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Geochemical Characteristic And Origin Of Shallow Reservoired Natural Gas And Dissolved Gas Of Crude Oil In The Central-north Area In Huanghua Depression

Posted on:2005-03-03Degree:MasterType:Thesis
Country:ChinaCandidate:X F LiFull Text:PDF
GTID:2120360125951002Subject:Institute of Geochemistry
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Dagang oilfields in the Huanghua depression have been built into a large-scale oil-gas producing area, after thirty years exploration. But the exploration difficulty is increasing with the increase of oil fields found. Now exploring more oil-gas pools in middle-shallow strata is an important problem for the progress of the oil field. The Lower Tertiary Shahejie formation in the central-north area of the Huanghua depression served as the most important source rock from which the oil in the medium to deep buried strata was derived. Oil exploration focus on the third member of the Shahejie formation. In recent years, more oil fields have been found in the shallow to medium strata in the depression, showing a good prospect of oil exploration. At the same time some new questions became arisen: (1) the geochemical characteristic, origin and genetic indicator of natural gas in the medium to shallow strata is still unknown, (2) the source of the natural gas is not clear. Because of these unsolved problems oil exploration in the medium to shallow strata has been affected. Besides in recent years, (1) the import of new technique for H isotopic measurement provide a new way for studying natural gas origin and gas source correlation however the H isotopic characteristic, genetic indicator and thermal evolutionary model of natural gas remained unsolved, (2) the noble gas isotopes have been applied in gas-source correlation but whether the dissolved gas in oil could be used in oil-gas-source correlation kept unknown. Therefore following we answered the problems on the origin, genetic indicators and source of the natural gas, we investigated the fractionation factors, genetic distinguishing indicators of natural gas H isotope and the thermal evolutionary models of oil-type gas, discussed the geochemical characteristic and source of noble gas isotopes in dissolved gas in crude oil and correlated gas source. After above research, we reached the following conclusions (in which the sixth, seventh, eighth are innovated conclusions):IV1. The natural gases from the middle-north area of the Huanghua depression have methane components from 68.2%to 97.1%, mainly in the range of 75%to 95%, averaging 84.3%(32); the components of heavy hydrocarbons change from 0.6% to 25.3%, mainly in the range of 0% to 20%, averaging 12.3%(32); the dryness coefficients in this part are from 0.77~0.99, mainly in the range of O.8to 0.9,averaging 0.88(32). The components of methane, heavy hydrocarbons and the range of C|/C1-5 show that the natural gases in this area are wet gases. Considering the geological conditions the gases mainly are oil-type associated gas. Gases with methane more than 95% and C\/C\.s values greater than 0.95 distribute in the west and east part of the Dagang oil field.2. The natural gases from the middle north area of the Huanghua Depression have 8 13C, values from -52.0%oto -37.0%o, averaging -44.9%; the 8 I3C2 values of the natural gases ranging from -33.8%oto -21.5%o, the mean value is -27.8%o. The 8 I3Ci values are mainly in the range of-48%oto -42%o, which represents that the natural gases from the middle north area of the Huanghua depression are oil-type associated gases; the gases from west Dagang oil field are mix gases of coal-type gases and secondary biogenic gases; the 8 I3C1 values are much heavier in Tangjiahe, which suggests they are coal-type gases generated in a mature stage.3. The carbon isotopic compositions of most hydrocarbons have a normal evolutionary series as 8 l3Ci< 8 13C2< 8 13C3< 8 I3C4. Some gases in the West Dagang oil field have a converse one which probably is mixed gases. According to the relationship of atomicity and the carbon isotopic values, we concluded that part of the gases of the Tangjiahe oil field is coal-type gas and part of gases from the West Dagang oil filed is mixed gases composed by coal-type gases and secondary biogenic gas, and the gases of the Tangjiahe oil field partly come from oil-type gases which generated from type I - II kerogen.4. According to the relati...
Keywords/Search Tags:Huanghua Depression, natural gas, crude oil, carbon isotope, hydrogen isotope, noble gas tracing
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