Page 293 - Introduction to Petroleum Engineering

PERFORMANCE OF AN UNCONVENTIONAL RESERVOIR 281

Fort Worth Basin
North South

Montague Comanche San saba Gillespie

County Wise Parker Hood Erath Mills Llano
Cretaceous
Cisco
Barnett
Canyon
outcrops
Strawn
Lower
Penn. Llano uplift
Barnett
Muenster Ellenberger
Arch

FIgURE 14.7 Cross section of the Fort Worth Basin.

was named the Barnett Shale. The Barnett Shale outcrop in San Saba County is
shown in Figure 14.7.
The Barnett Shale is part of the Fort Worth Basin. The shale is a very low perme‑
ability mud rock that is several hundred feet thick at depths of 5000–8000 ft.
Commercial quantities of gas are being produced from the shale in several north
central Texas counties (Figure 14.8). Production was not economically feasible until
Mitchell Energy and Development Company (MEDC), led by George P. Mitchell,
combined directional drilling and hydraulic fracturing (Steward, 2013).
MEDC drilled the discovery well for the Newark East Field in the Barnett Shale in
1981. Vertical wells drilled and completed in the shale produce gas at relatively low
flow rates because shale permeability can be as small as 0.01 md to 0.00001 md in
unfractured shale (Arthur et al., 2009). By 1986, MEDC had shown that shale gas
production depended on establishing a large pressure difference between shale matrix
and fractures and the amount of source rock contacted by induced fractures. The use
of hydraulic fracturing in the completion process was the first major technological
breakthrough to increase flow rate. Hydraulic fracturing in a vertical well tends to cre‑
ate horizontal fractures and increases shale gas production rate. Directional drilling of
horizontal wells was the second major technological breakthrough to increase flow
rate. A horizontal test well was drilled in the Barnett Shale in 1981 by MEDC and the
Gas Research Institute (GRI). GRI administered research funding provided by a sur‑
charge on natural gas shipments through interstate pipelines. Directional drilling
made it possible to drill and complete thousands of feet of shale. Hydraulic fracturing
along segments of the horizontal well created vertical fractures in the shale. The
combination of directional drilling and hydraulic fracturing resulted in commercial
shale gas production rates. MEDC merged with Devon Energy in 2002.