SPE 140507
Hydraulic Fracturing, Microseismic Magni
tudes, and Stress Evolution in the
Barnett Shale, Texas, USA
John P. Vermylen, SPE, and Mark D. Zoback, SPE, Stanford University
Copyright 2011, Society of Petroleum Engineers
This paper was prepared for presentation at the SPE Hydraulic Fracturing Technology Conference and Exhibition held in The Woodl
ands, Texas, USA, 24–26 January 2011.
This paper was selected for presentation by an SPE program committee following review of information contained in an abstract s
ubmitted by the author(s). Contents of the paper have not been
reviewed by the Society of Petroleum Engineers and are subject to
correction by the author(s). The material does not necessaril
y reflect any position of the Society of Petroleum Engineers, its
officers, or members. Electronic reproduction, distribution, or st
orage of any part of this paper without the written consent o
f the Society of Petroleum Engineers is prohibited. Permission to
reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must
contain conspicuous acknowledgment of SPE copyright.
Abstract
We present new techniques to analyze th
e effectiveness of hydraulic fracturing for stimulating production in shale gas
reservoirs. The case study we have analyzed
involves five parallel horizontal wells in the Barnett shale with 51 frac stages.
To investigate the numbers, sizes and types of microearthqu
akes initiated during each frac stage, we created Gutenberg-
Richter-type magnitude distribution plots to see if the size of
events follows the characteristic scaling relationship found in
natural earthquakes. We found that slickwater fracturing does generate a log-linear distribution of microearthquakes, but that
it creates proportionally more small events than natural earthqua
ke sources. Finding considerable variability in the generation
of microearthquakes, we have used the magn
itude analysis as a proxy for the “robustness” of the stimulation of a given stage.
We have found that the conventionally fractured well and the
two alternately fractured wells (“zipperfracs”) were more
effective than the simultaneously fractured wells
(“simulfracs”) in generating microearthquakes.
We also found that the later stages of
fracturing a given well were more successful in generating microearthquakes than
the early stages. This increase
in microearthquake activity in the latter frac st
ages correspond
ed with an in
crease in the
instantaneous shut-in pressure (ISIP). The net ISIP incr
ease was most pronounced in the simulfrac wells and least
pronounced in the zipperfrac wells. We have attempted to m
odel this increase as a cumulative “stress shadow” using an
elastic crack-opening model. However, even the maximum reason
able propped fracture aperture causes a stress increase that
is less than what was measured in the wells. Since the fractur
ing of the simulfrac wells took only half the time of the
fracturing of the zipperfrac wells, we believ
e that poroelastic effects associated w
ith time-dependent leak-off is controlling
the rate of ISIP escalation and the increas
e in microseismic creation. We are incor
porating poroelasticity in the model to full
y
integrate stress evolution and permeable volume creation.
