How to prevent Drill Pipe Washout

Introduction

Drill Pipe Washout in oil and natural gas is a sudden problem that can occur at any stage of drilling and may lead to drilling string separation and subsequent salvage during drilling operations, which will greatly increase time and cost. Therefore, it is necessary to analyze the possible causes of accidents and prevent them in advance

Precaution

As with all downhole problems, prevention is better than cure. The best way to prevent pipes washouts is to handle all tubulars and string correctly:

All threads and seal faces are to be inspected before make-up.

Correctly clean and dope (Thread Compound) all tool joints for drill pipes, drill collars, heavy weight drill pipes, …. etc.

Ensure the correct make-up torque is being applied.

Always use protectors to prevent damage to threads and seal areas.

Maintain good drilling practice to prevent all drill string vibrations.

All tubulars are to be inspected to a standard (drill pipe inspection) and at a frequency commensurate with operating conditions and in accordance with both business unit requirements and API RP7G.

Special Attention

In practical operation, special attention should be paid to the following points

When flushing to the bottom, check whether the actual system pressure drop matches the calculated value.

The driller and data engineer must always be aware of any changes in mud weight (please also check the mud balance testing program) or any work being carried out on the circulating mud system that may affect system pressure loss. (Circulating heavy slugs underground can simulate the pressure drop typically associated with pipeline washout in drilling oil and gas.)

The driller and data engineer must remain vigilant and report any unexplained pressure fluctuations.

The washout of oil and natural gas usually exhibits a typical sudden pressure drop, followed by a slow and continuous decrease in circulating pressure.

If there may be a problem

If there is suspicion of washout during drilling, the following measures should be taken:

Check if the pressure drop is independent of the decrease in pump stroke.

Pull the rope off the bottom and immediately stop the cycle.

Check ground systems such as rotating hoses, drag chains, high-pressure pipelines, etc. for leaks and potential offshore leaks.

Stop rotating, but continue operating the pipeline.

Check if the weight of the drill string has not changed.

If no leakage is found, restart the mud pump, but keep people away from the floor while pulling the bracket back through the rotating device.

Derrickman makes a sound on the pump and checks for ejections, etc.

The driller replaces the second pump or pump combination and rechecks the pressure.

Checking against previous SCR data is unlikely to be helpful as the circulating pressure involved is usually too low to be valuable.

The person in charge of the well site checks the pressure map for signs of characteristic pressure drop or pressure loss that may be attributed to the cleaning of the drill nozzle or signs of heavy slugs circulating around the system.

If the MWD tool is in the drill string, check if its pulse is still normal (a lack of pulse may indicate pipeline washout above the tool).

When the pipe column moves up and down, does the fluctuation of system pressure exceed the normal value? When the pipe string (especially drill pipe) changes from tension to compression, longitudinal crack washout may open and close

If there is no available pump test data, close IBOP (or riser valve, if IBOP is not designed to maintain pressure from above). Then use a mud pump to test the ground system to the previous circulating pressure.

When Washout While Drilling is Confirmed

Once it has been established that the pressure loss & pipe washout is indeed downhole then the drilling Site Leader must decide whether to circulate clean or not. This decision can only be taken at the time and with the full understanding of hole conditions etc.

Normal practice would be to pull straight out without circulating, however, circumstances such as having Nuclear Sources sitting in the reservoir, may dictate otherwise. String rotation should be avoided with a washout in the string.

In order to allow for easier detection, do not pump a slug but make sure the rig floorhands are not at risk of being sprayed with mud when the wash arrives back at the surface. Also, floormen should inspect each tool joint as it is broken and pay particular attention to the connection upsets and slip areas.

Action to be taken

Precautions for handling pipeline flushing during drilling include:

1.When attempting to locate scour, as mentioned above, surface system pressure testing of IBOP or riser valves is usually useful. However, it is important that the drilling supervisor witnessed the test in advance and understood the normal leakage rate that may occur during the testing of the mud pump.

2.A more accurate and potentially less destructive option for conducting static pressure testing is to conduct dynamic surface testing through a fixed throttle valve. It is possible to check the baseline pressure while drilling, but only within the casing.

3.If deemed appropriate, the drilling supervisor may attempt to use any of the following methods to locate the location of pipeline washout

4.After tripping out, if no signs of washout are found, consideration should be given to tripping the pipeline to the bottom to form and disconnect each connection. If it proves unsuccessful again, it may be necessary to perform pressure testing on the string in stages.

Method for determining the location of drill pipe washout

If water-based mud is used, carbide bombs may be dropped and the gas peak generated may lag (please also check: drilling lag time) to display the depth of washout.

If there is no MWD in the bottom hole assembly (please also check the type of bottom hole assembly), a soft wire signal device can be used. Tie a large plug knot on a 12 inch long cord and then untie the rope. Pump the flexible cable down into the pipe column and observe if the pressure slightly increases when the pipe column is partially blocked and flushed. At this point, the pump stroke can be used to calculate the position of the washing solution (in addition, Softline will make it easier to detect the washing solution during drilling).