The fast and slow discharge of CBM wells have a direct effect on the CBM wells dynamic permeability, and with the process of drainage and the change of pressure, the change of stress state and opening degree of cracks reduce the permeability area and affect the production capacity. The influence mechanism of coalbed gas permeability of fast and slow discharge has many theoretical bases, but most of them are not verified by the measured data and applied to the actual engineering. In order to analyze the slow discharge method and influence degree of the seepage capacity of the CBM well, it is necessary to carry out the shut in pressure recovery test, the constant pressure discharge test and the formation pressure recovery test.

Though research analyzes, the influence of after pressure drainage method on the seepage capacity of gas wells and the pressure result by using pressure recovery well test explanation, to realize the comprehensive assessment of CBM wells.

Single phase water state testing requirements:

Adopting the downhole shut-in method, the surface direct reading test technology, open-close-open drainage,  constant flow and pressure drop drainage is carry on during open well drainage stage (slow drainage for the first open well, quick drainage for the second open well), under the condition that the gas is not desorbed, the shut in pressure recovery test is carried out, and the pressure is reduced near the desorption pressure and the constant pressure drainage process will last for 30 days to test the change of water permeability in the process of  constant pressure drainage, and to test the formation pressure recovery condition again when we guarantee the gas is not desorbed.

For the collection of data points for open well flowrate pressure and shut-in pressure recovery, in order to maintain synchronization with the tubular pumps, the same sampling time intervals are used: one data point is taken every 5 minutes for the down, open well drainage and shut-in pressure recovery stages.

Test results

To verify the influence of the after-pressure discharge mode on the seepage capacity of gas wells.

The gas saturation of fracturing fractures with different gas discharge pressure after casing pressure is compared.

To verify the change of the seepage capacity of gas well and water in the process of stable casing pressure.

Compare the formation pressure recovery condition before and after casing pressure in the same well.

To verify the water producing capacity of the drainage process layer prior to stratified combined production and desorption.

Based on the test and analysis, combine the drainage reality, the influence of different drainage methods on the seepage capacity of gas-water reservoir two-phase flow is studied. At the same time, the stress state is evaluated by using the pressure recovery well test  results.