Downhole Gas Separators

Transcription

1 Gas Well De-Liquification Workshop Denver, Colorado February 27 March1, 2006 Downhole Gas Separators A Laboratory and Field Study Jim McCoy, Echometer Company Tony Podio, University of Texas at Austin Lynn Rowlan, Echometer Company Research Funds Provided by Echometer, ConocoPhillips, & Yates Petroleum

2 Efficiency Studies

3 Findings of Efficiency Study Motor is relatively efficient 83%. Pumping unit is relatively efficient 96%. Rod string is generally efficient 75%. Standard Downhole Pump is efficient unless damaged or worn 95%. Downhole Gas Separators above the formation can be very inefficient when free gas is flowing up the casing annulus %. Downhole gas separators below the formation were generally more efficient. Overall system efficiency should be approximately 55%.

4 Conclusions of Efficiency Study Gas interference in the pump was often the primary cause of low efficiency in the beam pump system. The downhole gas separator was not effective in wells that produce substantial gas up the annulus. The Downhole Gas Separator should be studied in the laboratory and in the field in an attempt to improve downhole gas separator performance.

5 Natural Downhole Gas Separator The most efficient downhole separator is the wellbore! The pump intake should be Below casing perforations if possible. The Natural Downhole Gas Separator is generally efficient.

6 Natural Gas Anchor A pump intake below bottom perforations is equivalent to a surface 2-phase separator Flow path takes advantage of Gravity Separation: most gas flows to top of vessel.

7 Downhole Gas Separators Above The Casing Perforations Were Often Inefficient Often, it is not possible to install the pump intake below the lowermost fluid entry point in the wellbore. No rat-hole Liner or Gravel Pack Other Well has Sand/Scale production problems The formation depth and well capacity exceeds the pumping system capacity so the pump is located uphole Operator preference

8 Gas Separator Above Perforations A pump intake above the top perforations is equivalent to a surface separator having the pump intake above the inlet with a perforated baffle and quieting chamber.

9 Collar Size Gas Separator Design The outside diameter of the tubing collar is the same as the outside diameter of the outer barrel. The larger diameter of the Collar Size Gas Separator compared to a Poor Boy Gas Separator offers considerably more liquid capacity. The Collar Size Gas Separators are about 6 feet in length. A joint of tubing can be added to the bottom if desired.

10 Poor Boy Gas Separator Seating Nipple Casing Collar Perforated Sub Dip Tube Collar Joint of Tubing Tubing Collars prevent perforated sub from laying against casing wall where liquid accumulates

11 Gas Separator Above Fluid Entry Some free gas migrates past the separator due to the upward flow of free gas in the liquid Pump Plunger Some liquid and gas is pulled into the gas separator on the pump upstroke During the plunger upstroke, the free gas escapes from the liquid if the gas upward slip velocity is greater than the liquid downflow velocity On the plunger downstroke, gas slips upward through the stationary liquid

12 Gas Separator Laboratory Equipment Air purge Hydrostatic Column The flow rates were measured, visually observed and recorded on video. Tests were mixtures of water and air. Flow Control to keep BHP constant L.C. Air out BHP Mix Pump Manifold Air Supply 15

13 Separator Testing Apparatus and Procedure Gas Rates injected into the well Up to 120 MSCF/Day (3400 M3/D) Liquid Rates Injected into the well From 100 to 750 Bbl/day ( M3/D) Pressure Measurements BHP, PIP, Separator exit pressure Gas Rates Flowing Through the Gas Separator 0-63, 0-886, SCF/day ( M3/D) All tests were continuous flow 15

14 Geometry of Separators Studied Tested the effect of the width of the outer barrel ports on separator performance Tested the effect of multiple rows of ports on separator performance Tested the effect of the diameter of the dip tube on separator performance Tested the effect of the position of the gas separator ports relative to the casing perforations: above, in-line and below.

15 Gas Separator Performance Evaluation Gas Separator Performance Evaluation Z = gas through separator Gas Rate through Separator (MSCF/day) X = liquid velocity in separator Y = gas velocity in casing annulus Y Z X Superficial Liquid Velocity inside Separator (in/sec) Superficial Gas Velocity in casing annulus (in/sec) Good Performance

16 Patterson Gas Separator The Patterson Gas Separators have tall narrow slots to prevent gas from entering the inside of the gas separator. The studies showed that the liquid flows into the separator through the lower slots. The newer designed Patterson Gas Separators being tested have one row of slots.

17 Slot Width Effect Slot Width Effect Gas Rate through Separator (MSCF/D) Gas Rate through Separator (MSCF/D) Patterson 1/4" slots Patterson 1/2" slots Superficial Liquid Velocity inside Separator (in/sec) 6 Superficial Liquid Velocity inside Separator (in/sec) 6 Superficial Gas Velocity in Casing Annulus (in/sec) Superficial Gas Velocity in Casing Annulus (in/sec) Patterson 3/4" slots Gas Rate through Separator (MSCF/D) Superficial Liquid Velocity inside Separator (in/sec) 6 Superficial Gas Velocity in Casing Annulus (in/sec)

18 Echometer Gas Separator The Echometer Gas Separators have large openings spaced closely together to allow liquid to flow into the separator with minimum flow resistance.

19 Echometer Gas Separator Performance Echometer Gas Separator Performance SEPARATOR TYPE: Echometer 1 (2 x 4" slots) Air and water entering below 10 psi Gas Rate through Separator (MSCF/D) Liquid rate entering the well (BPD) Gas rate entering the well (MSCF/D)

20 Effects of Port Geometry Effects of Port Geometry Poor Boy Patterson 3 Gas Rate through Separator (MSCF/day) Gas Rate through Separator (MSCF/day) Liquid rate entering the well (BPD) Liquid rate entering the well (BPD) Gas rate entering the well (MSCF/D) Gas rate entering the well (in/sec) Number of holes: 12 Diameter: 3/8 Number of slots: 8 Dimensions: 8" x 1/2"

21 Additional Data in Paper Additional laboratory data is presented in the paper. Time restraints do not permit showing all of the laboratory tests. 10

22 Field Applications 10

23 Collar Size Gas Separator Field Tests Vs. Poor Boy Gas Separator Vogt 8A - Improvement over Poor Boy Coalbed Methane Well - Improvement Jones 1- No Improvement over Poor Boy

24 Vogt 8 With Poor Boy Gas Separator

25 Vogt 8 Surface Card - Down 10 Minutes

26 Vogt 8 After Collar Size Gas Separator

27 Vogt 8 Surface Cards - Down 10 Min Position, Inches

28 Vogt 8 Results The Collar Size Gas Separator was successful. It separated the gas from the liquid and allowed only liquid to enter the pump as long as liquid was present in the wellbore.

29 Coalbed Well with Poor Boy Separator

30 Coalbed Well with Poor Boy Separator Flumping Flowing gas and liquid through pump

31 Coalbed Well with Collar Size Gas Separator

32 Coalbed Well with Collar Size Gas Separator

33 Coalbed Well Results The Collar Size Gas Separator was successful. It separated free gas from water and allowed only water to enter the pump as long as water was present in the wellbore above the separator. 5

34 Jones #1 5

35 Jones #1 with Poor Boy Separator

36 Jones #1 With Poor Boy Separator Pump Taps Bottom with a force of about 800 pounds. Intentional small hole in pump barrel above standing valve allows limited liquid to flow into pump barrel from the tubing.

37 Jones #1 With Collar Size Gas Separator

38 Jones #1 With Collar Size Gas Separator Differences in Tests Not Tapping Bottom Small hole in pump barrel above standing valve was removed.

39 Jones #1 Results The Collar Size Gas Separator slightly improved gas production over the Poor Boy Gas Separator. But, the pump was not full even though liquid existed in the casing annulus. The problem of separating the gas from the liquid before the liquid enters the pump may be related to the release of small gas bubbles from the oil which causes an emulsion that is difficult to separate.

40 Emulsion Test Start 5 Seconds 10 Seconds 15 Seconds 20 Seconds

41 Conclusions and Recommendations The best position to place a downhole gas separator is where the gas separator slots are below the majority of the casing perforations (if the pump intake cannot be located entirely below the perforations).

42 Conclusions and Recommendations The efficiency of the gas separator is a function of at least four variables: 1 The liquid superficial velocity inside the separator, 2 The gas superficial velocity in the annulus between the casing and the separator, 3 The geometry of openings in the outer barrel of the gas separator, and 4 The outer diameter of the dip tube.

43 Conclusions and Recommendations The 6 foot length of the gas separators tested (having a 5.5-foot long dip tube) results in relatively efficient separation. A longer downhole gas separator is not necessary unless debris is to be collected in the longer outer barrel. Tests are to be performed on gas separators shorter than 5 feet.

44 Conclusions and Recommendations The laboratory tests were performed with water and the results should apply to water producing wells.

45 Conclusions and Recommendations The Jones # 1 field testing of the Collar Size gas separator indicates that gas separator performance is affected by foaming oil conditions. The field test indicates that additional work should be performed on water, oil and gas mixtures especially when gas is being released from the oil in small bubbles.

46 Ongoing Project - Future Tests A variety of geometric port shapes Shorter dip tube lengths More viscous liquids Intermittent flow

47 Questions??