GB/T 39539-2020 in English

Analysis of the core content of the standard

This standard specifies a complete technical system for measuring the gas diffusion coefficient of shale reservoirs using equipment such as core holders, focusing on solving the problem of accurate measurement of diffusion coefficients in the range of 10^-3 to 10^-8 cm²/s.

Key instrument configuration requirements

Key points of experimental operation

Data processing method

Based on Fick diffusion theory, the diffusion coefficient is calculated by equations (1)-(5):

ln[πΦ0L2/4 - Q] = ln[πΦ0sin(λ1L)/(λ12L)] - λ12Dt

The linear fitting degree of the data in the second gas production stage is required to be >90%, and the final result needs to be rounded to 10 decimal places.

Implementation recommendations

1. It is recommended to use a constant temperature control system to maintain formation temperature conditions
2. For ultra-low permeability samples, the equilibrium time should be extended to more than 72 hours
3. Repeatability verification is required during data processing (≤10% deviation)

Standard evolution analysis

This standard integrates the equilibrium water preparation method of GB/T19560-2008 and the core analysis specification of GB/T29172-2012, and establishes a standardized measurement system for shale gas diffusion coefficient for the first time. Compared with the traditional method, the following are added:

• σ flow coefficient correction term
• Two-stage gas production analysis mode
• 10^-8cm²/s ultra-low diffusion coefficient measurement scheme