Lightning Protection for an Oilfield Automation And Instrumentation System
Authors: Skinner D.R. 
Published: December 2007

A description of lightning protection devices in a computer-monitored oilfield automation project located on the south high plains of West Texas near Levelland. Lightning damage was substantially reduced with the present protection system.

Introduction

For many years, the problem of protecting electrical systems from lightning discharges has plagued power and communications engineers. Only within the past few decades has lightning been a problem to engineers dealing with electrical power systems in oil fields. The problem of lightning protection in West Texas oil fields is unique because of the high concentration of elevated high-voltage lines above flat plains that attract lightning discharges.

Most modern, electrically operated oil fields have power distribution systems that are well protected from power distribution systems that are well protected from lightning discharges; and, in many cases, these systems are isolated by sectionalizers and other devices. Even if a portion of a field is disabled by lightning damage, the remainder of the field continues to function normally. This paper concentrates on protecting the low-voltage electronic instrument systems that are very susceptible to even minor voltage surges caused by lightning.

In the last several years, the tremendous expansion of oilfield automation and electronic surveillance equipment has required increased emphasis on protecting low-voltage instrument systems from lightning discharges. These systems use DC voltages of near zero to 50 v with 120-v AC-powersources. This paper deals with methods used in a major oilfield automation project to protect various parts of the system from lightning damage.

The lightning protection devices discussed are used to protect two of Amoco Production Co.'s computer-monitored oilfield automation projects located on the south high plains of West Texas near Levelland, Tex, plains of West Texas near Levelland, Tex, Fig. 1 shows schematically the automation project operating in one of the locations. This is a secondary waterflood unit with almost 700 wells. The unit is under the surveillance of a computer-monitored oilfield production automation system that utilizes about 1,500 status, production automation system that utilizes about 1,500 status, control, and measurement devices. It has about 150 miles of buried multiconductor cables ranging from 6- t50-pair cables. In this project, "pump-off" controllers are used to control the producing wells, have dry contacts, and indicate satisfactory controller operation and motor status. Water injection wells are controlled by mechanical pressure-regulating valves. The injection rates and pressures are monitored by the computer "reading" amplified signals from turbine meters and pressure transducers. pressure transducers. At satellite tank batteries, the status of tank levels, fire indicators, temperature, and other conditions is monitored with each end device having a set of dry contacts. Producing well tests are obtained by automatically Producing well tests are obtained by automatically switching individual flowlines to fired heater-treaters or separators using electrically operated ball valves. Dry contact meter pulses from these vessels are accumulated by the computer system to determine producing volumes and rates.

The telemetry system consists of master and remote telemetry units. Communication between telemetry units is accomplished by frequency modulation using buried copper conductors.

JPT

P. 1405