Bowland Shale well placement strategy – Part 2: Fracture simulations using a 3D geomechanical model and implications for stratigraphic and spatial horizontal well locations

Abstract

Hydraulic fracture modelling is a key component of a shale reservoir well placement strategy as it provides an indication of the typical lengths and heights of stimulated fractures and of the changes to the stress environment in which these are propagating. However, spatial and stratigraphic variations in the stress and geomechanical properties of shales make accurate modelling a challenging task. For the UK Bowland Shale, stacked horizontal wells targeting multiple stratigraphic intervals could be used to avoid large offset faults in a geologically complex area. However, it is not known how these intervals may respond to hydraulic fracturing and predicting the height and length of hydraulic fractures is necessary in order to assess the likelihood of vertical fracture interference across landing zones or propagation towards major faults. In the case of the former, intervals of high effective stress may be key to containing fractures within their desired target. Using a planar hydraulic fracture simulator, and a 3D geomechanical model incorporating dipping stratigraphy, the issue of predicting hydraulic fracture geometry in the Bowland Shale was assessed through a series of modelling exercises using well Preese Hall-1 and horizontal pseudo-wells. When pre-defined landing zones were targeted, narrow and long transverse fractures around 1 km from the well were simulated. When the simulation design mimicked perforation clusters placed at 12 m intervals along horizontal pseudo-wells, the effects of stress shadowing were acute and resulted in irregular fracture geometries. Furthermore, high effective stress intervals performed efficiently as barriers to vertical hydraulic fracture propagation, reinforcing the feasibility of using stacked production for the Bowland Shale. The modelling results were then used to discuss the possible placement of horizontal wells in a mapped, 100 km2 region around well Preese Hall-1, where up to 13 sites could be positioned, with a horizontal well length of around 1.5 km. Finally, by drawing on a well-established analogue for the Bowland Shale, it was estimated that up to 195 Bcf of gas could be produced from the 13 locations in the area if three stratigraphic intervals are produced from one location.