| dc.description.abstract | Hydraulic fracturing is the primary stimulation method within low permeability
reservoirs, in particular shale reservoirs. Hydraulic fracturing provides a means for
making shale reservoirs commercially viable by inducing and propping fracture
networks allowing gas flow to the wellbore. Without a propping agent, the created
fracture channels would close due to the in-situ stress and defeat the purpose of creating
induced fractures. The fracture network conductivity is directly related to the well
productivity; therefore, the oil and gas industry is currently trying to better understand
what impacts fracture conductivity.
Shale is a broad term for a fine-grained, detrital rock, composed of silts and
clays, which often suggest laminar, fissile structure. This work investigates the
difference between two vertical zones in the Fayetteville shale, the FL2 and FL3, by
measuring laboratory fracture conductivity along an artificially induced, rough, aligned
fracture. Unpropped and low concentration 30/70 mesh proppant experiments were run
on samples from both zones. Parameters that were controllable, such as proppant size,
concentration and type, were kept consistent between the two zones. In addition to
comparing experimental fracture conductivity results, mineral composition, thin
sections, and surface roughness scans were evaluated to distinguish differences between
the two zones rock properties. To further identify differences between the two zones,
90-day production data was analyzed.
The FL2 consistently recorded higher conductivity values than the FL3 at closure
stress up to 3,000 psi. The mineral composition analysis of the FL2 and FL3 samples
concluded that although the zones had similar clay content, the FL2 contained more
quartz and the FL3 contained more carbonate. Additionally, the FL2 samples were less
fissile and had larger surface fragments created along the fracture surface; whereas the
FL3 samples had flaky, brittle surface fragments. The FL2 had higher conductivity
values at closure stresses up to 3,000 psi due to the rearrangement of bulky surface
fragments and larger void spaces created when fragments were removed from the
fracture surface.
The conductivity difference between the zones decreases by 25% when low
concentration, 0.03 lb/ft^(2), 30/70 mesh proppant is placed evenly on the fracture surface.
The conductivity difference decrease is less drastic, changing only 7%, when increase
the proppant concentration to 0.1 lb/ft^(2) 30/70 mesh proppant. In conclusion, size and
brittleness of surface fracture particles significantly impacts the unpropped and low
concentration fracture conductivity. | en |
