Study On Characteristics Of Underground Fluid And Formation Of Reservoir In Tarim Oilfield

The main location of reposition and exploitation of the Tarim oilfield's is in Ordovician, with the karst seam hole and tectonic fissures being its major reservoir space which developed in unconformities on the top face of Ordovician. The occurrence modes and distribution patterns of the oil and gas in it are very complex. The oil, gas and water are closely interconnected in the process of oils' formation, migration, accumulation. In this paper, Ordovician in the Tarim oil fields is selected as the main study object. Multifarious related data are collected, such as stratum, geologic tectonic, Lithologic, lithofacies, drilling, riginal hydrogeology, water chemical components and many kinds of oil and gas exploration.Uusing of the information and the new theories and methods in sedimentation basin's fluid history analysis, the relation between formation, migration, accumulation of oils and gas with fluid hydro-chemistry and dynamics is systematically studied from the aspect of forming and evolvement of Tarim Ordovician oil field. The main researches and conclusions included as the following:The fluid dynamics and oil and gas transportation are researched and the model of nowadays hydro-dynamical fields are constructed, basing on the fluid potential calculated including of the oil, water and gas potential. The holistic characters of the nowadays hydro-dynamical fields in Tarim oil field shows that the oil and gas potential falling, and accordingly, the oil and gas transporting from the southern to the northern part in the basin. In the forming process of the hydro-dynamical field, the board of the partial hydro-dynamical unites was variable.Vertical zonation and planaration of ground water chemistry are studied with the complete use of the information about the water chemical components in many drilling holes. The hydro-dynamical fields in Ordovician can be divided into two kinds of unites, the freshening zone due to meteoric water leaching downwards, the concentration zone for evaporation near the ground surface, and freshening zone for the clay mineral dehydration. Planaration of ground water chemical fields is that the north part of Akekule Arch is freshening area due to meteoric water generally at the basin edge, the south part is freshening area for the mudstone-compaction-released water, and the main body of Ordovician of the Tarim oil field is in the concentration area by cross-formational flow and evaporation.Hydro-geochemistry and transportation of the fluid inclusion in karst seam hole and tectonic fissures are studied with applications of isotope techniques. In the formation of calcite vein, the sources of CO2 was very complex, through analysing carbon and oxygen isotope composition of calcite veins in the in karst seam hole and tectonic fissures and its marinecarbonate surrounding rock, on the other hand, the lower 8 0 reflected that the calcite vein was formed in a higher temperature hydrothermal fluid. Through the analysis of water-fluid oxygen isotope and carbon dioxide fluid isotopic composition, view that in the calcite sedimentation and cement in the corresponding layer, the water media mainly controled by deep hydrothermal fluid and got relatively small impact of atmospheric precipitation. The proportion of organic sources of carbon dioxide in the fluid is relatively small that meaning little or no organic carbon involved, and mainly from the hydrothermal fluid inorganic carbon. Hydro-geochemical characteristics of the related calcite vein in the fluid inclusion in the ancient karst corrosion seam hole and structure fissure are studied. Total hydrocarbon content for (water-soluble or gas phase + water-soluble) 1.5~49.4%, the average 14.0%, the gas phase accounting for 76.3% indicated that possibly fluid inclusion was capped happening to be in the oil field natural gas massively formative years. In gas-fluid two phase inclusion , the content of gas phase methane (CH4) is far higher than that of water-soluble methane, that indicated gas phase hydrocarbon being capped with high content of CH4, reflecting the oil field's high maturity state. The fluid inclusion in corrosion seam hole or filled in the calcite vein, the salt water content in 72.1~85%, CH4, water-soluble hydrocarbon compound generally bing very few or having no CH4, reflect the inclusion is possibly a product which catches in the later period of oilfield formation.The dynamical and hydrochemical characteristic of Ordovician system reservoir closely relating with the oil gas migration, accumulation and formation, the relation between them in different geologic history time are studied. The Ordovician system in Tarim oil field after deposition occurs five big scales tectonic movements which having decided five main hydro-geology cycle. The periodicity of the hydro-geology cycles had decided the petroleum and the mudstone squeezing water migration and the mobile gradualness, causing the petroleum's migration from the hydrocarbon-producing center toward the edge or link belt-shaped distribution gradually.