ESTIMATION OF DRILLING WASTES – AN ENVIRONMENTAL CONCERN WHILE DRILLING OIL AND GAS WELLS
Despite its numerous benefits the search and production of crude oil poses a lot of dangers to the environment. Among these include land, water and air pollution. Prominent among the major sources of E&P waste is drilling operations which form the second largest source of waste after production activities. The major drilling wastes are drill cuttings, drilling mud and obnoxious gas emissions. These wastes are introduced into the environment through intentional as well as accidental discharges and this expulsion into the environment has direct and indirect effects on aquatic life, personnel working on the rig, plants, flying birds, as well as the soil. This research work purposes to identify the various forms of drilling waste, their effect on the environment and to develop strategies in managing these waste effectively. The ability to effectively identify, quantify, classify and adopt strategies to eliminate or reduce the impact of drilling waste on the environment defines an effective waste management practice. In all situations source reduction of waste is the most favorable and economically feasible drilling waste management option and should in all cases be a priority over the other methods of waste management. However, this task of adopting an effective waste management tactics is not as simple as it looks. In its quest to developing effective strategies for managing drilling waste, it is identified that the quantity of waste generated plays an important role in drilling waste management. It dictates the type of waste management method to adopt, the design of waste boxes, waste disposal cost among others. A simple user-friendly spreadsheet is therefore developed for waste volume estimation. Again, a ten steps effective waste management procedure is developed to serve as guidelines for drawing waste management plans. Waste management plans should be updated regularly to capture changes in regulations, new technologies and new operations. In conclusion it is shown that the choice of the ideal drilling waste management is usually dependent on the local regulations in place, technical efficiencies, cost and the quantity of waste. The selection should always be therefore subjected to effective environmental, economic and technical analysis. As a result, a waste selection criterion has been developed which will help eliminate some of the options that are not favorable.
1.1 Problem Definition
Petroleum is among the world’s most important natural resources. It is the most significant and highly traded primary commodity in the international market (Illedare, et al., 1999) and has remained the world’s primary source of energy for both industrial and domestic applications since replacing coal early in this century. However, the finding and production of petroleum involves the generation of drilling waste which forms a major source of pollution in oil producing environment. Almost every process in the finding and production of petroleum generates wastes which impacts the environment negatively. Until 1980’s, little or no thought was given to the generation and disposal of cuttings and excess drilling fluids. Typically, these materials were discharged overboard in offshore operations or buried when drilling in land-based locations. The global environmental awareness in the late 1980s to early 1990s made the oil and gas industry and its regulators to understand and appreciate the potential environmental impact of drilling waste (Geehan, et al, 2000).
In an effort to manage and reduce the impact of drilling waste on the environment, a number of technologies and publications have been written. Technologies such as directional drilling, slim-hole drilling, coil-tubing drilling and pneumatic drilling are few of the drilling practices that generates less amount of drilling waste. A number of drilling waste management plans and programs have also been designed by different companies and researchers. Drilling waste management refers to ways by which drilling and associated wastes could be handled effectively in order to minimize their effect on the environment. Wastes that are usually associated with drilling operations are: - drill cuttings, contaminated drilling fluids and additives, gaseous contaminants from internal combustion engines, produced water as well as heavy metals. The principal aim of waste management is to ensure that waste does not contaminate the environment at such a rate or in such a form or quantity as to overload natural assimilative processes. Eliminating or minimizing waste generation is crucial, not only to reduce environmental liabilities but also operational cost (Richards, 2007). The waste hierarchy is a common waste management technique that has been reported in a number of literatures. This refers to the "3 Rs" Reduce, Reuse and Recycle, which classify waste management strategies according to their desirability in terms of waste minimization (Anon [a], 2011). However, this technique is not extensive enough. Before the waste hierarchy is effectively applied, it is desirable to identify, classify and estimate the quantity or the volume of waste to be generated. An effective waste management technique must incorporate all these factors.
The volume of drilling waste generated when drilling a well is also an important and costly factor, especially when the waste must be transported, treated, or disposed off-site(Fleming, et al., 2010). It is an important planning tool which is usually not mentioned in the drilling waste management process. Drilling waste could be better managed if the anticipated amount or volume is appropriately quantified. Unfortunately, very few publications have reported on drilling waste volume quantification and estimation methods. This study seeks to identify the various types of drilling wastes that pollutes the environment and how to minimize it. It presents an effective method to quantify the volume of drilling waste generated for an efficient waste management plan.
1.2 Literature Review
Environmental pollution and waste management is a broad and extensive study area with lots of publications. There is a tremendous amount of valuable information available on the environmental impact of petroleum operations and on ways to minimize that impact: however, this information are scattered among thousands of books, reports and papers making it difficult for industrial personnel to obtain specific information on controlling the environmental effects of particular operations (Reis, 1996). Again, very little of these materials focuses on waste volume quantification.
The paper outlines the processes for identifying appropriate waste management strategies in specific area of operation. These strategies consider environmental regulations, company policies, operational and economic factors. The management practices discussed includes waste minimization, storage, handling and disposal. The writer reiterated that waste management in the industry is really a problem and this is basically due to inadequate understanding of the waste management options available. The writer gave six basic steps for effective waste management. However, one very important basic step was not included which happens to be one of the objectives of this study: the estimation of the quantity of waste generated. In conclusion the writer specified that categorizing an area waste and determining appropriate management option improves understanding of wastes, waste management requirement and options. He further pointed that, writing and implementing the plan as suggested improves communication and implementation of the established waste management goals and standards.
Several of the processes used to reduce the environmental impact of drilling waste are counter-productive. They can increase drilling cost and often worsen the waste disposal problem rather than solving or relieving it. Bouse, et al. (2000), conducted a research on the importance of solid control and its relevance to waste management. It was realized that the most effective means of reducing the volume of waste generated by the drilling operation is through efficient removal of drilled solids. For example, in deep well drilling, a 10 % improvement in drilled solids removal can reduce the waste by as much as 8000 to 10000 barrels. The use of closed mud systems reduce the environmental impact of oil well drilling to an absolute minimal however; this requires the removal of all drilled solids and the reuse of the liquid discharged by the solids removal equipment. The cost of maintaining this practice makes it very difficult to justify except under very special circumstances, such as drilling in an urban environment or in areas in which government regulations prohibit the discharge of drilling fluid wastes. Moreover, the option of transporting waste to an off-location disposal site is very costly especially when the volume of liquids is large.
The most economical means of handling the waste control problem without jeopardizing the drilling operation is to: optimize solid removal thereby limiting the volume of waste generated, eliminate or reduce the use of contaminating muds and additives, avoid the commingling of contaminating and non-contaminating waste and finally, treat and dispose of waste on location. The treatment and disposal of non-contaminating waste is relatively simple and inexpensive. However, the disposal of contaminating waste such as liquids and cuttings from water-based mud containing diesel oil, heavy metals etc. pose serious problems. The authors presented a number of instances for the disposal of such waste materials: one of such being the injection into salt water sand behind the casing. Other possible methods are the use of microbes (Bouse, et al, 2000) to consume containing oil, incineration, solidification, burial and transportation to an approved disposal site. In conclusion, the authors stated that, the operation of solids removal equipment should be closely monitored and should be structured to determine the quantity of solids separated and the breakdown between high-gravity and low-gravity solids.
Flemming et al, (2010) carried out a study on various methods for estimating the volume of drilling waste generated, both onshore and offshore. Four ways of estimating waste were considered: Estimating volume in an earthen pit, estimating volume from fluid deliveries, estimating volume by mud usage mass balance and estimating volume with waste hauling data. These methods were compared to a mathematical computer model that has been developed. In this research, the writer revealed an approach to model the contents of the waste estimation by the earthen pit method: that is, to develop a spreadsheet that calculates the average content from one segment in depth to another. From the results, waste estimation by the fluid delivery and hauling data yielded similar estimates with about 5% difference. Secondly, the ratio of waste to hole volume using the fluid usage method showed a declining trend however, there is no such trend using the waste hauling method. The writers attributed this to the possibility of some waste-filled boxes of one hole being attributed to a another hole. In conclusion, the model was used to validate other methods and the results showed that the ratio of waste to hole volume is 20:1. This has been a close fit to the other offset records methods but the writers stressed that these programs must be used by experienced users because if wrong assumptions are made, waste volume estimates could be in gross error.
Richards et al. (2007), defines drilling waste as any solid or liquid generated by the drilling process. It can range from dry solid to pure liquids. Technologies exist that easily transport solids in dry and liquid forms (screw auger conveyors, pneumatic transport systems or vacuum transport systems, centrifugal pumps, piston pumps and progressive cavity pumps). However, drilling wastes are usually a combination of solids and liquids and this makes their transportation a challenge. Ideally but impracticable, drilling waste must be separated into solid and liquid phase to enable existing technologies to move them efficiently. A second preference which adds extra waste volume and has cost implications is to build slurries of controlled density, thereby enabling traditional pumps and tank systems to move the waste in slurry form. This paper, introduces the Brandt Transfer System (BTSTM), a patented pump and collection system designed to pump drilling wastes and heavy sludge’s. The writers introduce some criteria for evaluating the pump.
When evaluated for both fast and slow drilling conditions, the amount of waste generated was 0.667 bbl/ft and 0.084 bbl/ft respectively. It takes one (1) hour to fill the collection tank under fast drilling conditions where asunder slow drilling conditions, it takes 95 hours. The longer time will pose extra problems in that, the solids will settle through natural decantation process. However, the variable-speed cutter head feature of the system breaks up the sediments. The evaluation shows that, the system is suitable for both conditions. When evaluated against economic ability, the system proves highly economical, since it requires fewer personnel to operate and less energy requirement. Each barrel of waste moved during the slow drilling costs only 0.09 kilowatts (kWh) of electricity (about 8 cents). Finally, the system was evaluated against balanced environmental goal. The system reduces the impact on marine life and also results in less impact on surface environment since less energy will be used which will cause fewer emissions into the atmosphere. The writers in their conclusion stated that, new and more environmental laws are forcing the industry to change ingrained practices, thus creating the need for new technologies and thus, for a successful waste management project, proper storage and transportation of drilling waste must be given a priority.
Rana, (2008), reviews environmental aspects of Oil & Gas drilling in view of economics of the projects benefiting industry professionals. Exploration and Production (E&P) wastes are introduced into the environment through accidental spills, leaks, blowouts and drilling operations. These wastes toxic chemicals pose significant risks to the environment, human health as well as wildlife. The potential for accidental or routine release of drilling wastes into the environment is alarming and thus threaten to sustain the industry operations. Many of the toxic chemicals associated with oil and gas drilling are known to accumulate and magnify in the food chain posing a risk to aquatic organisms higher in the food chain, such as fish and birds. From past safety records and statistics, the researcher identified that harmful environmental incidences will continue to take place, but the effects of these pollutants on human health and the environment can be minimized through proper environmental monitoring and mitigation measures; including the use of modern technological advances. Such technologies include; smaller drilling pads, directional drilling, smart wells, slimhole, coiled tubing, and measurement while drilling. Again these technologies for the petroleum industry are developed primarily to increase oil recovery and reduce the cost of recovery. Reducing costs often goes with reducing the environmental impact of exploration, drilling and completion procedures.
Rana, (2008), made mention of the “Smarter, Farther, Deeper, Cleaner and Smaller” operations. He pointed out that these make good business sense and help to protect the environment. Most companies have realized that going one step farther to protect sensitive environments and avoiding pollution, pays them back in increased benefits and improved public relations. The impact of better management and advanced technologies for exploration, drilling, production and oilfield operation can be seen in reduced footprint and air pollution, better monitoring, recycling, and management of generated wastes. These further prevent loss or pollution, preservation of resources, and on-site recycling of energy byproducts, thus improving environment and reducing costs.
Kinigoma, (2001), studied the effect of drilling fluid additives on the Soku oil fields environment in the Niger Delta State of Nigeria. Soil and reserve pits in various locations were assessed for physico-chemical characteristics and heavy metal content using standard methods for water and wastewater analysis. Plant growth and other biomass were also assessed. The result showed that the levels of most physiochemical characteristics are generally within the limits of guidelines by regulatory authorities. However, trace metal levels are generally below toxic levels, except Fe, Ca and Mg, which were higher than recommended values. These high values of Fe, Ca and Mg (17.70-220.2; 11.03-296.80; and 12.62-75.71 ppm) respectively are characteristic of the Niger Delta Swamp soils. The writer in conclusion attributed the poor plant growth observed in the immediate vicinity of location of drilling operations, to the indication of the toxic effect of drilling fluids on the environment.
Seyle, et al. in 2002, also conducted an extensive offshore survey and environmental assessment of drilling additives offshore Brunei. A primary focus was to evaluate the environmental effects of disposal of Oil-Based Mud (OBM), Ester-Based Synthetic Mud (EBSM) and Water-Based Mud (WBM) in the tropical marine environment of the South China Sea. A number of well sites were surveyed for each of the mud types encompassing varying water depths (20 - 500 m) and time elapsed since drilling. Side-scan sonar, detailed hydrographic imaging, sea bed video, current information and benthic sampling results were also interpreted. Modified radial sampling patterns were used. The study concluded that the magnitude and persistence of environmental effects from discharge of drilling muds and cuttings range in order of severity from OBM to EBSM to WBM. The study found that the OBM and cuttings are toxic to marine life and can persist on the Brunei sea bed for over 13 years. WBM effects were however noted to be more widely dispersed (> 1200 m) and exhibited indications of faster benthos recovery (within 3 years than) than EBSM (typically dispersed within 200 m).
1.3 Scope of the Study
All activities related to Oil & Gas Exploration, Production, Storage and Transportation involve waste generation associated to potential risk to environment. Waste types are related to primary Exploration and Producing (E&P) activities. These activities are: Drilling operations, Completion operations, Production operations, Work-over operations, Gas plant operations. Wastes associated with drilling operations deserve special attention due to the quantity and complexity of the pollutants they carry. Drilling wastes (mud and cuttings) represents the second largest sources of waste in the industry. The volume of drilling wastes usually ranges from 1,000 to 5,000 m3 for each well. As a result, this study focuses on wastes generated through drilling operations. It does not however consider wastes generated during the preparation of drilling site, transportation and assembling of drilling rig, and the decommissioning of drilling operations. Completion and work-over wastes are also not considered.
It involves the identification and the minimization of the various forms of drilling waste, the estimation of the volume of drilling waste generated and the coding into Microsoft Excel to generate a user friendly program for drilling waste volume computation. Finally, this study outlines practical steps for effective waste management.
1.4 Objectives of the Study
The Objectives of this study are:
• To identify various types of drilling waste that impacts the environment negatively.
• To develop equations for waste volume computation and build a Microsoft Excel User friendly model for Waste Volume Estimation.
• To establish the best possible ways for minimizing drilling wastes.
• To develop a comprehensive waste management plan and to establish the best possible way of incorporating waste volume estimation into it.
1.5 Methodology and Materials Used
The following materials were used in the execution of this study:
• Internet and Library facilities from the African University of Science and Technology, AUST.
• Microsoft Office Suite (Excel and Word) The methodology used includes:
• Reviewing of relevant literature about the subject matter (drilling waste management).
• Developing of equations for drilling waste volume estimation.
• Programming of developed equations using Microsoft Excel Spreadsheet.
• Evaluation of parameters affecting waste volume and the validation of the excel program using data from literature.
• Integration of waste volume estimation into waste management and the development of a comprehensive waste management.
1.6 Organization of Thesis
The thesis is structured into five chapters. Chapter one gives a brief introduction and definition of the study problem. It also states the objectives and defines the scope and methodology used. Chapter two presents literature on drilling waste types and their repercussions on the environment. Environmental concerns based on location (offshore, onshore and deep offshore) is captured in chapter three whiles chapter four focuses on drilling waste minimization and management. It also covers the building of the spreadsheet model and its validation. Finally, chapter five summarizes the entire work and provides conclusions and recommendations for future work.
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