Study of Flow Interaction Between Multiple Stages in Long Horizontal Wells

Numerical simulation of flow inside a horizontal wellbore with multiple completion stages is presented. The aim was to study the blocking effect on the toe-end stages observed in long horizontal wells. An axisymmetric pipe geometry was used to model the wellbore, with circumferential inlets representing perforation stages. Firstly, using a simplified five-stage case with steady state flow conditions, the existence of three basic flow regimes - trickle flow, partially blocked flow and fully blocked flow - was established. Using these results, the phenomenon of blocking of upstream inlets near the toe by the downstream ones near the heel is explained. The existence of these flow regimes is consistent with well-log data obtained from a horizontal shale gas well with 31 completion stages at two different times during production.

To study the dynamic behavior of the completion stages when reservoir fluid flows into the wellbore, a basic reservoir depletion model was created using a pressure boundary condition at the circumferential inlets, varying in time. A lumped-parameter model was used to account for the pressure drop between two inlets separated by large axial distance. Different characteristic time scales, related to the depletion of the reservoirs, were identified. By varying initial conditions, the dynamic behavior of the system with multiple inlets was observed and analyzed. The transition of flow regimes with depletion of reservoirs is consistent with the observed behavior of the horizontal shale gas well.

A simple nozzle design was used to modify the entry of flow from the inlets into the wellbore. The interaction between wellbore stages in presence of nozzles is studied using a two-dimensional mesh with the reservoir depletion and inter-stage pressure drop model. The nozzle opening size was varied to achieve production enhancement over simulated time period. This provides an alternate method of inflow control that could be used to homogenize production from different well stages. This would make use of the already perforated pipe wall without having to use a screen around the production pipe.

In addition, three-dimensional geometry of a combustor was used to simulate flow from discrete perforations into the pipe crossflow. An initial analysis of flow through the nozzle design on a single inlet was conducted using a three-dimensional mesh. Mean flow analysis of these simulations and comparison of pressure drop between the nozzle and combustor cases is presented.