Hydrocarbon-forming organisms and dynamic evaluation of hydrocarbon generation capacity in excellent source rocks

Based on the conventional organic geochemical analyses of excellent marine source rocks, simulation experiment and ultra-microscopic organic petrology were applied to study the hydrocarbon generation capacity of different hydrocarbon-forming organisms in excellent source rocks. The bio-precursors of excellent marine source rocks, kerogen type of which belongs to Ⅱ, is mainly composed of benthos (or benthic algae), fungi and bacteria. The hydrocarbon generation potential of these source rocks is equivalent to type Ⅱ kerogen, among which benthic algae is equivalent to type Ⅱ₁ kerogen while fungi and bacteria are equivalent to type Ⅱ₂ kerogen. The planktonic algae ranks second in hydrocarbon contribution,equivalent to type Ⅰ kerogen. The hydrocarbon generation capacity of planktonic algae and benthic algae varies during different mature stages. And in the high-mature and over-mature stage, their hydrocarbon generation capacity and contribution to oil-cracked hydrocarbon are also different. As to the high-mature source rocks in the Lower Paleozoic, a dynamic evaluation is demanded in view of the oil and gas generating capacities of different hydrocarbon-forming organisms or kerogens during each mature stage. The dynamic evaluation of hydrocarbon generation capacity of different hydrocarbon-forming organisms is important for the explorations of both conventional and unconventional oil and gas resources.