Fracture and Pore Network Connectivity in Shales Related to Increased Hydrocarbon Production
Intrinsic shale anisotropy and the inhibition of vertical migration through shales is a well-known fact to geologists both in and out of the industry. What proves more difficult when producing these assets is that the pore network lacks a high degree of connectivity, which would promote fluid migration. A previous worker found very low effective porosity values—laboratory samples show porosity is only accessible near the edges of shale cubes—in areas, including the Barnett Shale, believed to be the product of low permeability caused by the aforementioned disconnected pore network. With pore connectivity inherently poor in shales, optimizing a reservoir's permeability, and therefore diffusion radius and reservoir efficiency, relies on inducing connectivity through the fracture network. Specifically, whether the induced fractures promote or discourage further pore-fracture connectivity. This knowledge gap has direct influences on production within shale reservoirs. Another previous worker described his troubles in network connectivity indirectly through the inability to increase fracture height across shale bedding planes.
Further investigation requires a dual, comprehensive look at petrophysical properties governing fluid migration and geomechanics to optimize hydrocarbon extraction. Improving the network's connectivity (natural/induced fractures with nano-pores) requires the stress manipulation around the well taking many factors in account. These factors include taking situ stresses (surrounding wells' influences on local stresses), rock heterogeneity, fracking fluid viscosity and production- driven depletion (and its subsequent effects on effective stresses). The extent of fracture growth and fracture spacing, as well as their influences on the diffusive capabilities of assets by increasing the permeability, is the target of study.
AAPG Datapages/Search and Discovery Article #90219 © 2015 GCAGS, Houston, Texas, September 20-22, 2015