited, this paper selects the Niutitang Formation shale as the research object. A data collection, geological investigation, experimental test and theory research is used in the study to analy the reservoir forming characteristic of the Niutitang Formation shale gas. The results are as follow.The Niutitang Formation is formed in a deep-water shelf deposit environment, which has a stable aquatic environment, with an average thickness 100 m and a gradually thickening trend from southeast to northwest. The Niutitang Formation buried depth is mainly controlled by tectonic development, with the depth between 500-3500 m and a gradually Increasing trend from south to north and from west to east. Regional structure is given priority to with rolling fold and reverse fault, which provides favorable conditions for shale gas generation and preservation.The block 2 of Fenggang extensive development of the Niutitang Formation black shale, with abundance of organic matter ranged from 2.15% to 6.50% which has a trend of increased from east to west and a trend of increased from top to bottom. The organic matter of shale is type Ⅰ and the thermal maturity has achieved high-over mature stage. The main composition of the mineral is quartz, feldspar and clay with clay mineral content around 25% on average, quartz and feldspar content around 70% on average. Clay minerals mainly consist of illite mixed layer and illite. Clay minerals provide plenty of adsorption surface area for shale gas, which in favour of rich integration hidden of shale gas.The Niutitang Formation in Block 2 of Fenggang is given priority to with thermogenic gas. There are five pore types in the target strata, intragranular pore, intercrystalline pore, organic pore, intergranular pore and dissolution pore that we can find out through the microscope and scanning electron microscope. Natural micro-cracks are well developed, forming a complex fracture network with air voids, macroscopic and microscopic cracks which much been filled in asphalt, pyrite, calcite, etc. The result of mercury injection experiment, low temperature liquid nitrogen adsorption test and carbon adsorption experiments shows that microporous, mesoporous and macroporous well developed. Microporous and mesoporous adsorption surface area is large enough which offers a wide range of adsorption space providing a large amount of adsorption space for shale gas, while the open pores with good connectivity offers a wide range of free gas occurrence space. On the whole, the condition of the target layer is good for shale gas occurrence. The maximum adsorption capacity of ZK2 drilling is between 1.18cm3/g to 5.65cm3/g, with a average of 3.57cm3/g, which shows the adsorption capacity is good.The Niutitang Formation in Block 2 of Fenggang has experienced continuous burial stage which ensures the smooth progress of the organic matter to oil and gas and generates a large number of shale gas, while the cretaceous strata’s uplift provides favorable conditions for the commercial development. Based on the reservoir microscopic factors relation with hydrocarbon study found that shale gas adsorption quantity obviously controlled by the organic carbon content, and almost has nothing to do with the mineral constituent, porosity. Comprehensive considering research area tectonism, sedimentation, buried depth and the reservoir microscopic factors influence on shale gas accumulation, the tectonic setting and buried depth are major factors of the favorable area. Advantageous area optimization parameters include areas favorable for structural stability with no fault throw more than 20 m and depth with a range from 1000 m to 3500 m. And research area is divided into two favorable areas for shale gas enrichment inclues favorable area I and II.