The Fluid Aeolotropism And Pool-Forming Dynamics Of Ordovician, Tahe Oilfield

Taking Organic geochemistry of fluid as a clue with structure and reservoir evolution, the paper study the characteristics of crude oil and gas of Ordovician on geochemistry in Tahe Oilfield, look for migration path of oil and gas and research on the relationship between fracture-vuggy system and distribution of oil and gas by macroscopic and microcosmic view, further analyze the impact of geochemistry on oil and gas accumulation., synthetically research on the dynamics of accumulation of oil and gas, finally point out the favorable area in Tahe Oilfield and its periphery. The main recognitions had be required as bellow:(1)The Ordovician is mostly composed of matured-high matured crude oil, which came from the same source rock with the main migration direction from south to north early while form east to west lately. The early-infilling oil experienced a strongly biodegradation which was the most heavily in the northwest and mixed by the second-infilling oil of high maturity. The oil of Ordovician is composed of two-stage infilling of different maturity obviously. The early infilling contained amply oil source of mid maturity and distributed in the all area, compared to the late-infilling oil of high-maturity.So the now-day crude oil is the result of the two mixed oil of different maturity.(2)The natural gas of Ordovician is typical petroliferous gas which came from the same source rock. It is a composite of gas that was generated from the sapropelic parent material of different maturity. Its maturity varied from mature degree to high-over mature degree which decreased from east to west and from southeast to northwest. The generating of natural gas is characterized by multi-stage and continuance.The nature gas has two-stage infilling,and was mixed. The first stage was amply gas asocciated with crude oil from southeast to northwest and from east to west. The second was pyrolysisdry gas, and areas of discharging was relatively smaller than the first time, confined on the edge of Well TK614-Well TK611-Well S80-Well TK711-Well T810X (K) -Well S114-3-Well S112-1.(3)There are five stages of fluid movement,and four stages of accumulation which mainly came about at early time;Vertically, the accumulation of oil and gas in Lower-Middle Ordovician took place early,and at late time the movement of oil and gas was not strong.But in the Upper Ordovician,the accumulation came about not only at eary time but also at late time with high maturity hydrocarbon.. in the east of Tahe Oilfield oil and gas accumulated at middle-late time with multi-stage infilling period.There were so many oil-gas infilling periods in the southeast ,and infilling period of oil-gas was relative simple,mainly came about early while less activity of hydrocarbon took place at late time.(4)The forming of pool in Ordovician of Tahe oilfield experienced late Hercynian, Indo-Chinese epoch, Yanshanian episode,Xishanian episode.The pools underwent a strong meteoric filtering,biodegradation in the Hercynian and Indo-Chinese epoch when the reservior was distroyed,then were infilled with oil and gas with high maturity and reconstructed in the Yanshanian-Xishanian episode.In the west and northwest heavy oil was reserved in the Hercynian , suffered from water washing and biodegradation while medium-light oil from Indo-Chinese episode and Yanshanian episode existed in the south and southeast of the oilfield.(5)Oil and gas were controlled by the structure formed by superposition of tectonic movement in the early and late Hercynian which resulted in palaeogeomorphology and degree of fracture growing. The latter decided the flowing direction of palaeocurrent and the degree of corrosion,which is the main factors of karstification.Especially,the superimposition of palaeostructure and Akekule uplift is the most favorable area for karst and fracture growing.The ubiquitous high angle fracture made all kinds of vugs into a large scale storage,so the fracture-vug system was divided into some blocks in the main oil zone on the plane. Stucture evolution controlled the formation and evolution of large scale fracture-vug system,the latter effected the system where oil and gas transported and accumulated,further determined the property of fluid in itself.(6)The formation of aeolotropism of reservoir fluid of Ordovician in Tahe was resulted from such factors as: aeolotropism of fracture-vug system,evolution of hydrocarbon source,multi-stage discharging and displacement,uplift and corrosion by water washing, epigenetic changes and fluids in reservoir bed mixing.(7)The hydrodynamic field, the formation and evolution of pore structure controlled the transportion,driving,and accumulation of oil and gas.The stage form middle-late Caledonian to early Hercynian was the first period for pool forming and the late Hercynian was the biggest period for hydrodynamic accumulation of oil and gas this area.The centrifugal flow of discharge water from compaction and gravity induced centripetal flow recharged by meteoric water took place at the same time in the Triassic depositional stage, and mature-high mature hydrocan continued to transport , infill into the Ordovician reservoirs with centrifugal flow,so the pools formed.(8)The factors that controlled the rules of distribution of oil ,gas and water were: reservoirs in crust of weathering,the process and degree of driving oil and gas, palaeohydrodynamic condition.(9)The next target for exploring are:①the north of ToPutai,special the zone of TP9—TP7,②S110—S113 fracture belt of NS-trending.③the southwest block of YuQi area.