North Sea chalk reservoirs are characterized by thick formations, low kv/kh-ratios and a low to medium degree of fracturing. Primary recoveries are generally low, in the range of 15-20%. Utilization of horizontal wells could be an efficient tool to increase production rates and improve recoveries from these fields.
A comparative dual porosity reservoir simulation study of horizontal and vertical wells in a North Sea naturally fractured chalk reservoir has been performed. The numerical results are compared to single phase, analytical solutions to investigate the validity of the latter approach. A future strategy for the application of horizontal wells in these fields is also discussed.
The study shows that analytical approaches are valid only for initial screening purposes. To ensure an improved productivity, horizontal wellbore sections should be drilled as long as possible (> 600 m) to maximize the benefit of the steeply dipping natural fracture pattern present in the fields. Numerical results are presented which identify the sensitivity of the horizontal well performance to key properties of the chalks and to different horizontal well trajectories. The study verifies that horizontal water injectors may enable injection into the low-productivity flank intervals of the chalk reservoirs. In a waterflooding environment, the study shows that horizontal wells can be utilized to minimize water production and thereby sustain the future production from the chalk fields.