Method and system for quantitatively evaluating kerogen swelling oil in shale

A method for quantitatively evaluating kerogen swelling oil in shale, comprising:

• establishing, by a molecular modeling software, different types of kerogen molecular models;
• loading each of the kerogen molecular models into a graphene slit-type pore composed of a lamellar structure to obtain an initial model;
• subjecting each initial model to energy minimization (EM) and relaxation to obtain a compacted kerogen aggregate model, comprising:
• subjecting the initial model to EM and 200 ps relaxation at 75° C. under 20 MPa by using a molecular dynamics software to obtain a compacted kerogen aggregate model;
• simulating an annealing process of the compacted kerogen aggregate model to obtain a kerogen slit-type pore, comprising:
• subjecting the compacted kerogen aggregate model to 200 ps relaxation for warming;
• and
• subjecting the kerogen aggregate model, after the relaxation warming, to 2 ns simulation, cooling and pressurization by using an isothermal-isobaric ensemble (NPT ensemble) at 800° C. under normal pressure to obtain the kerogen slit-type pore;
• loading shale oil molecules into the kerogen slit-type pore to obtain an initial model of swelling and adsorption of shale oil in kerogen;
• assigning a value to a force field of the shale oil molecules and kerogen molecules in the initial model of swelling and adsorption of the shale oil in the kerogen to obtain a density of the kerogen and the shale oil;
• plotting a density curve of the kerogen and the shale oil according to the density of the kerogen and the shale oil;
• calculating kerogen swelling oil mass according to the density curve of the kerogen and the shale oil, comprising:
• calculating the kerogen swelling oil mass by
• Q
• oil
• =
• ∫
• L
• o
• ⁢
• 1
• L
• o
• ⁢
• 2
• S
• model
• ·
• ρ
• oil
• ⁢
• dL
• according to the density curve of the kerogen and the shale oil,
• where Qoil is the kerogen swelling oil mass;
• Lo1 is a start position of an intersection between the kerogen density curve and the shale oil density curve;
• Lo2 is a stop position of the intersection between the kerogen density curve and the shale oil density curve;
• Smodel is a cross-sectional area of the swelling and adsorption model of the shale oil in the kerogen;
• ρoil is the shale oil density curve;
• determining per-unit kerogen swelling oil mass according to the kerogen swelling oil mass;
• determining the kerogen swelling oil mass in different evolution stages according to the per-unit kerogen swelling oil mass, comprising:
• deriving kerogen mass mx in different evolution stages;
• calculating the kerogen swelling oil mass in different evolution stages by
• Q
• s
• =
• Q
• w
• ·
• m
• k
• ·
• f
• s
• according to the per-unit kerogen swelling oil mass Qw and the kerogen mass mk in different evolution stages;
• where Qw is the kerogen swelling oil mass, mk is the kerogen mass in different evolution stages, fs is a swelling ratio reduction coefficient in different evolution stages, and
• m
• k
• =
• m
• f
• ·
• F
• t
• +
• m
• s
• =
• (
• HI
• 0
• /
• 1000
• )
• ·
• F
• t
• +
• (
• 1
• -
• HI
• 0
• ·
• 0.083
• /
• 100
• )
• ,
• where mf is a mass of a convertible part of the kerogen, with a unit of g;
• ms is a mass of a non-convertible part of the kerogen, with a unit of g;
• HI0 is an original hydrogen index, with a unit of mg/g TOC;
• 0.083 is a carbon conversion coefficient of the original hydrogen index, dimensionless;
• Ft is a conversion rate, dimensionless;
• carrying out a pyrolysis gas chromatography (PY-GC) test on an immature shale sample from a target region, and calibrating chemical kinetics parameters of a primary cracking of kerogen in the target region based on results of the pyrolysis gas chromatography test and principles of chemical kinetics so as to determine a conversion rate Ft of the target region according to a burial history and thermal history of the target region;
• determining an original hydrogen index HI0 of the target region according to geochemical data of the target region;
• and
• obtaining a type of kerogen, a kerogen mass and a current evolution stage of the target region to determine a kerogen swelling oil mass in the target region based on the conversion rate and the original hydrogen index of the target region.