Drillpipe Conveyed

Key Takeaways

• The economic case for drillpipe-conveyed perforating in horizontal and extended-reach wells is based on the comparison of total costs including rig time, service costs, and completion quality: a wireline-conveyed perforating run in a horizontal well typically requires specialized tractors (motorized wireline conveyance devices) or the well to be produced or pumped to provide flow to push the wireline tool to depth, both of which are expensive and time-consuming; DPC perforating uses the drill string that is already in the wellbore during the completion phase to convey the gun string, eliminating the wireline tractor cost and avoiding the flow-back or pump-in operations needed to push wireline to depth; the tradeoff is that DPC perforating requires the drill rig to remain on location while the perforating operation is performed (the drill string cannot be released while the guns are attached), adding rig time cost that may exceed the wireline tractor savings on shorter horizontal wells; for long horizontals (5,000-15,000 feet in Permian Basin shale completions) and ultra-extended-reach wells (horizontal sections exceeding 20,000 feet), the inability to convey wireline tools without tractors or pumping makes DPC perforating the operationally simpler and often less expensive option.
• DPC perforating systems must address the challenge of firing the guns reliably at a depth where the surface crew has limited communication with and control over the downhole tools: the most common firing mechanisms are the tubing pressure-actuated firing head (which fires the guns when annular or tubing pressure exceeds a preset threshold, activated by surface pump pressure), the drop-bar or go-devil firing head (which fires the guns when a weighted bar dropped from surface impacts the firing head), and the through-pipe wireline firing head (which uses a slim wireline run inside the drill pipe to provide electrical firing current and detonation confirmation to surface); the pressure-actuated head is simple and reliable but requires careful design of the pressure threshold to avoid accidental firing from drilling fluid pressure during run-in, and to ensure reliable firing when the target pressure is applied; the through-pipe wireline head provides the best firing control and diagnostic capability but requires the slim wireline to negotiate the drill string connections without damage, which limits the wireline's ability to pass through certain drill string configurations.
• Drillpipe-conveyed formation logging in deviated wells follows the same operational sequence as DPC perforating but uses formation evaluation sensors rather than perforating guns: the logging tool string is attached to the bottom of the drill string with a wireline head connection, the wireline cable is run through the drill pipe to connect the tool electrically to surface, and the drill string is lowered to bring the tool to the bottom of the logged interval; the drill string is then pulled upward at a controlled logging speed while the tool sensors measure formation properties and transmit them up the wireline cable to the surface acquisition unit; the logging speed is limited by the same torque-and-drag considerations that govern all drill string operations in deviated wells, and the requirement to maintain a constant speed for correlation-quality log data adds complexity compared to a standard wireline log; despite these complications, drillpipe-conveyed logging provides measurement quality equivalent to standard wireline logging and is routinely used in extended-reach wells in mature fields like the North Sea where the deviation profile prevents wireline log acquisition without DPC conveyance.
• The safety considerations for DPC perforating differ from wireline perforating in ways that require specific procedure modifications: in DPC perforating, the perforating gun string is physically connected to the drill string and is inside the blowout preventer (BOP) stack when first being run in the wellbore, requiring specific wellbore preparation (setting a balanced fluid column that prevents formation fluids from flowing while the guns are in the BOP) and BOP configuration (ensuring the ram configuration can accommodate the gun string OD without activating a blind shear ram that could cut the gun string); the disconnection of the spent gun string from the drill pipe after firing and retrieval requires either a mechanical release mechanism in the gun string or a wireline-run disconnect tool, both of which must be verified functional before the guns enter the wellbore; post-firing inspection of the retrieved gun string and any undetonated charges follows the same explosive safety protocols as wireline perforating, but the physical environment of a drill rig floor rather than a wireline truck requires adaptation of the explosive handling procedures to the rig's layout.
• Pipe-conveyed logging (PCL) addresses a specific problem in the logging-while-drilling (LWD) versus wireline decision for deviated wells: LWD provides real-time measurements during drilling but with lower tool sophistication and fewer sensor types than available in wireline tool strings; wireline logging provides higher-quality measurements with more sensor options but cannot reach bottom in high-angle wells without DPC conveyance; drillpipe-conveyed wireline logging combines the access capability of the drill string with the measurement quality of wireline sensors, providing a pathway to obtain high-quality formation evaluation data in wells where neither pure wireline nor pure LWD provides an adequate solution; in fields where the formation evaluation data quality directly affects completion design decisions (such as the gamma ray and neutron-density log quality needed for petrophysical analysis in carbonate reservoirs), the PCL approach is justified by the improvement in data quality over LWD even when the LWD data is technically available from the drilling phase.