Hydrocarbon Generation And Phase Behaviour Prediction Of Yanchang Shale In Southeast Ordos Basin

Shale oil and gas mainly refer to the occurrence of hydrocarbon accumulation in mud and shale rocks.Industrial oil and gas flow from terrestrial shale formations has been achieved and the Ordos Basin where the first terrestrial shale gas well located has become the representative exploration region.With kerogen type ranging from I to III and relative low thermal evolution stage,terrestrial shale differs from marine shale significantly.As the research subject of this dissertation,Yanchang terrestrial shale in Southeast Ordos Basin(SOB)is analyzed by experimental comparison,multivariate mathematical statistics and geological evolution modeling.With the primary goal of hydrocarbon generation and phase behaviour,we conducted kinetics evaluation,oil and gas content analysis and prediction of petroleum composition and phase changing.Organic rich shale developed in Chang 7 and Chang 9 of Yanchang formation,its thickness is generally between 50 m and 120 m.TOC content of the investigated samples generally varies from 1.0%to 4.0%with Ro ranging from 0.6%to 1.0%.Most rock samples are in the oil to wet gas maturity range.The organic matter is predominantly type ?2 kerogen which is derived from algae and bacteria material influenced by terrigenous debris input.The dominant activation energy distribution ranges from 48 to 51 kcal/mol with a frequency factor A=2.2O×1012S-1.The organic matter generates hydrocarbons over a very broad temperature range(?65“C)with the biggest transformation ratio of 70%.The gas fraction is mainly generated from kerogen conversion.The content of quartz varies from 18.0%to 43.0%with an average of 30.4%,and the content of clay ranges from 20.0%to 66.0%with an average of 44.8%.Compared with American marine shale,Yanchang shale presents higher content of clay mineral.Organic pore,intraparticle pore,interparticle pore and microfracture provide storage space for oil and cgas in Yanchang shale.The contents of adsorption gas,desorption&residual gas and oil are assessed as 2.0?4.0 m3/t,1.1?2.9 m3/t and 2.0?12.0mg/grespectively.TOC is the critical factor for shale oil and gas content characterization.The gas fraction generated from Yanchang shale in SOB mainly consists of n-C1,n-C2 and n-C3,while the liquid phase is dominated by compounds of groups C7-15 and C16-25.For the organic matter conversion range from 10%to 70%,the GOR ranges from 83.6 to 168.2 Sm3/Sm3,the Psa1 ranges from 93.5 to 126.3 bar,and the Bo ranges from 1.36 to 1.70 m3/Sm3.The Bo displays linear correlations with GOR and Psa1.After hydrocarbons generation,the shale formation in east area(Xiasiwan)of Ordos Basin lifted influenced by Yanshan tectonic stage.Consequently the burial depth and reservoir pressure decreased and a two-phase fluid occurred.In contrast,the burial depth and reservoir pressure of the shale formation in west area(Zhenjing)increased and the single liquid phase system was maintained.In this dissertation,we analyzed dynamic process of Yanchang hydrocarbon generation,determined hydrocarbon content(gas and oil)and its variation rule quantitatively and established phase behaviour evolution model.All the research results could provide optimizational geological parameters for resource evaluation and give direction of exploration and exploitation for shale oil and gas in theory.