Optimising Fluid Choices for Landfarm Applications
Authors: Hall John A. , Seaton Simon , Visser Suzanne 
Published: February 2016

A well established method for bioremediation of drilled cuttings and adhering base fluids is the use of landfarming or composting. All base fluids are amenable to this method.

However, degradation of organic materials takes place over different timescales, and there is potential for toxic residues to affect the future use of land to which cuttings have been applied. This paper describes a project where a degradation of a range of different commonly use base fluids was investigated and the use of various commercial accelerants was also tested to determine their impact on degradation rates. It subsequently describes an investigation into plant and animal toxicity of soils to which base fluids have been applied.

Introduction

Recent concern about the environmental risks associated with diesel-based drilling muds has encouraged consideration of alternate base fluids for the production of drilling muds. Of interest is the development of a drilling mud which performs efficiently in the drilling operation and can be treated by landfarming with no adverse environmental consequences. The purpose of the present research was to determine the degradability and ecotoxicity associated with several base fluids. The test fluids included synthetic olefins, esters, paraffin-based petroleum oil and diesel.

Objectives

The overall objective was to develop a drilling fluid formulation that degrades readily and rapidly in soil leaving no ecotoxic residual after the fluid has degraded to a stable treatment endpoint. Specific objectives of the present research were to compare the biodegradability of seven candidate base fluids in a clay loam soil, and also to evaluate the toxicity of the fluid residuals remaining in the soil following biodegradation to a stable endpoint to a range of ecological receptors (plants, earthworms, springtails).

Methods

Properties of Test Base Fluids

The first seven fluids listed in Table 1 were tested for both biodegradability and ecotoxicity. They included a diesel, a petroleum distillate (mineral oil), paraffin-based petroleum oil (paraffin), two synthetic olefins (C16/18 IO; C14 LAO) and two esters (ester; alternate ester). An alkane/alkene blend was tested only for its biodegradability potential using the respiration monitoring approach. With exception of the paraffin, all of the test fluids are insoluble in water.

Properties of Receiving Soil

The receiving soil was a loam obtained from a pasture site near Turner Valley, Alberta. Soil physical/chemical properties indicate that the receiving soil is a relatively fertile soil with a neutral pH and low conductivity (Table 2). These properties are conducive to promoting the degradation of hydrocarbons.

Experimental Methods

Biodegradability of Base Fluids

Prior to initiating the research, the soil was passed through a 4-mm sieve, homogenized and tested for moisture content. Moisture content was determined gravimetrically by measuring the weight of three samples of soil before and after drying at 80ºC.

Respiration Monitoring

Soil microbial activity is highly dependent on carbon availability to the microbial biomass and, therefore, is a valuable tool for monitoring the degradation of bio-available hydrocarbons in the soil. Three aliquots of field moist receiving soil, each equivalent to 100 g dwt, were sprinkled with two grams of each of the first seven test fluids listed in Table 1. Three replicates were also run with no base fluid additions as controls. Each base fluid replicate was amended with 400 µg N/g dwt and 80 µg P/g dwt so that fluid degradation would not be constrained by low nutrient conditions. Previous studies have demonstrated that it is essential that available nitrogen be sufficient to allow rapid and complete degradation of any highly bioavailable carbon in the drilling fluids. Soil moisture was adjusted to approximately 40% (dwt), and each sample was placed in a glass tube and incubated at 22ºC.