Environmental Considerations for 3D Seismic in Louisiana Wetlands
Authors: Browning Gordon , Dillane Tony , van Baaren Peter , Dietz David 
Published: December 2007

SPE 3578l

Louisiana swamps have been host to seismic crews for many years. Results from recent 3D surveys indicate that well planned and executed seismic operations have a minimal and short term impact in these environmentally sensitive wetlands. Pre-planning identifies challenges that require use of improved technology and work procedures. These include multi-channel radio telemetry recording systems, ramming of dynamite and hydrophones as opposed to drilling, DGPS positioning and co-ordin and use of Airboats, buggies and helicopters. In addition to minimal environmental impact, increased data quality, reduced cost and shorter project duration have been achieved as a result of these efforts.

Unlike 2D surveys, where profile positioning is flexible, 3D surveys involve high density coverage over many square miles operated by numerous personnel. Survey design includes minimizing repeated traffic and crossing points. Survey operations require environmental participation and commitment from every person involved in the project. This includes a thorough orientation and training program with strong emphasis on environmental sensitivity and awareness.

Close co-ordination between regulatory agencies, clients and the contractor is a key factor in all aspects of the survey planning and operation. Benefits from these efforts are significant, measurable and continue to improve.

Introduction

The Louisiana Wetlands, (See figure 1), have for many years been host to seismic exploration. These environmentally sensitive areas range from open marshland and thick cypress swamp to mangrove swamp, shallow lakes and coastal transition zones. They extend from the State of Mississippi to the State of Texas and go inland for many miles from the Gulf of Mexico. The parishes where most Wetland exploration occurs are, from east to west, St Bernard, Plaquemines, Jefferson, Lafourche, Terrebone, St Mary, Assumption, St. Martin, Vermilion and Cameron.

A typical 3D survey would entail crossing levees, marshland, shallow lakes and agricultural land.

Water conditions range from salt and fresh to brackish. The Louisiana Wetlands are home to an extensive range of wild life including alligators, nutrias, rats, snakes, raccoons, deer, pelicans, cranes, and many other bird species. Many species of reptiles birds and mammals are protected and / or on the endangered species list.

Wetland areas are often open to the public for leisure activities such as fishing, boating and hunting. Practically all shallow open wetland areas in Louisiana are commercially fished seasonally, with shrimping and oyster collection being the main business.

3D seismic data acquisition surveys require high density coverage over many square miles necessitating the use of much equipment and many personnel. Unlike 2D operations where single line recording is relatively short, 3D rations require that the source and receiver lines be positioned over a longer period of time. This is directly related to the size of the survey and how many channels and shots are required to obtain data. Survey sizes are typically 60 to 120 square miles.

Seismic acquisition is only a very small part of the oil and gas exploration and production picture. Compared with production facility installation, laying pipelines or the historical drilling practices of cutting access canals the impact of seismic crews is minimal. Whereas production facilities are permanent, seismic exploration should leave no ending marks on the landscape.

The environmental challenge

The challenge of operating seismic acquisition crews in the Louisiana wetlands is to minimize or eliminate the impact that crew operations could have on the prospect area's environment.

Methods used to overcome the challenge.

Preplanning

To minimize the environmental impact to the Wetlands extensive preplanning of all surveys is required, the importance of which cannot be overemphasized.

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