Abstract
Horizontal injection wells could be widely used in geological storage projects to provide large injectivities into formations with less favorable permeability-thickness products. Injection induced fracturing, which plays an important role in injection and storage risk assessment, is much more complex for horizontal well than vertical well,. The temperature variation of formation around wellbore due to cool CO2 injection introduces thermo-elastic stress which dramatically decrease critical fracture pressure under some strategies. According to the definition of thermo-elastic stress, the temperature profile of CO2 in horizontal wellbore essentially determines its magnitude.
A model is developed to describe heat transfer between wellbore fluid and surrounding formations by extending our previous heat transfer model of vertical wellbore. In the model, CO2 flux along horizontal wellbore is divided to uniform and non-uniform flux. Mass flow rate of the former case is linear; in the latter case, mass flow rate depends is non-linear and depends of the pressure drop along the wellbore, which is related to friction loss.
The model analyzes factors that affect temperature difference between wellbore CO2 and formation by several dimensionless groups: (1) dimensionless ratio of the rate of heat transfer to the rate of advective transport of enthalpy in vertical wellbore; (2) the length ratio of horizontal well over vertical well; (3) dimensionless friction factor. With new criterion by considering the influence of thermo-elastic stress, we optimize perforation zone of horizontal wellbore to prevent fracturing. Additionally, the influence of formation properties wellbore pressure is discussed to estimate safe perforation zone of horizontal wellbore.
