A method and device for determining the free adsorption ratio of shale gas reservoirs

Abstract

The invention discloses a method and a device for determining a free adsorption ratio of a shale gas reservoir. The method comprises the following steps of (1) determining a corresponding critical pore radius when the contents of free gas and adsorbed gas in a gas-bearing pore of the shale gas reservoir are equal; (2) determining a pore size distribution spectrum of the gas pore of the shale gas reservoir; (3) dividing the pore size distribution spectrum into an adsorbed gas dominant pore space and a free gas dominant pore space; (4) respectively obtaining the free gas content and the adsorbedgas content in the adsorbed gas dominant pore space and the free gas dominant pore space; (5) determining the total gas content of the adsorbed gas dominant pore space and the total gas content of the free gas dominant pore space; and (6) determining the free adsorption ratio. An effective method for rapid evaluation of the free adsorption ratio and the gas content of the shale is provided and the application range of a nuclear magnetic resonance experiment new method in the comprehensive assessment of the shale reservoir is expanded to a certain extent.

Description

technical field [0001] The invention relates to the technical field of oil and gas geophysics, and more specifically, to a method and a device for determining the free adsorption ratio and gas content of shale gas reservoirs. Background technique [0002] Shale gas refers to a kind of unconventional natural gas resource that occurs in organic-rich mud shale and other lithological interlayers in the form of free and adsorption. It is widely distributed around the world and has huge reserves. Mining and utilization prospects. [0003] The gas content of shale gas reservoirs is a key core parameter that needs to be evaluated in the process of shale gas exploration and development. The gas content directly determines the quality and quality of shale gas reservoirs. Accurate evaluation of gas content plays an extremely important role in many links in shale gas exploration and development decision-making, resource evaluation and production. In the evaluation of gas content, when...

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Problems solved by technology

The evaluation methods mentioned above are widely used in the current shale gas content evaluation, and have achieved good application results to a certain extent. However, this method for determining the free adsorption ratio has the following shortcomings: One is reflected in the evaluation of the adsorbed gas content, that is, the operation of the isothermal adsorption experiment under the condition of simulating formation temperature and pressure (high temperature and high pressure) is complicated and expensive, which undoubtedly increases the difficulty and cost of the evaluation. The other is reflected in the free gas content. In terms of calculation, different from conventional reservoirs, it is difficult to accurately evaluate the effective porosity and gas saturation of shale gas reservoirs, which will lead to deviations between the calculation results of free gas content and the actual situation to a certain extent. Third, in the pores of shale gas reservoirs, especially in the pores of organic matter, there is no strict boundary between free gas and adsorbed gas, and the two can dynamically switch when external conditions change. Method The theoretical basis of the method for evaluating the free adsorption ratio is still to be discussed and verified

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