Method To Pump Bridge/Frac Plugs at Reduced Fluid Rate

Abstract

Abstract This case-history paper presents hardware and a method to enable pumping frac plugs and bridge plugs into horizontal wells, using substantially less fluid than used by conventional pumpdown means. Cases presented are from operations in the Barnett Shale formation of north Texas. The system presented was developed in response to (1) the need to conserve well fluids used and (2) high pumping rates needed to pump frac plugs and bridge plugs to setting depths in horizontal holes. Fluids bypassing the plug without exerting enough push on the plug necessitated application of high pump rates and total fluid volumes. Advantages of (1) using new sealing methods to reduce fluid requirements, and (2) following a set of procedures to pump plugs to the setting depth in horizontal wells are numerous:Total volume of water needed is greatly reduced.Lower pumping rates allow for the use of wireline when tight formations are encountered.Precludes the requirement to bring in more expensive and time-consuming methods of placing the plugs to depth, such as hydraulic tractors or coiled tubing units.Saves time and fluid costs.Reduces chances of damaging reservoirs with excess pumpdown fluid.Fluid flow around the sealing device provides a jetting action ahead of the tool to disperse sand and debris ahead of the plug in horizontal casing, based on field experience.As compared to that of hydraulic tractors, the system enables high travel rate for wireline, up to 150 ft/min. The paper presents procedures for running plug-sealing devices that reduce the bypass of fluid between the plug and casing wall. The system has been in use for about 1 year; field experience, lessons learned, and application tips are also presented. Introduction Plug Placement In using hydraulic-fracturing stimulation to enhance production from multiple zones of horizontal wells, operators usually employ bridge plugs or "frac" plugs to isolate pay zones of the well so that fracturing fluids are pumped only into targeted zones. These plugs are traditionally installed on tubing (jointed or coiled tubing) or wireline. In wireline placements, plugs may be pushed to desired depths by pumping water behind the plug or by pushing plugs down with a hydraulic "tractor." Installing and setting the plugs in vertical wells is relatively routine; however, placement and setting processes followed for horizontal hole sections are more challenging. To avoid the expense of using hydraulic tractors or coiled tubing (CT) units, operators attempt to push the plugs downholedown hole ahead of a column of water. Much of the water bypasses the plug, requiring high pumping rates to generate enough "push" to propel the plug to setting depth. This excessive use of water increases the logistical load and can damage formations that are sensitive to water. Further, tight formations do not accept the water readily, so more pump pressure is required. If the formation is especially tight, it may not be possible to pump the plug to setting depth. Plug Removal For years, both cast-iron and retrievable-type bridge plugs have been popular with oil and gas operators for achieving zonal isolation in multi-zone wells to perforate, treat, or isolate the zones independently for remedial work without damaging the formation.