Experimental Study of Defoamer Effect on Methane Desorption on Longmaxi Shale, China

Abstract

AbstractKnowing methane desorption is of great importance for the design of gas production rate from gas wells in shale reservoirs. Many researches have been conducted to understand the effect of the slickwater as a hydraulic fluid on the reduction of methane desorption from shale. However, the slickwater has multiple components and no article has been published to address the role of defoamer as its major composition in the reduction of methane desorption. In this paper, we designed an experimental apparatus based on volumetric method to analyze methane adsorption isotherm and the effect of defoamer on the methane desorption. Three isothermal models including Langmuir model, Freundlich model and Dubinin-Radushkevich model were applied to find the best fitting for the methane adsorption and desorption experimental data. The results show methane adsorption on the shale can be best fit by Langmuir model while the desorption can be best fit by Freundlich model. An obvious hysteresis occurs between adsorption and desorption isotherms. The desorption isotherm before defoamer treatment is obviously higher than that after, reflecting defoamer can reduce the amount of adsorbed gas. The effect of defoamer on the desorption efficiency was analyzed according to the first derivative of Freundlich equation. The results show that the desorption efficiency before defoamer treatment is lower than that after when the pressure is bigger than 1.91 MPa. Furthermore, before and after defoamer treatment, the ratios of adsorbed gas to free gas all increase while the equilibrium pressure decreasing. Before defoamer treatment, the ratio is significantly smaller than that after, when the pressure is lower than about 19 MPa. The accumulative gas production before defoamer treatment is clearly lower than that after, indicating the defoamer can stimulate methane desorption and maintain the gas pressure to produce. These results can be used for optimizing the slickwater formulation and gas well production design.KeywordsShale gasDefoamerMethane desorptionAdsorption isothermDesorption efficiency