Quantitative Evaluation of Imbibition Damage Characteristics of Foaming Agent Solutions in Shale Reservoir

Abstract

Shale reservoirs are characterized by extremely low porosity and permeability, poor connectivity, and high content of clay minerals. This leads to the reservoir being vulnerable to imbibition damage caused by foaming agent solutions during foam drainage gas recovery. It results in the decrease of reservoir permeability and the reduction of gas well production and ultimate recovery. Therefore, as the most commonly used foam drainage gas production, it is particularly important. This study is structured as follows. First, we analyze and evaluate the characteristics of shale reservoirs within the target area, and that of mineral composition and microscopic pore throat structures. Second, we study foaming agent types and two types are selected to be applied in subsequent sensitivity tests. Simultaneously, the nuclear magnetic resonance (NMR) method was used to study the microscopic characteristics of reservoir damage and imbibition damage of shale, caused by the impact of foaming agent solutions during the foam drainage and gas recovery processes. Finally, it is concluded that the degree of damage to the core permeability is minimized when the concentration of foaming agents is 0.4–0.6%. A trend has been established for increased damage to the cores with increasing exposure time. Additionally, this study provides technical guidance for damage evaluation and reservoir protection in shale reservoir exploitation.