Downhole Pressure Monitors

Downhole Pressure Monitors• Halliburton Pressure Transmission Systems (PTS) have been in use at SYU since 1984 (Hondo) & 1993 (Harmony & Heritage)

• Have installed over 60 downhole pressure gauges

• Installed in all new drillwells unless not mechanical feasible (eg. dual strings or ESP’s)

Hondo Platform

Platform Hondo is located in offshore California in the Santa Barbara Channel. The water depth is between

900' and 1200'.Hondo was discovered in 1968 and the initial

production began in 1981

Presently26 active wellbores.

14 Wells that are on gaslift or 54% of the total active wellbores

Hondo PlatformHondo Platform

Platform Heritage is located in offshore California in the Santa Barbara Channel. The water depth is

between 900' and 1200'.Heritage was brought on line in 1993.


28 Wells that are on gaslift or 72% of the total active wellbores.

BackgroundHarmony Platform is located in offshore California in the

Santa Barbara Channel. The water depth is between 900' and 1200'.

Harmony was brought on line in 1993.


23 Wells that are on gaslift or 74% of the total active wellbores.

Gas Lift Optimization Using Downhole Pressure Monitors

•Downhole gauges can measure downhole pressure at depth real time

• Can change any condition (eg. Choke position, g/l rate, viscosity reducer) and immediately see effect on downhole pressure

• If downhole pressure increases then drawdown has decreased therefore we know fluid rate has decreased

• If downhole pressure decreases then drawdown has increased therefore we know fluid rate has increased

• Can change g/l rate and viscosity reducer and immediately determine if there is an impact on rate

BHP

1/20/04 11:13:15 AM 1/27/04 9:08:55 AM6.91 Day(s)

8P741-3

PSIG

890

900

875

925888.36

8P741-3

PSIG

The flowing BHP fell from 895 to 890 psi.

Gas-Lift Rate

1/20/04 11:12:15 AM 1/27/04 9:07:50 AM6.91 Day(s)

8F741

MSCFD

1

1.5

0.5

21.4095

8F741

MSCFD

When the gas lift rate was changed from 1.2 to 1.4MCFD.

Example of Gas Lift Optimization at SYU

Reservoir Surveillance Using Downhole Pressure

Monitors• With downhole gauge can measure shut in downhole pressure by simply shutting in well and measuring fluid level using echometer

• Knowing fluid level we can adjust pressure at the gauge to either the perforation depth or datum depth

• We can get a shut in pressure whenever the well is shut in with no mechanical risk from using wireline in the hole

• These pressures are used to determine if reservoir is being depleted too quickly and we need injection of gas or water

Completion Surveillance Using Downhole

Pressure Monitors• With downhole gauge can perform a pressure buildup test everytime the well is shut in

• With the data from the pressure buildup test reservoir engineer or service co. can determine the productivity of the well (PI) and well damage (skin)

• With this analysis we can determine how effective the completion is and then determine if remedial work is required such as acid stim or scale treatment, etc.

•If you have multiple gauges can use to calibrate and validate your wellbore hydraulic model (NODAL)

PTS Pressure Transmission System

Technology Review

What is PTS?

• An economic alternative method to electronic gauges for the monitor of down hole pressures

• Uses a gas filled capillary tube to convey bottom hole pressure to surface monitor

• Halliburton has applied this proven technology for 30 nearly years

Pressure Transmission System (PTS)

No Electronics No Moving Parts

Capillary Tubing TheoryCapillary Tubing Theory

GAS

PressureMonitoring Equipment

Pressure Chamber

Chamber Ports

Capillary Tubing

Pack-Off

Capillary tubing theory is based on a closed system at the top and an open

system on bottom. Such as covering a straw and pushing down into fluid

Very little fluid enters the straw and a force is exerted at the top of the

straw

Without a seal at the top, fluid enters to the same

height as outer fluid level and no force is exerted at the top


GAS


Compressed Gas Pressure in System to

Monitor BHP

Well Bore Gas

Pressure

Well BoreFluid Pressure

+

=

Gas is bubbled over and the fluid level inside the system is pushed to the bottom of the chamber

After the gas has equalized with the

BHP, the injection of gas is stopped

Gas Movement Inside Chamber

When Pressure Drops To Lowest Point

Chamber Is Full Excess

Gas Escapes

When Pressure Increases

Fluid Rises In Chamber. Our Goals Is To Not Let Fluid Enter

the Capillary Tubing

Gas Correction


GAS


Gas Weightneeds to be corrected for.

This calculation uses TVD and Temperature.

Gas correction example.

Uncorrected BHP 1000 PSI

Weight of Gas 20 PSI

True BHP 1020 PSI

Gas Correction Factors

• Gas weight will change with temperature and pressure

• Gas correction uses True Vertical Depth (TVD) of the chamber not the Measured Depth (MD)

• Helium is used whenever possible as the system gas

• Helium has a liner compressibility with temperature and nitrogen does not.

• Nitrogen is approximately 7 times the weight of helium

Gas Correction with and without DTS

• With DTS we can use real time temperature changes to correct for the weight of the gas column

• If no DTS system is used, we must use an average temperature to correct for the weight of the gas.– The average temperature can be derived from previous

surveys or by logging well with a temperature tool.

– The corrected pressure can be derived thought post processing of the raw data.

Gas Corrections Example Helium

Raw Pressure

PSIAverage Temp

Deg FCorrectedPressure

Difference in PSI if not corrected for changing

temp

500 170 518.3

500 120 519.9 -1.6

1500 170 1552.1

1500 120 1556.4 -4.3

3000 170 3096.9

3000 120 3104.1 -7.2This shows the difference if we corrected the pressure assuming an average temperature of 170 deg F but the actual temperature was 120 deg F

TVD 9000 ft

System Accuracy

System Accuracy

• System accuracy is based on correction of gas weight, transducer accuracy and the fluid level change in the chamber.

• Gas weight calculations are as accurate as we are to knowing the average temperature.

• Transducer accuracy is based on the type of transducer that is installed.

• System resolution .02 to .05 PSI

System Accuracy

• Quartz Transducer.– Accuracy of ± 0.015%FS to 0.02%FS

– Resolution of 0.01 psi

– Drift

• At surface temperatures (< 85°C) .001 % FS/yr

• 150 to 200 C ,02% FS/yr

• Strain Gauge– Accuracy of ± 0.04% FS

– Combined Non-linearity, Hysteresis and Repeatability: +0.04 Best Straight Line (BSL) (option A)

– Stability: 0.1% F.S./annum

PTS Advantages• No Downhole Electronics

– All downhole components are free of electronic parts nothing to get damaged after installation

• Suitable for Harsh Environments– Temp > 800F– Corrosives well conditions– Vibration resistant

• Check System Integrity From Surface– Transducers and data recording devices can be checked from

surface without well intervention– Chamber integrity can be checked without system retrieval

• Flexible– System can be installed in many configurations– System can be installed with DTS options

PTS Advantages

• Accurate– Quartz/Strain Pressure Gauge– Correction of helium gas column either in real time or

post processing

• Rugged– The parts can be installed, removed and reran into same or other wells– Long track record

• Easy to Install and Maintain– The system can be installed and maintained by non engineered personnel

• Wellhead Penetration Simplicity– Wellhead exits use standard fittings– Most wellhead companies already have designs for control line exits– Wellhead penetration is economic

PTS Advantages

• Splices and Connections– Splices are done quick and easy with tube to tube unions

– Connections are none electronic and only require ferrule type fittings

• Economic Pricing– Systems typically run 50% to 75% of typical EDHG

systems

System Maintenance

System Maintenance Concerns

• Maintenance– What is required

• Purging and leak checking

• Transducer checks

– Frequency of maintenance

• Depends on testing we recommend one per Qtr minimum

Downhole Equipment

Used at ExxonMobil SYU

SYU Typical Installation

ChamberInternal Sensing

1/8” Capillary Tube (Pressure)1/4” Safety Valve Tube3/8” Chemical Injection Tube

Surface Equipment Real Time Pressure Read-out

Capillary Tubing

Extended Chamber DesignInternal Sensing

Internal Sensing

Ports are on the inside tubing of the chamber

Extended Chamber Design

Clamp Protectors

Clamp Protectors

Control Line Installation Units

ExxonMobil SYU Project Overview

• Starting Dates– Hondo 1984– Heritage & Harmony 1993

• Installation Types Quantities – PTS Pressure System 60– Chemical Injection 46– Subsurface Safety Valves 86– 1” Diluent Tube 9

• Maximum Installation Depth 19,400 ft

• Failures (PTS System) 1

Questions ?

Documents

Downhole Pressure Monitors