Objectives/Scope

Waterflooding has been the main development method for maintaining the formation energy in low-permeability reservoirs. Often these reservoirs are characterized by poor sweep and high water cut of oil wells due to natural fractures. Streamline technology is an ideal tool for optimization of waterflooding operations. One of the main advantages of streamline simulation is to display paths of fluid flow and to calculate rate allocation factors. However, describing fluid transport in fractured low-permeability reservoirs entails additional challenge because of the complicated physics arising from matrix-fracture interactions.

Methods, Procedures, Process

In this paper we demonstrate a straightforward workflow for optimizing injection rate based on a comprehensive analysis of injector efficiency (IE). First, the streamline model including improved transfer function and non-Darcy flow of matrix is generalized to describe fluid transport. In particular, the streamline time of flight concept is utilized to develop a general dual porosity dual permeability system of equations for water injection in naturally fractured reservoirs. The streamlines can be derived from the flux field of this model that represent a snapshot of the flow pattern within the reservoir, well drainage region information and fluid allocation changes with the flood progression. Second, using an analytical calculation to compute weighting factors for injection/production rate targets from a derived ranking of the wells (IE). Finally, reallocation of injected fluid volumes from low-efficiency to high-efficiency injectors improves volumetric displacement and sweep efficiency in the less swept areas of the reservoir. The application of this workflow is demonstrated with a real-field example of an fractured low-permeability sandstone reservoir in Chang Qing oilfield in China where the pattern balancing has led to incremental production over the 5 years forecast in which the IE average of the field is the benchmark while obeying facility constraints.

Results, Observations, Conclusions

The results indicate that water cycling was quantified by streamline simulation and water injection with a decrease of 30-40% on the maximum principal stress direction causes in a reduction in the produced water volumes. A new water injection strategy was implemented, and a decrease in water cut on this challenge sector was achieved in the targeted producers.

Novel/Additive Information

This work provides a comprehensive case study and useful method for better understanding the fractures on waterflooding performance and optimizing production plan of maximizing oil recovery on the fractured low-permeability reservoir.

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