Estimating Ultra Low Permeability at Multiple Locations Using Simultaneous Impulse Tests: A Fit for Purpose Pressure Transient Solution and Its Field Application

摘要

One of the major challenges in efficiently developing ultra-tight or shale reservoirs is to obtain reliable permeability distribution. Ultra low permeability and very strong stratification or heterogeneity in the formations require conducting long duration tests at multiple locations in a well to attain a complete reservoir characterization. Because of these characteristics, existing tools or methods that work well for conventional reservoirs are usually not applicable for ultra-low permeability formations. An innovative reservoir monitoring/testing tool system was developed and successfully applied to fields in both USA and Canada (Zhan et al. 2016). The tool created multiple pressure pulses at targeted locations simultaneously along monitoring wells for zonal in-situ permeability estimations as well as long term formation pressure monitoring. Existing pressure transient solutions are incapable of handling the measured data when potential zonal pressure interferences appear. A fit-for-purpose pressure solution, the associated optimization algorithm and suitable data interpretation workflow, was developed to analyze the data whenever commercial software tools are inadequate. The new solution fully considers all impulses as well as potential interferences among them through suitable superposition. In-situ permeability values at all involved zones can be obtained through a combination of individual impulse analyses and systematic multiple impulse inversions. The new pressure transient solution was verified through comprehensive synthetic cases using numerical simulations. The results show that the solution can handle either fully or partially open wellbore in each zone and properly considers cross-flow between formation layers. In addition, it allows any number of perforated intervals and formation layers where the number of the perforated intervals is less than that of the formation layers. Field examples demonstrates applicability of the new solution and the data interpretation workflow to formation permeability down to tens of Nano-Darcy. The detailed zonal permeability distribution in the formation enables a more representative reservoir model for better hydraulic fracturing design and field development optimization.