| In China, the Songliao Basin is the biggest petroliferous basin with Cenozoic fresh water lacustrine facies. Qijia-Gulong sag is a second-order structural zone in the basin, in which the north is Qijia sag, and the south is Gulong sag. As known, formation of the Songliao Basin has approximately undergone five stages, in which the rift stage, the downpunching stage and the atrophy balance stage deposit the main deposition cover strata in Qijia-gulong sag. And the mudstones of Qingshkou 1st member (qn1), Qingshkou 2-3nd member (qn23) and Nenjiang 1st member (n1) are three sets of main hydrocarbon source rocks, in the sag, whose organic matter type is sapropelic, and the deposition is large scale fresh water semideep-deep lacustrine facies (with sea ingression process).And the organic matter is abundant, distribution is wide, the thickness is great. In general, the Nenjiang formation is at the thermo-catalysis stage, and the considerable proportion of Qingshankou formation has entered pyrolysis stage as condensate oil-gas generating; the depth threshold is about 1200m, and the condensation oil gas threshold is around 1900m. The nowadays geotemperature in sag may be equal to the maximum paleogeotemperature. Formation temperature and pressure is all high in south and low in north. And overpressure mainly develops in the south below Putouhua oil layer. In the Qijia-Gulong area, there are quite many exploratory wells which produce oil and gas synchronously; most of the gas/oil ratio is low. In this paper, first, by the experiential rule, primarily choose wells and consider some factors, such as the primitive geochemical material, and then pick out 5 wells 6 oil layers, with the experiential rule, the computation phase diagram method, and the experimental phase diagram method from the various distinction, finally obtain the result that the English 51 well Putouhua oil layer and the Gu 109 well Putouhua oil layer are condensate gas pools, the Gu 31 well Heidimiao oil layer is a gas pool with condensation oil . The Ying 51 well has 5 oil-gas layers (F, qn1, G2, G1, P), the top Putouhua oil layer is the condensate gas reservoir, the G2 layer, by the phase state distinguish, is a oil layer with gas cap. The samples from 5 oil-gas layers of Ying 51 well are all carried on many geochemical analyses. According to the Ying 51 well and the Gu 109 well geological backgrounds and the oil gas component analysis, find that it is difficult to explain perfectly by the phase state origins that have been proposed (such as primary, differentiation, gas washing, gas irruption). Compared with the black oil, the prominent characteristic of condensate and condensation oil is mainly of the light quality components, and most is gasoline fraction. For the oil-oil correlation and the oil-source correlation, using the biomarkers parameter is often difficult to be effective. Considering thermo-evaporation is physical process, in thermo-evaporation process, ratios of the compounds whose natures are close cannot change greatly. In this article, we attempt to use chromatograph fingerprint technology to carry on the oil-oil correlation. Based on thermo-evaporation experiment, choose 16 pairs of compound ratio as the fingerprint, which are neighboring, have separate effect, and considerablely high peak in the spectrogram. According to the synthesis contrast between chromatograph fingerprint, the gas isotope, especially monomer hydrocarbon isotope, believe that in Ying 51 well, Putouhua condensate oil and gas and underlying oil and gas are from the same source, also are relative to the G2 level oil gas closely. As a result of the environment of deposition similarity, the conventional parameters, steroid and terpene, can not differentiate three sets of main source rocks effectively. After the analysis of source rocks chromatograph data, the paper has established Pr/nC17, Ph/nC18 standard for distinguishing Qingshankou Formation and Nenjiang Formation. And by the standard, find that the oil-gas of Ying 51 well 5 oil layers all comes from the Qingshankou Formation. Evaluating source rock hydrocarbon generation quantificationally in the horizontal distribution is the foundation of condensation oil gas forecast. After comparing the merits and demerits of each method, choose the high pressure vessel watering simulation method and the limited parallel first level reacted the chemical kinetics model appraises the oil gas quantity generated by source rock. Due to the condensate makeup the light oil, the common dichotomy cannot reflect this characteristic, as a result, carry on the special experiment, demarcate the trichotomy (C1~5, C6~13, C14+) the chemical kinetics parameters, which lays the foundation for the quantitative evaluation of gas generation quantity, "the light oil" generation quantity, and "the heavy oil" generation quantity of the hydrocarbon source rocks in the area. The thermo-evaporation fractionation is the reason for condensation gas phase state in Ying 51 well and the Gu 109 well, which is one important view of this article. Demonstrate it from the geology, the modeling, the theoretical analysis and many other aspects. (1) The condensation gas layer distributes in oil layers top of homologous source and has close relation with lower part oil-gas layer, which indicates the possibility of thermo-evaporation function. (2) The oil component relations between the Ying 51 well P condensate and the G2 oil, and between the Gu 109 well area condensation oil and black oil, the parameter relations between toluene/ heptane and heptane/methyl cyclohexane, are consistent with the law displayed in evaporation experiment. (3) According to the temperature, pressure and average components of the two oil-gas reservoirs, G2 , P reservoirs in Ying 51 well, relative volatility of C1/C2～nC22/nC23 and the partial commonly used compound (for example Pr/nC17, the normal heptane/toluene and so on, altogether 7 pairs) are calculated if P layer hydrocarbons component accumulation from the G2 layer thermo-evaporation. The component content ratios measured from G2, P oil gas samples are well consistent with the theoretical relations which is restrained by relative volatility. And carry on the similar comparison in the Gu 109 well, in the same way, support the thermo-evaporation fractionation mechanism. (4) Trend of methane content variety with depth in different districts also has provided the supplement evidence for the existence of thermo-evaporation function. After districting, become the charts, all sub-areas displayed by the thermo-evaporation fractionation pattern are located in the Gulong sag. (5) Evaporated hydrocarbon compound needs to divulge through the top of cap rock to upside, this kind of micro leakage channel may be cap rock itself micropore, also can be the cap rock existence micro crack even some minor faults. The former studies indicate that there is the existence of this kind of micro crevasse, in mudstones of the Gulong sag Qingshankou Formation, which can be vapors channel for upward migration. This article has proven the existence of oil cracking into gas from 4 aspects: (1) Oil cracking gas andkerogen degradation gas have different component characteristics, Puxi oilfield and the Gu 6 well area Putouhua oil layer mainly manifest the mixing effect for oil cracking gas and kerogen degradation gas. (2) The simulation experiment for oil heating indicates that when the crude oil is heated up to the point, Ro=1.2～1.6%, oil starts to crack into gas, and δ13C1 generated by oil cracking obviously change to be lighter in the early stage of oil cracking. (3) In this article, Qijia-Gulong nature gas δ13C1 becoming lighter just may explain that the kerogen degradation gas mixes up with the gas from early oil cracking. (4) Combining hydrocarbon generated section with bury history, it is could be know that qn1 and qn23 mainly generate and exclude the mature oil, but the light hydrocarbon parameters indicate that most Qijia-Gulong crude oil is high-mature oil. The author believes that majority of high-mature oil results from continuing mature, which can qualitatively interpretate why placanticline is the mature oil distribution area, but the Gulong sag is the high-mature oil distribution area. It could be obtained that the oil cracking is at the early stage according to Qingshankou Formation's Ro situation and the hydrocarbon generating section. The oil cracking gas provides the supplement matter for the thermo-evaporation. Meanwhile, based on the preliminary analysis, believe that the oil to gas is the main reason for the unusual pressure in the Gulong sag. The gas washing is another origin for which the condensation oil gas forms. This article defines concepts of the relative solubility, α, and the residual ability, h, deduces the equations to express component change relations related to αand h; examines the influence of gas-oil ratio, temperature and pressure on αwhen gas washes occurs, and the changes of partial geochemical parameters in different gas wash condition. In terms of the above theoretical achievement, analyze the component characteristics and the main relations between geochemical parameters of three oil gases in Gu 31 well (to be upward, in turn P, H2, H1), and believe that in Qingshankou Formation, natural gas washes the H2 reservoir which has already formed along the fault upward migration and gathers at upside and forms H1 gas reservoir. As gas washing occurs at low temperature, low pressure, small oil enters in the gas phase, moreover, the temperature and pressure of H1 reservoir are lower, therefore H1 contains few condensation oil. According to the chemical kinetics achievement and the source rock growth situation, calculate the C14+ oil generated mass of n1, qn23 and qn1 in Qijia-Gulong area, in turn, is163.1×108t, 191.4×108t, 156.3×108t, the C6～13 oil generated mass is 28.2×108t, 90.0×108t, 104.8×108t, the C1～5 gas generated mass is 3.51×1011m3, 33.83×1011m3, 108.15×1011m3; the expelled oil mass is 95.3×108t, 167.1×108t, 197.9×108t, the expelled gas mass is 0.66×1011m3, 22.0×1011m3, 103.3×1011m3, total generated light oil mass is 223.0×108t, and total expelled oil mass and gas mass is 460.4×108t and 126.0×1011m3. We see that the light oil mass is less than half of the total oil mass, comparing with the condensate major part for the gasoline fraction, there is great difference. Even if make use of qn1 which the expelled gas mass is the biggest to calculate, the gas-oil ratio can not reach the general requirement for the condensation gas pool formation, in fact, which is the internal cause for the Qijia-Gulong area difficult to form the primary condensation gas pool. In general, although the condensate gas mainly is composed of light oil and gas, at most conditions,light oil and gas cannot always form the condensate gas pool, only in the middle of the sag where temperature and pressure are higher, and only when the component composition and the gas-oil ratio is proper, there is the possibility to form the condensate gas pool. Thephase state origin of Ying 51 well and the Gu 109 well condensate furtherly show the strict conditions to be needed to form the condensation gas pool in the Qijia-Gulong area. Based on the former experience and the Qijia-Gulong realities, regard the natural gas transport-gather coefficient as 5‰～3%, in the area natural gas resources quantity is situated between 730～4370×108m3. Considering the practice of condensation gas formation in the area, it is reasonable to believe that 10% of natural gas resources can form condensate gas, and use medium condensate content gas-oil ratio 5000m3/m3 to caluclate, then in the region of interest the condensate resources quantity is situated between 150～870×104m3, and the corresponding the condensate gas is 73～437×108m3. The superimposition shows the primary factors which may possibly affect the condensation gas pool to form and distribute, that is, the light oil generating intensity isoline, the natural gas generating intensity isoline, the Putouhua oil layer temperature isoline and n1 section mudstone percentage isoline which is regarded as important region cap rock in area(reflecting preserving condition), It is observed that, the Gu 124-Gu 86 well area should be the most advantageous distribution area for growing the condensation gas pool, while Ying 8 well area and the Gu 933-Jin 45 well area might be better areas where light oil and natural gas generating intensity are higher but other conditions are not synchronously best. Considering the thermo-evaporation fractionation as the main mechanism to formed the condensation gas pool in the area, the areas whose faults grow better, through which can link upper and lower oil layers in the advantageous area, are good target for exploring condensate gas pool, which need more work on the geology and the geophysics.
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