What Actually Controls SRV? Three Concepts to Debate a Stimulation or Stimulate a Debate!

摘要

It is generally believed that creating a Stimulated Rock Volume (SRV) is a good thing. Completion engineers talk about creating complexity, geologists talk about stimulating a natural fracture network, geomechanicists highlight the importance of low stress anisotropy. But how much do these concepts matter and can we actually do anything about them, or do we get what we're given? A review of producing formations from plays across North America shows that there are three primary types of sub-surface heterogeneity at the length-scale of a well-bore that should be considered together as controls on SRV: natural fractures, bedding (layering) anisotropy and stress changes. Typically bedding and stress variability are over-looked as SRV controls. The impact of each form of heterogeneity on SRV depends more on the magnitude of the change rather than the existence of the heterogeneity within the rock. Natural fractures may contribute to a SRV where there is a geometrically-connected network in the presence of low horizontal stress anisotropy, however the contribution would be mostly unpropped conductivity. A low horizontal stress anisotropy alone, without natural fractures, is not likely to enhance a SRV because the most stress-anisotropic lithology may not be the optimal landing zone for a lateral. Bedding anisotropy (e.g. fine-scale layering, or laminations) and vertical stress changes can be the source of fracture initiation and propagation problems, and may cause an 'apparent SRV' in some plays, when treating pressure is close to, but not necessarily exceeding overburden. After a critical assessment of each control, in the form of a debate, it is concluded that if a rock has the potential for a SRV to be generated, as indicated from microseismic, then; a) not every type of complexity necessarily creates value, b) it is difficult to optimize the conductivity within an SRV, and c) it is possible to severely limit the SRV potential of a rock by not accounting for the three main sub-surface controls, together.