| CPC G01N 33/241 (2013.01) [G01N 15/088 (2013.01)] | 12 Claims |
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1. A grading evaluation method for high-maturity gas source rock based on hydrocarbon generation and expulsion simulation, comprising following steps:
establishing a change curve of a hydrocarbon generation yield to determine a classification boundary of source rocks based on a hydrocarbon generation thermal simulation experiment, comprising following steps:
sorting out geochemical test data of a source rock of a target layer in a study area, and analyzing geochemical index characteristics of the source rock Total Organic Carbon (TOC), a maturity, an organic matter type, a residual hydrocarbon S1, a cracked hydrocarbon S2, an amount of CO2 produced by organic matter pyrolysis S3, a pyrolysis hydrocarbon peak temperature Tmax, and a hydrogen index HI; selecting source rock samples in the target layer, and carrying out the hydrocarbon generation thermal simulation experiment to obtain a hydrocarbon generation volume at different evolution stages, obtaining information of the residual TOC, S1, S2 and hydrogen index HI of experimental samples at different maturities by testing;
restoring an original TOC and an original HI of the experimental samples by using a theory of material balance;
based on experimentally obtained hydrogen index HI at different maturities and a restoration of original HI, using an optimized fitting equation to fit the hydrogen index HI at a low-maturity stage, and obtaining a distribution curve of the hydrogen index HI in a whole maturity range;
using an original hydrogen index HIo minus the hydrogen index HI at different maturities, calculating and obtaining the hydrocarbon generation yield of the source rock; and
obtaining characteristics of hydrocarbon generation components by combining the hydrocarbon generation simulation experiment, obtaining a relative proportion change of the hydrocarbon generation components at the low-maturity stage by fitting a change trend of the relative proportion of different components, obtaining a change curve of the hydrocarbon generation yield at the low-maturity stage, and obtaining a change curve of the hydrocarbon generation yield in different maturity stages;
establishing a change curve of hydrocarbon expulsion of source rocks to determine the classification boundary of source rocks based on a principle of material balance, comprising following steps:
carrying out an isothermal adsorption experiment of methane in the source rock samples, and establishing an evaluation model of methane adsorption gas in the source rocks by combining TOC, strata pressure and temperature;
establishing an evaluation model of free gas by using a gas state equation through combining collected data of a source rock porosity, a water saturation, a strata temperature, a pressure, a gas compression factor and a rock sample density, and then obtaining an evaluation model of source rock retained gas; and
establishing a relationship between the maturity and a burial depth, the strata temperature and pressure according to a burial history and a thermal history to obtain a maximum retained gas volume distribution curve of the source rock under different maturities; according to a generation-retained-expulsion method, and according to a relationship between hydrocarbon generation volume curve and the maximum retained gas curve under different maturities, calculating a change curve of a hydrocarbon expulsion volume under different maturities;
determining the classification boundary of the source rocks to obtain a spatial distribution of different types of the source rocks based on the change curve of the hydrocarbon generation yield and the change curve of hydrocarbon expulsion of the source rocks, comprising following steps:
establishing a change curve of hydrocarbon expulsion efficiency with TOCi of any source rock under a certain maturity Roj, that is, a hydrocarbon expulsion efficiency curve; and
when the hydrocarbon expulsion efficiency curve begins to be greater than 0, a corresponding TOCi value is a lower limit of an effective source rock at this maturity; when the change rate of hydrocarbon expulsion efficiency at two adjacent points begins to be less than 10%, a corresponding TOC value is a lower limit of a high-quality source rock at this maturity; it is considered that under this maturity, the effective source rock is evaluated when the original TOC value is greater than the lower limit of the effective source rock, and less than the lower limit of the high-quality source rock; the high-quality source rock is evaluated when the original TOC value is greater than the lower limit of the high-quality source rock; obtaining the change curve of hydrocarbon expulsion efficiency with TOCi under different maturities by changing Roj; obtaining a classification boundary of the effective source rock and the high-quality source rock under different maturities according to a source rock boundary division method;
obtaining the spatial distribution of different types of the source rocks by combining logging interpretation according to the classification boundary of the source rocks, comprising following steps:
based on an improved ΔlgR method, combining with acoustic and resistivity curves, carrying out a regression analysis according to in a TOC interpretation model, and establishing a prediction model of source rock organic matter abundance;
obtaining a maturity under different burial depths by combining the burial history and the thermal history of a study area, and obtaining a relationship between the maturity and the burial depth by fitting the maturity and the burial depth; and
obtaining an organic carbon content under different burial depths by using a source rock organic matter abundance model established by acoustic and resistivity curve; obtaining the maturity under different burial depths according to the relationship between the maturity and the burial depth; identifying a vertical distribution of effective source rocks and high-quality source rocks in a plurality of wells by combining the classification boundary of the source rocks under different maturities; and realizing a spatial distribution characterization of different types of source rock thickness in the study area by counting thickness of different types of source rocks in the plurality of wells and combining well coordinates;
restoring the original TOC and the original HI of the experimental samples to classify the source rocks by using the theory of material balance, comprising following steps:
restoring an original organic carbon content TOCo and an original hydrogen index HIo, as shown in Equation (1):
TOCo×(1−Do)=TOCi×(1−Di) (1)
in Equation (1), TOCo and TOCi denote the original organic carbon content of the sample and a current organic carbon content of the sample respectively; Do and Di denote an original degradation rate and a residual degradation rate respectively, and Do and Di represent a ratio of effective carbon Cp and organic carbon Ct of the source rock; the original degradation rate Do is related to an organic matter type of the source rock, according to Tmax and HI data obtained from an investigation of the study area, a source rock type is identified, and the original degradation rate of the sample is selected; the effective carbon Cp is obtained by using a conversion coefficient of carbon conversion to hydrocarbon volume, and then Di is obtained, as shown in Equation (2):
Di=Cp/Ct=((S1+S2)×0.083)/TOCi (2)
wherein S1 is residual hydrocarbon; S2 is cracked hydrocarbon;
a calculation formula of an original hydrocarbon generation potential S2o of the sample is shown in Equation (3):
S2o=(TOCo×Do)/0.083 (3)
the restoration of the original hydrogen index HIo is shown in Equation (4) as follows:
HIo=S2o/TOCo (4).
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