Abstract
Steamflood with conventional vertical wells results in poor vertical sweep efficiency and steam breakthroughs when it is applied to heavy oil reservoirs. The use of horizontal producers provides a larger contact area with the reservoir resulting in a better drainage and therefore enhancing the well productivities by improving the steam sweep efficiency.
This study explores and compares the efficiencies of steamflooding in an improved version of an inverted 7-spot pattern with a vertical injector in the center and horizontal producers versus vertical producers in a representative numerical geological model from the Orinoco Oil Belt.
The simulation of the complex displacement processes1 combined with the well configuration results in challenging computational issues. As a result of the mechanisms involved in steamflooding, including oil viscosity reduction, steam condensation into hot water, large mobility ratio differences in the displacement processes, etc., the Grid Orientation Effects (GOE) could be significant. A grid selection process was performed to reduce grid orientation effects comparing the steam displacement in a Cartesian grid versus those from an unstructured Perpendicular Bi-sector (PEBI) grid.
Once the grid was established, sensitivity analyses were carried out to define the optimal design parameters to improve sweep efficiency and reduce recovery times. The parameters analyzed were: (1) placement of the horizontal producers within the vertical reservoir pay, (2) placement of the toe and heel of the horizontal producers, and a sensitivity analysis to (3) bottom hole flowing pressure, and (4) steam injection rates.
Reservoir conditions were also studied to explore the effects of: (1) pay thickness, (2) variation of horizontal permeability, (3) permeability anisotropy generated from geostochastic distributions, (4) and previous cold production, in the overall process performance.
The use of PEBI grids allowed to model in a more accurate way complex thermal-compositional displacement processes involving horizontal wells not aligned with the orthogonal Cartesian axes, and demonstrated that steamflooding using horizontal producers offers the potential to improve conventional schemes achieving higher oil recoveries from heavy oil reservoirs.
