Abstract: Presently, the testing temperature and pressure of the shale adsorption isotherm cannot usually reach that of the reservoir. To solve this problem, the hightemperature/highpressure test methods were designed, and the characteristics of shale adsorption isotherm under reservoir temperature/pressure were analyzed. In addition, variations in free and adsorbed gas with changing reservoir pressure were calculated in accordance with the actual shale core model; the effect of adsorbed gas on the characteristics of gas production was also studied by examining the pressure controlled production of helium & methane using whole diameter shale core. Results show that gas adsorption by visual assessment increases initially with increasing pressure and decreases after peak. It is found that under low pressure conditions, gas adsorption calculated by Langmuir extrapolation is close to that of high pressure experiments; but under high pressure conditions, total gas content calculated by low pressure Langmuir theory is overvalued by about 9.2%. Moreover, below the critical desorption pressure, desorbed gas causes gas production to increase per unit differential pressure; while above the critical desorption pressure, adsorbed gas hardly affects gas production. During the early development, reservoir pressure ranges slightly below the critical desorption pressure so that the adsorbed gas contributes very little to gas production. Therefore making full use of free gas is key to high efficiency reservoir development.

Key words: shale, adsorption, gas content, diffusion, seepage, high pressure