attachment 8 mini-frac report for suncor lewis f1/06-27-092 … · 2019-02-14 · suncor lewis...

$: Attachment 8 Mini-Frac Report for Suncor Lewis F1/06-27-092 … · 2019-02-14 · SUNCOR LEWIS 6‐27‐92‐8 Minifrac Interpretation Page 3 of 9 In a minifrac test, the in situ$
Attachment 8

Mini-Frac Report for Suncor Lewis F1/06-27-092-08W4M


OverviewThe SUNCOR LEWIS 6‐27‐92‐8 Well (UWI F1/06‐27‐092‐08W4/0, Licence # 0473316) was tested by mini‐

frac stimulation to establish closure pressure for caprock integrity purposes. In the Lewis area, the

McMurray Formation is overlain by the Wabiskaw A and the Lower Clearwater, which serves as the

caprock for many SAGD operations within the Athabasca. One metre intervals were tested within each of:

1. the McMurray Formation sand

2. the Wabiskaw A silt

3. the Lower Clearwater shale

The McMurray interval was tested by mini‐frac test for four frac/falloff cycles starting on Jan 13th, 2015.

The detailed analysis is contained in the “McMurray Interval” section of this report. The interpreted

fracture closure gradients ranged from 16.9kPag/m to 18.7kPag/m compared to a calculated overburden

gradient of 21.0kPag/m. The lower mini‐frac gradient is an indication that the minimum in‐situ stress is

not in the vertical direction and that the fracture is vertical.

The Wabiskaw A interval was tested by mini‐frac test for two frac/falloff cycles and one frac/flowback

cycle starting on Jan 14th, 2015. The detailed analysis is contained in the “Wabiskaw A Interval” section of

this report. The interpreted fracture closure gradients of the frac/falloff tests ranged from 21.5kPag/m to

22.6kPag/m compared to a calculated overburden gradient of 21.0kPag/m. The consistency between the

two gradients suggests that the minimum in‐situ stress is vertical and the fracture is horizontal.

The Clearwater shale interval was tested by mini‐frac test for two frac/falloff cycles and one frac/flowback

cycle starting on Jan 17th, 2015. The detailed analysis is contained in the “Lower Clearwater Interval”

section of this report. The interpreted fracture closure gradients of the frac/falloff tests ranged from

21.8kPag/m to 22.3kPag/m compared to a calculated overburden gradient of 21.0kPag/m. The

consistency between the two gradients suggests that the minimum in‐situ stress is vertical and the

fracture is horizontal.

SUNCOR LEWIS 6‐27‐92‐8 Minifrac Interpretation Page 2 of 9

Figure 1: Well Logs, Vertical Stress and Minifrac Closure Pressure

McMurray Wabiskaw Clearwater

Test Depth mGL 122.3 99.6 91.3

Minifrac Closure Stress Mean kPag 2216 2187 2012

Minimum kPag 2061 2143 1993

Minifrac Closure Gradient

Mean kPag/m 18.12 21.96 22.04

Minimum kPag/m 16.85 21.52 21.82

Standard Deviation kPag/m 0.86 0.55 0.23

Standard Deviation/Mean % 4.8% 2.5% 1.1%

Vertical Stress

Stress kPag 2568 2093 1913

Gradient kPag/m 21.00 21.01 20.96

Closure Relative Error % ‐13.7% 4.5% 5.2%

Fracture Orientation Vert Hz Hz

Table 1: Analysis Summary


In a minifrac test, the in situ failure conditions are created and the pressure required to propagate

fractures can be measured. The pressure where fractures start to close is the basis for safe SAGD operating

pressure since this is the minimum pressure required to open a pre‐existing fracture. This represents the

case where there are existing natural fractures or that the higher formation breakdown pressure has been

exceeded. A safety factor, typically 0.8, is also applied in the determination of safe operating pressure.

The method used to interpret the minifrac data are based on flow regime recognition described in SPE

Paper 157843 titled The Use of Pressure Transient Analysis Tools to Interpret Mini‐Frac Data in Alberta

Oilsands Caprocks.

Tight zones like the Lower Clearwater shale and Wabiskaw A silt show signature Bourdet and Mattar

derivative responses to closure on the Log‐Log plot. The Bourdet derivative has a 3/2 slope and the Mattar

derivative is horizontal (zero slope). The derivative responses are consistent for no‐flow and flowback

falloffs. All of the Clearwater and Wabiskaw minifracs responded in this manner.

For zones with more permeability, like the McMurray, pressure leaks off rapidly and the closure

dominated pressure regime (i.e. 3/2 Bourdet slope or zero Mattar slope) is not seen in the log‐log plot.

Closure occurs simultaneously with fracture flow dominated pressure response (1/2 slope). When the

transient is beyond the fracture, it must be fully closed. Therefore, start of closure is almost simultaneous

with the start of fracture flow.


McMurrayIntervalThe McMurray interval was tested by minifrac test for four frac/falloff cycles starting on Jan 13th, 2015.

The test was analyzed in the Calgary office in near real‐time to help direct field operations, final

interpretation occurred after field operations were complete. The interpreted fracture closure gradients

ranged from 16.85kPag/m to 18.74kPag/m for the four falloff cycles. This document uses the interpreted

start of closure as the appropriate measure for determining fracture gradient (see overview). The

perforation interval was 124.0‐125.0mKB, the downhole gauge landing depth was 126.0mKB and the

difference between ground level and Kelly bushing is 2.2m, resulting in MPP depth of 122.3mGL (below

ground level).

Pressures were recorded at the pump outlet, the wellhead and downhole, all at 1 second intervals. The

pressure input data for Ecrin was created by shifting the downhole gauge data by 2kPa so that the surface

readings before running the gauge were 0kPa. Pressure was then reduced by 15kPa to translate the

pressure up 1.5m from gauge depth to mid‐point of perforations (MPP) using a water gradient. The data

was loaded into Ecrin in absolute (kPaa) units assuming a local gauge to absolute pressure adjustment of

93kPa, however, the fracture gradients and pressure quoted in this document are in kPag. The depth from

ground level to MPP was used to calculate the fracture gradient.

Figure 2: McMurray Interval Tests

The following naming convention was used to denote test information:

1. Type of test: falloff (FO) or flowback (FB)

2. Type of pick: start of closure (SOC) or end of closure (EOC)


Here are the results of the four falloff cycles in the McMurray interval:

Cycle # Type of Test Injection Rate Injection Duration Breakdown SOC EOC Closure Gradient

FO/FB L/min mins kPag kPag kPag kPag/m

1 FO 50 10 6927 2271 1481 18.57

2 FO 50 10 3734 2292 1566 18.74

3 FO 50 10 2994 2241 1567 18.32

4 FO 70 10 2677 2061 1482 16.85

Table 2: McMurray Interval Minifrac Interpretation

The method used to interpret the minifrac data are based on flow regime recognition described in SPE

Paper 157843. The minifrac induced fractures close quickly in the McMurray due to higher permeability.

The fracture closure is not the dominant pressure regime in these tests and the diagnostic fracture closure

(3/2 derivative slope) is not seen. The signature ½ Bourdet derivative slope on the Log‐Log plot is seen on

all tests suggesting that the fracture is a vertical infinite conductivity fracture which is consistent with a

fracture stimulation. An overburden stress gradient was calculated by aggregating the surface bulk density

log from a well at 10‐27‐92‐8w4 with the main hole (below surface casing) bulk density log in the minifrac

well at 6‐27‐92‐8w4, resulting in 21.0 kPag/m. The average McMurray minifrac gradient was 18.12kPag/m

(lowest calculated gradient 16.85kPag/m). Closure gradient is less than overburden for all cycles and also

less than the Wabiskaw and Clearwater gradients. The geomechanical picks are made directly from the

diagnostic plots and are independent of the formation characteristics.


WabiskawAIntervalThe Wabiskaw A interval was tested by minifrac test for two frac/falloff cycles and one frac/flowback cycle

starting on Jan 14th, 2015. The test was analyzed in the office in near real‐time to help direct field

operations, final interpretation occurred after field operations were complete. The interpreted fracture

closure gradients ranged from 21.52kPag/m to 22.58kPag/m. This document uses start of closure as the

appropriate measure for determining fracture gradient. Results are consistent with a horizontal fracture

based on the depth and density of the formation. The perforation interval was 101.3‐102.3mKB, the

downhole gauge landing depth was 103.0mKB and the difference between ground level and Kelly bushing

is 2.2m.








Figure 3: Wabiskaw Interval Tests

After the first injection and fall‐off cycle a second injection cycle was initiated and aborted after several

seconds due to operational issues. Pressure was then bled down by flowback and left to stabilize for

roughly 80 minutes. A successful second injection and fall‐off cycle was then performed. The aborted cycle

is visible in the input data; however, in this report references to the second cycle refer to the successfully

completed one.







1 FO 50 10 4113 2143 1785 21.52

2 FO 70 10 4937 2170 1406 21.79

3 FB 90 9 4734 2249 1551 22.58

Table 3: Wabiskaw Interval Minifrac Interpretation

The diagnostic plots of all three cycles show the 3/2 slope Bourdet derivative fracture closure. The closure

picks are based on the flow regime recognition and are described in SPE Paper 157843. Closure gradient

is slightly higher than the calculated overburden gradient for all cycles. An overburden stress gradient was

calculated by aggregating the surface bulk density log from a well at 10‐27‐92‐8w4 with the main hole

(below surface casing) bulk density log in the minifrac well at 6‐27‐92‐8w4, resulting in 21.0 kPag/m. The

average Wabiskaw minifrac gradient was 21.96kPag/m (lowest calculated gradient 21.52kPag/m). The


fracture is horizontal. The geomechanical picks are made directly from the diagnostic plots and are

independent of the formation characteristics.


LowerClearwaterIntervalThe Clearwater interval was tested by minifrac test for two frac/falloff cycles and one frac/flowback cycle

on Jan 17th, 2015. The test was analyzed in the office in near real‐time to help direct field operations, final

interpretation occurred after field operations were complete. The interpreted fracture closure gradients

ranged from 21.82kPag/m to 22.28kPag/m. This document uses start of closure as the appropriate

measure for determining fracture gradient. Results are consistent with a horizontal fracture based on the

depth and density of the formation. The falloffs are likely more accurate than the flowback result due

variability in flowback rate as the pressure declines. The perforation interval was 93.0‐94.0mKB, the

downhole gauge landing depth was 95.0mKB and the difference between ground level and Kelly bushing

is 2.2m.








Figure 4: Clearwater Interval Tests







1 FO 50 10 4016 1993 1612 21.82

2 FO 70 10 4194 2009 1555 22.00

3 FB 90 9 3922 2035 1535 22.28

Table 4: Clearwater Interval Minifrac Interpretation

The diagnostic plots of all three cycles show the 3/2 slope Bourdet derivative fracture closure. The closure

picks are based on the flow regime recognition and are described in SPE Paper 157843. Closure gradient

is slightly higher than the calculated overburden gradient for all cycles. An overburden stress gradient was

calculated by aggregating the surface bulk density log from a well at 10‐27‐92‐8w4 with the main hole

(below surface casing) bulk density log in the minifrac well at 6‐27‐92‐8w4, resulting in 21.0kPag/m. The

average Clearwater minifrac gradient was 22.04kPag/m (lowest calculated gradient 21.82kPag/m). The


fracture is horizontal. The geomechanical picks are made directly from the diagnostic plots and are

independent of the formation characteristics.

attachment 8 mini-frac report for suncor lewis f1/06-27-092 … · 2019-02-14 · suncor lewis...

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