Simple Method Tracks Charge Performance
Authors: Sukup Richard A. , Ott Russell E. , Robson Mike K. , Bell W.T. 
Published: December 2007

Optimization of completion and perforating parameters can improve well productivity when perforators perform as expected. A simple, economical method is presented for correlating field perforator performance to API data. The method provides a basis for manufacturing control that can ensure that field perforator charges will perform consistently within specific ranges.

Introduction

Effective well-completion design depends on reasonably accurate knowledge of performance characteristics of the selected charge-gun perforating system. Perforators that perform as expected can provide the desired well performance. On the other hand, substandard performance may result not only in disappointing production but also in uncertainty as to its cause. In development wells, these uncertainties can result in expensive remedial measures to offset suspected gun deficiencies; in exploration wells, wrong decisions, with far-reaching effects, can be made.

Field and laboratory evidence clearly indicates that actual field-charge performance does not always conform to published API RP 43 data. This paper examines the technical reasons for disparities between field-charge performance and API data. Fundamental difficulties that exist in performance control during manufacture and factors that could affect charge performance after manufacture are evaluated. Means to reduce potential performance degradation and results of laboratory tests performed to qualify the disparities induced by variations in production-control test targets used for performance verification during manufacture are presented. Finally, a simple and economical method is advanced for determining how field charges perform relative to API data. Elements of the method provide a basis for the manufacturer to control performance so that the field charges will perform consistently within specified ranges.

Perforator Performance - Crucial to Productivity

In terms of providing maximum well productivity, the four principal perforation performance parameters are effective shot density, penetration, shot phasing, and entrance-hole diameter. The relative importance of each parameter varies according to completion type. Regardless of completion type (natural, sand-control gravel pack, or stimulated), effective shot density (the number of perforations actually producing) is the most important parameter. While effective shot density is affected by completion procedures (underbalanced vs. overbalanced), charge performance is also crucial.

In a natural completion, productivity depends strongly on penetration, with shot phasing and hole size ranking lower in importance. In sand-control gravel-pack completions, effective shot density and hole size are important factors in optimizing pressure drop across the perforation tunnels for a given flow rate. In stimulated or fractured completions, shot density and hole size are critical because they governfluid flow characteristics.the ability to deliver fluid and proppant to desired locations), andhydraulic horsepower requirements.

It is clear that regardless of type, effective completion design requires reasonably accurate knowledge of perforator-performance characteristics and ensurance that the characteristics are maintained within closely defined limits.

The Shaped-Charge Perforator

The shaped charge comprises three basic components: liner, case, and explosive (Fig. 1). As indicated in Fig. 2, detonation of the explosive within the shaped charge collapses the metallic, conically shaped liner into a high-velocity jet of metal that penetrates the casing and into the formation. The penetrating mechanism is one of punching. The pressures generated by the jet overcome the strength of the casing and formation and force material radially away from the axis of the jet.

The shaped charge must penetrate at large distances from its origin. Maximum penetration requires that the jet be carefully aligned. Fig. 3a shows a flash X-ray photograph of a well-formed jet and Fig. 3b shows a less-effective jet. The alignment of the latter is faulty, with a significant disturbance in the forward portion of the jet. Departure of portions of the jet from the geometric axis results in reduced penetration performance compared with a well-formed jet. Misaligned portions of the jet strike the side of the perforated hole already developed, rather than the end, and as a result, their energy is wasted.

JPT

P. 1026^