The evaluative methods on shale gas roductivity using the DFIT 2014. 9. 18 Dr. Sangyu Jang T.H. Kim, G.S. Lee C.H. Shin
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.
1. Introduction Contents 2. DFIT(diagonal fracture injection test) 3. Pre-closure analysis 4. After-closure analysis 5. Summary and future works
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
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)
DFIT or Mini frac test Ewens, 2012 Perforation Installation of ressure gauge Injection Shut-in and record
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
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
PRE-CLOSURE ANALYSIS Fracture Closure Pressure Nolte, 1982
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)
Calculated Sandface Pressure (kpa(a)) Liquid Rate (m 3 /d) Injection data for Well A Data Chart 90000 0 85000-500 80000-1000 75000-1500 70000 65000-2000 60000-2500 55000-3000 50000 45000-3500 40000-4000 35000-4500 30000-5000 25000 20000-5500 15000-6000 10000 0.48 0.50 0.52 0.54 0.56 0.58 0.60 0.62 0.64 0.66 0.68 0.70 0.72 0.74 0.76 0.78 0.80 0.82 Cum Time (h)
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 ) 2 4 3 4 ) ( g( t 4 ) (1 t 3 (1 t ( t t t ) D )sin ((1 t D ) g D ) 1.5 1 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)
G-function analysis of Well-A Pressure deendent leak-off -> Existence of fracture! SHmax
Oil base micro-imager
G-function analysis of Well-B Pressure deendent leak-off
G-function analysis of Well-C Normal leak-off wellbore
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.
AFTER CLOSURE ANALYSIS Fracture Closure Pressure Nolte, 1982
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) ' 7.43173 ln ln 711 ) ( ) ( 2 s C r k t kh QT P m P m w t a i wf Conventional gas well test
Nolte Linear flow Soliman-Craig Linear flow w t i C L kc t F L w ( t) i Vinj 31.05 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
Linear and Radial flow lot for well A
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 : 6.0519 10-4 ft/min 1/2 Permeability : 9.98 d Initial ressure for radial flow : 5,317 si Fracture half-length : 16.6 ft
Permeability estimation k c 0.086 t G c f Er 0.01 0.038 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 = 4.4351uD Case G-function(Baree) Nolte Soliman Well A(μD) 4.4351 11.6 9.98 24
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.
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