2006 2006 International International Sucker Rod Sucker Rod Pumping Pumping Workshop Workshop Pump Intake Pressures Pump Intake Pressures Pump Intake Pressures in Viscous Crude in Viscous Crude in Viscous Crude Lynn Rowlan Lynn Rowlan
Accurate BHP Calculation Requires: Accurate BHP Calculation Requires: Accurate BHP Calculation Requires: � Stabilized Stabilized flow conditions flow conditions � Stabilized flow conditions � Determination of Liquid Level � Determination of Liquid Level � Determination of Liquid Level � Measurement of casing pressure � Measurement of casing pressure � Measurement of casing pressure � Measurement of casing pressure � Measurement of casing pressure � Measurement of casing pressure � buildup rate (at Producing and Static buildup rate (at Producing and Static buildup rate (at Producing and Static Conditions) Conditions) Conditions) Wellbore description � Wellbore description � Wellbore description � Oil, water and annular gas densities � Oil, water and annular gas densities � Oil, water and annular gas densities �
Stabilized PBHP Stabilized PBHP Stabilized PBHP Pt Pc � Requires a Requires a Constant Constant � Production Rate Production Rate Gas � Requires a Requires a Stabilized Stabilized � Fluid Level and Casing Fluid Level and Casing Pressure Pressure FL Oil + Gas Note: In a Note: In a stabilized stabilized well, the Liquid above well, the Liquid above Pump Brine the pump intake is 100% OIL the pump intake is 100% OIL Gradient PBHP regardless of well’ regardless of well ’s water s water- -oil oil- -ratio. ratio.
Separation of Fluids Separation of Fluids Separation of Fluids Pt in a Stabilized Well in a Stabilized Well in a Stabilized Well Pc � The Liquid above the pump The Liquid above the pump � intake is 100% OIL. intake is 100% OIL. � Oil gradient: 3ft = 1 psi Oil gradient: 3ft = 1 psi? ? � Gas � Liquid below pump intake Liquid below pump intake � contains more water than contains more water than FL well test water- -oil oil- -ratio. ratio. well test water Oil + Gas � Liquid Liquid below pump intake below pump intake � Pump exhibits BRINE gradient. exhibits BRINE gradient. Brine Gradient � Brine gradient: 2 ft = 1 psi Brine gradient: 2 ft = 1 psi � PBHP
Liquid Level Above Formation Liquid Level Above Formation with Free Gas Flow from the Reservoir with Free Gas Flow from the Reservoir 1. Gaseous Gaseous Liquid Column exists Liquid Column exists 1. above the Perforations. above the Perforations. 2. Producing BHP = 2. Producing BHP = Casing Pressure + Casing Pressure + Gas Column Pressure + Gas Column Pressure + Gaseous Oil Pressure to Pump + Pressure to Pump + Gaseous Oil Gaseous Water Pressure to bottom. Pressure to bottom. Gaseous Water
Annular Gaseous Liquid Column Exists Annular Gaseous Liquid Column Exists Annular Gaseous Liquid Column Exists Pt When: When: When: Flowline Pc Gas is flowing flowing from the from the � Gas is � casing annulus. casing annulus. The Casing pressure � The Casing pressure � Gas builds up when the when the builds up casing valve is closed. casing valve is closed. Gaseous Liquid Column Pump Gas enters through perforations and is Gas enters through perforations and is Dip Tube bubbling through annular liquid from bubbling through annular liquid from Perfs Liquid + Gas perforations to gas/liquid interface. perforations to gas/liquid interface.
Determination of Gaseous Determination of Gaseous Liquid Column Gradient Liquid Column Gradient � Determined experimentally on a given Determined experimentally on a given � well. well. � Develop experimental correlation from Develop experimental correlation from � large number of tests and apply to large number of tests and apply to measured pressure and gas flow rate. measured pressure and gas flow rate. Reference: Reference: “ “Acoustic Producing BHP Acoustic Producing BHP” ” � Computed from mechanistic model Computed from mechanistic model � (not accurate in most cases) (not accurate in most cases)
Liquid % from Back Pressure Liquid % from Back Pressure Test Pt Test Flowline Pc Back Pressure Given: Given: Valve Gas � Constant Production Constant Production High � FL � Annular Gas Rate Annular Gas Rate � Gaseous Liquid Column with 10 - 15% � Annular Area Annular Area � Liquid � Fluid Properties Fluid Properties � Pump Determine Liquid Determine Liquid Percent in Gaseous Percent in Gaseous Liquid Column Liquid Column Perfs Low PBHP
Basis for Experiment: Basis for Experiment: Increase Pressure => Move Liquid Level Increase Pressure => Move Liquid Level Pressure increase = 220 psi Pressure increase = 220 psi Fluid Level Fluid Level 2300 ft 2300 ft Drop 2300 ft Drop 2300 ft Gradient= 220/ 2300 = Gradient= 220/ 2300 = 0.095 psi/ft 0.095 psi/ft
The Pressure at any Depth in in a Gaseous Liquid Column is a Gaseous Liquid Column is The Pressure at any Depth Independent of Surface Pressure at Stabilized Conditions of Surface Pressure at Stabilized Conditions Independent Q=constant
Pressure versus Depth Traverse Pressure versus Depth Traverse in the Annulus in the Annulus Gradient is Gradient is computed computed from from measured measured pressures P 1 P pressures 1 and levels and levels P 2 P 2
Back Pressure Test Setup Back Pressure Test Setup
Back Pressure Test Setup Back Pressure Test Setup
Back Pressure Regulator Loop Back Pressure Regulator Loop
Automatic Annular Liquid Level Automatic Annular Liquid Level and Casing Pressure Monitoring and Casing Pressure Monitoring
Procedure for Liquid % Test Procedure for Liquid % Test Procedure for Liquid % Test 1. Maintain Well at Normal 1. Maintain Well at Normal Pumping Conditions. Pumping Conditions. 2. Obtain Liquid Level Depth Obtain Liquid Level Depth 2. and the Casing Pressure. and the Casing Pressure. 3. Increase casing pressure 3. Increase casing pressure with back pressure with back pressure regulator and allow well to regulator and allow well to stabilize. stabilize. 4. Obtain Obtain NEW NEW Liquid Level Liquid Level 4. Depth at NEW Casing Depth at NEW Casing Pressure. Pressure. 5. Repeat Steps 3 & 4, until 5. Repeat Steps 3 & 4, until Liquid Level is Near Pump. Liquid Level is Near Pump.
Casing Pressure vs. Time Casing Pressure vs. Time
Liquid Level vs. Time Liquid Level vs. Time
Gaseous Gaseous Gaseous liquid column liquid column liquid column gradient test gradient test gradient test using back using back using back pressure valve pressure valve pressure valve to set casing to set casing to set casing pressure while pressure while pressure while pumping rate pumping rate pumping rate is kept is kept is kept constant. constant. constant.
Gaseous Column Height vs. Casing Gaseous Column Height vs. Casing Pressure for 150 MCF/D in 5” & 2-7/8” Pressure for 150 MCF/D in 5” & 2-7/8”
Annular Annular Annular Gaseous Gaseous Gaseous Preliminary heavy oil Liquid Column Liquid Column data Liquid Column Effective Effective Effective Gradient Gradient Gradient Factor Factor Factor Adjusted Liquid Level Adjusted Liquid Level Actual Field Collected Data Points
Back Pressure Test Setup Back Pressure Test Setup Direct annular Direct annular gas flow gas flow measurement measurement was was necessary to necessary to establish establish correlation on correlation on basis of Q/A basis of Q/A and verify and verify validity of Q validity of Q determined determined from dp/dt dp/dt from
Annular Gas Flow – dP/dT Measured Annular Gas Flow – dP/dT Measured Close Casing Close Casing Valve Valve dP dP Casing Casing Pressure dT dT Pressure increase as a increase as a function of function of time is a time is a measure of measure of casinghead casinghead gas flow rate gas flow rate
Time = 0 Time = 4 min. Casing Valve Closed During Test Gas flow out= 45 MCF/D 46.2 49.4 psi psi Gas flow into well = 45 MCF/D PBHP = 572.8 psi
Calculation of annular gas flow rate is based on the Gas Gas increase in casing pressure per unit time during the casing pressure buildup test. Using the real gas law: Flow Flow P 1 *V 1 = Z 1 n 1 RT 1 at time t 1 and Calculation Calculation P 2 *V 2 = Z 2 n 2 RT 2 at time t 2 where in the well: V 1 = V 2 = volume of annulus minus volume of liquid T 1 = T 2 = average temperature R = gas constant P 1 =initial casing pressure P 2 = pressure at end of casing buildup test n 2 ,n 1 = number of moles of gas in annulus Then solve for (n 2 -n 1 ) which is the increase in gas mass during the time (t 2 -t 1 ) and convert to standard cubic feet per day.
Requirements for Accuracy Requirements for Accuracy � Test should be short (2 to 10 minutes) so that inflow of gas and producing bottom hole pressure remain almost constant. � Measured casing pressure buildup vs. time should be linear indicating a constant gas rate. � ID of casing, OD of tubing and well depth data are correctly entered in well database.
Producing BHP Producing BHP
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