CHARACTERIZATION OF FRACTURES AND THEIR EFFECT ON RESERVOIR DIRECTIONAL FLOW IN TENSLEEP

SANDSTONES, WYOMING

Peigui Yin& Shaochang Wo

Enhanced Oil Recovery InstituteUniversity of Wyoming

Laramie, Wyoming

A B

TENSLEEP SANDSTONE RESERVOIRS, WYOMING

A

B

PresentedReservoir

Major Reservoirs Cores Outcrops

Marine Carbonate

Eolian Sandstone

60

65

70

75

80

85

90

95

100

0 20 40 60 80 100

Wat

er C

ut (%

)

Recovery Factor (%)

TENSLEEP PRODUCTION

FRACTURE TYPES IN TENSLEEP SANDSTONES

• Gouge-filled fractures

• Mineral-filled fractures

• Partially-filled fractures

• Open fractures

Barriers or baffles

Conduits

Gouge-filled Fractures in Cores

Gouge-filled Fractures

Mineral-filled Fractures in Cores

Mineral-filled Fractures in Outcrops

Partially-filled Fractures in Cores

Open Fractures in Cores

FAULT AND FRACTURE DISTRIBUTION IN OUTCROPS

1000 ft

?

Flat Top Mountain

Gouge-filled fractures on Outcrops

Brokenback AnticlineBighorn Mountain

Zeisman DomeBighorn Mountain

Sinks CanyonWind River Range

Cottonwood Creek Ferris Mountain

FRACTURE PERMEABILITY ANDFRACTURE ORIENTATION IN A RESERVOIR

• 3-D reservoir structure construction

• Curvature calculation to indicate fracture intensity

• Average matrix permeabilities of wells from core analysis and well log data

• Total permeabilities of wells from matching wells’ production history

• Multi-well flow simulation to verify fracture orientation and estimate average fracture/matrix permeability ratio

Fractures

Open

Partially-filled

Filled

FRACTURE DISTRIBUTION IN CORES(From the Presented Tensleep Reservoir)

Fracture Spacing vs. Core Porosity

5 5.5 6 6.5 7 7.5 8 8.58

8.5

9

9.5

10

Average Porosity (%)

Ave

rage

Fra

ctur

e Sp

acin

g (ft

)

Average core porosity

Mahoney Dome: Estimated Permeabilities From Well Productions

1112

14

1718

2021

23

24

25

2627

34

36

41

4546

19 56

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

Ave

rage

Per

mea

bilit

y ar

ound

Wel

ls, m

d

Estimated Permeability from Production (with Well Number)

Average Permeability from Log Correlation

ESTIMATED TOTAL PERMEABILITY FROM PRODUCTION HISTORY vs

AVERAGE MATRIX PERMEABILITY FROM CORES AND WELL LOGS

estimated permeability from production – average permeability = fracture permeability (+ -)

(total permeability)

(matrix permeability)

DISTRIBUTION OF MATRIX PERMEABILITY

Fractures

Open

Partially-filled

Filled

FracturePermeability

+ Permeability (Total Perm>Matrix Perm)

- Permeability (Total Perm<Matrix Perm)

DISTRIBUTION OF FRACTURE PERMEABILITYElevation

CURVATURE DISTRIBUTION FOR THE PRESENTED RESERVOIR STRUCTURE

Gaussian Curvature Maximum Curvature Minimum Curvature

Mean Curvature Dip Curvature Strike Curvature

Curvature vs. Fracture Permeability

0

100

200

300

400

500

600

700

-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70Difference between Production Perm. and Log Correlation Perm., md

Cur

vatu

res,

10^

6/ft

(10^

9/ft

for G

auss

ian

Cur

vatu

re)

MaximumMinimumGaussianMeanDipStrike

1712

19

216

Observation Well

Active Well

WELL INTERFERENCE TEST

Fracture Orientation

Measured and Simulated BHP Drop Down in Well 12(from well interference test)

1600

1650

1700

1750

1800

1850

1900

0 5 10 15 20 25 30 35 40Testing Time, days

BH

P D

rop

Dow

n in

Obs

erva

tion

Wel

l 12,

psi

Well 16 shut-in Well 19 shut-in

Well 2 shut-in Well 19 on

Well 2 on Well 17 shut-in

Simulation matched permeabilities:

Permeability at N30oE (Ky) = 18 md

Permeability at S60oE (Kx) = 3 md

N30oE

S60oE

Measured BHP

Simulated BHP

CONCLUSIONS & APPLICATIONS

• Four different types of fractures are observed in the Tensleep well cores and outcrops: gouge-filled, mineral-filled, partially-filled, and open fractures.

• Open and partially-filled fractures can act as conduits for reservoir flow, whereas gouge- and mineral-filled fractures can act as barriers or baffles.

• Fracture permeability is estimated by subtracting average matrix permeability (from core analysis and log data) from totalpermeability (calculated from production history).

• Curvatures calculated from 3-D reservoir structure may predict fracture intensity but show no good correlation with fracture permeability in the Tensleep sandstones.

• Fracture orientation is obtained through well interference tests. • Multi-well flow simulation is used to verify fracture orientation

and estimate average fracture/matrix permeability ratio.