Evaluation method for hydrocarbon expulsion of post- to over-mature marine source rocks

A method of exploring a formation using an evaluation method for hydrocarbon expulsion of post- to over-mature marine source rocks comprises steps of:

• A) collecting samples of post- to over-mature marine source rocks to be evaluated from a formation;
• B) establishing a hydrocarbon expulsion evolution profile of the post- to over-mature source rocks comprises steps of:
• calculating a hydrocarbon generation potential index and an equivalent vitrinite reflectance based on a pyrolysis experiment of the collected samples of post- to over-mature source rocks;
• and
• establishing the hydrocarbon expulsion evolution profile of the post- to over-mature source rocks based on the hydrocarbon generation potential index and the equivalent vitrinite reflectance, wherein
• the hydrocarbon generation potential index is
• 100
• ×
• S
• 1
• +
• S
• 2
• /
• T
• O
• C
• ,
• wherein S1, S2 are hydrocarbon yields per unit mass of source rock samples heated to 300° C. and 300-600° C. respectively, mg•HC/g;
• TOC is total organic carbon (TOC) per unit mass of the post- to over-mature source rocks, mg/g;
• and the equivalent vitrinite reflectance is Ro, Ro = 0.0078Tmax — 1.3654, wherein Tmax is a maximum peak pyrolysis temperature in the pyrolysis experiment of the post- to over-mature source rocks;
• C) determining a critical condition for the hydrocarbon expulsion of the post- to over-mature source rocks, inverting original hydrocarbon generation potential of the post- to over-mature source rocks, and establishing a hydrocarbon expulsion model for the post- to over-mature source rocks comprises steps of:
• obtaining a homogenization temperature distribution map of fluid inclusions according to an inclusion experiment;
• determining a main peak value of a homogenization temperature for a first phase of the fluid inclusions based on the homogenization temperature distribution map of the fluid inclusions;
• and
• obtaining a corresponding minimum Rmin of an isotherm at the main peak value of the homogenization temperature of the first phase of the inclusions according to a depositional burial history and a thermal evolution history of a typical well, wherein Rmin is a critical maturity Roe for hydrocarbon expulsion corresponding to the critical condition for hydrocarbon expulsion;
• wherein determining of inverting the original hydrocarbon generation potential of the post- to over-mature source rocks comprises:
• obtaining a hydrocarbon generation potential index envelope according to the hydrocarbon expulsion evolution profile of the post- to over-mature source rocks;
• obtaining a fitted relation Ig based on the equivalent vitrinite reflectance and the hydrocarbon generation potential index envelope by the following equation:
• Ig = He-:CRo-C) + d, wherein a, b, c and d are constants;
• and
• obtaining the original hydrocarbon generation potential Iog of the post- to over-mature source rocks based on the fitted relation and the critical maturity for hydrocarbon expulsion by the following equation:
• I
• o
• g
• =
• a
• 1
• +
• e
• −
• b
• R
• oe
• −
• c
• +
• d;
• D) determining a hydrocarbon expulsion rate and cumulative hydrocarbon expulsion of the post- to over-mature source rocks;
• E) calculating the hydrocarbon expulsion of the post- to over-mature source rocks based on steps A) through D);
• and
• F) wherein when the calculated hydrocarbon expulsion of the collected sample post- to over-mature source rocks to be evaluated of the formation meets a predetermined threshold, exploring the formation.