[PPT] - Stable Isotope Geochemistry Helps in Reducing out-of-zone Hydraulic PowerPoint Presentation

SLIDE 1

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

SLIDE 2

Introduction/Outline

The Bakken Formation: a Unique Reservoir
Hydraulic fracturing in the Bakken: the Evolution
Stable Isotope Geochemistry
Case studies
Conclusions

SLIDE 3

The Bakken Formation: a unique reservoir

Location: The Williston Basin of USA and Canada (part
f the Western Canada Sedimentary Basin)
Aerial extent: 520 000 km2
Lithology: a thin (ca. 13 metres) dolomitic silt/sandstone

sandwiched between two organic-rich shales (10 % TOC)

Age: Late Devonian to Early Mississippian
Total oil in place: 300-500 billion bbl, ca. 40 API
Reservoir: 0.01 to 1.0 md; over-pressurized, H2O <Sw

in US, normal P, >Sw in Canada

Recoverable oil: 3.0 to 24 billion bbl (hydraulic

fracturing)

Current production: >600,000 bbl/d and increasing

SLIDE 4

Williston Basin and the Bakken Fm.

BAKKEN FM

SLIDE 5

SLIDE 6

Hydrogeology of the Williston Basin (Cross-section A-A’)

Tertiary Cretaceous Jurassic Mississippia n Devonian Silurian Ordovician and Cambrian

recharge discharge

BAKKEN

SLIDE 7

Hydraulic Fracturing in the Bakken: the Evolution

After ConocoPhilips, 2010

SLIDE 8

SERIOUS PROBLEM: Excessive water production

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

SLIDE 9

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

SLIDE 10

After Rostron and Holmden, 2000

SLIDE 11

Well type/status: Most wells vertical, fractured, a few

non-fractured

Water/brine co-production: from 0 to 30 % (wct.)
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

SLIDE 12

Case Study 1: 36 Bakken wells

2H (‰, VSMOW) 18O (‰, VSMOW)

Local Meteoric Water Line

Average Local Precipitation (drilling/frac fluids)

Mississippian (Lodgepole) Bakken

SLIDE 13

Case Study 1: 36 Bakken wells

2H (‰, VSMOW) 18O (‰, VSMOW)

Local Meteoric Water Line

Average Local Precipitation (drilling/frac fluids)

Mississippian (Lodgepole)

90 % 70 % 80 % 40 % 50 % 60 % 10 % 20 % 30 %

Bakken

SLIDE 14

“Contour” map of the amount (%) of external (Mississippian/Lodgepole Formation) water in the co-produced aqueous fluid

Case Study 1: 36 Bakken wells

SLIDE 15

Results - all wells:
External water present: 89 % of samples
Volume: 6 to 40 % vol., average:15 % (n=36)
Source: 100 % Mississippian (Lodgepole) formation-

water origin

Outcome:
Data was used successfully in a mathematical

model to prepare area for a pilot secondary oil recovery project

Study prompted an increase of the number of new

horizontal wells in the area

Case Study 1: 36 Bakken wells

SLIDE 16

Case Study 2: a Larger Area

 Sampling: 2006 - present  Number of samples: 1,126  Number of wells: 587

Horizontal wells: 297 Vertical wells: 290

 Number of wells sampled more than twice (time

series): 153

 Percentage of all wells stimulated: >90%

SLIDE 17

Case Study 2: a Larger Area

SLIDE 18

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

50 100 150 200 250 10 20 30 40 50 60 70 80 90 100 More

Number of samples External water (%)

Case Study 2: a Larger Area

SLIDE 19

Vertical wells:
56 % of all verticals contain 10% of more external fluid
Average: 34 % (n=156)
Horizontal wells:
68 % of Hz contain 10% or more external fluid
Average: 33 % (n=202)

10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 More 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 More

Number of samples External water (%) External water (%) Vertical wells Horizontal wells

Case Study 2: a Larger Area

SLIDE 20

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

SLIDE 21

Case Study 3: Geochemistry and Geophysics

Client: PetroBakken Energy Ltd.
Problem: Excessive water production in fractured horizontal wells

from the Viewfield Bakken Oil Field, Saskatchewan. Wells fractured at regular 75 m intervals.

Step 1: Isobrine Solutions identified a significant percentage of

external water (Nisku/Birdbear Fm.) in these wells

Step 2: Seismic data “dip mapping” established structural anomalies
f “salt” collapsing in the deeper Palaeozoic sediments and

identified zones of natural fracturing near the wells

Step 3: Well bore microseismic imaging also confirmed open

fractures proximal to the fractured intervals in one of the wells

Solution: A new well was completed with hydraulic fracturing

spaced at predetermined intervals that avoid proximity to detected natural fractures.

SLIDE 22

Well A - Hydraulic fractures every 75m. Well B - Hydraulic fractures away from the natural fractures

Initial production - 280bbls/day Average prod. 30 - 165bbls/day &45 % WC Production at 90 - 40bbls/day & 80 % WC

WELL A WELL B

1 1000 100 10 1 2 40 3 50 60 70 80 90 100 1 30 60 90 120 150 180 210 240 270 300 1 1 100 1000 2 40 3 50 60 70 80 90 100 30 60 90 120 150 180 210 240 270 300

Initial production - 280bbls/day Average prod. 30 - 200bbls/day & 35% WC Production at 90 - 100bbls/day & 40 % WC

Case Study 3: Geochemistry and Geophysics

SLIDE 23

Conclusions

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

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 %)

Fracture propagation outside the thin (!) Bakken zone is a

rather common phenomenon and may contribute to excessive water co-production

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

rder to optimize production