The effect of Specialty Chemicals on the Minimum Lift Velocity to Unload a Gas Well

Transcription

1 Gas Well De-Liquification Workshop March 1-3, 2004 The effect of Specialty Chemicals on the Minimum Lift Velocity to Unload a Gas Well Sunder Ramachandran Sr. Development Scientist Baker Petrolite Baker Petrolite BAKER HUGHES

2 Outline of Talk I. Introduction II. Effect of Surfactants on Fluid Properties III. Physics of Well Unloading IV. Modeling of Wells V. Implication on Ultimate Recovery for a well VI. Chemical Compatibility for Wells and Capillaries VII. Results VIII.Summary and Conclusions 2

3 I. Introduction: Gas Production in U.S.A. Since 1993 total annual natural gas consumption has been greater than 20 Tcf (EIA) Gas well completions added each year have increased from 13,000-14,000 to over 22,000 per year in 2001 (EIA) Close to 25 % of well capacity comes from wells less than a year old. (EIA) Decline rates in new Texas wells (1/3 of U.S Supply) have changed from 20 % in the first year for wells drilled in the 1970 s and 1980 s to more than 55% for wells drilled in 1998 and 1999 (SPE 70018) Surplus capacity is little more than 10 % of the average consumption 3

4 I. Sizing of a Gas Well with a steep decline Sizing of the inner diameter becomes difficult At early stages, large diameters are desirable In later stages, when gas velocities become low, the gas cannot carry water out of the well bore. Here smaller diameters will aid production Several equations exist to determine the gas velocity at which liquid loading occurs Underground storage wells act as both injection and production wells. Wells may be needed to be killed to be repaired and to prevent leakage of gas 4

5 I. Elements of Current Paper Effect of Surfactants on Surface Tension and Foam Quality Physics of Unloading Scientific Identification of Foamer Opportunities Implication of Foamers on Ultimate Recovery Chemical Compatibility of Foamers Case Study for Dewatering Production Wells Case Study for Dewatering Gas Storage Well 5

6 II. Effect of Surfactants on Fluid Properties Foam is a low density phase in which gas is entrained within a thin layer (lamella) or layers of surfactant containing water. 6

7 II. Dependence of Foam Height with Concentration and Salinity 600 Foam height (cm) Product A in Deionized Water Product A in NACE Brine Product B in Deionized Water Product B in NACE Brine Product C in Deionized Water Product C in NACE Brine Concentration (ppm) 7

8 II. Effect of Condensate on Foam Height Foam Height (cm) Product D Product E % Condensate Increasing

9 Surfactants lower Surface Tension 75 Surface Tension (mn/m) CMC Concentration (ppm) 50 hz 10 hz 5 hz 3 hz 1 hz 9

10 III. Physics of Unloading Weber Number Ratio of kinetic energy in fluid divided by energy required to form liquid droplet ( Controls diameter of droplet) Decreasing the liquid surface tension lowers the diameter of droplet formed in a gas stream N v ρ d σ g We g p = v 2 g ρ d g σ p gas velocity gas density particle diameter surface tension 10

11 III. Physics of Unloading Terminal Settling Velocity Velocity at which gas carries the liquid droplet. This is effected by shape and the drag coefficient. Formula changes with shape (spherical formula shown) Drag coefficient changes with gas viscosity and density v g g ρ C p d = p ( ρ ρ ) 4gd d p 3C ρ g g Gravitational constant particle density drag coefficient 11

12 III: Bottom Line: Surfactants dewater wells by Lowering density of the droplet Reducing surface tension and make smaller droplets Magnified Entrained Liquid Drop Magnified Entrained Foam Drop Brine Brine and Foamer Gas Flow Gas Flow 12

13 IV. Well Modeling: Parameters for a sample Gas Well Table 2. Parameters for a sample gas well Parameter Value Temperature of Interest in Gas Well 83 F Bottom hole Temperature 200 F Relevant Pressure in Gas Well 71 psi Tubing inner diameter inch Gas specific gravity 0.6 Chloride level in brine 0 mg/l Water Production Rate 1 bbl/d Condensate Production Rate 0 bbl/d Gas Production Rate 126 mscfd 13

14 Results of Model Velocity (ft./sec) Product B1 Product B2 Product B3 Product B4 Product B5 Product B6 Product B7 Product B8 Product B9 Product B10 Product B11 Product B12 Product B13 Product B14 Product B15 Product B16 Product B17 Product B18 Actual Gas Velocity Concentration (ppm) 14

15 V. Production Rate at which loading occurs 1200 Production Rate at which loading occurs without foamer (mscfd) Production Rate (mscfd) Tubing Inner Diameter (in.) Production Rate at which loading occurs with 500 ppm Product F Production Rate at which loading occurs with 500 ppm Product G Production Rate at which loading occurs with 500 ppm Product H Production Rate at which loading occurs with ppm Product F Production Rate at which loading occurs with ppm Product G Production Rate at which loading occurs with ppm Product H 15

16 V. Implication on Ultimate Recovery 250 Cummulative Production (mmscf) Cummulative Production until loading occurs without foamer (mmscf) Cummulative Production until loading occurs with 500 ppm Product F (mmscf) Cummulative Production until loading occurs with 500 ppm Product G (mmscf) Cummulative Production until loading occurs with 500 ppm Product H (mmscf) Cummulative Production until loading occurs with ppm Product F (mmscf) Cummulative Production Rate until loading occurs with ppm Product G (mmscf) Cummulative Production Rate until loading occurs with ppm Product H (mmscf) Tubing Inner Diameter (in.) 16

17 VI. System Compatible and Stable Chemica Temperature stability to 400 F (204 C) Capillary injection string compatibility Stable for gas lift Low corrosivity Emulsion Testing needed at Separator to choose best product for process Testing with defoamer to ensure no effect on separator Multifunctional chemistries Corrosion Scale Paraffin Max Temp for Gas Lift Thermal Corrosion & Pour Point Flash Point Stability Foamer Combo < - 20 o F > 100 o F Product A 350 o F X Product B 275 o F X X Product C 180 F 225 F X Product D 275 o F X Product E 400 o F X Product F X Product G X 17

18 2/1/2003 VII. Case History of a Production Well VII. Case History of a Production Well MCF/Day 0 1/1/2002 2/1/2002 3/1/2002 4/1/2002 5/1/2002 6/1/2002 7/1/2002 8/1/2002 9/1/ /1/ /1/ /1/2002 1/1/2003 Day 10 gal/day Csg - 3-1/2" T ub - T ubingless I j 3/8" C ill Product I - 100% MCF/D Chem Rate 0

19 VII. Gas Storage Well Case Study Table 3. Parameters for gas storage well Parameter Value Temperature of Interest in Gas 60 F Well Bottom hole Temperature 100 F Relevant Pressure in Gas Well 80 psi Tubing inner diameter 5.0 inch Gas specific gravity 0.6 Chloride level in brine 0 mg/l Water Production Rate 1 bbl/d Condensate Production Rate 0 bbl/d Gas Production Rate 900 mscfd 19

20 VII. Results of Model Gas Velocity (ft./sec) Product A1 Product A2 Product A3 Product A4 Product A5 Product A7 Actual Gas Velocity Concentration (ppm) 20

21 Result of Using Foamer on Gas Storage Well Product was delivered down the gas tubing and shut in for a day. Next morning well was brought up, a large amount of water was unloaded from the well. Fluid level on the well was measured to be zero. When a production test was made on the well, the well had identical production test characteristics, it had 40 years ago. 21

22 VIII. Summary and Conclusions Surfactants lower liquid surface tension and create foam The amount of gas entrained in a foam vary with salinity, amount of condensate and product type. This effects different unloading equations 22

23 VIII. Summary and Conclusions Computer Model can identify promising candidates for foamer treatment Chemicals must be compatible with the well and method of delivery 23

24 VIII. Summary and Conclusions Surfactants have been used to dewater gas production and storage wells They can increase production and deliverability of natural gas 24