Downhole Gas Separator Selection

Transcription

1 Gas Well Deliquification Workshop Sheraton Hotel, February 17 20, 2013 Downhole Gas Separator Selection James N. McCoy & Lynn Rowlan

2 Feb , Downhole Gas Separator Selection Many operators with medium to high capacity wells who have low production rates and low pump fillage ask the question: What kind of downhole separator should be used?

3 Downhole Gas Separator Principle of Operation Gas Separator Liquid Capacity is Based on the Following Principle: The outer pipe can be the casing or the outer barrel of a gas separator. The inner tube is the inlet to the pump. GAS BUBBLES FLOW UPWARD IN OIL OR WATER AT A RATE OF APPROXIMATELY 6 INCHES PER SECOND. THUS, GAS BUBBLES WILL BE RELEASED FROM A LIQUID COLUMN IF THE DOWNWARD LIQUID VELOCITY IS LESS THAN 6 INCHES PER SECOND. A LIQUID COLUMN HAVING AN AREA OF 1 SQUARE INCH TRAVELLING AT 6 INCHES PER SECOND IS A RATE OF 50 BPD. Feb ,

4 What Kind of Separator is Needed? ESP Producing 5 MMCF/D of CO2 Gas Free Gas flows in the annulus, if the casing pressure builds up after the casing valve is closed. Feb ,

5 Dynamometer and Acoustic Analysis of Seating Nipple Type Gas Separator Performance Casing Pressure Buildup 4.13 psi/min ~ 298 MscfD Annular Gas Flow Rate 88.6 Effective Plunger Stroke with 87% Pump Fillage Gas Separator with Seating Nipple Feb ,

6 Natural Gas Separator The most efficient downhole gas separators locate the pump intake below the lowest gas entry point. Gas is not pulled down to the pump perforations unless the liquid velocity is greater than 6 inches per second. Maximum capacity is obtained using casing annulus. 6

7 Natural Gas Anchor Feb ,

8 Tubing Conveyed Downhole Separator System Gravity separation is the governing principle for downhole gas separators. slip pump Insert Separator has less capacity than using the casing ID. Downward Liquid velocity greater than 6 inches per second in separator pulls gas into pump. liquid in separator gas in separator Feb ,

9 Sorry Poor Boy Gas Separator Limited Flow Area and Small Holes Tubing Collars prevent perforated sub from laying against casing wall where liquid accumulates Seating Nipple Collar Casing Perforated Sub Dip Tube Collar Joint of Tubing Feb ,

10 Feb , Poor Boy Gas Separator Liquid Capacity

11 Many Modifications of Poor Boy Gas Separator Seating Nipple Casing Collar Perforated Sub Dip Tube Collar Joint of Tubing Feb ,

12 Collar Size Separator Eliminates Poor Boy Deficiencies A good separator must balance annular flow area, separator flow area, dip tube diameter and pressure drop. Outer barrel OD same as collar OD. Thin short wall outer barrel and short dip tube. Large inlet ports distributed around outer barrel facilitate entry of liquid. Feb ,

13 Collar-Sized Gas Separator Specifications Designed with thin-wall tubing, large ports and minimum lengths to optimize gas separation from the liquid that enters the pump. Set 5.5 foot long separator 3 joints below tubing anchor. OD of outer barrel of gas separator is the same OD as the tubing collar. Collar at the top of separator attaches to bottom of pump seating nipple. Optimum size dip tube is permanently mounted inside the outer barrel. A bull plugged joint of tubing can be run below the bottom half-collar for a solids collection chamber if desired instead of the bull plug. 13

14 Collar Size Separator - Gas and Liquid Capacity To get gas capacity of a specific installation multiply the table value by the Pressure at the Pump Intake (psi) and divide by

15 Poor Boy Separator Franks #1 Casing Pressure Buildup.25 psi/min ~ 18 MscfD Annular Gas Flow Rate 34.4 Effective Plunger Stroke with 34% Pump Fillage Feb ,

16 Collar Sized Gas Separator Franks #1 Casing Pressure Buildup 1.8 psi/min ~ 161 MscfD Annular Gas Flow Rate Production of 100 BPD with a Full Pump Feb ,

17 GAS Should NOT Flow Too Fast Past Outside Gas Separator MIST FLOW Gas Velocity should be less than 10 ft/sec in Annulus Between ID of Casing and OD of Gas Separator Feb ,

18 Liquid Moves Slower in Separator Than Inside Pump Chamber 1.8 sec SV Opens Pump Plunger Velocity 4.17 sec SV Closes Liquid Velocity Inside Separator Feb ,

19 Feb , 2013 Bubble Size Impacts Rise Velocity 6 in/sec 3 in/sec 1 in/sec Clift, Grace and Webber (1978)

20 During 5 th Stroke 1 in/sec Bubble is Pulled into Bottom of the Dip Tube Plunger Dia Inch Plunger Area sq.in. Pump Depth 10,540 feet 2 3/8" Collar Sized Gas Separator Area between Dip Tube and Barrel ID - OD sq.in. Begin 0 - SV Opens SV Closes 4.17 End sec SPM

21 Feb , Collar Sized Gas Separator Results of Early Field Tests Installed in over 300 wells Increased production by an average of 25% in those wells with additional production capacity. Reduced pumping time by an average 50% in wells with Pump-Off controllers.

22 Feb , Packer Gas Separator Inner tube can hold a pump or simply be a long small dip tube to a pump landed above. Uses gravity separation like the Poor Boy except more separation area and capacity. Higher cost and higher risk of mechanical and sand problems. Page Oil Tools 1957

23 Top Collar Pump Gas Separator Design Formation Fluid Outlet Fluids from the formation flow upward to the gas separator and then flow through a concentric annulus to an outlet at the top of the separator which discharges on one side into the casing annulus. The gas rises and the liquid falls in the casing annulus. Casing Seating Nipple Pump Inlets The pump inlet is located at the bottom of the gas separator causing the pressure drop from the liquid at the bottom of the separator to the pump inlet to be negligible. Bottom Collar Formation Fluids Diverter cups or Packer or Stinger Diverter Cups or a packer or tail pipe with packer is located below the Separator to force formation fluids into the separator. 23

24 Feb , 2013 Gas Separator Selection Criteria 24 Use Packer Type when dp/dt >2 Use Collar Type when dp/dt <2 Average of all data

25 Determine Gaseous Liquid Column Gradient Below Liquid Level Adjusted Liquid Level If Liquid Rate is Low, Poor Boy Gas Separator May be OK Transition from Collar Sized to Packer Type Gas Separator 25

26 Downhole Gas Separator Selection Criteria Feb ,

27 Conclusions Best gas separation performance is obtained by locating the pump intake below the gas entry point. Proper gas separator selection when pump intake is above the formation must take into account casing annulus gas production rate and well liquid production rate. Use casing pressure buildup rate to help select Gas Separator Type. Use % Liquid Surrounding Separator with % Pump Fillage to Determine Separator Performance Feb ,

28 Copyright Rights to this presentation are owned by the company(ies) and/or author(s) listed on the title page. By submitting this presentation to the Gas Well Deliquification Workshop, they grant to the Workshop, the Artificial Lift Research and Development Council (ALRDC), and the Southwestern Petroleum Short Course (SWPSC), rights to: Display the presentation at the Workshop. Place it on the web site, with access to the site to be as directed by the Workshop Steering Committee. Place it on a CD for distribution and/or sale as directed by the Workshop Steering Committee. Other use of this presentation is prohibited without the expressed written permission of the author(s). The owner company(ies) and/or author(s) may publish this material in other journals or magazines if they refer to the Gas Well Deliquification Workshop where it was first presented. Feb ,

29 Disclaimer The following disclaimer shall be included as the last page of a Technical Presentation or Continuing Education Course. A similar disclaimer is included on the front page of the Gas Well Deliquification Web Site. The Artificial Lift Research and Development Council and its officers and trustees, and the Gas Well Deliquification Workshop Steering Committee members, and their supporting organizations and companies (here-in-after referred to as the Sponsoring Organizations), and the author(s) of this Technical Presentation or Continuing Education Training Course and their company(ies), provide this presentation and/or training material at the Gas Well Deliquification Workshop "as is" without any warranty of any kind, express or implied, as to the accuracy of the information or the products or services referred to by any presenter (in so far as such warranties may be excluded under any relevant law) and these members and their companies will not be liable for unlawful actions and any losses or damage that may result from use of any presentation as a consequence of any inaccuracies in, or any omission from, the information which therein may be contained. The views, opinions, and conclusions expressed in these presentations and/or training materials are those of the author and not necessarily those of the Sponsoring Organizations. The author is solely responsible for the content of the materials. The Sponsoring Organizations cannot and do not warrant the accuracy of these documents beyond the source documents, although we do make every attempt to work from authoritative sources. The Sponsoring Organizations provide these presentations and/or training materials as a service. The Sponsoring Organizations make no representations or warranties, express or implied, with respect to the presentations and/or training materials, or any part thereof, including any warrantees of title, non-infringement of copyright or patent rights of others, merchantability, or fitness or suitability for any purpose. Feb ,

30 The problem of separating the gas from the liquid before the liquid enters the pump may be related to the creation of small gas bubbles from the drop in pressure of liquid in the dip tube as the oil travels to the pump inlet. Start 5 Seconds 10 Seconds 15 Seconds Feb , Seconds 30