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
OW
)
18O (‰, VSMOW)
Local Meteoric Water Line
Average LocalPrecipitation
(drilling/frac fluids)
Mississippian (Lodgepole)
Bakken
Case Study 1: 36 Bakken wells2
H (‰
, VSM
OW
)
18O (‰, VSMOW)
Local Meteoric Water Line
Average LocalPrecipitation
(drilling/frac fluids)
Mississippian (Lodgepole)
90 %
70 %
80 %
40 %
50 %
60 %
10 %
20 %
30 %
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
0
50
100
150
200
250
0 10 20 30 40 50 60 70 80 90 100 More
Num
ber o
f sam
ples
External water (%)
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)
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100 More0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100 More
Num
ber o
f sam
ples
External water (%) External water (%)
Vertical wells Horizontal wells
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
WELL A WELL B
10
1000
100
10
1 0
20
40
30
50
60
70
80
90
100
10
30 60 90 120 150 180 210 240 270300
1
10
100
1000
0
20
40
30
50
60
70
80
90
100
30 60 90 120 150 180 210 240 270300
0
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
