Part 16 Horizontal Well Testing

Chapter 16 Horizontal Well Testing M stafa On Mustafa Onurr

1

Useful References • • • • • • •

Kuchuk, F., Goode, P.A., Brice, B.W., Shrerrard, D.W., Thambynayagam, “Pressure-Transient Analysis for Horizontal Wells,” JPT, Aug 1990, 1022-1030 (paper SPE 18300). Odeh, A.S., and Babu, D.K.: “Transient Flow Behavior of Horizontal Wells: Pressure Drawdown, and Buildup Analysis,” SPEFE March 1990, 7-15. Odeh, A.S., and Babu, D.K.: “Productivity of a Horizontal Well,” SPERE Nov. 1989, 417-421. Abbaszadeh M Abbaszadeh, M. and Hegeman Hegeman, P P.S.: S : “Pressure-Transient Pressure Transient Analysis for a Slanted Well in a Reservoir With Vertical Pressure Support,” SPEFE (September 1990) 277. Kuchuk, F., Goode, P.A., Wilkinson, Thambynayagam, R.K.M.: “PressureTransient Behavior of Horizontal Wells With and Without Gas Cap or Aquifer,” SPEFE, March 1991, 86-94 (paper SPE 17413). Kuchuk, F., and Habashy, T.: “Pressure Behavior of Horizontal Wells in Multilayer Reservoirs With Crossflow,” SPEFE, March 1996, 55-66. Thompson, L.G., and Temeng, K.O., “Automatic Type-Curve Matching for Horizontal Wells,” paper SPE 25507, March 1993. 2

Useful References •

• • • • •

Onur, M., Hegeman, P.S., and Kuchuk, F.J.: “Pressure-Transient Analysis of Dual Packer-Probe Wireline Formation Testers in Slanted Wells,” paper SPE 90250 presented at the SPE Annual Technical Conference and Exhibition held in Houston, Texas, U.S.A., 26–29 September 2004. Ozkan, E.: “Analysis of Horizontal-Well Responses: Contemporary vs. Conventional”, SPEREE, Aug 2001, 260-269. gy PennWell Publishing g Co. Tulsa, OK., Sada, D.J.: Horizontal Well Technology, 1991. Bourdet, D.: Well Test Analysis: The Use of Advanced Interpretation Models, Elsevier Science B.V., Amsterdam, The Nethelands, 2002. Horne, R.: Modern Well Test Analysis-A Computer-Aided Approach, Second Edition, Petroway, Inc., Palo Alto (1995). Modern Reservoir Testing, Schlumberger publication, Houston, TX, 1994.

3

1

Introduction ƒ Since 1980’s, horizontal wells have been extremely popular. The major purpose is to enhance reservoir contact and hence well productivity. ƒ In general, a horizontal well is drilled parallel to the reservoir bedding plane (see below figure θw = 90o), while a vertical well is drilled perpendicular to the bedding plane (θw = 0o). The wells intersecting the bedding plane with an angle θw different from 0 to 90o are called slanted (or deviated) wells. rw

θw

(x,y,z)

h zw

z

z y

θ

x

4

Introduction (Cont’d) ƒ The increase in the applications of horizontal (and also slanted) wells has brought an impetus development of the procedures to evaluate the performances and productivity of horizontal wells. ƒ Here, we will focus only on the interpretation of pressure transient measurements from horizontal wells to be able to determine formation parameters that control performance and productivity of horizontal wells. ƒ

However, I should note that interpretation of pressure transients is much more difficult than interpretation of those from vertical wells: — 3D nature of the flow geometry (so many parameters affecting the pressure behavior of the horizontal well; This makes the application of classical conventioal analysis methods very difficult. Non linear regression seems to be the most useful) 5

Introduction (Cont’d) — Considerable wellbore storage effects (this mask critical reservoir flow regimes, e.g., early-radial flow governed by the vertical permeability of the reservoir. Deconvolution can be useful to eliminate wellbore storage effects, but requires accurate measurements of “sandface” rates, although there are “wellbore storage” deconvolution methods not requiring “sandface rate” measurements which assume that a constant wellbore storage model is adequate to represent the wellbore storage effect) effect). — Wellbore haydraulic (conductivity of the wellbore is in general finite). — Non uniform skin effect along the wellbore. — Selective completions along the horizontal well. — Heterogeneities in vertical direction as well as lateral directions. 6

2

Pressure Transient Behavior of a Horizontal Well

7

Basic Flow Regimes—Infinite System in the x-y Plane kz

kx x

Early (or Vertical) radial flow due to convergence of flow only in the vertical (y-z) plane normal to the well axis. Slope of p vs. lnt controlled by

k y k z Lw

μ

Intermediate-time linear flow regime (occurs if Lw >> h) Slope of p vs. sqrt(t) controlled by

k yφ ct Lw h

μ

z

ky y

Late (or Horizontal) radial flow (some people referred to as pseudo-radial flow). Slope of p vs. lnt controlled by

kxk y h

μ

8

On Anisotropic Permeability • If we define principal directions of permeability as kx, ky ( in x-y plane) and kz (z is the vertical direction), then –

k x ≠ k y ≠ k z (3D anistotropic reservoir).

– k x = k y = k h , k z = k v ( k h ≠ k v ) (isotropic in the x-y plane, but anisotropic in the z-direction)

• For vertical wells, the radial flow is governed by the horizontal permeability, k h (= k x k y ) • For horizontal wells, early radial flow is governed by the geometric mean of kh and kv, while late-radial flow is governed by horizontal permeability, only. 9

3

On Anisotropic Skin Factor • If we have anisotropy in permeability in the horizontal and/or vertical plane, this causes our well to be an ellipse in the equivalent isotropic system, and this appear as skin effect on pressure. Horizontal/Vertical plane well

⎡4 k / k + 4 k max / k min ⎤ rw′ = rw ⎢ min max ⎥ 2 ⎥⎦ ⎣⎢

kmax kmin

s ani

⎛⎡4 k /k + 4 k max / k min ⎤ ⎞⎟ = − ln ⎜ ⎢ min max ⎥