Henry E. Rogers

Tailpipe Disconnects Ideal for Setting Cement Plugs in Complex Wellbores; Procedures and Case Histories Provided

The primary goal of operators and drilling contractors is to safely, economically, and efficiently drill more holes in less time to enable completion and production operations to begin. However, unplanned events that introduce unexpected and costly delays often occur during the drilling phase. These unplanned events must be dealt with in a timely and effective manner to enable drilling operations to continue. One event type common to drilling operations is the need to set openhole cement plugs for plug back, kickoff, or curing loss-circulation intervals. The time and cost associated with spotting cement plugs directly impacts well operations and is often classified as nonproductive time (NPT) by operators, especially if initial plugs fail to achieve the purpose for which they were set. Placing cement plugs in today’s complex wellbores and the increased costs associated with these operations necessitates the use of plug designs and procedures that have been designed to reduce risk and utilize new technologies and documented processes to achieve the desired results. Reviewing current practices for deploying new technology helps to optimize overall plug cementing operations in both vertical and extended-reach wellbores. However, there are a number of challenges associated with setting cement plugs in an openhole well. Most importantly, drillpipe can become differentially stuck across a lost-circulation zone, and the plug can become contaminated with the intermixing of the mud, resulting in inadequate isolation or insufficient strength. An innovative tool (Rogers et al. 2004) has been designed to meet the challenges associated with setting cement plugs. The tool connects sacrificial/drillable tubing to the drillpipe and allows an operator to trip into the well and spot the cement plug across the problematic zone. Once cement is placed, the tool is disengaged and the operator trips the drillpipe out of the hole, leaving the cement plug and tubing undisturbed. The sacrificial tubing can be drillable; therefore, the operator can drill through the plug or commence other operations, as required. This paper discusses the challenges operators face when setting cement plugs and how risks and NPT are reduced with this innovative plug-setting process and tool. Well examples are documented from case histories to illustrate the success and lessons learned. Introduction Drilling for natural resources all over the world is not getting easier. To maintain current production levels in a demanding market, operators are forced to either drill into mature fields or into unconventional reservoirs. Production from a mature formation will reduce the pore pressure, and this reduced pore pressure can lead to a lower fracture gradient. The chances of lost circulation while drilling into these lower-fracture-gradient zones continue to increase. As the reservoir depletes, an operator might drill the next well deeper to capture the resources from a deeper zone. This too exposes the operator to the risk of drilling through this shallower depleted zone. Unique challenges are likely to occur when an operator decides to drill an unconventional reservoir; for example, lost circulation of drilling fluids to a cleated or vugular formation might occur. A properly designed cement slurry is the best choice to heal these lost-circulation events (Garvin and Moran 1991; Economides et al. 1998). Cement can be squeezed into the lost-circulation zones and, when set, it will strengthen the wellbore. The cement plug is drilled through, leaving the residual cement setting inside these problem zones. Cement plugs can be placed by bullheading down drillpipe into the loss zone or balanced across the loss zone. There are challenges with both of these operations.