After-Closure Analysis for Naturally Fractured Reservoirs: Field Examples

Abstract

AbstractEconomic optimization of fracture stimulation designs requires accurate reservoir description (ie. permeability and permeability thickness) and an understanding of the deliverability mechanism (ie. natural fractures versus conventional matrix). This paper presents a technique which allows an engineer to evaluate a mini-frac injection in a similar manner to a conventional pressure transient test for the identification of productive natural fractures. Following a brief theoretical background to this new methodology, this paper provides a field validation study in oil and gas fields on two continents.Identifying natural fractures drives certain changes in stimulation design. Techniques designed specifically to stimulate natural fractures include low gel loadings, energized fluids and 100 mesh sand for natural fracture preservation1,2.A recently published mini-frac evaluation technique using the After-Closure pressure information3 provides a methodology which can identify productive natural fractures. Using this methodology, this paper delivers a retrospective evaluation of mini-frac information using data from tight gas fields in Central Australia and an oil field in Algeria. In addition, the results are validated with independent constraints such as pre-closure mini-frac analysis, conventional well testing, image logs and core analysis.Finally, the results of this evaluation are distilled into a simple field implementation methodology which can be incorporated into a conventional pre-frac injection sequence.