Method for Determining Gas Content in Low to Medium Maturity Fine Grained Rocks

Abstract

A method for determining the gas content in fine-grained rocks of low to medium maturity is provided. The method includes providing the original sample and the deoiled sample; dividing the specific pore size range of the fine-grained rock; obtaining the excess isothermal adsorption gas volume curve per unit pore volume by molecular simulation; obtaining the calculated isothermal adsorption gas volume curve of the deoiled sample; The measured isothermal gas volume curve of the oil sample; the approximate comparison between the measured isothermal gas volume curve of the deoiled sample and the calculated isothermal gas volume curve; according to the approximate comparison results, determine whether to re-divide the specific pore size range and obtain the unit pore volume excess isothermal gas volume curve and comparing; obtaining the calculated excess isothermal adsorption gas capacity curve of the original sample; subtracting the calculated excess isothermal adsorption gas capacity curve from the measured isothermal gas capacity curve of the original particle sample to obtain its dissolved gas capacity curve; and obtaining the dissolved gas capacity of the fine-grained rock at any pressure. The method enables precise determination of natural gas content in fine-grained rocks.

Description

technical field [0001] The invention relates to a method for determining the natural gas content in medium-low maturity fine-grained rocks. Background technique [0002] Sedimentary rocks composed of clay-grade or silt-grade sediments with a particle size of less than 62 μm are called fine-grained rocks, which are important reservoir rocks for unconventional oil and gas such as shale gas and tight sandstone gas. In fine-grained rock reservoirs such as shale, the natural gas is mainly methane gas, including three different occurrence states of free gas, adsorbed gas and dissolved gas. Accurately obtaining the natural gas content, relative proportion and total gas content of different occurrence states in fine-grained rocks is of great significance for evaluating fine-grained rock gas reservoir resources and selecting gas reservoir development methods. [0003] At present, in the high-maturity fine-grained rocks in North America and southern my country (that is, fine-grained ...

AI Technical Summary

Problems solved by technology

However, due to the existence of a large amount of liquid hydrocarbons that contain dissolved gas, only using methane isothermal adsorption experiments will bring large errors in the determination of the adsorbed gas content of medium-low maturity fine-grained rock samples, which will affect the calculation results of free gas.

In addition, the composition of liquid hydrocarbons in fine-grained rocks is relatively complex, and the solubility calculated only by the black oil model has a large relative error, which will also affect the calculation results of dissolved gas.

[0005] Therefore, there are large relative errors in the current conventional methods for obtaining gas volumes in different states of occurrence of fine-grained rocks with medium and low maturity, which leads to the inability to accurately predict the amount of underground reservoir resources. There are greater risks in the exploration and development of layered natural gas

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