Hydro-mechanical behaviour of GPK4 during the hydraulic stimulation - - PowerPoint PPT Presentation

June 29 - 30, 2006

Hydro-mechanical behaviour

• f GPK4 during the hydraulic

stimulation tests – Influence of the stress field

• X. Rachez, S. Gentier, A. Blaisonneau

BRGM

BRGM/Geo-Energy unit

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 2

Objectives of our modeling work

> Understand which physical mechanisms are

involved in the hydraulic stimulation of the well in crystalline rocks

> Extract the main parameters playing a role in the

hydraulic stimulation

Focus hereafter on the influence of the stress

field on the HM behavior of GPK4 during the stimulation test

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 3

What it could happen during the hydraulic stimulation of a well (if we exclude thermal effect...)

σh σH σV

In continuous homogeneous and isotropic medium

σH σV σh

But in general, the granite is already fractured

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 4

More in details...

Un Us σV σH σH σh

Evolution of the hydraulic aperture is linked to the normal displacement (Un) and the tangential displacement (Us)

closure of the fracture

Un

Us initial state

• pening : reduction of the normal component

release of the shearing

Increase of the aperture

Well To T1 T2 Tf

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 5

3DEC code

> Based on the Distinct Element Method

• allows finite displacements and rotations of discrete bodies,

including complete detachment,

• recognizes new contacts automatically,
• perfect for modelling discontinuous media, such as fractured

rock masses

> Fractured rock mass considered as a blocks assembly, cut

by joints/discontinuities

• blocks are rigid or deformable,
• joints behaviour is governed by springs that takes into account

the opening/closing of the fractures as well as their shearing.

> Flow takes place only in the fractures (blocks are

impermeable). Flow is laminar and obeys the cubic law

Hydro-mechanical coupling

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 6

Fractured rock mass

> Take into account with 3DEC the selected

fractures that cross the well

• 9 fractures for GPK4

> Generate them in

a parallelepiped volume

GPK4 GPK4 400m 1000m 400m

> Take into account

the well geometry (here, centred and vertical)

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 7

Injection under P = Pi + ∆ P

well

> Stimulation test

• Apply an overpressure in the well. Value taken from the real

stimulation test conducted in the GPK4 well.

• FISH HM coupling procedure
• Calculate the injected flowrate at the well, in each fracture
• Stop the run when equilibrium between in and out flowrates is

reached

Hydraulic stimulation

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 8

Boundary and Initial HM conditions

σH σh σv

North East

Pi = ρ g y

> Boundary conditions > Pressures

• Hydrostatic field

> Stress field

• From in situ measurements

1) either Klee and Rummel, 1993, 2) or Cornet et al. (to be published)

y = 0 X (East) Z (North) Y (Vertical Upwards) σz σx

x = z = 0 x=z=0

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 9

Stress field

> Klee and Rummel, 1993

σh = 15.8[MPa] + 0.0149[MPa/m] (depth[m]-1458) σH = 23.7[MPa] + 0.0336[MPa/m] (depth[m]-1458) σv = 33.8[MPa] + 0.0255[MPa/m] (depth[m]-1377) σH oriented N170°E ± 15°

> Cornet et al. (2006, to be published)

σh = (0.54 +/- 0.02)* sv σH = (0.95 +/- 0.05)* sv σv = 1377*0.024[MPa] + 0.0255[MPa/m] (depth[m]-1377) σH oriented N175°E +/- 6°

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 10

Stress regime ?

500 1000 1500 2000 2500 3000 3500 4000 4500 5000 50 100 150 Stress (MPa) Depth (m) Sh(1) SH(1) SV(1) Phyd SV(2) SH(2) Sh(2) Shmin(2) Shmax(2)

σh

Phyd

σH σV

?

• 1. Klee and Rummel (1993)

σH : N170°

• 2. Cornet et al. (2006?)

σH : N 175° Strike slip regime Normal fault stress regime

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 11

GPK4 - Influence in terms of flow in well

5 10 15 20 10 20 30 40 50 60 70 Total well flowrate [l/s] Overpressure P [MPa]

In-situ Stress Field n°1 Stress Field n°2

> Very little difference

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 12

GPK4 - Influence in terms of flow at fractures

> Very little difference

10 20 30 40 50 3.00 6.00 9.00 13.75 15.50 18.30 Overpressure stages [MPa] (flow in fract#1) vs (total flow in well) [%] SF#1 - F1 SF#2 - F1 10 20 30 40 50 3.00 6.00 9.00 13.75 15.50 18.30 Overpressure stages [MPa] (flow in fract#2) vs (total flow in well) [%] SF#1 - F2 SF#2 - F2 2 4 6 8 10 12 14 16 18 3.00 6.00 9.00 13.75 15.50 18.30 Overpressure stages [MPa] (flow in fract#3) vs (total flow in well) [%] SF#1 - F3 SF#2 - F3 2 4 6 8 10 12 14 16 18 3.00 6.00 9.00 13.75 15.50 18.30 Overpressure stages [MPa] (flow in fract#4) vs (total flow in well) [%] SF#1 - F4 SF#2 - F4 2 4 6 8 10 12 14 16 18 3.00 6.00 9.00 13.75 15.50 18.30 Overpressure stages [MPa] (flow in fract#5) vs (total flow in well) [%] SF#1 - F5 SF#2 - F5 2 4 6 8 10 12 14 16 18 3.00 6.00 9.00 13.75 15.50 18.30 Overpressure stages [MPa] (flow in fract#6) vs (total flow in well) [%] SF#1 - F6 SF#2 - F6 2 4 6 8 10 12 14 16 18 3.00 6.00 9.00 13.75 15.50 18.30 Overpressure stages [MPa] (flow in fract#7) vs (total flow in well) [%] SF#1 - F7 SF#2 - F7 2 4 6 8 10 12 14 16 18 3.00 6.00 9.00 13.75 15.50 18.30 Overpressure stages [MPa] (flow in fract#8) vs (total flow in well) [%] SF#1 - F8 SF#2 - F8 2 4 6 8 10 12 14 16 18 3.00 6.00 9.00 13.75 15.50 18.30 Overpressure stages [MPa] (flow in fract#9) vs (total flow in well) [%] SF#1 - F9 SF#2 - F9

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 13

GPK4 - Influence in terms of shear disp.

Normal fault stress regime Strike slip regime

Tangential displacements more concentrated in some fractures Tangential displacements more spread Us max ∼ 6 cm Us max ∼ 13 cm

x 2

∆P = 18,3 MPa

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 14

GPK4 – Influence in terms of F1 shear disp.

> Max shear along intersection with F4, not close

to the well, greater with strike slip regime well F4 well F4

∆P = 18.3 MPa Us max = 7-9 cm Us max = 3-5 cm

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 15

GPK4 – Influence in terms of F2 shear disp.

> Max shear along intersections with F3 & F4,

greater with strike slip regime well well F4

∆P = 18.3 MPa Us max = 9-11 cm Us max = 5-7 cm

F3 F4 F3

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 16

GPK4 – Influence in terms of F4 shear disp.

> Max shear along intersections with F1 & F3,

greater with strike slip regime well well

∆P = 18.3 MPa Us max = 13 cm Us max = 5-7 cm

F2 F3 F1 F2 F3 F1

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 17

GPK4 – Influence in terms of block disp.

> Blocks instability with strike slip regime

∆P = 18.3 MPa

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 18

GPK4 – best fit of ∆P-Q stimulation curve

45 15 0.25 0.5 F9 40 150 2.50 5.0 F8 40 150 2.50 5.0 F7 40 150 2.50 5.0 F6 45 150 2.50 5.0 F5 40 75 1.25 2.5 F4 40 150 2.50 5.0 F3 45 150 2.50 5.0 F2 45 15 0.25 0.5 F1 Best fit 45 150 2.5 5.0 F1 to F9 Previous runs Friction angle ϕ (°) Max. aperture amax [mm] Resid. aperture ares [mm] Initial aperture a0 [mm] Fracture N°

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 19

GPK4 – best fit – influence in terms of flow

2 4 6 8 10 12 14 16 18 20

10 20 30 40 50 Total well flowrate [l/s] Overpressure ∆P [MPa]

In-situ Stress Field n°1 Stress Field n°2

> Very little difference

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 20

GPK4 – Best Fit – F1 shear disp.

> Limited and comparable F1 max shear,

around the well well well

∆P = 18.3 MPa Us max = 1-3 cm Us max = 1-3 cm

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 21

GPK4 – Best fit – F2 shear disp.

> F2 max shear around the well, and along

intersections with F3 & F4 well well F4

∆P = 18.3 MPa Us max = 7-9 cm Us max = 5-7 cm

F3 F4 F3

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 22

GPK4 – Best fit – F4 shear disp.

> /2 F4 hydro apertures change drastically the F4

HM behaviour. Max shear not close to the well well well

∆P = 18.3 MPa Us max = 3-5 cm Us max = 3-5 cm

F2 F3 F1 F2 F3 F1

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 23

GPK4 – Best fit – F7 shear disp.

> F7 max shear disp. far away from the well,

greater with normal fault stress regime well well F9

∆P = 18.3 MPa Us max = 5-7 cm Us max = 7-9 cm

F9

June 29 - 30, 2006 ENGINE Meeting, “Stimulation of reservoir and induced microseismicity” > 24

Conclusions

>Great importance of the stress field, depending on the HM fractures properties >Looking only at the ∆P-Q stimulation curve obtained with 3DEC is not satisfactory >Max shear displacements are not located close to the well >Blocks instability with the strike slip regime is unrealistic

• Either the stress field taken into account does not reflect the real in-situ one,
• And/or, the HM fractures properties are not appropriate.

Work in progress

>New Fractures constitutive law taking into account damage during shearing >New conceptual hydraulic model, taking into account the 3 wells >Thermal coupling