Acoustic Determination of Producing and Static

Bottomhole Pressures

Acoustic Determination of Producing and Static

Bottomhole Pressures

TWM Well Analyzer SeminarTWM Well Analyzer Seminar

Reference Papers: SPE 14254 and SPE 13810

Purpose of Performing anPurpose of Performing anAcoustic Fluid Level SurveysAcoustic Fluid Level SurveysPurpose of Performing anPurpose of Performing anAcoustic Fluid Level SurveysAcoustic Fluid Level Surveys

Well Performance and Potential AnalysisWell Performance and Potential Analysis

based on calculated bottom hole pressures.

Pump SubmergencePump Submergence Some operators shoot the well only to determine the amount of liquid above the pump. This is inefficient use of the fluid level information.

TWM Computes TWM Computes Wellbore Wellbore

Pressures from Pressures from liquid level surveyliquid level survey

Right HalfRight Half of BHP Tab ANSWERS THE of BHP Tab ANSWERS THE FOLLOWING QUESTIONS:FOLLOWING QUESTIONS:

Right HalfRight Half of BHP Tab ANSWERS THE of BHP Tab ANSWERS THE FOLLOWING QUESTIONS:FOLLOWING QUESTIONS:

1.1. What is the depth to the top of the liquid?What is the depth to the top of the liquid?

2.2. Does liquid exist above the pump?Does liquid exist above the pump?

3.3. What is the percentage of liquid in the annular fluid What is the percentage of liquid in the annular fluid

column?column?

4.4. Is gas flowing up the annulus? At what rate?Is gas flowing up the annulus? At what rate?

5.5. What are the pressures at the casing head, fluid level, What are the pressures at the casing head, fluid level,

pump intake and opposite formation ?pump intake and opposite formation ?

6.6. What is the pump submergence ?What is the pump submergence ?

BHP tab, page 111BHP tab, page 111

Bottom Hole PressuresBottom Hole PressuresBottom Hole PressuresBottom Hole Pressures

Annulus Fluid Distribution is a Function Annulus Fluid Distribution is a Function of Well’s Producing Conditionsof Well’s Producing Conditions

BHP is computed from fluid level BHP is computed from fluid level surveys taken with acoustic fluid level surveys taken with acoustic fluid level instruments.instruments.

BHP = BHP = Surface CasingSurface Casing Pressure + Pressure + Pressure due to the Pressure due to the columns of fluidscolumns of fluids in in the annulus.the annulus.

““The well is like a pressure gage with The well is like a pressure gage with a long stem”.a long stem”.

PBHPPBHP

PcasingPcasing

P g/lP g/l

Pressure Gradients for Common LiquidsPressure Gradients for Common Liquids

Fresh Water = 0.433 psi/ftFresh Water = 0.433 psi/ft

Field brine = 0.5 psi /ftField brine = 0.5 psi /ft

30API Oil = 0.38 psi/ft30API Oil = 0.38 psi/ft

10API Oil = 0.433 psi/ft10API Oil = 0.433 psi/ft

GeneralizationsGeneralizations

3 ft of oil column = 1 psi3 ft of oil column = 1 psi

2 ft of brine column = 1 psi2 ft of brine column = 1 psi

Column Pressure CalculationsColumn Pressure Calculations

Pgc = gas column pressure, psiPgc = gas column pressure, psi

Pc = casinghead pressure, psiPc = casinghead pressure, psi

L = height of gas or liquid column, feetL = height of gas or liquid column, feet

Accurate BHP Calculation Requires:Accurate BHP Calculation Requires:Accurate BHP Calculation Requires:Accurate BHP Calculation Requires:

StabilizedStabilized flow conditions flow conditions Determination of Liquid LevelDetermination of Liquid Level Measurement of casing pressureMeasurement of casing pressure Measurement of casing pressure buildup rate Measurement of casing pressure buildup rate

(at Producing and Static Conditions)(at Producing and Static Conditions) Oil, water and annular gas densitiesOil, water and annular gas densities Wellbore descriptionWellbore description

StabilizedStabilized flow conditions flow conditions Determination of Liquid LevelDetermination of Liquid Level Measurement of casing pressureMeasurement of casing pressure Measurement of casing pressure buildup rate Measurement of casing pressure buildup rate

(at Producing and Static Conditions)(at Producing and Static Conditions) Oil, water and annular gas densitiesOil, water and annular gas densities Wellbore descriptionWellbore description

Stabilized PBHPStabilized PBHPStabilized PBHPStabilized PBHP

Requires a Requires a Constant Constant Production Rate and WORProduction Rate and WOR

Requires a Requires a StableStable Casing Casing PressurePressure

Requires a Requires a StableStable Fluid Fluid Level Level

Gas

BrineGradient

Oil + Gas

Pump

Pc

Pt

PBHP

FL

Gas

BrineGradient

Oil + Gas

Pump

Pc

Pt

PBHP

FL

Separation of Fluids Separation of Fluids in a Stabilized Wellin a Stabilized Well Separation of Fluids Separation of Fluids in a Stabilized Wellin a Stabilized Well

TheThe Liquid above the pump Liquid above the pump intake is 100% OIL regardless of intake is 100% OIL regardless of well test water-oil-ratio .well test water-oil-ratio .Oil gradient: 3ft = 1 psiOil gradient: 3ft = 1 psi

Liquid below pump intake contains Liquid below pump intake contains more water than well test water-oil-more water than well test water-oil-ratio.ratio.

LiquidLiquid below pump intake exhibits below pump intake exhibits BRINE gradient.BRINE gradient.

Brine gradient: 2 ft = 1 psiBrine gradient: 2 ft = 1 psi

Downhole Video Shows:Downhole Video Shows:

Effect of oil slip velocity on water Effect of oil slip velocity on water holdup causes water to holdup causes water to accumulate below pump intake.accumulate below pump intake.

Effect of wellbore inclination on Effect of wellbore inclination on oil/water and gas/liquid oil/water and gas/liquid distribution.distribution.

Flow from perforations is not Flow from perforations is not uniform.uniform.

Fluid Distribution in Annulus of Pumping WellsFluid Distribution in Annulus of Pumping Wells

Gas Gradient

Liquid Gradients

Gas & Liquid Mixture Gradients

Liquid Level at FormationLiquid Level at Formation

1. Casing Head Pressure is the 1. Casing Head Pressure is the Major PortionMajor Portion of of PBHPPBHP..

2. Pressure due to Gas Column is 2. Pressure due to Gas Column is Generally SmallGenerally Small

3. Pump intake and liquid level 3. Pump intake and liquid level are near perforations.are near perforations.

Liquid Level Above Formation with Liquid Level Above Formation with NO Free Gas Inflow from the ReservoirNO Free Gas Inflow from the Reservoir

1. Liquid above tubing intake is1. Liquid above tubing intake is 100% oil..

2. Producing BHP = 2. Producing BHP =

Casing Pressure +Casing Pressure +

Gas Columm Pressure+Gas Columm Pressure+

Oil Gradient to Pump +Oil Gradient to Pump +

Primarily Primarily Water gradientgradient below pump intake.below pump intake.

No Free Gas in Annulus LiquidNo Free Gas in Annulus LiquidNo Free Gas in Annulus LiquidNo Free Gas in Annulus Liquid

The Operator Closes the The Operator Closes the Casing Valve and the Casing Valve and the Casing Pressure Casing Pressure does not does not increase.increase.

Or the Casing Pressure is Or the Casing Pressure is less less than the Flowline than the Flowline Pressure.Pressure.

Gas

BrineGradient

Oil

Pump

Pc

Pt

PBHP

FL

Oil,Water,Gas

Gas

BrineGradient

Oil

Pump

Pc

Pt

PBHP

FL

Oil,Water,Gas

When:When:When:When:

100 % Liquid below Fluid Level

Liquid Level Above Formation Liquid Level Above Formation with Free Gas Flow from Perforationswith Free Gas Flow from Perforations

1.1. GaseousGaseous Liquid Column exists Liquid Column exists above the Perforations.above the Perforations.

2. Producing BHP = 2. Producing BHP =

Casing Pressure +Casing Pressure +

Gas Column Pressure +Gas Column Pressure +

Gaseous Oil Gaseous Oil Pressure to Pump +Pressure to Pump +

Gaseous WaterGaseous Water Pressure to bottom. Pressure to bottom.

Annular Gaseous Liquid Column ExistsAnnular Gaseous Liquid Column ExistsAnnular Gaseous Liquid Column ExistsAnnular Gaseous Liquid Column Exists

Gas is Gas is flowingflowing out from the out from the casing annulus.casing annulus.

The Casing pressure The Casing pressure builds builds upup when the casing valve is when the casing valve is closed.closed.

Gas

Liquid + GasPerfs

Pump

Flowline

Pc

Pt

Gaseous LiquidColumn

Dip Tube

When:When:When:When:

Gas enters through perforations and is Gas enters through perforations and is bubbling through annular liquid from bubbling through annular liquid from perforations to gas/liquid interface.perforations to gas/liquid interface.

Producing BHP CalculationProducing BHP Calculation

Requires measuring the fluid level and casing pressure

Requires determining pressure gradient of gaseous liquid column. ( density of gas-liquid mixture in wellbore)

Pressure gradient of gaseous liquid column depends mainly on % liquid

Determination of Gaseous Liquid Column GradientDetermination of Gaseous Liquid Column Gradient

Determined experimentally on a given well by Determined experimentally on a given well by running liquid level depression test.running liquid level depression test.

Develop experimental correlation from large Develop experimental correlation from large number of tests and apply to measured number of tests and apply to measured pressure and gas flow rate.pressure and gas flow rate.Reference: “Acoustic Producing BHP”Reference: “Acoustic Producing BHP”

Computed from mechanistic modelComputed from mechanistic model(not practical in most cases)(not practical in most cases)

Liquid % from Liquid Level Depression TestLiquid % from Liquid Level Depression Test

Given:Given: Constant ProductionConstant Production Annular Gas RateAnnular Gas Rate Annular AreaAnnular Area Fluid PropertiesFluid Properties

Determine Liquid Determine Liquid Percent in Gaseous Percent in Gaseous Liquid ColumnLiquid Column

Gas

Low PBHPPerfs

Pump

Flowline

Pc

Pt

Gaseous LiquidColumn with 10 - 15%Liquid

HighFL

Back Pressure Valve

Back Pressure Test SetupBack Pressure Test Setup

Basis for Experiment: Increase Pressure => Depress Liquid Level

Basis for Experiment: Increase Pressure => Depress Liquid Level

2300 ft2300 ft

Pressure increase = 220 psiPressure increase = 220 psi

Fluid Level Fluid Level Drop 2300 ftDrop 2300 ft

Gradient= 220/ 2300 = Gradient= 220/ 2300 = 0.095 psi/ft0.095 psi/ft

Pressure versus Depth Traverse in the AnnulusPressure versus Depth Traverse in the Annulus

0

2000

4000

6000

8000

10000

12000

14000

0 100 200 300 400

Pressure, psiD

epth

, fe

et

Pc=30 Pc=250

Gradient is computed from measured pressures and levels

Gradient is computed from measured pressures and levels

PPLL1LL1

PPLL2LL2

Back Pressure Test SetupBack Pressure Test Setup

Back Pressure Regulator LoopBack Pressure Regulator Loop

Back Back Pressure Pressure RegulatorRegulator

Automatic Annular Liquid Level and Casing Pressure MonitoringAutomatic Annular Liquid Level and Casing Pressure Monitoring

Remote Remote Fired Gas Fired Gas Gun and Gun and Pressure Pressure TransducerTransducer

Procedure for Liquid % TestProcedure for Liquid % TestProcedure for Liquid % TestProcedure for Liquid % Test

1.1. Maintain Well at Normal Maintain Well at Normal Pumping Conditions.Pumping Conditions.

2.2. Obtain Liquid Level Depth Obtain Liquid Level Depth and the Casing Pressure.and the Casing Pressure.

3.3. Increase casing pressure Increase casing pressure with back pressure regulator with back pressure regulator and allow well to stabilize.and allow well to stabilize.

4.4. Obtain Obtain NEWNEW Liquid Level Liquid Level Depth at NEW Casing Depth at NEW Casing Pressure.Pressure.

5.5. Repeat Steps 3 & 4, until Repeat Steps 3 & 4, until Liquid Level is Near Pump.Liquid Level is Near Pump.

Casing Pressure Casing Pressure and Liquid Level and Liquid Level During Liquid During Liquid Level Depression Level Depression Test.Test.

Pumping rate is Pumping rate is kept constant kept constant during test.during test.

Casing Pressure Casing Pressure and Liquid Level and Liquid Level During Liquid During Liquid Level Depression Level Depression Test.Test.

Pumping rate is Pumping rate is kept constant kept constant during test.during test.

Gaseous Column Height vs. Casing Pressure for 150 MCF/D in 5” & 2-7/8”Gaseous Column Height vs. Casing Pressure for 150 MCF/D in 5” & 2-7/8”

Annular Annular Gaseous Gaseous

Liquid Column Liquid Column Effective Effective Liquid Liquid

FractionFraction vs. vs.

Q/A or Q/A or (dp/dt)*D(dp/dt)*DLLLL

Annular Annular Gaseous Gaseous

Liquid Column Liquid Column Effective Effective Liquid Liquid

FractionFraction vs. vs.

Q/A or Q/A or (dp/dt)*D(dp/dt)*DLLLL

Actual Field Collected Data Point

Preliminary heavy oil data

Annular Gas Flow – dP/dT MeasuredAnnular Gas Flow – dP/dT Measured

Close Casing Valve

Close Casing Valve

Casing Pressure increase as a function of time is a measure of casinghead gas flow rate

Casing Pressure increase as a function of time is a measure of casinghead gas flow rate

dPdP

dtdt

Gas flow into well = 45 MCF/D

Gas flow out= 45 MCF/D

Time = 0 Time = 4 min.

46.2 psi

49.4 psi

PBHP = 572.8 psi

Casing Valve Closed During Test

Calculation of annular gas flow rate is based on the increase in casing pressure per unit time during the casing pressure buildup test. Using the real gas law:

P1*V1 = Z1n1RT1 at time t1 and

P2*V2 = Z2n2RT2 at time t2 where in the well:

V1 = V2 = volume of annulus minus volume of liquid

T1 = T2 = average temperature

R = gas constant

P1 =initial casing pressure

P2 = pressure at end of casing buildup test

n2,n1 = number of moles of gas in annulus

Then solve for (n2-n1) which is the increase in gas mass during the time (t2-t1) and convert to standard cubic feet per day.

Gas Flow CalculationGas Flow Calculation

Requirements for Accuracy of dp/dt TestRequirements for Accuracy of dp/dt Test

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 and PIP - TWM ProgramProducing BHP and PIP - TWM Program

Equivalent Gas-Free Liquid HeightEquivalent Gas-Free Liquid HeightEquivalent Gas-Free Liquid HeightEquivalent Gas-Free Liquid Height

Gas

Low PBHPPerfs

Pump

Flowline

Pc

Pt

Gaseous LiquidColumn with 10 - 15%Liquid

HighFL

Gas

Low PBHPPerfs

Flowline

Pc

Pt

Gas-FreeLiquid

Gas FreeFL

“Remove” gas from annular fluid column

Gas Free Liquid - TWM ProgramGas Free Liquid - TWM Program

Static Bottom Hole Pressure, Static Bottom Hole Pressure, SBHP SBHP (Reference: “Acoustic Static BHP)(Reference: “Acoustic Static BHP)

Static Bottom Hole Pressure, Static Bottom Hole Pressure, SBHP SBHP (Reference: “Acoustic Static BHP)(Reference: “Acoustic Static BHP)

Driving Pressure available to Driving Pressure available to push the fluids to the wellborepush the fluids to the wellbore

Generally GUESSEDGenerally GUESSED

Need within +/- 15%Need within +/- 15%

Operator Should MeasureOperator Should Measure StaticStatic Fluid LevelFluid Level and Casing Pressure and Casing Pressure in wells shut-in for any reason.in wells shut-in for any reason.

TWMTWM or or AWP2000AWP2000 compute the compute the SBHPSBHP

Calculation of SBHPCalculation of SBHPCalculation of SBHPCalculation of SBHP

Gas

Brine

Oil

Pc

Pt

Static FL

Well Shut-in

SBHP

Static BHP = Static BHP =

Casing Pressure +Casing Pressure +

Gas Column Pressure +Gas Column Pressure +

Oil Column Pressure +Oil Column Pressure +

Water Column Pressure.Water Column Pressure.

Note: Fluids Segregated by GravityNote: Fluids Segregated by Gravity

WOR produced after shut-inWOR produced after shut-inWOR produced after shut-inWOR produced after shut-in

Cannot Accurately Predict Cannot Accurately Predict WOR during after-flow. WOR during after-flow.

Assume that during after flow the Assume that during after flow the WOR remains same as WOR remains same as measured by well test.measured by well test.

Gas

Brine

Oil

Pc

Pt

Static FL

Well Shut-in

SBHP

Program computes location of Program computes location of water/oil interface from wellbore water/oil interface from wellbore geometry and geometry and last measuredlast measured producing fluid levelproducing fluid level

Static Bottom Hole Pressure, Pump Intake near PerforationsStatic Bottom Hole Pressure, Pump Intake near Perforations

Liquid Level @ Pump Liquid Level Above Pump

For Improved Accuracy Static Bottom Hole Pressure: Push Liquid Level near PumpFor Improved Accuracy Static Bottom Hole Pressure: Push Liquid Level near Pump

1.1. Increase Casing Pressure Increase Casing Pressure while pumping.while pumping.

2.2. Push the Liquid Level to Push the Liquid Level to

the Pump Intake the Pump Intake before before shutting-inshutting-in the well. the well.

3.3. Shut-in well and monitor Shut-in well and monitor liquid level and casing liquid level and casing pressure.pressure.

Minimizes error due to uncertainty Minimizes error due to uncertainty of fluid gradient and WOR of fluid gradient and WOR

during afterflowduring afterflow..

Minimizes error due to uncertainty Minimizes error due to uncertainty of fluid gradient and WOR of fluid gradient and WOR

during afterflowduring afterflow..

Static Bottom Hole Pressure, Determination w/ High PumpStatic Bottom Hole Pressure, Determination w/ High Pump

Liquid Level @ Pump Liquid Level Above Pump

Determination of Accurate SBHPDetermination of Accurate SBHPDetermination of Accurate SBHPDetermination of Accurate SBHP

Well should be shut-in for a time sufficient to Well should be shut-in for a time sufficient to stabilize casing pressure and fluid level. stabilize casing pressure and fluid level.

Periodic fluid level measurements identify Periodic fluid level measurements identify stabilized conditions.stabilized conditions.

More accurate calculation of More accurate calculation of StaticStatic BHP BHP entering the entering the ProducingProducing Fluid Level, Casing Fluid Level, Casing Pressure, and Casing Pressure Buildup Rate Pressure, and Casing Pressure Buildup Rate before well is shut-inbefore well is shut-in into the SBHP into the SBHP worksheet.worksheet.

SBHP worksheet in TWM programSBHP worksheet in TWM program

% Liquid

Pressure Transient Test Best method for SBHP

Pressure Transient Test Best method for SBHP

Computed from CasingheadPressure, Annular Fluid Level andDensity of Gas and Fluid Columns

Computed from CasingheadPressure, Annular Fluid Level andDensity of Gas and Fluid Columns

Summary of Determining BHPsSummary of Determining BHPsSummary of Determining BHPsSummary of Determining BHPs StaticStatic and and ProducingProducing BHP can be determined BHP can be determined

from acoustic liquid level surveys.from acoustic liquid level surveys.

Accurate casing pressure and Accurate casing pressure and casing pressure casing pressure buildupbuildup rate determines % Liquid.rate determines % Liquid.

BHP = Surface Casing Pressure + Pressure from BHP = Surface Casing Pressure + Pressure from the column of fluids in the annulus.the column of fluids in the annulus.

Fluid Distribution is a Function of Well’s Fluid Distribution is a Function of Well’s Producing ConditionsProducing Conditions

Questions ?Questions ?Questions ?Questions ?