American Oil and Gas Reporter - July 2015 - 79

SpecialReport: New Products/Technology

Study Measures Marcellus Frac Results
By Thomas H. Wilson,
Ariel K. Hart
and Peter A. Sullivan

MORGANTOWN, W.V.-A study conducted by Energy Corporation of America
(ECA) and West Virginia University examined the distributions of microseismic
events associated with zippered hydraulic
fracture treatments of six Marcellus Shale
wells on a multiwell pad in Greene Co.,
Pa.
Numerous events produced during the
treatment of one well were located close
to events produced while treating nearby
wells. The distribution of these proximal
cross-well microseismic events is interpreted to represent areas of overlapping
stimulation or repeated stimulation. Proximal cross-well microseismicity also is a
possible indicator of critically stressed
strata (strata close to failure) that may be
prone to rupture in response to small
pressure disturbances produced by fluid
injection in strata undergoing hydraulic
fracture treatment.
For clarification, proximal cross-well
microseismic events are events produced
by the treatment of a stage along one
lateral that are located close to events
produced during the treatment of stages
in adjacent laterals. Cross-well events
are used to distinguish proximal events
from cross-stage events that could be
produced along the length of a single lateral. Using these data to identify fracture
propagation out of the target zone or in
areas of the reservoir already stimulated
by previous stages may allow operators
to adjust stimulation parameters stageby-stage to minimize refracturing of the
same reservoir volume while keeping
fractures in zone.
The analysis was restricted to events
located within 75 feet of one another
that were produced by treatments of different wells. Such proximal microseismic
event clusters were observed both in the
targeted Marcellus Shale reservoir interval
and, out of zone, several hundred feet
above the reservoir. Many of the events
located in out-of-zone clusters were proximal.
ECA provided the 3-D seismic, microseismic and well data used in the
study. Schlumberger Petrel™ and IHS
Kingdom Suite™ software supported the
analyses. The research was funded through

the Houston Advanced Research Center's
Environmentally Friendly Drilling Program as part of the Research Partnership
to Secure Energy for America.
The Marcellus is located at an approximate depth of 8,200 feet in this part
of Greene County. The geologic structures
across the region consist of low-amplitude,
first- and second-order anticlines, and
synclines consistent with the area's position within the Appalachian Basin.
Remnant tectonic stress associated
with the deformation of strata overlying
the Marcellus Shale may produce local
distributions of critically stressed strata.
Inflation of reservoir intervals produced
by fluid injection during stimulation may
lead to rupture in surrounding areas without the aid of direct fluid interconnection.
The energy released through proximal
cross-well ruptures can be computed directly from microseismic data.
The six horizontal wells were completed using a zippered approach to hydraulic fracture treatment. In this approach,
the treatment of individual stages moves

across the pad to frac the same stage in
adjacent wells working from toe to heel.
The evaluation did not include an analysis
of waveforms, but examined the distributions of events located near one another
to define areas of overlap between well
treatments.
Because in-zone proximal cross-well
events represent the areas of overlap in
the stimulated reservoir volume, determining the ratio of energy released by
proximal events during fracture treatment
to the total energy released during treatment
provides a quantitative measure of overlapping stimulation. These events could
result from a combination of additional
stimulation or restimulation. If the events
result from stimulating additional rock
volume, then additional reservoir is being
opened for production. If these events
are simply reopening the same fractures,
then treatment efficiency is reduced.
Depth-Converted Seismic
Depth-converted 3-D seismic data
were used to provide the subsurface strati-

FIGURE 1
Marcellus Well Locations and Depth-Converted Amplitude

JULY 2015 79

American Oil and Gas Reporter - July 2015

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