The Diagenesis Of Pyroclastic Rock In Nanbeier Depression Of Tamuchage Basin

Pyroclastic rock are a kind of transition rocks between lavas and sedimentary rocks,in which tuffaceous sands and tuffite are volcano sedimentary rocks ,tuff are the pyroclastic rock.Volcaniclastic rocks with industrial reservoir discovery, it began to be concerned about. In this paper,Nanbeier area Tamuchage Basin as an example, studying on the diagenesis and reservoir characteristics of pyroclastic rocks, and authigenous mineral of volcaniclastic rocks impact on the the reservoir characters were analyzed.Through the identification of routine thin sections, the rock types of Tongbomiao and Nantun of Nanbeier Depression mainly sandstone, followed by tuffaceous sands, as well as small amounts of tuff and tuffite;Nantun mainly the lower part of tuffaceous sands and tuffite , followed by sandstone and tuff.The use of ordinary thin-section identification, cast thin-section and SEM analyisis, combined with information collected on Tongbaomiao Foamation and Nantun Foamation volcaniclastic rocks diagenesis reservoir characteristics were studied. Main types of diagenesis include compaction,devitrification,alteration, mineral cement metasomatism, such as corrosion dissolution, in which the role of compaction to end tuff diagenesis unique way.According to the symbiotic of authigenic minerals in, determination the diagenetic paragenesis is alteration,devitrification,authigenic clay mineral coating- compaction-smectite, illite-chlorite,quartzmicrolite-siderite-dissoultion,kaolinite-albite-ferrocalcite-ankerite.Diagenetic facies can be devideed into carbonate mineral cement metasomatism, kaolinite filling phase, authigenic mineral microlite,compaction dissolution.According to vitrinite reflectance, the maximum pyrolysis temperature of rock, clay mineral assemblages and Eamonn in the mixed-layer smectite ratio and so on, to determine Nanbeier depression Tongbomiao- Nantun Formation of the overall composition of rocks in the diagenetic phase A for a view.Nanbeier Depression Tongbomiao - Nantun sandstone porosity types include original pore, intercrystal pore, split pore,solution pore. Pore structure of the evaluation, Nanbeier Depression Tongbomiao - Nantun pore structure of the main level in the main category, followed by poor-grade pore structure, good low-level pore structure. Pore structure and rock type is closely related to tuffaceous sands and tuffite pore structure corresponds to poor level of note-level and pyroclastic rocks of good reservoir sandstone in general.Reservoir properties based on analysis of the data shows that the Depression Nanbeier Tongbomiao is the whole low porosity and low permeability type, belonging to the lower part of Nantun low porosity and low permeability in the reservoir, the upper part of Nantun low for low-comte permeability reservoir, so the lower part of Nantun better reservoir properties in the Copper Bowl Shaximiao reservoir.Nanbeier Depression Tongbomiao- Nantun porosity shown in the vertical four abnormal high porosity zone, and are developed in the lower part of Nantun. The first abnormally high porosity with depth for the 1650-1720m; second abnormally high porosity with depth for the 1880-1920m; third abnormally high porosity with depth for the 2100-2240m; fourth with abnormally high porosity of the buried deep for the 2630-2680m.Transverse, mass behavior on north sag of east sub-sag in the lower part of the Nantun Formation were good in the southern sag of east sub-sag, and the mass behavior on southern sag of east sub-sag better than north sag in Tongbomiao-Nantun Formation.Nanbeier Depression volcanic clastic reservoir diagenesis on the reservoir properties have a certain impact, including the authigenic mineral formation of influence. Cementation of carbonate minerals or metasomatism of the reservoir has a double effect, in the superficicl part carbonate minerals filling pore blocked resulting in reduced porosity, and deep part to account for most of the carbonate minerals replacement feldspar, quartz and other debris, they are mostly reservoir properties of the impact is not much, and sometimes within the carbonate mineral dissolution of the tablets to improve the porosity. Chlorite cladding preserved primary porosity on maximum, and the kaolinization on feldspar, albitezation is improved the reservoir properties. Nanbeier depression developt four abnormally high porosity, because the percolation filtration of atmosphere water and evolution of organic matter, which I, II, III with abnormally high porosity into account and the percolation filtration of atmosphere wate, and the fourth with an extraordinarily high porosity relevent to the evolution in organic matter.