| Carbonate hydrocarbon resourses play an important role in the world's resourses,and the carbonate hydrocarbon accumulation research has been the hot point in the petroleum geology study.The Ordovician carbonate rocks in the Tazhong area,Tarim Basin,have excellent hydrocarbon accmulation condition,which own great resource potential.Based on the lastest exploration and development results,hydrocarbon reservoirs not only can distribute in the structural slope or depression but also in the structural highs,which indicated the hydrocarbon migration controlled by the buoyancy and other dynamics,and the Ordovician reservoirs are different from the normal and deep basin hydrocarbon reservoirs.Thus,the conventional or unconventional hydrocarbon accumulation mechanism that exist today can not explain the formation and distribution of Ordovician carbonate hydrocarbon reservoirs,and the new hydrocarbon accumulation analysis idea/method should been found.Based on the lastest hydrocarbon exploration and development data of Ordovician in the Tazhong area,Tarim Basin.In order to analyzing geological features,hydrocarbon accumulation mechanism,and dsitribution mode of the Ordovician hydrocarbon reservoirs,the workflow of this paper includes integrating the geological,geophysical,geochemical,mathematical statistics,and physical simulation experiment methods to investigate the formation and distribution of hydrocarbon reservoirs.The results show the hydrocarbon reservoirs in the Ordovician have features as following:(1)Reservoir superimposedly developed in vetical and hydrocarbon widely distributed in plane;(2)Hydrocarbon widely distributed from high area to low area with enriching in the fault belts;(3)Hydrocarbon distributed in high porosity area as well as the low porosity area;(4)Hydrocarbon distributed in high pressure area as well as the low pressure area;(5)Ordovician has high production area and low production area;(6)Ordovician has hydrocarbon from the early accumulation stage as well as late accumulation stage.The complexly geological features controlled by six factors:(1)Excellent reservoirs controlled hydrocarbon enriching in the relatively high porosity and permeability area.(2)Micro-high controlled hydrocarbon enriching in the relatively high position.(3)Hydrocarbon accumulated near the faults and with the unconformity.(4)Caprocks provided reservoir preservation condition.(5)Hydrocarbon enriched near the source rocks.Hydrocabon accumulation mechanism was featured with multi-souce rocks,multi-dynamic,and multi-stage.The evolution of reservoir physical properties controlled the superimposition of accumulation dynamics.In the early Caledonian,the Ordovician reservoirs feature with low porosity and permeability,and the hydrocabon,generated from the Lower Ordovician-Cambrian source rocks,enriced in the relatively high porosity and permeability area to the lithologic hydrocarbon reservoir by the capillary force.From early Caledonian,the Ordovician reservoirs feature with local high porosity and permeability,and the hydrocabon,generated from the Ordovician amd Cambrian source rocks,were enriced in the micro-high to the anticlinal hydrocarbon reservoir by the buoyancy.The mixture of hydrocarbon from lower Ordovician-Cambrian and middle-upper source rocks reservoir physical properties controlled the superimposition of hydrocarbon sources.The mixture of hydrocarbon in the Lianglitage Formation is controlled by the faults.With the distance increasing from the faults,the maturity of hydrocarbon decreased.The mixture of hydrocarbon in the Yingshan Formation is controlled by the unconformity.Beside the abnormity in the faults,the maturity of hydrocarbon was unitive.In a word,hydrocarbon was introduced into the Ordovician through 11 charging points.With the distance increasing from the charging points,the hydrocarbon mixture intensity decreased.The temporal-spatial matching of multi-souce rocks and multi-dynamic controlled the hydrocarbon accumulation process.In the early Caledonian,hydrocarbon mainly generated from lower Ordovician-Cambrian souce rocks,and accumulated into the lithologic reservoirs by the capillary force.From late Caledonian to Hercynian,hydrocarbon,generated from lower Ordovician-Cambrian and middle-upper Ordovician,mixed with each other,and accumulated into the continuous reservoirs by buoyancy and capillary force.In the Himalayan,the hydrocarbons,mainly generated from lower Ordovician-Cambrian,are mainly nature gas,and accumulated into the continuous reservoirs with multi-phase.The Ordovician reservoirs,Tazhong area,are the superimposed,continuous hydrocarbon reservoirs with reforming by multi-phase tectonic evolvement.Multi-type reservoirs existed superimposely in the single trap or the same intervals.That is to say the reservoirs featured with the continuous distribution with the normal anticline reservoir and deep-basin reservoir.Due to the multi-phase structure reformation and adjustment,the reservoir physical property had been improved,fluid property and phase states had been changed,and trap form/hydrocarbon distribution had been adjusted.As a result,reservoir superimposedly developed in vetical and hydrocarbon widely distributed in plane.The superimposed,continuous hydrocarbon reservoirs with reforming by multi-phase tectonic evolvement mainly distributed in the area where combination controlling index of anticlinal trap or lithologic trap is larger than 0.5,and the bigger RFSI is,the more likely hydrocarbon accumulated in the reservoir.Use the combination controlling index to predict the anticlinal reservoirs in the Ordovician,Tazhong area,mainly distributed in the No.10 and No.40 fault zone.Lithologic reservoirs mainly distributed in the No.1 Fault Zone as well as Tazhong No.10 fault zone.Areas of the two types of favorable target superimposition are the most favorable target and they more likely to occure hydrocarbon accumulation and priority for exploration and development. |
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