This paper describes our recent observations relative tothe repeated shut-ins of the high-pressure oil and gaswells in the Gulf of Mexico. The current MineralManagement Service regulation requires that in the caseof an emergency such as hurricanes, fires, spills,pipeline problems, etc., the subsurface safety valve slamshut in 45 seconds but the flapper at the end of its travelactually slams instantaneously against the well flowingpressure. The type of subsurface safety valve installedfor this purpose is a flapper, which is kept open by anhydraulically activated spring. Once the spring receivesthe triggering signal, it will close the flapperinstantaneously. The instantaneous shut-in appears tocause a water hammer effect in the form of strong cyclicpeak pressure, which travels down the tubing into theperforations. This extra pressure builds up cyclically inthe reservoir rock near the well boreuntil it is attenuated with time. After the emergencycondition has passed, theoperator puts the well back on production. We haveobserved, at least in three deep wells with highlyconsolidated reservoir rocks, that not only did they losefluid production, but they also produced a great deal ofpulverized, highly angular rock fragments. Themicroscopic analysis of the rock fragments showpatterns of reflected and propagated tension fractures,stick-slip sheared surfaces, and catastrophic failures ofsilica, feldspars, and various types of grain-bondingcements such as siderite. We have concluded that thewells lost production due to well sanding and that thewell sanding was induced by cyclic hammering pressureand cyclically induced and propagated micro fracturesextending all the way into the water bearing formationbelow or above the producing zone. Furthermore, theseinduced Hammering Waves detrimentally changed thecyclic effective stresses around the perforations.
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