Introduction to and Benefits of Tubing-Conveyed Perforating
Authors: Robson Michael K. 
Published: December 2007

Tubing-conveyed perforating (TCP) technology has grown dramatically duringthe past 5 years. This paper presents a general overview of state-of-the-artTCP systems and operating techniques and discusses the TCP benefits and thetradeoffs involved in the use of conventional wireline perforating. The TCP gunstring, with spacers and selected accessories, is run into the well on the endof a testing or completion string, and the guns are positioned across the zonesof interest (Fig. 1). When the TCP string is positioned with a nuclear-typelogging device, the surface well-control equipment installed, and the desiredpressure underbalance established, the guns are fired. The result is pressureunderbalance established, the guns are fired. The result is simultaneousperforation of all selected intervals with high-performance gun systems in anoptimal pressure environment.

Benefits of TCP

Operational Efficiency. TCP allows the well operator to perforate long, orwidely spaced, intervals simultaneously on a single trip into the well ratherthan having to make multiple runs on wireline. The difference between TCP andwireline-perforating rig time depends on interval length and the number ofwireline descents vs. the additional time to position the string and to readythe well for TCP operations. However, TCP exposes the gun to the wellenvironment longer than wireline perforating, a concern in high-temperatureoperations. TCP gives the well operator an opportunity to perform a flow testimmediately after perforating. Impulse type testing techniques can be used toidentify the extent of wellbore damage before large investments in stimulationor gravel packing are made. In addition to impulse testing, a variety of othertesting and completion equipment can be combined with the TCP string to providefor comprehensive reservoir evaluation immediately after perforating.

Underbalanced Perforating. An underbalance, established between theformation and wellbore pressures before the TCP guns are fired, creates aninstantaneous and controlled surge of formation fluids into the well, whichcleans the perforations and enhances the well's productivity andinjectivity.

Safety.

Surface well-control equipment is installed and tested beforeperforating, guaranteeing complete safety throughout all phases of the TCPoperation. phases of the TCP operation. High-Performance Perforating Systems. Gun size is limited by the ID of the casing, permitting use of the largestpossible charges permitting use of the largest possible charges (either deeplypenetrating or big-entry-hole type) and high shot densities. Guns can beconfigured to provide the optimum shot density and pattern for the specificapplication.

TCP Completion Types

Temporary TCP Completions. In a temporary TCP completion, the guns are runinto the well at the end of a workstring. After the guns are fired, and time isallowed for cleanup and testing, the well is killed with a nondamagingcompletion fluid and the TCP string is removed. Completionprocedures-backwashing, acidizing, procedures-backwashing, acidizing, fracturing, or gravel packing then be implemented. Large Intervals or MultizoneWells. Large intervals or wells where several widely spaced zones arecommingled into a single production string are completed efficiently productionstring are completed efficiently on a temporary workstring. After perforating, the well is killed with a nondamaging perforating, the well is killed with anondamaging completion fluid and the gun string is removed. This system affordsthe benefits of TCP while providing an alternative to leaving the gun string inthe well where it could interfere with future operations. Gravel-Packed Wells. High-shot-density TCP guns loaded with big-entry-hole charges shotunderbalanced are used to perforate a zone to be gravel packed. After perforatea zone to be gravel packed. After cleanup, the well is killed with anondamaging completion fluid and the guns are retrieved to permit the runningof screens and installation of the gravel pack. Testing. A well-control valvecan be used in conjunction with TCP to provide a quick look at thenear-wellbore region by impulse testing. A longer-duration drillstem test (DST)provides for a more detailed analysis of the commercial potential of thereservoir through observation of the types of fluids recovered and the flowrates. The DST/TCP combination ensures optimum perforation cleanup and providesreservoir performance characteristics. The system involves TCP guns run below aretrievable packer and a set of DST tools. Immediately after firing, the wellis tested by alternately flowing and shutting in to develop the desiredreservoir information.

Permanent TCP Completions. In a Permanent TCP Completions. In a permanentTCP completion, the guns are run of permanent TCP completion, the guns are runof the end of the final completion string. The wellhead and safety equipmentare installed before firing. The guns remain in the well after the perforatingoperation and may be dropped into the rathole if desired.