Stable Isotope Geochemistry Helps in Reducing out-of-zone Hydraulic Fracturing … ·...
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Stable Isotope Geochemistry Helps in Reducing out-of-zone Hydraulic Fracturing and Unwanted Brine Production from the Bakken Reservoir S. Arkadakskiy and B. Rostron Isobrine Solutions Inc., University of Alberta
Transcript of Stable Isotope Geochemistry Helps in Reducing out-of-zone Hydraulic Fracturing … ·...
Stable Isotope Geochemistry Helps in Reducing out-of-zone Hydraulic Fracturing and Unwanted Brine Production from the Bakken Reservoir
S. Arkadakskiy and B. RostronIsobrine Solutions Inc., University of Alberta
Introduction/Outline
o The Bakken Formation: a Unique Reservoir
o Hydraulic fracturing in the Bakken: the Evolution
o Stable Isotope Geochemistry
o Case studies
o Conclusions
The Bakken Formation: a unique reservoir
o Location: The Williston Basin of USA and Canada (part of the Western Canada Sedimentary Basin)
o Aerial extent: 520 000 km2
o Lithology: a thin (ca. 13 metres) dolomitic silt/sandstone sandwiched between two organic-rich shales (10 % TOC)
o Age: Late Devonian to Early Mississippiano Total oil in place: 300-500 billion bbl, ca. 40 APIo Reservoir: 0.01 to 1.0 md; over-pressurized, H2O <Sw
in US, normal P, >Sw in Canadao Recoverable oil: 3.0 to 24 billion bbl (hydraulic
fracturing)o Current production: >600,000 bbl/d and increasing
Williston Basin and the Bakken Fm.
BAKKEN FM
Hydrogeology of the Williston Basin(Cross-section A-A’)
TertiaryCretaceousJurassicMississippianDevonianSilurianOrdovician and Cambrian
rechargedischarge
BAKKEN
Hydraulic Fracturing in the Bakken: the Evolution
After ConocoPhilips, 2010
SERIOUS PROBLEM: Excessive water production o What is the source of co-produced water?
• Flowback water (drilling/fracturing fluid)• Natural water in the reservoir (water leg, in-zone water)• External water from nearby water-rich zones via natural or
man-made fracturing
Stable Isotope Geochemistry Stable isotope systems (2H, 18O, 13C, 37Cl, 81Br, 34S, 87Sr/86Sr)
Halogen tracers (total Cl, Br and I concentrations) measured with a novel methods (INAA and ENAA) at the SLOWPOKE nuclear reactor (University of Alberta).
A proprietary database of 4,500+ samples in western Canada and the USA (a large number of these from the Bakken)
A note: 2H and 18O provided the background for understanding the nature and origin of formation waters/brines (i.e., Epstain and Mayeda, 1956; Clayton et al. (1966); (Kharaka and Carothers, 1986; Knauth and Beeunas, 1986; Sheppard, 1986; Hanor,1987; Longstaffe, 1989, etc.). The oil industry has been rather slow in applying stable isotope geochemistry
After Rostron and Holmden, 2000
o Well type/status: Most wells vertical, fractured, a few non-fractured
o Water/brine co-production: from 0 to 30 % (wct.)
o Potential aqueous fluid sources:• Bakken formation-brine (reservoir water)• Flowback water (drilling/frac fluid, local surface
water)• Mississippian (Lodgepole) formation-water• Three Forks (Birdbear/Nisku) formation-water
Case Study 1: 36 Bakken wells
Case Study 1: 36 Bakken wells2
H (‰
, VSM
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18O (‰, VSMOW)
Local Meteoric Water Line
Average LocalPrecipitation
(drilling/frac fluids)
Mississippian (Lodgepole)
Bakken
Case Study 1: 36 Bakken wells2
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Local Meteoric Water Line
Average LocalPrecipitation
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Mississippian (Lodgepole)
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Bakken
“Contour” map of the amount (%) of external (Mississippian/LodgepoleFormation) water in the co-produced aqueous fluid
Case Study 1: 36 Bakken wells
o Results - all wells:o External water present: 89 % of sampleso Volume: 6 to 40 % vol., average:15 % (n=36) o Source: 100 % Mississippian (Lodgepole) formation-
water origin
o Outcome: o Data was used successfully in a mathematical
model to prepare area for a pilot secondary oil recovery project
o Study prompted an increase of the number of new horizontal wells in the area
Case Study 1: 36 Bakken wells
Case Study 2: a Larger Area
Sampling: 2006 - present Number of samples: 1,126 Number of wells: 587
Horizontal wells: 297Vertical wells: 290
Number of wells sampled more than twice (time series): 153
Percentage of all wells stimulated: >90%
Case Study 2: a Larger Area
o Results from all wells:• Flowback fluid (surface water): 95 wells or 9 % (removed from further
calculations) Mostly wells that have produced less than 200 % of the volume of drilling/fracturing fluid
• External fluid: 61 % of all wells• Volume: from 10 to 100% (average 34 %, n = 358)• Origin of fluid: 100 % Mississippian (Lodgepole Fm.), only 6 wells
contain Nisku/Birdbear Fm. formation-brine
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Case Study 2: a Larger Area
o Vertical wells:• 56 % of all verticals contain 10% of more external fluid• Average: 34 % (n=156)
o Horizontal wells: • 68 % of Hz contain 10% or more external fluid• Average: 33 % (n=202)
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Case Study 2: a Larger Area
o Outcome: Results from the (ongoing) study coincided with several measures taken by Client in order to minimize water production
• Changes in the position of the horizontal wells with respect to the Bakken/Mississippian contact
• Decrease of the size of individual fracs• Increase of the number of individual fracs per well• In June 2012 Client has initiated a comprehensive
study to further integrate geochemical data in their exploration and production activities
Case Study 2: a Larger Area
Case Study 3: Geochemistry and Geophysics
o Client: PetroBakken Energy Ltd. o Problem: Excessive water production in fractured horizontal wells
from the Viewfield Bakken Oil Field, Saskatchewan. Wells fractured at regular 75 m intervals.
o Step 1: Isobrine Solutions identified a significant percentage of external water (Nisku/Birdbear Fm.) in these wells
o Step 2: Seismic data “dip mapping” established structural anomalies of “salt” collapsing in the deeper Palaeozoic sediments and identified zones of natural fracturing near the wells
o Step 3: Well bore microseismic imaging also confirmed open fractures proximal to the fractured intervals in one of the wells
o Solution: A new well was completed with hydraulic fracturing spaced at predetermined intervals that avoid proximity to detected natural fractures.
Well A - Hydraulic fractures every 75m. Well B - Hydraulic fractures away from the natural fractures
Initial production - 280bbls/dayAverage prod. 30 - 165bbls/day &45 % WCProduction at 90 - 40bbls/day & 80 % WC
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Initial production - 280bbls/dayAverage prod. 30 - 200bbls/day & 35% WCProduction at 90 - 100bbls/day & 40 % WC
Case Study 3: Geochemistry and Geophysics
Conclusionso Stable isotope geochemistry along with other tools has been
used to identify different aqueous fluids in co-produced waters/brines from hydraulically fractured horizontal wells in the Bakken Formation
o Presence of significant quantities of external fluid from nearby water-rich zones is established in a great number of water/brine samples (e.g., >60 %)
o Fracture propagation outside the thin (!) Bakken zone is a rather common phenomenon and may contribute to excessive water co-production
o Companies aware of the above have been applying corrections to the size, number and/or distribution of hydraulic fracturing sites along the well bores of new wells in order to optimize production
