IV. Surge Reduction System - a. What is Surge Reduction?

Surge reduction reduces excessive surge pressure experienced when ‘conventionally’ running close tolerance liners or sub-sea casing strings. A surge reduction system reduces the surge pressure that would otherwise break down the last casing shoe or a section of the open hole. It also reduces surge pressure by minimizing the returns that normally are pushed up the small annulus of the liner/casing or the liner/hole. The majority of the displacement volume flows up the inside of the liner/casing and crosses over to the drill pipe/casing annulus above the liner or sub-sea running tool. This redirected flow is made possible by the use of a "diverter" sub and is facilitated by use of auto-fill float equipment. The system addresses a major industry concern: running liner hanger equipment with drilling fluid containing large amounts of cuttings and debris. By changing the flow path of the drilling fluid up through that equipment with the largest opening float equipment available today, the system minimizes that effect. The system is able to handle large amounts of cuttings and wellbore debris routinely encountered during drilling operations. Surge reduction tools are designed to run with any mechanical or hydraulic set liner hanger or sub-sea running tool. In addition, tandem sets of the diverter sub can be run with large diameter sub-sea casing strings that are using a drillpipe stinger for cementing purposes. Operators also are using the diverter subs for reducing surge while running tie-backs instead of using bleeder caps, thus reducing rig time having to manage fluid over-flow.