| Abstract |
In this work, we investigate the transient pressure and temperature behaviors of liquid-dominated geothermal reservoirs containing single-phase liquid water. Investigation is conducted by using a 2D (r-z) non-isothermal model that couples both the mass and thermal energy balance equations rigorously and considers various modes of production/injection well conditions and outer reservoir boundary conditions of no-flow/constant-pressure with or without constant-temperature in the vertical and lateral directions. Using this model, a sensitivity study with respect to various reservoir properties (such as porosity, permeability, skin, thermal conductivity, rock density and rock heat capacity) is conducted for investigating the information content of the sandface pressures and temperatures at source/sink locations as well as some selected observation points along the wellbore. In the sensitivity study, the effects of the reservoir parameters on temperature and pressure responses were quantified through the use of sensitivity coefficients, which are defined as the derivatives of temperature or pressure data with respect to the natural logarithm of the parameter of interest. The results of the sensitivity study reveal which reservoir parameters can be reliably estimated from temperature and pressure measurements in cases where non-linear parameter estimation methods are employed for history matching. Based on the results of these synthetic cases assuming homogeneous single-layer systems, it is shown that, depending on the mode of production or injection (constant-rate production, or shut-in following production or fall-off following injection, etc.), the sandface pressures and temperatures show sensitivities to parameters like porosity, permeability, rock thermal conductivity, rock density and rock heat capacity. For instance, we show that the reservoir permeability has no considerable effect on the sandface temperature for the constant-rate injection case, whereas it has a relatively significant effect on the temperature for the constant-rate production case at especially low permeability. It has also been found that skin (due to damage or stimulation around the well) and permeability have significant effects on sandface temperatures when injection is performed at a constant-pressure. However, it is observed that sandface temperature changes do not exceed 2 to 3 K for most of the constant-rate production cases studied. Such small changes may be difficult to measure in practical field applications. |