U.S. Maharaj, R. Mungal and R. Roodalsingh

Abstract

Our national oil company (Petrotrin) is faced with declining oil production and increasing volumes of co-produced water. An environmental monitoring programme was set up to identify and quantify the major contaminants in our produced waters. The programme was designed so that data could be used for determination of impact on the environment, assist in pollution abatement technology selection and meaningful setting of regulatory standards.

The discharge of highly saline produced water with elevated levels of oil & grease was identified as major concerns. Alternative strategies for handling those effluents were identified, in which, the highly saline waters will be incorporated. Seventeen (17) produced waters were analysed on five (5) occasions to determine the levels of free, emulsified and dissolved oil. The dissolved organics were found to be the major contributor to the oil & grease value, with relatively smaller amounts of free and emulsified oil. This implied that the current technology for free oil removal at most installations are efficient. In order to comply with the current regulatory limit for oil & grease discharge, secondary and tertiary technologies would have to be implemented.

Introduction

The Petroleum Company of Trinidad and Tobago (Petrotrin), a merger of two national oil companies (Trintoc and Trintopec) is faced with declining oil production and increasing volumes of co-produced water. Current production is 32,000 barrels/day of crude oil and 48,000 barrels per day of water. This volume is expected to increase as our fields mature further and greater emphasis is placed on heavy oil exploitation using steam injection. The production operations of Petrotrin span the entire Southern Basin of Trinidad as shown in Fig. 1.

Produced water is now widely recognised to be a complex mixture containing both organic and inorganic constituents. Organic material is present in produced waters to levels as high as 0.2% and comprises materials such as oil, non hydrocarbon organics and dissolved organics. Sodium chloride together with small amounts of ions such as potassium, calcium, magnesium, bicarbonates, sulfates and trace quantities of heavy metals and radionuclides contribute to the inorganic composition.

In Trinidad, the tradition has been to discharge produced waters generated from oil operations to nearby rivers, streams and shorelines, after removal of crude oil. Currently, our Ministry of Energy regulates the oil & grease levels to a maximum of 50 ppm averaged on a monthly basis. Growing awareness of environmental concerns led our Company to a commitment to the preservation of the environment in which we operate. With the understanding that our operating environment is different to others worldwide, we embarked upon a produced water monitoring programme in 1993 with the following objectives:

  • To identify and quantify the major contaminants present in our produced water effluents.

  • To determine the impact of our produced water discharges on the environment.

  • To provide data that would assist in meaningful setting of regulatory standards.

  • To provide data to be used in decision making regarding investment in pollution abatement technology.

Trinidad is a small island state of 4,827 square kilometres with its own peculiarities such as: the presence of saline, brackish and fresh water environments, natural oil seeps and asphalt outcrops, and a rainy/dry season tropical climate. The major oilfields are situated within forested and agricultural areas on land and in fishing habitats offshore. The adoption of regulatory standards from international agencies without consideration of the local characteristics, would likely lead to inappropriate environmental regulations being enforced with the consequence of over and/or under protection of the environment.

Programme Design

In the design of the monitoring programme, it was necessary to consider the objectives of the programme, the resources available, the lack of existing data and the special characteristics of the operating environment within Trinidad.

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