T2Well—An integrated wellbore–reservoir simulator

At its most basic level, management of subsurface fluid resources involves a system comprising the wellbore and the target reservoir. As discrete pathways through geologic formations, boreholes and wells are critical to the success of many water, energy, and environmental management operations. Although many stand-alone simulators for two-phase flow in wellbores with various levels of sophistication have been developed, simulating non-isothermal, multiphase, and multi-component flows in both the wellbore and in the porous or fractured media reservoir as an integrated system remains a challenging yet important task. The difficulties include (1) different governing equations apply to the wellbore and the reservoir that need to be solved efficiently in a uniform framework, (2) the significant contrast in temporal and spatial scales between the wellbore and the reservoir that results in a very challenging set of stiff partial differential equations, and (3) other complexities (e.g., dry-out) that can be caused by flow processes between the wellbore and the reservoir. To address the need to simulate coupled wellbore–reservoir flow, we have developed T2Well, a numerical simulator for non-isothermal, multiphase, and multi-component flows in the integrated wellbore–reservoir system. The new model extends the existing numerical reservoir simulator TOUGH2 to calculate the flow in both the wellbore and the reservoir simultaneously and efficiently by introducing a special wellbore sub-domain into the numerical grid. For grid blocks in the wellbore sub-domain, we solve the 1D momentum equation of the mixture (which may be two-phase) as described by the drift-flux model (DFM). A novel mixed implicit–explicit scheme for friction in the wellbore is applied to facilitate the solution of the momentum equation, while other variables are calculated fully implicitly. Applications of the new simulator to problems in various fields are presented to demonstrate its capabilities.