Improved Radio-Frequency Silence Guidelines for Wireline Perforating
- Raymond Dickes (Schlumberger) | Mark Nordquist (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE International Conference on Health, Safety, and Environment in Oil and Gas Exploration and Production, 29-31 March, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2004. Society of Petroleum Engineers
- 2.2.2 Perforating, 7.2.1 Risk, Uncertainty and Risk Assessment, 5.6.1 Open hole/cased hole log analysis
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Transmitters operating in the radio-frequency (RF) spectrum create thepotential for accidental detonation of electroexplosive devices (EEDs). Thisrisk is magnified by the potential for an EED to be ballistically connected toother explosives, the widespread use of EEDs in oil- and gas-well perforatingservices, and the proliferation of radio transmitters.
To prevent accidental detonation, wireline logging operations have relied onradio-silence procedures for the past 50 years. For these procedures to beeffective, the well logging crew must identify radio transmitters and thenensure they are disabled when they are within the defined radio-silence zone.The size of the zone varies with the frequency and power of the radiotransmitter, and the size and type of the antenna attached to the EED.
In the past, one or more radio-silence zones were established based onstudies performed using antennae and EEDs typical in mining operations. A majoroilfield service company has improved this technique through a new studyspecific to wireline logging-the details of which are presented in this paper.This study has led to smaller radio-silence zones while maintaining perforatingsafety.
An EED, commonly referred to as a blasting cap or detonator, starts thedetonation of the explosives used in an oil- or gas-well perforating gun. Byapplying electrical energy, the EED detonates, and this initiates the otherexplosives in the perforating gun. Uncontrolled sources of electrical energy,such as RF transmissions, have the potential to cause an accidental detonationin most EEDs used in oil- and gas-well perforating guns.
The user of an EED must control RF energy to prevent accidental detonation.Companies providing perforating services typically use one of three safetystrategies to prevent accidental detonations: RF silence, site risk analysis,or the use of RF-immune EEDs. RF silence is a relatively simple strategy,benefiting from clear rules, and needing only limited hazard analysis foreffective application. Site risk analysis requires a more detailed andexpensive site-specific analysis of the hazards for effective implementation.Using an RF-immune EED relies on the design of the EED, or engineeringcontrols, for its effectiveness.
RF silence policies establish one or more RF silence zones surrounding theperforating operation. The size of an RF silence zone is dependent upon theEED, the number of RF transmitters considered, the frequency and power of theRF transmitters, and the antenna attached to the EED. Safe distances for RFsilence zones are derived from previously published studies that are based onantennae and EEDs typical in mining operations.
Schlumberger has improved the RF silence technique by commissioning a newstudy based on antennae and EEDs typical to wireline operations. This providedthe missing technical data for wireline operations. This company has maintainedperforating safety while decreasing radio-silence zones, reflecting the resultsof the study.
The majority of oil- and gas-well perforating guns have three basicexplosive components: an EED, a detonating cord, and shaped charges. EEDs areinitiated by electrical energy, and generate enough energy to detonate thedetonating cord and shaped charges, which are ballistically connected to theEED.
There are several different categories of EEDs, each of which can beorganized by the power required to detonate them and whether they use a primaryhigh explosive. In Safety Strategies for Operating Electroexplosive Devicesin a Radio-Frequency Environment,1 EEDs are categorized asfollows:
Category 1 - A low-power EED using a bridge wire and a primary highexplosive
Category 2 - A low-power EED using a bridge wire and a primary highexplosive, but with additional resistance (approximately 50 ohm) added toincrease safety
Category 3 - Either a low-power EED using a bridge wire and a primary highexplosive, but with an electronic circuit used to increase safety; or an EEDwithout a primary high explosive requiring a few watts to detonate (e.g., asemiconductor bridge)
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