Study Of Carbonate Source Rocks Evaluation Criterion

In China, sediment trap of carbonate rocks is large, oil generation from carbonate rocks has been the focus which geologists and geochemists are- concerned about. Most of carbonate source rocks in our country are high-maturity, over-maturity, therefore, neither does the existing assessment method of argillaceous source rocks in China fit for the evaluation of this sort of source rocks, nor can copy the foreign evaluation of lower maturity carbonate source rocks. Based on practical and geological conditions, this paper sets up a set of assessment method of carbonate source rocks, and puts forward a set of organic enrichment evaluation criterion of carbonate source rocks.Traditional evaluation of source rocks is mainly about hydrocarbon generation, only when the generated oil gas from source rocks is expelled in the form of separate phase, can it be useful for the form of pool. Therefore, the evaluation of hydrocarbon expelling capacity of source rocks is more practical for the instruction of oil gas exploration than that of hydrocarbon generation capacity. In this paper, based on the principle of material balance, divide the tough problem of expelling hydrocarbon into relatively and easily investigated problems of hydrocarbon generation, residual and diffusion hydrocarbon.Study oil source rocks and gas source rocks respectively. The evaluation of oil source rocks is based on magnitude of the expelling oil (expelling oil quantity=net oil quantity-residual oil quantity), and the evaluation of gas source rocks is based on magnitude of expelling gas (quantity of expelling gas= gas quantity of generation-adsorption-dissolving in oil-dissolving in water-diffusion).Systematically investigate the hydrocarbon generation of organic matter (oil and gas generation from organic matter and oil to gas), residual hydrocarbon of source rocks (residual liquid hydrocarbon of rocks, gas adsorption of rocks, gas dissolving in oil and gas dissolving in water) and gas diffusion etc. Take the conditions of Tarim as an example, calculate quantity of oil and gas generation, residual liquid hydrocarbon, gas adsorption, gas dissolving in oil, gas dissolving in water, and gas diffusion under different geologic conditions, then according to the principle of material balance, work out oil expelling and gas expelling quantity. Lastly establish theoretical, industrial threshold value of organic enrichment of source rocks and grading evaluation criterion under different source rocks thickness, hydrocarbon potential, superface depth conditions.The main content and achievements are listed as following:1. For the first time, put forward a new research approach which uses the principle of material balance as the theoretical basis, and make grading estimation of carbonate source rocks by the quantity of hydrocarbon expelling. As a result, establish the evaluation criterion of source rocks on the basis of quantitative calculation, instead of pure experience, then estimate oil source rocks and gas source rocks respectively.2. For the first time, take Tarim basin as an example to establish theoretical, industrial threshold value of organic enrichment of carbonate source rocks. Calculate gas quantity of generation, adsorption, dissolving in oil, dissolving in water, diffusion of unit area carbonate rocks at different geologic conditions.And then according to the material balance principle, figure out the corresponding organic carbon content when gas being started expelling from source rocks with separate phase. Regard it as the theoretical threshold value (TOCmjn) of gas source rocks at that same geologic condition. Based on the study, find that TOCmi,, decreases with the increasing source rocks thickness; decreases at first and then increases with the increasing maturity and decreases with the better organic-matter type.3. For the first time, set up grading estimating criterion of oil source rocks and gas source rocks with the hydrocarbon expelling intension. Figure out the corresponding organic carbon content threshold value, and...