Study Of Threshold Value Of Organic Enrichment Of Carbonate Gas Source Rocks

In China, Most of carbonate source rocks are low organic enrichment and high-maturity, over-maturity, therefore, neither does the existing assessment method of argillaceous gas source rocks in China fit for the evaluation of this sort of source rocks, nor can copy the foreign evaluation of lower maturity carbonate gas source rocks.the value of carbonate gas source rocks is an important thing that determines the investment and oriention of exploration.Since the generated gas from gas source rocks is expelled in the form of separate phase, can it be useful for the form of pool.so,the expelling gas value of carbonate gas source rocks is more important, this paper, based on the principle of material balance, divide the tough problem of expelling hydrocarbon into relatively and easily investigated problems of gas hydrocarbon generation, residual and diffusion gas hydrocarbon and evaluate gas source rocks in temis of the magnitude Of expelling gas; hydrocarbon(quantity of expelling gas= gas quantity of generation-adsorption-dissolving in oil-dissolving in water-diffusion).This paper take the conditions of Tarim as an example, calculate quantity of gas generation, residual gas 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 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. put forward a new research approach which uses the principle of material balance as the theoretical basis, and quantificationally make grading estimation of carbonate gas source rocks by the quantity of hydrocarbon expelling.2. take Tarim basin as an example to establish theoretical, industrial threshold value of organic enrichment of carbonate gas 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 (TOCmin) of gas source rocks at that same geologic condition.3. set up grading estimating criterion of gas Source rocks with the gas hydrocarbon expelling intension. Figure out the corresponding organic carbon content threshold value, and plot grading estimating plates of oil and gas carbonate source rocks in Tarim basin. Through anasynthesis, sum up organic enrichment grading estimating standard of oil source rocks and gas source rocks in our country (type II organic matter, mature carbonate rocks).4. distinguish the concepts of gas actual diffusive flux and maximal diffusive flux; and calculate respectively. We find that maximal diffusive flux can be several times even scores of times larger than actual diffusive flux. Using maximal diffusive flux to substitute actual diffusive flux, which will overestimate diffusion losing and bring biggish error for estimate of gas source rocks and resource evaluation of gas pool.5. Study kinetics behavior of oil generation, gas generation from organic matter in carbonate rock and oil to gas. And calibrate kinetic models using experimental data. Make it possible to calculate quantity of oil generation, gas generation from carbonate source rocks quantificationally and dynamically.6. According to the results of calculation,discuss the effect factor of Threshold value of of organic enrichment.