Horizontal wells in liquids-rich shale plays are now being drilled such that lateral and vertical distances between adjacent wells are significantly reduced. In multistacked reservoirs, fracture height and orientation from geomechanical effects coupled with natural fractures create additional complications; therefore, predicting well performance using numerical simulation becomes challenging. This paper describes numerical-simulation results from a three-well pad in a stacked liquids-rich reservoir (containing gas condensates) to understand the interaction between wells and production behavior.

Numerical Simulation

The reservoir simulator used for this study was designed to handle ­unstructured-grid-based simulation cases. Most of the numerical reservoir simulators that are used for modeling horizontal wells with multiple hydraulic fractures are based on structured grid cells in which the hydraulic fractures are modeled as symmetric biwing fractures perpendicular to the wellbore. In most cases, they use local grid refinement (LGR) to incorporate the hydraulic fractures into the model, which generally works well if a single well is involved and the grids are not tied to the Earth models. However, if the wells and the hydraulic fractures are not orthogonal to the Earth-model grids or if the reservoir contains nonorthogonal secondary fractures (natural or induced), modeling them with LGR becomes a challenge. When multiple wells that are not parallel are drilled from a single pad, properly representing the wells with hydraulic fractures in a structured-grid-based reservoir-simulation model becomes even more challenging. By contrast, the unstructured-grid-based reservoir models are not restricted by any of these limitations—they can have any geometry, size, or orientation for the wells and can include primary hydraulic fractures, secondary fractures, and open natural fractures. Instead of using grid cells that are parallel in shape, the unstructured grid cells can have any arbitrary shape. Incorporating realistic induced hydraulic fractures in a reservoir model is easier if unstructured grids are used.