This is a simple practical Field Guide for performing Straddle Packer tests (pressure testing) in the field. The document is prepared by Ankan Basu and should be used only as a guidance. Every project is different. Modify your needs as required in the field. Contact author for further assistance at firstname.lastname@example.org
- Prepare Packer Set up.
- Go to desired Packer test interval.
- Run 3 well volume of water before inflating the packers.
- Inflate Packers – apply pressure based of depth and height of water column above the packer.
- Apply pressure – usually applied P=0.5xdepth of packer.
- Spend 5-20 minutes to stabilize the system.
- Take flow measurements at desired interval.
- Once flow is stabilized, deflate packers and move to the next zone.
|Goal of Packer Tests: Determine Permeability of Rock Strata|
Before Packer Test:
Understand the Project and goal:
- Why a Packer Test is required?
- What kind of accuracy level is expected from the study? (Larger Packer Interval vs Shorter Packer interval)
Gather Site Specific information
- Get general geologic map of the area if available.
- Check for existing borehole log or geophysical log in the vicinity of the site.
- Get location map, road direction, total depth of drill hole, drill hole id and related information.
Get ready before you leave office
- Open reel Tape Measures-300 Feet; multiple depending on the depth of the drillhole.
- Stop Watch
- Measuring Tape
- Water Meter
- Pocket Knife
- Field notebook
- Field log sheets
Driller’s will bring:
- Nitrogen Tank-should carry at least two
- Different types of pressure gauges (such as 0-200; 0-300; 0-400; 0-600 psi)
- Flow meters -Must carry multiple ones
- AQ rods or 1 inch water line.
While Drilling the borehole
- Geologic log
- Fracture log
- take photographs
- Look for fractures, slikensides, broken zones, coal seams and coal spars and other potential zone of high water flow.
- Schedule geophysical logging
Geophysical Logging of borehole for Packer Test
- Open hole geophysical logging is recommended if borehole condition is stable that allows the caliper tool to detect any fracture.
- Run temperature log to see any possible movement of water indicated by change in water temperature (and resistivity too).
- Acoustic Televiewer: Acouistic Televiewer (ATV Log) is widely used for fracture detection in the subsurface and also useful to determine dip of beds etc. Read more about Acoustic Televiewer.
Before starting Packer tests
- Check water table elevation
- Determine test zone intervals based on all available information including photographs, acoustic televiewer log, E-log, caliper log, temperature log etc.
- While determining the test zone intervals, do not set the top or bottom packers in soft zones, fractures or in the coal seams. The packer may rupture while inflating in contact with a fracture and the packer may not seal properly when in contact with the coal seam.
- Write down all zones to be tested in order on a page for quick reference.
- Have some idea about the flow-rate in different zones to be tested based on available information. Such as a highly fractured zone is expected to show high flow-rate.
- Examine setup of the flow-meter, water gauge, bypass valve, take photograph of the setting.
- Examine packers, set up packer assembly, measure packer length, interval length etc.
- Measure distance of the flow gauge above ground.
- Set up a reference point point for depth calculation.
|Steps of running Running Packer Tests|
Practical Tips and Troubleshooting Packer Tests •
Calibration check: Use bucket with 1-5 gallons mark to check calibration, fill up the bucket up to 5 gallons and check the reading at the flow meter. Very rarely 5 gallons at the difference in reading at the flow meter would equal to 5 gallons in the bucket. Usually the flow meter reads less flow. Use calculator to get conversion factor.
Example: 4 gallon at flow meter=5 gallons at the bucket
Calibration factor=1.25 X flow meter reading.
Accuracy Check 1: Some flow meter respond to pressure and record flow when there is no actual flow. Close the valve to the HIGH PRESSURE LINE so that no flow is going to the packer assembly, apply pressure at the water gauge between 0-150 PSI. In ideal situation, there should not be any flow. But some flow meter show higher flow with higher pressure when there is NO FLOW at all. Change flow meter.
Accuracy Check 2: Some flow meter works great at higher flow but could not detect low flow. Let the water run under very low pressure and collect the water with a bucket. Test it as low as 0.1 GPM (10 minutes to fill up 1 gallon at the bucket). Trial and Error to get required flow.
Do NOT use too much Pressure: Different types of flow meters are made for different purposes and they all have different limit of maximum pressure that they can perform. If you apply more pressure than the flow meter is built for, it will break. Commonly the bottom part the flow meter breaks due to high water pressure.
Read the manual of the particular flow meter: Check the range of pressure for which the flow meter works (see manual). If working in a deep borehole, talk to the drillers before reaching the site about high capacity flow meter. Drillers should carry multiple flow meters.
After each test wide open the BYPASS VALVE.
- Check for possible leaks in the airline
- Check for possible leaks in the pipes, joints and connectors
- Inflate packers at surface up to 90 PSI (max) to check that the packers are inflating properly.
- Keep it inflated at a set pressure for 5 minutes. If the pressure at the N2 pump drops, you have a leak. Search and fix.
- If the pressure is stable, go to next step – PACKER TEST at the CASING.
- Inflate packer up to 250 PSI.
- Run water between 10 to 150 PSI.
- If flow meter records any flow-then either the packers are not sealing properly or the flow meter is responding to pressure. Change flow meter and rerun test till you get 0 gpm flow in the casing.
- After the test in the casing, go down to the bottommost zone to be tested and start testing
Required Back Pressure
- Before starting each test run at least 3 well volumes of water to remove any air bubble before inflating the packers.
- While going down hole, make sure each joints between the AQ rods (or the 1 inch water line) is sealed properly. Use “THREAD SEALER” if required.
- Look for leaks at the adapter near ELBOW and valves for leaking water.
- Keep enough slack in the airline at the top of the packer assembly (at least 1 feet).
DO NOT use too much of inflation pressure
- Use enough pneumatic pressure to inflate the packers at certain depths properly.
- But if too much of pressure applied to inflate the packers-
- •Packer may rupture
- •Rock strata may fracture
- •Too high back pressure may cause other accidents too.
Troubleshooting Packer Tests
- Air line blew off (more common)
- Packers busted (Packers can rupture if set at a fracture zone)
- Packers may not be sealing properly, increase packer inflation pressure, rerun the test.
- If still getting high flow in higher inflation pressure – Flow meter may be responding to pressure when there is NO FLOW. Test flow meter.
- Other possible cause- possible leak in the joints of the AQ rods. Find a zone of crystalline sandstone. Run the test.
Note: I had 1.5 -2.0 gpm of flow in a 200 feet strata composed of tight shale and sandstone (seen from core, verified by Acoustic Televiewer log). Bad data due to flow meter responding to PRESSURE.
No Flow for a long thickness of the strata may also indicates mechanical problem.
- Some flow-meter can not record very low flow (0.01-0.04 gpm or less).
- Check manual for the particular flow-meter for lower sensitivity range.
- Perform Accuracy test 2 for the flow meter.
Article by Ankan Basu; P.G; Coal Geologist. Contact Ankan Basu for your project needs at email@example.com
Here is the POWERPOINT PRESENTATION prepared by Ankan Basu for Packer tests in the field.