Presentation on theme: "The University of Texas at Austin Downhole Gas Separator Performance In Sucker Rod Pumping System Beam Pumping Workshop Houston, Texas October 4 - 7, 2005."— Presentation transcript:
The University of Texas at Austin Downhole Gas Separator Performance In Sucker Rod Pumping System Beam Pumping Workshop Houston, Texas October 4 - 7, 2005 Manuel Guzman Augusto Podio
Overview Description of the problem System schematic Bubble flow forecast Gas separation testing facilities Pump volumetric efficiency for actual wells Conclusions
What Is The Problem? Design and selection of downhole gas separators are usually made using heuristics. Generally the performance is much below than expected.
V liquid in anchor V plunger V slip V gas in anchor Downhole Separator System
Gas Velocity Inside the Anchor V plunger Net gas velocity is difference between gas slip velocity (up) liquid velocity (down) liquid velocity (down) Liquid velocity depends on: ID of anchor OD of dip tube Plunger diameter and velocity
Instantaneous Liquid Flow Rate Conventional D plunger =1 in Ls=86 in 8.45 SPM 200 BPD Upstroke Downstroke
Forecast for Different Bubble Sizes Clift, Grace and Webber (1978) Stroke 1Stroke 2 Stroke 3 Bubble motion inside a separator with rod pump. Diam. Dip tube=1.5 in Plung. Diam.=1.5 in Conventional Unit, Ls=86.3 in, 8.45 SPM. Flow rate=151 BPD
Gas Separator Testing – Univ. of Texas 50 ft high/ 6 in. diam.
Gas Separator Testing – Univ. of Texas Perforations Separator Inlet Slots Dip Tube Separator Tube Casing
Liquid rate of the pump the well (BPD) Gas rate entering the well (MSCF/D) Gas Rate through Separator (MSCF/D) SEPARATOR TYPE: Echometer 1 (2 x 4" slots) Air and water entering below 10 psi Separator Performance (Continuous Flow)
Downhole gas separator selection With several options of separators it is difficult to select the right one. Two common situations: I have a well with specific conditions, which separator is my best choice? I have a separator, In which kind of well can I use it efficiently?
Example 200 BPD and 100MSCFD with a 7 casing Patterson 1 using a 3 1/2 separator would offer the best performance Inputs (liq. rate, gas rate, csg. diam.) Region of zero gas thru pump Gas is entering the pump Boundary obtained with lab data Outputs (separator, dimensions)
Superficial Liquid Velocity inside Separator (in/sec) Superficial Gas Velocity in casing annulus (in/sec) Gas Rate through Separator (MSCF/day) PATTERSON 1 (OD DIP TUBE = 1; # OF SLOTS =8; DIMEN. OF THE SLOTS =8" x 1/8") Pc = 10 psi; POSITION OF THE SEP. = ABOVE THE PERFORATIONS What If This Were a Rod Pumped Well? Superficial Liquid Velocity varies during the stroke
Sucker Rod Simulator A special butterfly valve was built and installed in the return line It will be automatically operated to obtain the desired on/off time Flow will be measured using a mass flow meter after the valve Pipe ½ in shaft 2 in Motor z x 6 in Drive
Intermittent Flow Behavior Gas enters the pump only during a fraction of the 5 sec. upstroke. Gas column moves uniformly during each stroke. Bubble size distribution changes with during stroke. Patterson 8 Flow rate = 275 BPD Gas rate = 55 MSCFD Pump speed =6 SPM (1 stroke = 10 sec)
Calculated Pump Liquid Fraction (Fluid Entering Below Ports) A reduction in pump liquid fraction was found when dip tube diameter was increased (Echometer 2 & Patterson 5) Up to 87% of liquid fillage can be achieved None of the evaluated separators reached the goal of 100%
Conclusions The instantaneous flow rate during the pump stroke should be used for the separator design. The gas flow rate in the casing has a major effect on the gas separation efficiency. Separator efficiency depends on the stroke length (Ls), plunger speed and the dip tube diameter, for each given geometry in a rod pump well. Visual observation confirms that the best way to maximize the gas separation is to set the intake below the perforations, if possible.
Future work: carry out additional intermittent flow tests to validate the mathematical predictions. Special thanks to: Yates Petroleum Q&A Session
The University of Texas at Austin Downhole Gas Separator Performance In Sucker Rod Pumping System Beam Pumping Workshop Houston, Texas October 4 - 7, 2005
Effect of Geometry Liquid rate entering the well (BPD) Gas rate entering the well (MSCF/D) Gas Rate through Separator (MSCF/day) Liquid rate entering the well (BPD) Gas rate entering the well (in/sec) Gas Rate through Separator (MSCF/day) PoorboyPatterson 3 Number of holes: 12 Diameter: 3/8 Area 1.3 in 2 Number of slots: 8 Dimension: 8" x 1/2Area 32 in 2
Background Research Understanding and Combating Gas Interference in Pumping Wells. Joe Clegg, 1963 Another Look at Gas Anchors. Joe Clegg, 1989 Characterization of Static Downhole Gas Separators. Jorge Robles, 1996 The Effect of Geometry on the Efficiency of Downhole Gas Separator. Omar Lisigurski, 2004
Mark II (3OD, 1 Dip Tube)
Rotaflex (3OD, 1 Dip Tube)
Liquid Fraction (Mark II, fluid entering below the anchor ports)