Assessment of Sand-face Pressure and Temperature Behaviors of Single-Phase Liquid-Water Geothermal Reservoirs during Injection and Falloff Tests

摘要

This study focuses on the evaluation of sand-face pressure and temperature behaviors during cold water injection into single-phase liquid-water geothermal reservoir and a falloff period following the injection. In recent years, important technological developments (higher resolutions and better accuracy) in temperature gauges have made temperature data valuable in addition to pressure to obtain precious reservoir information data that could not be obtained from pressure data alone by history matching. From this point of view, some cases including different injection/falloff and variable-rate injection scenarios are taken into consideration in this study to be able to understand some interesting pressure and temperature responses arising from colder water injection into a hotter geothermal reservoir and study the sensitivities of various rock parameters (porosity, permeability, skin, and thermal conductivity) to the temperature in a fully-penetrated vertical well or to the pressure and temperature at an observation point (probe) along the wellbore for an homogeneous or anisotropic reservoir during those modes. In this work, a 2D (r-z) non-isothermal in-house simulator verified by commonly used two thermal reservoir simulators, which can also model some important mechanisms such as Joule-Thomson effects (heating/cooling), transient adiabatic fluid expansion/compression, convection, and conduction, have been used to investigate the aforementioned behaviors. In this study, thermal effects taken place by the cold water injection into the hot reservoir on the sand-face pressure are explained in detail and verified by some analytical expressions available in the literature. It has been revealed that density and mobility differences that cold water injected and original geothermal reservoir fluid have cause those effects. Hence the sand-face pressure exhibits interesting behaviors depending on the outer reservoir boundary condition (infinite-acting, insulated, and Dirichlet) considered as well. According to the sensitivities of various rock properties to the sand-face temperature, it has been observed that particularly falloff period may contain valuable information about some reservoir parameters such as permeability, skin, and thermal conductivity to take into account those in history matching. Additionally, it is possible to state that increasing skin enhances the temperature change at the sand-face in relation to the more pressure drop and skin effect on temperature is more pronounced during falloff period compared to injection.