There is not yet a defined relationship between stimulation volume and long term producing volume in low permeability (nanodarcy scale) "reservoirs". To quantitatively describe producing volume, we define the distances at which stimulated horizontal wells show sustained connectivity by interpreting field pressure data to understand communication with neighboring wells over a series of time steps at 2, 6, 8, and 12 months after completion. We show how to design and execute pressure transient tests, how these field results yield conclusive evidence of proper well spacing, and how other methods to assess stimulated reservoir volumes compare.
Our procedure takes weeks to perform, and may be applied to make unplanned shut-in events useful reservoir characterization tools. Coordination between geology, reservoir engineering, and field engineers is required to successfully execute these tests. The results show we have a powerful tool for tuning of development plans well in advance of years' worth of production commonly used for such decisions.
From frac hits, microseismic, and tracer results we observe a continuous reduction in the stimulated volume around horizontal wells from the instant of completion through early production. To describe the continued evolution of the producing volume, we define producing volume half-lengths at 2, 6, 8, and 12 months. Armed with measurements of half-length stabilization in the early months of production, we confidently define the upper limit of well spacing for future development. Although we cannot yet define economically optimal overlap between producing volumes, this upper limit allows operating groups to set the correct length scale for future investigations.
Results from our pressure communication studies are compatible with other methods of greater uncertainty, longer timelines, and higher cost. Traced fluid and proppant, microseismic events, and frac hits represent stimulation that may not relate to long term productivity. Pressure communication between stimulated wellbores defines the capability of the stimulation to maintain permeability at the test production time step. However, these other measurements do help bound the evolution of stimulated reservoir volumes in a manner compatible with our pressure communication results.