Characterisation of Contaminated Soil by Crude Oil Associated with Produced Water and an Evaluation of Oil-contaminant Biodegradation
a report by
Hashim R Abdol Hamid1 and Maher AR Sadiq Al-Baghdadi2
1. International Technological University, London; 2. Higher Institute of Mechanical Engineering, Yefren
Produced water is water trapped in underground formations that is brought to the surface along with oil or gas. It is by far the largest- volume byproduct or waste stream associated with oil and gas fields worldwide.1–3
and gas fields reach maturity.4–6
Water production quantities continue to increase as oil Produced water characteristics and
physical properties vary considerably depending on the geographical location of the field, the geological formation with which the produced water has been in contact for thousands of years and the type of hydrocarbon product being produced. Produced water properties can even vary throughout the lifetime of the reservoir.
report that US wells produced an average of more than seven barrels of water for each barrel of oil. For crude oil wells nearing the end of their productive lives, water can account for as much as 98% of the materials brought to the surface. The development of effective produced water management strategies poses a big challenge to the oil and gas industry today.
The volume of produced water from oil and gas wells does not remain constant over time; in fact, the water-to-oil ratio increases over the life of a conventional oil or gas well. For such wells, water makes up a small percentage of produced fluids when the well is new. Over time the percentage of water increases and the percentage of product declines. Lee et al.7
Produced water is basically a mixture of formation water and injected water, but also contains smaller quantities of dissolved organics (included hydrocarbons), suspended oil (non-polar), dissolved minerals, traces of heavy metals, solids (sand, silt) and production chemicals. Therefore, produced water is the principal source for hydrocarbon discharges from the petroleum sector to the environment. Total petroleum hydrocarbon (TPH) is the constituent of produced water that receives the most attention in both onshore and offshore operations, while salt content (expressed as salinity, conductivity or total dissolved solids [TDS]) is also a primary constituent of concern in onshore operations. In addition, produced water contains many organic and inorganic compounds that can lead to toxicity.7
Some of these naturally occur in produced water, while others are related to chemicals that have been added for well-control purposes. These vary greatly from location to location and even over time in the same well. The many chemical constituents found in produced water, when present either individually or collectively in the high concentrations, can present a threat to the environment’s ecosystem. Produced water can have different potential impacts depending on where it is discharged. A great deal of scientific research has been carried out to determine the consequences of short- and long-term exposure to produced water on the environment. Due to the increasing demand on energy resources, the oil and gas production industry has the potential to cause significant damage to the structure and function of ecosystems and poses significant threats to the environment.
© TOUCH BRIEFINGS 2010
At onshore oilfields, produced water is usually discharged into surface evaporation pits, which can have serious negative effects on groundwater sources and livestock, therefore potentially harming soil and consequently farming communities (see Figures 1 and 2). Acute events, such as surface disposing and spills, can cause loss of life and extensive damage to local environments. In response to the growing need to address environmental contamination, many remediation technologies have been developed to treat soil, leachate, wastewater and groundwater contaminated by various pollutants, including both
in situ and ex situ methods.8
A particular contaminated site may require
a combination of procedures to allow the optimum remediation for the prevailing conditions. Biological, physical and chemical technologies may be used in conjunction with one another to reduce the contamination to a safe and acceptable level.9,10
The application of
biotechnological processes involving micro-organisms is gradually expanding with the objective of solving environmental pollution problems. The bioremediation process presents numerous advantages compared with other techniques employed to remove pollution (extraction with solvents, addition of chemical oxidisers, etc.) One of the best approaches to restoring contaminated soil is to make use of micro-organisms that are able to degrade the toxic compounds in the bioremediation process. Many factors affect the bioremediation process: concentration of the pollutants, application of nutrients, the population count of micro-organisms and treatment by surfactant.
Case Study
Contaminated soil around a disposal pit of produced water at a selected oilfield was chosen as a case study area (see Figure 3). The produced water was directly disposed without any sort of management to the disposal pit so it causes an environmental impact and damage to the round area, especially the soil. The hydrocarbon content in the soil shows that the soil around the pit suffers from high pollution by crude oil base hydrocarbons, and this is an expected result due to long-term disposal of produced water on the surface pit (see Figure 4).
Site Mapping and Sample Collection
The first step of the research was the surveys that were carried out to map the disposing pit at the oilfield and to locate the sampling points of the contaminated soil. The second step was collection of the samples. The collection and preparation of samples are important aspects of any assessment programme. The samples were taken in a way that will avoid the introduction of systematic bias or non-systematic errors. The collection methods and the sample size were chosen to ensure that the samples obtained were representative of the environment from which they were taken. Physical techniques were applied to make the sample homogeneous so that further sub-sampling would ensure the material taken for analysis was wholly representative. The main objectives of the sampling programme at the site were to collect four produced water samples from the pit for full analysis, to characterise the main
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