Kinetics and model of gas generation of source rocks in the deepwater area, Qiongdongnan Basin

In order to investigate the hydrocarbon generation process and gas potentials of source rocks in deepwater area of the Qiongdongnan Basin, kinetic parameters of gas generation （activation energy distribution and frequency factor） of the Yacheng Formation source rocks （coal and neritic mudstones） was determined by thermal simulation experiments in the closed system and the specific KINETICS Software. The results show that the activation energy （Ea） distribution of C1–C5 generation ranges from 50 to 74 kcal/mol with a frequency factor of 2.4×1015 s–1 for the neritic mudstone and the Ea distribution of C1–C5 generation ranges from 49 to 73 kcal/mol with a frequency factor of 8.92×1013 s–1 for the coal. On the basis of these kinetic parameters and combined with the data of sedimentary burial and paleothermal histories, the gas generation model of the Yacheng Formation source rocks closer to geological condition was worked out, indicating its main gas generation stage at Ro （vitrinite reflectance） of 1.25%–2.8%. Meanwhile, the gas generation process of the source rocks of different structural locations （central part, southern slope and south low uplift） in the Lingshui Sag was simulated. Among them, the gas generation of the Yacheng Formation source rocks in the central part and the southern slope of the sag entered the main gas window at 10 and 5 Ma respectively and the peak gas generation in the southern slope occurred at 3 Ma. The very late peak gas generation and the relatively large gas potential indices （GPI：20×10^8–60×10^8 m^3/km^2） would provide favorable conditions for the accumulation of large natural gas reserves in the deepwater area.

Prediction and quantification of effective gas source rocks in a lacustrine basin:Western Depression in the Liaohe Subbasin,China

Due to limited data on the geochemical properties of natural gas,estimations are needed for the effective gas source rock in evaluating gas potential.However,the pronounced heterogeneity of mudstones in lacustrine successions complicates the prediction of the presence and geochemical characteristics of gas source rocks.In this paper,the Liaohe Subbasin of Northeast China is used as an example to construct a practical methodology for locating effective gas source rocks in typical lacustrine basins.Three types of gas source rocks,microbial,oil-type,and coal-type,were distinguished according to the different genetic types of their natural gas.A practical three-dimensional geological model was developed,refined,and applied to determine the spatial distribution of the mudstones in the Western Depression of the Liaohe Subbasin and to describe the geochemical characteristics(the abundance,type,and maturation levels of the organic matter).Application of the model in the subbasin indicates that the sedimentary facies have led to heterogeneity in the mudstones,particularly with respect to organic matter types.The effective gas source rock model constructed for the Western Depression shows that the upper sequence(SQ2)of the Fourth member(Mbr 4)of the Eocene Shahejie Formation(Fm)and the lower and middle sequences(SQ3 and SQ4)of the Third member(Mbr 3)form the principal gas-generating interval.The total volume of effective gas source rocks is estimated to be 586 km^(3).The effective microbial,oil-type,and coal-type gas source rocks are primarily found in the shallow western slope,the central sags,and the eastern slope of the Western Depression,respectively.This study provides a practical approach for more accurately identifying the occurrence and geochemical characteristics of effective natural gas source rocks,enabling a precise quantitative estimation of natural gas reserves.

Modeling of the whole hydrocarbon-generating process of sapropelic source rock

Based on experimental data from hydrocarbon generation with a semi-open system, hydrocarbon generation kinetics modeling in gold tube of closed system, high temperature pyrolysis chromatography mass spectrometry experiment with open system and geological data, the characteristics of whole hydrocarbon-generating process, hydrocarbon expulsion efficiency and retained hydrocarbon quantity, origins of natural gas generated in high-over mature stage and cracking temperature of methane homologs were investigated in this study. The sapropelic source rock has a hydrocarbon expulsion efficiency of 30%-60% and 60%-80% in the major oil generation window(with Ro of 0.8%-1.3%) and high maturity stage(with Ro of 1.3%-2.0%) respectively; and the contribution ratio of kerogen degradation gas to oil cracking gas in total generated gas in high maturity stage is about 1:4. The degradation gas of kerogen accounts for 20%, the retained liquid hydrocarbon cracking gas accounts for 13.5%, and the amount of out-reservoir oil cracking gas(including aggregation type and dispersed oil cracking gas) accounts for 66.5%. The lower limit of gas cracking is determined preliminarily. Based on the new understandings, a model of the whole hydrocarbon-generating process of source rock is built.

Mesh model building and migration and accumulation simulation of 3D hydrocarbon carrier system

Migration and accumulation simulation of oil and gas in carrier systems has always been a difficult subject in the quantitative study of petroleum geology. In view of the fact that the traditional geological modeling technology can not establish the interrelation of carriers in three dimensional space, we have proposed a hybrid-dimensional mesh modeling technology consisting of body(stratum), surfaces(faults and unconformities), lines and points, which provides an important research method for the description of geometry of sand bodies, faults and unconformities, the 3 D geological modeling of complex tectonic areas, and the simulation of hydrocarbon migration and accumulation. Furthermore, we have advanced a 3 D hydrocarbon migration pathway tracking method based on the hybrid-dimensional mesh of the carrier system. The application of this technology in western Luliang Uplift of Junggar Basin shows that the technology can effectively characterize the transport effect of fault planes, unconformities and sand bodies, indicate the hydrocarbon migration pathways, simulate the process of oil accumulation, reservoir adjustment and secondary reservoir formation, predict the hydrocarbon distribution. It is found through the simulation that the areas around the paleo-oil reservoir and covered by migration pathways are favorable sites for oil and gas distribution.

Geochemical Characteristics and Hydrocarbon Generation Modeling of the Paleocene Source Rocks in the Jiaojiang Sag,East China Sea Basin

Jiaojiang sag in the East China Sea Basin is at the earlier exploration stage,where characterizing hydrocarbon generation of source rocks is important to understand oil-gas exploration potential.Utilizing geochemical and basin modeling analysis,hydrocarbon generation capacity and process of the Paleocene E_(1)y,E_(1)l and E_(1)m formations were investigated.Results show that E_(1)y and E_(1)l mudstones are high-quality source rocks with Type Ⅱ kerogen,which is dominated by both aquatic organisms and terrestrial higher plants deposited in sub-reduced environment.E_(1)m mudstone interbedded with thin carbonaceous mudstone and coal is poor-quality source rock with Type Ⅲ kerogen,whose organic matter was originated from terrestrial higher plants under oxidized environment.Controlled by burial and maturity histories,E_(1)y and E_(1)l source rocks experienced two hydrocarbon generation stages,which took place in the Late Paleocene and in the Middle to Late Eocene,respectively,and had high hydrocarbon generation capacity with cumulative hydrocarbon volume of 363 and 328 mg/g,respectively.E_(1)m source rock only had one hydrocarbon generation process in the Late Eocene,which had low hydrocarbon generation capacity with cumulative hydrocarbon volume of only 24 mg/g.The future oil-gas exploration in the Jiaojiang sag should focus on hydrocarbon generation center and select targets in the central uplift formed before the Miocene with high-quality traps.

The generation and its sealing condition of natural gas in the Tadong area

Focusing on the two natural gas exploration geological problems with abundant source of oil cracking gas in the late stage and the sealing condition of the oil cracking gas reservoir,the kinetics of oil cracking gas and the evaluation parameters of gas cap rock are adopted to the study on the natural gas accumulation conditions in the Tadong area. Both the study on the kinetics of oil cracking gas and the statistical results of reservoir bitumen reveal that the geological formation of oil cracking gas in the Tadong area is located in the top of Cambrian. Two kinds of oil cracking gas geological models at least,namely well Mandong-1's early rapid generation model(Middle Ordovician-end Silurian) and peak cracking model(with the natural gas conversion rate >90%) ,namely well Yingnan-2's two-stage generation model of oil cracking gas,have been set up. The oil cracking gas of Yingnan-2 in the late stage is very significant in the evaluation of natural gas exploration in the Tadong area. The evaluation results of the cap rock show that the microscopic parameters of cap rock from the lower assemblage of Cambrian-Ordovician are better than those from the upper assemblage. The former has strong capillary sealing ability and higher cap rock breakthrough pressure than the upper assemblage,with strong sealing ability,so that natural gas dissipates mainly by diffusion. According to the above investigations,the lower assemblage Cambrian-Ordovician natural gas of Kongquehe slope,Tadong low uplift and Yingjisu depression in the Tadong area prospects well.