Hydrofracturing, commonly referred to as well fracking, stimulation or hydrofracking, is a well development process that involves injecting water under high pressure into a bedrock formation via the well. This is intended to increase the size and extent of existing bedrock fractures, thereby enlarging the network of water bearing fractures and size of the area supplying water to the well.
The oil well fracking procedure is often used to increase well yields of new deep drilled wells with marginal or inadequate production rates. It may also be applied to older existing wells that have progressively diminished recovery rates over time usually caused by mineralization and incrustation of rock fractures.
Field personnel were preparing a high pressure pump truck to perform a routine chemical batch inhibition job on a 8 inch gathering system pipeline. During the pressure test of the temporary high pressure piping a one-inch hammer union failed and blew apart. The fitting, rated for 6000 psi, failed at a test pressure of approximately 1700 psi. When the fitting separated there was sufficient reactive force on the pipeline riser to significantly bend the 3/4 inch pipe nipple attaching the isolated valve to the pipeline. This bending force exceeded the strength of the pipe nipple (threaded) causing it to crack and leak high-pressure sour gas. Fortunately both workers at the site were able to safely evacuate and no injuries resulted.
The hammer union fittings were badly worn and had some thread damage. The wear was likely due to cumulative use, and existed prior to installation at this location significant thread damage likely existed prior to coupling the fittings for this job. There was insufficient thread engagement on the coupling union to hold the test pressure, allowing the threads to shear and the coupling to come part. The temporary piping, which included the high-pressure hose (30 meters), a back flow prevention device did not have the air bled out before bring the piping up to the test pressure to check for blockage or to gas free the system prior to hydro-testing. The hammer union likely fitting failed instantly and escaping high-pressure air and liquid created bending stress on the pipeline connection riser causing it to bend and crack below the isolation valve. The pipeline connection riser used for this job was located downstream of the facility isolation valve, which necessitated de-pressuring of approximately 7.5 km of 8 inch pipeline, adding to the length of time necessary to bring the leak under control.
All high pressure piping equipment used in this type of service must have a quality control program in place. The program should address regular inspection, testing and replacement of fittings and hoses when wear or damage is evident. Companies using or providing this type of equipment should check with their supplier or the fitting manufacturer for information on acceptable wear limits and inspection techniques.
Field personnel supervising these types of pressure pumping operations should verify their service providers have such programs and the workers involved are knowledgeable prior to commencing the job. Insure all “working” connections (those used routinely or in the continuous service) are located on surface facility lines between isolation valves, which can be quickly closed in the even of a piping or equipment failure. This will significantly reduce the amount of gas that will need to be bled-down and minimize the amount of gas that could leak in the event of an incident.
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