Oil And Gas Resource Assessment In Middle-Lower Cambrian Of Bachu Uplift In The Tarim Basin

Bachu uplift is in the western end of the central uplift zone of the Tarim Basin, which is clamped by Southwest Depression and Awati Depression which are the favorable oil and gas source in this area. since the long period of Hercynian, Bachu area has already been in the dumping site of uplift and slope, Form the Hercynian, hydrocarboncan from Southwest Depression and Awati Depression source rocks could be directly gathered in Bachu uplift area.Bachu area locate in the hinterland of the Tarim Basin who is a large Superimposed basins, Preserving conditions are critical for the accumulation of hydrocarboncan. There are thick gyprock caprock in the Middle—Lower Cambrian formation in this area,which has favorable preserving conditions concerned all the time.Although this area experienced many times resource assessment, detailed resource evaluation for the formation under the Middle—Lower Cambrian series gyprock caprock has not been done by now. This thesis aims to evaluate the hydrocarboncan source rocks and reservoir and seal condition , establish a dynamic evolution model of hydrocarbon accumulation, then calculate hydrocarbon resources in Bachu uplift in the Middle—Lower Cambrian series.Predicting the favorable accumulation area of hydrocarboncan ,serving for making.exploration decision.Bachu area Middle—Lower Cambrian source rocks mainly developed within Lagoon facise and other low energy environment facise .The lithology of the carbonate source rocks main is microcrystal dolostone and argillaceous dolomite, which are accompanied by gypsum and salt rocks.The thickness of this source rocks is generally less than 200 m.,which is belong to medium - good source rocks (with TOC > 0.4% as the minimum standard); Organic matter is mainly sapropel-type class (I type), which is made up by original organic debris by invertebrates, algae, bacteria and other low biological composition; maturity of organic matter is in the high - over mature stage.In Bachu uplift, the Middle—Lower Cambrian microcrystal and algal dolomite reservoir belonging to quasi-syngenetic origin was formed by capillary condensed sea water dolomitisation. Although penecontemporaneous dolomite reservoirs property are slightly worse,whose genneral lithology are microcrystal dolostone,argillaceous dolomite and gypsum dolomite.But penecontemporaneous dolomite also forms reservoir pore space though Post-reform, especially for algal dolomite containing algal organic matter.This thesis uesing basin modeling software—petromod9.0 completed the basin numerical simulation of Middle—Lower Cambrian in Bachu uplift. Geohistory simulation indicates:since Cambrian,Bachu area had experienced the transforming from depression to uplift. Present tectonic uplift began in Hercynian and formed in the Himalayan. Basin thermal history simulation indicates:at the end of Caledonian, the maturity of organic matter of bachu zone had entered oil threshold(Ro>0.5%),To Hercynian end, the maturity of organic matter had been reached to wet gas( Condensate)phas(eRo:1.3%-2.0%);Bachu zone was uplifted and eroded during the whole Mesozoic,the result of which was the ecolution of organic matter maturity became slow.Now the maturity has reached to dry gas phase(Ro:2.0%-4.0%).though the Computational simulations of hydrocarbon quantity,the result of total Hydrocarbon quantity is 108.656 gigaton including 60.347 gigaton oil and 48.309 gigaton gas. Awati Depression was the main Center for hydrocarbon,the source rock of this area began to generate hydrocarbon in the end of Middle-Ordovician and got to peak in the end of Permian.After Triassic,because of the tectonic uplift and earth temperature declining.there are few hydrocarbon generated by Cambrian source rock.Using IES's unique combinatorial simulation algorithm ((hybrid method) for simulating migration and accumulation history of hydrocarbon.The result is that there are 0.1508 gigaton hydrocarbon including0.0053 gigaton oil and0.1455 gigaton gas. Gas oil ratio is 0.037.According to comprehensive analysis of oil and gas accumulation conditions, combined with the result of basin modelling, the Middle—Lower Cambrian of Kalashayi tectonic zone and Mazhatage tectonic zone are the favorable exploration area.