Unique Electrical Detonator Enhances Safety in Explosive Operations: Case Histories
Authors: Motley Jerry , Barker James 
Published: December 2007

The electroexplosive devices most commonly used in today's oilfield operations include hot-wire detonators, resistorized detonators, exploding bridgewire devices, and exploding foil initiators. Each of these detonators functions differently and is subject to inherent operational, safety, and/or economic drawbacks. To overcome limitations of the present devices, a new type of electrical detonator has been designed. The new device, designated the rig-type environment detonator, utilizes semiconductor bridge technology and deflagration-to-detonation techniques with secondary explosives and does not require primary explosives, special surface firing panels, or downhole firing units in order to function. The new detonating device is insensitive to common wellsite hazards from radio transmissions, electrostatic discharge, cathodic protection, and welding, which have caused problems with other detonators, and thus, can significantly enhance operational safety. In addition, the new device is cost efficient and versatile as the different embodiments of the device allow it to be easily adapted for use with other common downhole explosive hardware and surface firing panels.

A description of the qualification tests to which the new detonator has been subjected will be presented and will compare its safety and operational capabilities to that of other traditionally used devices. Case histories of its usage to date and evaluations from independent testing authorities in both the U.S. and U.K. attest to its safety and reliability for oilfield explosive operations.

Introduction

Many of the services such as jet perforating of wellbores, tubing and casing cutting, and wellhead and platform removal that are conducted in oilfield operations today are run on electric wireline, and electroexplosive devices (EEDs) are needed to initiate the explosive trains for these services. Hot-wire detonators, resistorized detonators, exploding bridgewire (EBW) devices, and exploding foil initiators (EFIs) have traditionally been used for this purpose. These devices are often subjected to environments that have potential for stray electrical and electromagnetic hazards with possible sources being electric batteries (12- and 24-volt), cathodic protection systems (potentials to 50 VDC), welding units (potentials to 70 VDC), and radio frequency (RF) transmissions.

The hot-wire and resistorized detonators are extremely sensitive to these hazards, so much so that it is a required practice when using these devices to shut down cathodic protection, welding, and radar/radio transmissions before conducting explosive operations. In addition, stray voltages greater than 0.25 volts must be traced and corrected before commencing explosive operations.

On the other hand, the EBW and EFI devices are so insensitive to wellsite electrical hazards that they require a special downhole, high-voltage, firing unit (and sometimes surface firing panel) to function. Because of this insensitivity, when using the EBW and EFI systems, the requirements for shutting down of cathodic protection, welding and RF transmissions can often be waived. Also, they can be used in environments where stray voltages are in the range of 30 to 40 volts. This is possible because their functioning voltage is on the order of 150 to 160 volts, which provides an ample margin of safety. The primary drawback of EBW and EFI detonators, however, is their high cost, which can range from several hundred to several thousand dollars per shot. A secondary drawback to EBWs and EFIs is their difficulty to adapt to existing explosive hardware such as select-fire systems and bottom-fired port plug guns.

A new type of electrical detonator has been developed to overcome the hazard limitations of hot-wire and resistorized detonators as well as the extensive cost and adaptation limitations of EBW and EEl devices. The method of operation for the new device, the rig-type environment detonator (RED), is based on semiconductor bridge technology and deflagration-to-detonation techniques with secondary explosives. This new detonator is insensitive to common wellsite hazards, and its safe method of operation allows certain operational procedures to be waived during performance of perforating services.

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