Interwell Connectivity in Tight Formations

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A significant amount of oil and gas are present in formations having permeability less than 0.1 md. Although these tight reservoirs typically have small well spacings, not all well pairs exhibit connectivity because of the reservoir heterogeneity. Measuring connectivity can improve model realism and identify important geological controls sufficiently that field management can be made more reliable. In this study, we use the Capacitance Model (CM) to evaluate interwell connectivity. In order to render the CM suitable for tight reservoirs, we modified the model by adding a pseudo-well (CM-PW). This modification lets us apply the model to any areal window of interest and cope with long-transient periods in the production well flow rates. The CM-PW was tested with several heterogeneous simulation cases, which revealed that calculated connectivities from the tight permeability reservoirs agreed with results from higher permeability cases with only minor errors (< 7%). We applied the CM-PW to selected waterflooded areas from the East Pembina (Cardium Formation) and the Forget North (Bakken Formation) fields. As a further improvement on the existing CM analysis, horizontal wells were included in our field analyses. In the East Pembina Field, we could identify the effects of net local principal stress and hydraulic fracturing proppant amounts on the interwell connectivity. Pre-stimulation interwell connectivities are consistent with the maximum horizontal stress direction. We found that a change in connectivity was directly proportional with proppant tonnage. Also, the effect of the conglomerate layer on connectivity was studied. We found that strongest pseudo well connectivities are directed to the conglomerate-bearing region and the connectivities were related to the formation flow capacity. Finally, we also observed connectivity behavior consistent with the expected sandbody extent as identified through geological studies. In the Forget North Field connectivity study, we correlated well-to-well connectivities with geological and seismic analyses. We found that the natural fracture intensity and the Lodgepole Formation aquifer may be causes of long distance connectivity. It is well known that the CM evaluation is affected by the formation diffusivity. Using the analogy with heat conduction, we propose a method to determine an “area of influence” for an injection well. The method includes recognition that, in addition to the diffusivity, the injection rate frequency content affects the area size. The method was applied to determine the areal window size for the CM-PW application in tight oil reservoirs. From simulated and field applications, we observed that the interwell distance at the connectivity limit is within 3 to 5% of the interwell distance estimated from the heat conduction-based method. The modified CM allows us to extend the application to important new reservoir cases. The two field studies once again show the important role of geological features on reservoir communication. Finally, the importance of the injection rate frequency spectrum on the CM measurement opens up a new understanding of the injection well influence in reservoir performance.
Reservoir Characterization, Interwell Connectivity, Tight Formations, Capacitance Model, CM-PW, Bakken Formation, Cardium Formation, Halo Oil Reservoir
Mirzayev, M. (2018). Interwell Connectivity in Tight Formations (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/31895