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

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

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 km 2 o Lithology: a thin (ca. 13 metres) dolomitic silt/sandstone sandwiched between two organic-rich shales (10 % TOC) o Age: Late Devonian to Early Mississippian o Total oil in place: 300-500 billion bbl, ca. 40 API o Reservoir: 0.01 to 1.0 md; over-pressurized, H 2 O < Sw in US, normal P, > Sw in Canada o 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’) recharge discharge Tertiary Cretaceous Jurassic Mississippia n Devonian Silurian BAKKEN Ordovician and Cambrian

After ConocoPhilips, 2010 Hydraulic Fracturing in the Bakken: the Evolution

SERIOUS PROBLEM: Excessive water production What is the source of co-produced water? o • 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 (  2 H,  18 O,  13 C,  37 Cl,  81 Br,  34 S, 87 Sr/ 86 Sr)  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:  2 H and  18 O 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

Case Study 1: 36 Bakken wells 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 Local Meteoric Water Line Bakken  2 H (‰, VSMOW) Average Local Precipitation (drilling/frac fluids) Mississippian (Lodgepole)  18 O (‰, VSMOW)

Case Study 1: 36 Bakken wells Local Meteoric Water Line Bakken 10 % 20 %  2 H (‰, VSMOW) 30 % 40 % 50 % Average Local Precipitation 60 % (drilling/frac fluids) 70 % 80 % 90 % Mississippian (Lodgepole)  18 O (‰, VSMOW)

Case Study 1: 36 Bakken wells “Contour” map of the amount (%) of external (Mississippian/Lodgepole Formation) water in the co-produced aqueous fluid

Case Study 1: 36 Bakken wells o Results - all wells: o External water present: 89 % of samples o 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 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%

Case Study 2: a Larger Area

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 250 200 Number of samples 150 100 50 0 0 10 20 30 40 50 60 70 80 90 100 More External water (%)

Case Study 2: a Larger Area Vertical wells: o 56 % of all verticals contain 10% of more external fluid • Average: 34 % (n = 156) • Horizontal wells: o 68 % of Hz contain 10% or more external fluid • Average: 33 % (n = 202) • 100 100 Horizontal wells Vertical wells 90 90 80 80 Number of samples 70 70 60 60 50 50 40 40 30 30 20 20 10 10 0 0 0 10 20 30 40 50 60 70 80 90 100 More 0 10 20 30 40 50 60 70 80 90 100 More External water (%) External water (%)

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 3: Geochemistry and Geophysics Client: PetroBakken Energy Ltd. o Problem: Excessive water production in fractured horizontal wells o from the Viewfield Bakken Oil Field, Saskatchewan. Wells fractured at regular 75 m intervals. Step 1: Isobrine Solutions identified a significant percentage of o external water (Nisku/Birdbear Fm.) in these wells Step 2: Seismic data “dip mapping” established structural anomalies o of “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 o fractures proximal to the fractured intervals in one of the wells Solution: A new well was completed with hydraulic fracturing o spaced at predetermined intervals that avoid proximity to detected natural fractures.

Case Study 3: Geochemistry and Geophysics WELL A WELL B 100 1000 100 1000 90 90 80 80 100 70 70 100 60 60 50 50 40 40 1 3 10 0 3 0 0 2 2 0 0 1 1 0 0 0 1 1 0 0 30 60 90 120 150 180 210 240 270 30 60 90 120 150 180 210 240 270 300 300 Well B - Hydraulic fractures away from the natural Well A - Hydraulic fractures every 75m. fractures Initial production - 280bbls/day Initial production - 280bbls/day Average prod. 30 - 165bbls/day &45 % WC Average prod. 30 - 200bbls/day & 35% WC Production at 90 - 40bbls/day & 80 % WC Production at 90 - 100bbls/day & 40 % WC

Conclusions o 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