The evaluative methods on shale gas productivity using the DFIT

Transcription

1 The evaluative methods on shale gas roductivity using the DFIT Dr. Sangyu Jang T.H. Kim, G.S. Lee C.H. Shin

2 This is the Eternal Flame Waterfall, on Shale Creek, in Chestnut Ridge Park, near Buffalo, New York. A ocket of natural methane gas in an alcove below the waterfall sees out through a fracture in the rocks.

3 1. Introduction Contents 2. DFIT(diagonal fracture injection test) 3. Pre-closure analysis 4. After-closure analysis 5. Summary and future works

4 Introduction Sand stone Formations Tight Formations Shale Formation Milli-darcies 1 x 10-3 D Micro-darcies 1 x 10-6 D Nano-darcies 1 x 10-9 D

5 The limit of conventional well test method for shale formation. Low ermeability, Long transient time Build-u, Draw-down, flow test is imossible Needs for raid test method for shale/tight formation. Mini fracture test(dfit) Effective ermeability using DFIT(diagonal fracture injection test)

6 DFIT or Mini frac test Ewens, 2012 Perforation Installation of ressure gauge Injection Shut-in and record

7 Diagonal Fracture Injection Test (Mini frac test) PRE CLOSURE ANALYSIS Formation Breakdown Pressure Fracture Closure Pressure Instantaneous Shut in Pressure(ISIP) Fracture Gradient = ISIP / Formation Deth Net Fracture Pressure (Δ net ) = ISIP - Closure Pressure Fluid efficiency = Gc/(2+Gc) : G c is the G-function time at fracture closure Formation Leak Off Characteristics AFTER CLOSURE ANALYSIS Formation ermeability (k) Reservoir ressure ( i ) Net Horizontal Stress(closure ore ressure) Fracture Closure Pressure Nolte, 1982

8 Research Trend Nolte (1979) G-function and fracture ressure decline analysis Castillo(1987), Mukherjee(1996), Baree(1998) Pressure deendent leak-off vs. G-function, dp/dg, GdP/dG lot Gu et al(1993), Nolte(1997), Benelkadi and Tiab (2004) After closure time function, Imulse fracture test Soliman et al. (2005) / Craig and Blasingame (2006) Short term test Meyer (2007) Mass and momentum equation for 2D-fracture

9 PRE-CLOSURE ANALYSIS Fracture Closure Pressure Nolte, 1982

10 General information Horn River (Kiwigana) British Columbia Alberta Located in north eastern British Columbia Horn River Grou(Muskwa Fm., Otter Park Fm., Evie Fm.) Aroximately 2,500m below surface Average 170m thick, Average TOC : 4.3% Comosed of siliceous, organic rich shale (high quartz content)

11 Calculated Sandface Pressure (kpa(a)) Liquid Rate (m 3 /d) Injection data for Well A Data Chart Cum Time (h)

12 Definition of G-function G function : dimensionless time function relating shut-in time to total uming time G( t g( t g( t t g g o o D D D D ) ) ( g( t 4 ) (1 t 3 (1 t ( t t t ) D )sin ((1 t D ) g D ) o ) t 1.5 D (For high leak-off) (For low leak-off) D ) 0.5 ) t 0.5 D (For low leak-off) (For high leak-off)

13 G-function analysis of Well-A Pressure deendent leak-off -> Existence of fracture! SHmax

14 Oil base micro-imager

15 G-function analysis of Well-B Pressure deendent leak-off

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17 G-function analysis of Well-C Normal leak-off wellbore

18 Summary It could be ossible to find out the leak-off behavior and fracture related reservoir roerties for shale formation by re-closure analysis G-function analysis data and OBMI data were comared to validate the existence of natural fracture near well bore and reliable correlation is found with this methods.

19 AFTER CLOSURE ANALYSIS Fracture Closure Pressure Nolte, 1982

20 Combing the continuity equation, the equation of motion, and the EOS t k c r r r r t 1 t z k c r z r r r t 1 Diffusivity eqn. Real gas law Gas comressibility, seudo state (ф, μ, z constant) ' ln ln 711 ) ( ) ( 2 s C r k t kh QT P m P m w t a i wf Conventional gas well test

21 Nolte Linear flow Soliman-Craig Linear flow w t i C L kc t F L w ( t) i Vinj C khx t 2 f t 1 t 0.5 Radial flow m w t R1 Qt 251,000 kht Qt kh 251,000 m t i w i F Qt 251,000 F kht R1 R1 c 0 c R1 c Radial flow V inj w( t) i (1694.4) kh t Vinj mr2 (1694.4) kh Vinj kh (1694.4) m i w ( t 1 t R2 0) 1 t

22 Linear and Radial flow lot for well A

23 Reservoir roerties from 2 methods(well A) Nolte method Soliman-Craig method Permeability : 11.6 d Initial ressure for radial flow : 5,324 si Leak-off coefficient : ft/min 1/2 Permeability : 9.98 d Initial ressure for radial flow : 5,317 si Fracture half-length : 16.6 ft

24 Permeability estimation k c t G c f Er z 1.96 f : Viscosity of injected fluid (=1 c, assumtion) z : Net fracture extension ressure above closure ressure(9873 si) G c : G-function closure time (=32.705h) E: Young s modulus(=3.35msi) r : Storage ratio(=1) ø : orosity(=0.04) C t : Total comressibility(=5.09x10-5 /si) Calculate K = uD Case G-function(Baree) Nolte Soliman Well A(μD)

25 Summary and further study DFIT results in the Kiwigana shale formation were resented. The results have good consistency between other analytical methods and will be used for hydraulic fracturing job effectively. The need for the rolonged shut-in time is realized to analyze the radial flow regime in DFIT. Permeability estimation equation is useful for rough calculation. Many roduction characteristics of shale gas reservoir need to be monitored to correlate reservoir roerties. Influence on adsorbed gas and stress deendent rock roerties should be considered to evaluate more recisely.

26 Thank you for your attention!