ABSTRACT
The horizontal wells, drilled in the Dan field of the Danish sector were initially stimulated with acid fracture treatments, the industry standard for a chalk reservoir. The placement of these treatments proved effective, however, the long term production was limited due to the low formation integrity and consequent collapse of the induced fracture system.
Propped fracture treatments replaced the acid treatments and the benefits to productivity were quickly seen. However, the placement of proppant in some of the Dan horizontal wells was difficult, and in some cases impossible using conventional techniques.
The difficulties in placement of proppant in the Dan field have been attributed to near wellbore tortuosity. This phenomenum occurs due to a variety of situations, namely when well trajectory is not in line with fracture direction, poor cement integrity in the perforated region, and perforation dominated creation of complex fracture patterns in the near wellbore vicinity.
This paper describes the mechanism of tortuosity and its effect on fracture stimulation treatment placement by reviewing several field examples of this phenomenon. The paper also reports modelling procedures utilized to predict the effect of tortuosity. Practical guidelines for removing tortuosity are provided, which have greatly increased the probability of successful proppant placement.
Through better understanding of tortuosity, modifications to completions and stimulation procedures have been implemented which have resulted in over 200 propped fracture treatments being successfully placed from horizontal wells in the Dan field.
