Perforating the Horizontal Well
Authors: King G.E. 
Published: December 2007

Perforating a horizontal well may seem no different from Perforating a horizontal well may seem no different from perforating a vertical well. Horizontal well attributes, which perforating a vertical well. Horizontal well attributes, which are extremely attractive for fluid recovery and reservoir management. are controlled or enhanced only partially by the selection of perforating equipment. Considering the impact of perforating on other variables of horizontal completions. perforating on other variables of horizontal completions. however. makes clear the importance and differences of perforating. perforating. First, perforating is a factor only for cased holes. Cased completions. rather than openhole or slotted-liner completions. are less common but have some advantages in unstable formations or zones requiring isolation in the horizontal section. Second, the penetration. entrance-hole requirements. and materials being penetrated are the same as for a vertical well. Sediment penetration direction makes a minor difference to shaped-charge penetration. The major penetration differences result from requirements of the completion or stimulation and the effect of a decentralized casing and gun.
Perforating basics are altered by casing and perforating-gun decentralization in a horizontal wellbore. Phased perforating guns enhance flow and highlight the effect of clearance on the performance of the perforating charge. The clearance, that performance of the perforating charge. The clearance, that distance from the outside of the perforating gun to the inside wall of the casing. affects both the entrance-hole diameter and penetration. Because the gun is decentralized by gravity in any penetration. Because the gun is decentralized by gravity in any inclined wellbore. the clearance must be considered. The clearance effect on gun performance for big-hole and deeply penetrating charges is shown by the curves in Fig. 1. penetrating charges is shown by the curves in Fig. 1. Entrance-hole diameter, as illustrated by these data, is optimal within certain clearances. Penetration (Fig. 2) falls off rapidly for clearances less than 2.4 in. [less than 6.1 cm] for a deep-penetrator charge and for clearance between 0.5 and 2 in. [1.3 and 5.1 cm] for the big-hole charge. The data (Figs. 1 and 2) are based on composite cases; each charge behaves differently and must be selected on the basis of its performance in a gun/casing system. The charge performance at the different clearances requires consideration of the perforating-gun size and centralization effects in the wellbore when hole size and penetration are important. In most cases, the largest gun that penetration are important. In most cases, the largest gun that can be fished is recommended. Improved methods of gun centralization are available. The effects of casing centralization are a factor, especially in large horizontal holes. Perforating design in decentralized casing sections may require penetration through a thicker cement sheath over the pipe in a horizontal hole.
Positioning guns in a horizontal well is a challenge to gun conveyance and depth control. Movement of wireline-conveyed guns by gravity is very troublesome past 550 of hole deviation. Tubing-conveyed perforating (TCP) and coiled tubing move guns in highly deviated wells. TCP systems are expensive. but have strength and gun-selection advantages, while the coiled tubing offers cost and time savings with lighter. smaller gun systems.
Horizontal-well depth control and gun positioning is complicated because the gamma ray log. the traditional depth-control device, shows little formation character variation alter the hole turns horizontal. Additionally, the problems of perforating-gun conveyance apply to the collar locator and perforating-gun conveyance apply to the collar locator and porosity device used for gun positioning in the horizontal well. porosity device used for gun positioning in the horizontal well. Accurate tubing-length measurements for TCP or special logging conveyances are needed for depth control in horizontal wells. The importance of depth or gun position depends on formation homogeneity and the required depth-control accuracy in placing perforations for gravel packing or fracturing.
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