Reelwell Drilling Method Makes Use of Dual-Conduit Drillstring

Abstract

Young Technology Showcase The Reelwell drilling method (RDM) is a drilling solution using a unique flow arrangement. RDM employs drillpipe where an inner string is installed to form a dual-conduit drillstring. This allows the fluid and cuttings from the bottom of the well to return to the surface through the inside of the drillstring. RDM enables improved hole cleaning, reduced possibility for washouts, and improved downhole pressure control. RDM has unique features for managed-pressure drilling (MPD) and extended-reach drilling (ERD). A special feature of RDM is that it allows MPD and underbalanced operations (UBO) to be performed with a heavy fluid in the well annulus by means of the Reel-well multigradient system. This implies that MPD and UBO can be performed with two well barriers and, thus, improved safety. RDM started its development in 2004 and has been through several full-scale tests. In 2009, the system was used for the first time for directional drilling with MPD in a land well in Norway. In 2010, RDM was used for the first time in a live shale gas well in Canada. These operations have validated RDM and its features and are important steps proving its potential. Arrangements and Rig Description Fig. 1 presents a schematic of the system. The system is based on a dual-channel drillstring, where one flow path is used to convey the drilling fluid into the well down to the bit and the other channel is used for the return fluid from the bottom of the well. This arrangement implies a modification of the drilling fluid flow arrangement. The following special tools and arrangements are used. Dual Drillstring (DDS). The DDS can be manufactured in various sizes; the current size used consists of 6⅝-in. drillpipe adapted with 3.5-in. inner pipe that has been fitted with stab-in innerstring connectors. The DDS is handled on the rig floor as conventional drillpipe. Topdrive Adapter (TDA). A dual-conduit swivel connects the rig’s topdrive unit to the dual drillstring and enables rotation of the drillstring by the top drive. The TDA is connected to the surface flow control unit through an additional separate stand pipe and mud hose. Flow Control Unit (FCU). The FCU is a control valve arrangement equipped with pressure and flow sensors and permits accurate control of the in/out flow in the RDM system. The control unit connects to all the flow paths of the system, as shown in Fig. 1. Dual-Float Valve (DFV). The DFV is a device located at the bottom of the DDS. The DFV includes a flow cross-over from the well annulus into the return channel of the DDS. The DFV incorporates valves that isolate the drillstring from the well during connections. In the fail-safe default position, the DFV closes both channels of the DDS. A conventional BHA is made up below the DFV.