Seismic stimulation for enhanced oil production

Transcription

1 Seismic stimulation for enhanced oil production Eirik G. Flekkøy, University of Oslo Mihailo Jankov, Olav Aursjø, Henning Knutsen, Grunde Løvold and Knut Jørgen Måløy, UiO Renaud Toussaint, University of Strasbourg Steve Pride, Lawrence Berkeley Labs

2 Outline Field observations Pore scale intro and elements of theory Lattice Boltzmann and experiments Moving up from pore scale: Network models and experiments Transversal versus longitudinal stimulation Effects of compressibility

3 FIELD EVIDENCE FOR SEISMIC STIMULATION Earthquakes or hammers, as in this case: Oil Production (B/day) Oil Cut Oil Production stimulation applied Increase in Oil Production after Stimulation at Occidental s Elk Hills Field, California Oil cut %

4 Water extraction wells:

5 Context: As much as 70% of the world s oil is in known reservoirs but is trapped on capillary barriers and is effectively stuck. Seismic Stimulation: A seismic wave is to shake the stuck oil loose and get it flowing again toward a production well.

6 The n condition for a stuck oil bubble: 1 ΔP = σ Rdown 1 R up the production pressure drop along the bubble is just balanced by a capillary-pressure increase Beresnev et al., 2005

7 The production-gradient force that always acts on the fluids: acceleration of grains F = P / 0 Δ Poroelasticity determines the seismic force acting on the fluids: where F S H ρ B = c ρ + θ p f 1+ 4G 3KU wavelength-scale fluid-pressure gradient θ is the seismic strain rate.

8 The seismic force adds to the production gradient and can overcome the capillary barrier whenever: where S = S c F k 0 φ 2 σ k φ H F F S 0 S S c 1 stimulation criterion dimensionless stimulation number (a type of capillary number) = critical threshold of stimulation number (purely geometry dependent) and where k is permeability and φ is porosity.

9 Lattice Boltzmann model Hydrodynamics comes from mass- and momentum conservation: c c 3 2 c 1 G. McNamara and G. Zanetti 1986

10 Lattice-Boltzmann Movie NOTES No green arrow = no applied forcing Single green arrow = production-gradient only Double green arrow = two periods of seismic stress + production-gradient when stimulation is applied, bubbles coalesce creating a longer stream of oil that flows even in absence of stimulation

11 Snapshots and average oil speed during the four stages of a typical production run : running average

12 Total volume of oil production with (solid symbols) and without (open symbols) three cycles of stimulation applied (F s = F o ): Less of a stimulation effect because at 33% saturation, oil cannot form a continuous stream across system. More of a stimulation effect because at 50% saturation, coalescence can result in oil forming a continuous stream across system

13 A tiny experiment:

14 Lattice Boltzmann and experiments

15 Towards larger scales:

16 Experiments:

17 Displacement structures depend on velocity and viscosities and gravity:

18 Experimental setup:

19 Experiment movie- no oscillations

20 With parallel oscillations: (Ca=0.0004) a=0.8 g a=2.6 g

21

22 Corresponding network simulations:

23 ..and with transverse oscillations:

24 The different frequencies and accelerations: No oscillations Parallel osc: Transverse osc:

25 Lattice Boltzmann Longitudinal and transverse oscillations

26 Resulting, end saturations of wetting fluid:

27 An experiment with compressibility: Q=const.

28 Linear elastic response of both air and local plate displacements may model fluid compressibility under much higher pressures.

29 Elastic response gives finite skin-depth: Diffusion equation For damped oscillations: f / Hz x /cm D

30 Results Flow direction 0.2 Hz 0.9 Hz 4.0 Hz Pressure amplitude (Pa) low high

31 Phase diagram Frequency (Hz) IP-like structure Finger-like structure Foam within fragmented structure Amplitude (Pa)

32 Phase diagram 2 Frequency (Hz) Amplitude (Pa)

33 Closer look Fragments Coexistence of both phases in pore spacesfoam

34 Conclusions Transverse stimulation more efficient than parallel stimulation, at least for high fractions of invading fluid Smaller scale coalescence potentially more efficient at smaller volume fractions Compressibility gives skin-depth Simplified (network) and 2D simulations (Lattice Boltzmann) capture experiments Quantification, analysis and scaling laws still lacking