Summary
Installing sand control in long horizontal wells is difficult and particularly challenging in offshore fields. It is, therefore, imperative to make decisions with regard to the most optimum completion type objectively and based on reliable assessment of the sanding potential and its severity over the life of the well for the intended production target. This paper introduces a predictive tool that forecasts not only the initiation of sanding, but also its rate and severity in real time.
A series of well-documented experiments on a large-size horizontal wellbore was simulated using a finite difference numerical model. The model accounts for the interaction between fluid flow and mechanical deformation of the medium, capturing various mechanisms of failure. The model allows capturing the episodic nature of sanding and the resulting changes in the geometry and formation consistency and behavior within the sand impacted regions. Sand detachment is simulated by removal of the elements that are deemed to have satisfied the criteria for sanding based on considerations of physics, material behaviour and laws of mechanics. The proposed numerical model is designed to account for many of the factors and mechanisms that are known to influence sanding in the field and as such can be used as a practical tool for predicting the frequency and severity of sand bursts and changes in operating conditions that can be considered for mitigating or managing such problems.
The model shows reasonable agreement with the experimental results in terms of borehole deformation and sanding rates. The model correctly predicted initiation of shear failure from the sides of the borehole and its propagation to the boundaries of the sample. It was further seen that the propagation of the shear failed zone resulting from sand production agreed well with the numerical pattern of failure growth upon removal of elements satisfying the sanding criteria. The approach and concepts used are considered suitable for application to field problems involving horizontal wells.
Introduction
A significant proportion of the future oil and gas production is expected to come from sand-prone reservoirs, many of which are offshore. While these reservoirs are highly prolific they are complex to develop and manage. Typical cost of completing a major offshore well exceeds $100 million and these wells are expected to remain productive for 20 years and longer. The control of solids production in these high-rate wells over the life of the well is a challenge and requires a good understanding of the mechanical behavior of the formation under a variety of conditions. Various options are available, ranging from placing active sand control, such as gravel pack and frac pack, to natural completion, such as a cased and perforated hole. Objectivity is required in choosing the correct completion type, which must account for the production strategy and natural changes in the reservoir such as changes in the stress state, permeability, and multiphase flow, including water cut. Once the completion type is chosen, it must be operated optimally to maximize production while maintaining efficiency and longevity. For instance, in sand-control completions, operations must be tailored to mitigate generation and transport of fines that can cause plugging of the gravel pack and lead to screen erosion, whereas in natural completions, the emphasis would be in preventing formation sand production or keeping it under the tolerance that can be handled by the facility. Utilization of a reliable sand production prediction tool is essential in selecting the optimum completion technique and optimization of the operational conditions.