Estimation of Drilling Wastes–an Environmental Concern While Drilling Oil and Gas Wells
Chapter One
Objectives of 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.
CHAPTER TWO
TYPES OF DRILLING WASTES AND THEIR EFFECTS ON THE ENVIRONMENT
Introduction
Drilling activity is a major operation in the upstream petroleum industry which impacts negatively on the environment as it generates significant amount of wastes. Environmentally responsible actions require an understanding of these wastes and how they are generated. From this understanding, improved operations that minimize or eliminate any adverse environmental impact can be developed, (Reis, 1996). The wastes generated during any drilling operation includes: drilling cuttings, drilling fluids, chemical additives, heavy metals, as well as air pollutants.
Types of Drilling Waste
During drilling operations, drilling fluid or mud is pumped down the drill string to lift drill cuttings to the surface. The drilling fluid together with the suspended drill cuttings and some heavy metals are carried through the annulus to the surface where the cuttings are separated from the fluid and the fluid is re-injected to lift more cuttings. The solid cuttings are then either treated and disposed off, grinded into slurries and injected or kept in a waste pit for further treatment and disposal. From the ongoing, five major types of wastes could be associated with drilling
operations: drill cuttings, contaminated drilling fluid, contaminated additives, air pollutants and heavy metals.
Drilling Fluids
Drilling fluids, simply referred to as mud are fluids used in drilling operations to remove drill cuttings from the wellbore. They also perform other functions such as cooling and lubrication of the bit, maintaining well stability and balancing underground hydrostatic pressure.
These fluids are pumped down the drill pipe, through the bit, to carry the drill-cuttings through the annulus back to the surface. Depending on the continuous phase fluid, drilling fluid systems are either water-based (aqueous) or non-aqueous emulsion systems.
Aqueous Based Fluids
Aqueous Based Fluids or Water-Based Mud (WBM) are the types of drilling fluids that use water or brine as the continuous phase fluid. Water-based drilling mud most commonly consists of bentonite clay (gel) with additives such as barium sulfate (barite), calcium carbonate (chalk) or hematite. Various thickeners are used to influence the viscosity of the fluid, e.g. xanthan gum, guar gum, glycol, carboxymethyl cellulose, polyanionic cellulose, or starch.
Deflocculants are also used to reduce viscosity of clay-based muds; anionic polyelectrolytes (e.g. acrylates, polyphosphates, lignosulfonates (Lig) or tannic acid derivates such as Quebracho) are frequently used (Anon. (a), 2011).WBM’s are considered as environmentally better alternative for Non-Aqueous Based Fluids (NAF), and where possible their use is favored over NAF. The physical/chemical characteristics, and thus the applicability in drilling operations, of WBM are different compared to NAF. Even though WBM are environmentally favorable, for technical and safety reasons NAF may be required in situations where drilling operations are more complex. It
is, therefore, common practice for WBM to be used for drilling the upper section of the well and NAF for the more complex sections (TMD, 1998). Some advantages of using WBM include: lower environmental impact and enhanced worker safety through lower toxicity, elimination of Polycyclic Aromatic Hydrocarbons, faster biodegradability, and lower bioaccumulation potential(CAPP, 2001).Table 2.1, gives a summary of typical elemental composition of common constituents of WBM.
CHAPTER THREE
ENVIRONMENTAL ISSUES BASED ON LOCATION
Introduction
The process of drilling oil and gas wells generates large volumes of drill cuttings and used muds. Onshore and offshore operators have employed a variety of methods for managing these drilling wastes. In offshore, options are limited to cuttings reinjection, offshore discharge and transportation to onshore disposal facility (Veil, 2002). This is as a result of the limited space and stringent environmental regulations governing an offshore drilling operation. As a result some offshore wastes have to be transported to an onshore facility for treatment and disposal. Onshore operations however, have a wider waste management options. The selection of a disposal method for a particular location depends on other factors which must be evaluated extensively before implementation. The main aim
should be towards ensuring an environmentally safe waste disposal approach at the lowest possible cost. This chapter explores the various waste management options based on location (offshore and onshore).
Managing Waste Offshore
In drilling operations, drilling mud is pumped down the drill string and ejected through the nozzles in the drill bit at high velocity and pressure to lift cuttings to the surface. At the surface, solids control equipment is used to remove the unwanted solids from the drilling fluid to provide the maximum practical recovery of drilling fluid for re-use (OGP, 2003). The recovered drilling fluid is re-circulated down the drill string to lift more cuttings
and the cycle continues. The remaining solid component which forms the waste stream is then subjected to one of these disposal methods: Offshore Discharge, hauling to Onshore Facility or reinjection into the formation. Managing waste in an offshore operation is usually more challenging and costly than on onshore operation. This is due to the stringent environmental regulations governing offshore drilling operations as well as limited space
available for operation. The flow chart below (Figure 3.1) shows how drilling waste is managed in an offshore operation.
CHAPTER FOUR
MINIMIZATION AND MANAGEMENT OF DRILLING WASTE
Introduction
Waste management refers to ways by which the generation and pollution of waste could be controlled to minimize or eliminate its negative impact on the environment. Over the past decade, there has been an increasing international concern for proper waste management in order to minimize their potential to cause harm to human health and the environment. The overall aim of managing drilling waste is to cut down on cost. As a result, effective and responsible waste management has been a key element of any organization’s environmental management system.
Besides, effective waste management practices will not only be a valuable tool for waste minimization programs, but also, source of data in the event of any question of liability for contamination, and site remediation. Waste management includes the incorporation of a hierarchy of waste management practices in the development of waste management plans. Being able to identify and quantify waste stream and assessing its potential impacts on the environment can help provide a baseline for identification of opportunities to improve practices. The potential
benefits to a company that implements an effective waste management practices include (RCC,
1993):
CHAPTER FIVE
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
Summary
The objectives of this study are (1) to identify various types of drilling waste that impacts the environment. (2) to develop equations for waste volume computation and to generate a Microsoft Excel User-friendly Program for Waste Volume Estimation. (3) to establish the best possible ways of minimizing drilling wastes. (4) to develop a comprehensive waste management plan and establish the best possible way of incorporating waste volume estimation into it. From chapter 2 of this study, the main type of drilling wastes are drill cuttings,
contaminated drilling mud and gas emissions. These wastes form the second largest sources of waste in the E&P industry after produced water which is considered as production waste. In order to effectively manage drilling waste, it is very important to know the quantity of waste that is expected. Different equations for waste volume computations were reviewed in chapter 4 and a spreadsheet program for waste estimation developed. It was presented that the hole length, bit size, geology and SRE are the main drivers that affects the volume of waste generated. These understanding help to plan ahead for the expected volume of waste. Knowing the anticipated quantity of waste, various measures could be employed to minimize the waste volume. Chapter 4 further details methods like efficient solids removal equipment, slim hole drilling, coil tubing drilling and horizontal well drilling as measures of minimizing the volume of waste generated. There are a number of waste management methods
available. An extensive explanation of the different methods has been captured in chapter 3. From these explanations, a simple drilling waste screening and selection criteria has been outlined. This screening process will help to eliminate some of the different waste management Options that are not relevant. Owing to the third objective, a ten steps waste management procedure has been outlined and is captured in chapter 4.
Conclusions
Based on the theoretical and practical observations made from this research work, the
following deductions and conclusions can be made:
Waste volume estimations plays a critical role in managing drilling and associated waste and should at all-times be estimated and incorporated into the waste management plan. A Microsoft Excel Model has been developed to this effect.
The disposal and waste management cost is directly related to the volume of waste generated and as such, minimization as a waste management method must be a priority to other methods.
Selection of the optimum drilling waste management method must always be subjected to extensive environmental, technical and economic analysis as these are the main drivers. A screening criteria has been developed to help quicken the decision making process.
For effective drilling waste management, the ten waste management steps must be followed
critically.
Recommendations
Owing to the limited time for this research work, the following are recommended:
More comprehensive study should be done on the waste management screening criteria using real field data.
The multi-criteria selection application in Geographic Information Systems (GIS) and a more engineering technique like Operations Research (OR) could be used to select the optimum waste management method.
It is understood from this research that, waste management in general is a problem in Africa.
One way to tackle this problem is to sensitize the public about the environmental effects of drilling waste on the environment. It is therefore recommended that an institution like AUST should incorporate waste management as a course into its academic curricular.
REFERENCES
- Aird, P. 2008: Drilling Waste Management Technology Descriptions, USDOE (2008) http://web.ead.anl.gov , Date Accessed: 15th August, 2011.
- Anon 2011: Drilling Engineering Lecture Notes, Heriot-Watt University, Department of Petroleum Engineering, Edinburgh, Scotland, (2011)
- Anon (a) 2011: “The importance of oil” http://www.scienceclarified.com/OiPh/Petroleum.html # ixzz1QktPNPpO, Date accessed: 10th, August, 2011
- Anon (b) 2011: Waste Management, – Wikipedia, the free encyclopedia, http:// en.wikipedia.org /wiki/ aste_Management, Date accessed: 10th, August, 2011
- Anon (c) 2011: Drilling Fluids, (http: // en.wikipedia.org /wiki/ Drilling_fluid # Composition _of_ drilling_mud), Date Accessed: 31st July, 2011
- Canadian Association of Petroleum Producers, CAPP, 2001: Offshore Drilling Waste Management Review, Technical Report, February, 2001, Reviewed by July, 2003, DOCs # 25022
- Carole Fleming, Catalin Ivan, William A. Piper: 2010: “Theoretical and Practical Models for Drilling Waste Volume Calculation with Field Case Studies”
- CEF Consultants Ltd, CEF, 1998: “Exploring for Offshore Oil and Gas”, No. 2 of Paper Series on Energy and the Offshore. Halifax, NS, <http:www.cefconsultants.ns.ca/2explore.pdf> [Accessed on May 18, 20111