COMPARATIVE STUDY BETWEEN OVERBALANCED AND UNDERBALANCED OIL DRILLING METHODS.


COMPARATIVE STUDY BETWEEN OVERBALANCED AND UNDERBALANCED OIL DRILLING METHODS.

ABSTRACT

The technique used worldwide while drilling is known as overbalanced drilling. Which is defined as the drilling process where the hydrostatic pressure used exceeds the formation pressure. This is done with the main purpose of “killing” the well. However, there are numerous problems that accompany overbalanced drilling. Such problems are differential pipe sticking, loss of circulation, formation damage and other problems. A relatively new technique was introduced, known as underbalanced drilling, where the well is being drilled with a hydrostatic pressure less than that of the formation. Correct and proper execution of such technique eliminates problems associated with overbalanced drilling. More precisely, underbalanced drilling solves the issues of formation damage, differential pressure sticking and loss of circulation. On the other hand, underbalanced drilling has its own problems as well. Additionally, underbalanced drilling increases the rate of penetration and provides other uses discussed in this project.  The objective of this paper was to compare between overbalanced and underbalanced drilling and ascertain which method is most suitable in all aspects. Finally, it can be concluded that UBD provides lower drilling costs, increased rate of penetration (ROP) and less hole problems when it was compared to overbalanced drilling of the same formations.

Table of Contents   

CERTIFICATION    i

DEDICATION    ii

ACKNOWLEDGEMENT    iii

ABSTRACT    iv

LIST OF FIGURES    vii

LIST OF TABLES    viii   CHAPTER 1:    INTRODUCTION    1

1.1 Background study:    1

1.2 Overbalance Drilling Operation:    2

1.3 Underbalanced Drilling Operation:    3

1.4 Underbalanced Gases    6

1.5 Underbalance Techniques    6

1.6 Statement of problem    8

1.7 Aims and Objectives    8

1.8 Scope and Limitation    8

1.9 Methodology    8   CHAPTER 2:    LITERATURE REVIEW    9

2.1    HISTORICAL OVERVIEW OF DRILLING IN THE OIL INDUSTRY    9

2.2    THE EMERGENCE OF DRILLING TECHNIQUES    11

2.3    WELL SELECTION    14

2.4    KINDS OF UNDERBALANCED DRILLING    16

2.5    Case Study of an Underbalanced Drilling Operation in East Asia    16   CHAPTER 3:    METHODOLOGY    18

3.1    REVIEW OF THE DIFFERENCES BETWEEN OVERBALANCE AND UNDER BALANCE DRILLING    18

3.2    COMPARATIVE ANALYSIS BETWEEN UNDERBALANCED AND CONVENTIONAL OVERBALANCED DRILLING IN THE GULF OF SUEZ USING A DRILLING SIMULATOR    20

3.2.1    Extracted Data    20

3.2.2    INTERPRETATION OF RESULTS    22

3.2.3    ADVANTAGES OF UNDERBALANCED DRILLING OVER OVERBALANCE DRILLING    30

3.2.4    DISADVANTAGES OF UBD    32   CHAPTER 4:    ANALYSIS    34

4.1    LABORATORY SCREENING TECHNIQUES    34

4.1.1    UNDERBALANCED LABORATORY EVALUATION    34

4.1.2    OVERBALANCED LABORATORY EVALUATION    35

4.2    TYPES OF RESERVOIRS SUITABLE FOR UNDERBALANCED DRILLING    36

4.3    COMMON MECHANISMS OF FORMATION DAMAGE DURING   OVERBALANCED AND UNDERBALANCED DRILLING   OPERATIONS    38

4.4    SURFACE EQUIPMENT REQUIREMENTS    40   CHAPTER 5:    CONCLUSION AND RECOMMENDATION    42

5.1    CONCLUSION AND RECOMMENDATION    42

5.1.1    CONCLUSION    42

5.1.2    RECOMMENDATION    43

REFERENCES    44

LIST OF FIGURES

Figure 1.1: Conventional overbalance drilling    3

Figure 1.2: Underbalanced Drilling    5

Figure 1.3: Gas injection via parasite string    7

Figure 3.1: underbalanced drilling through zone 1    22

Figure 3.2: Underbalanced drilling through zone 1 (progressing)    23

Figure 3.3: Underbalanced drilling through zone1 (progressing)    23

Figure 3.4: Underbalanced drilling through zone 2 (the underbalanced conditions have been compromised)    25

Figure 3.5: Overbalanced drilling, zone 1 (progressing)    26

Figure 3.6: Overbalanced drilling through zone 2 (progressing)    27

Figure 4.1: Typical surface equipment for UBD operation    40

LIST OF TABLES

Table 3.1: Showing Pressure profile of the drilled formations    24

Table 3.2: Showing the BHA used    24

Table 3.3: Showing the mud used    24

CHAPTER 1:   

CHAPTER 1:    INTRODUCTION

1.1 Background study:

The main purpose of drilling vertical or horizontal wells is to produce maximum recoverable oil at minimum cost. Traditionally, wells have been drilled overbalance with the hydrostatic pressure of the drilling fluid greater than the pressure in the formation. Unfortunately, drilled wells with overbalance are subject to formation damage with varying degree of severity, depending upon the drilling conditions. This is mainly due to the invasion of drilling fluids during drilling operations. The formation impairment or skin due to drilling fluid invasion around the well bore reduces well productivity. This is especially true for wells completed either open hole or with slotted liner due to the difficulty to undertake any stimulation job to alleviate formation damage problems. (S.Z. Jilani et al.)

Nowadays, horizontal wells are preferred over vertical wells because they offer a net productivity enhancement as well as an increase of the contact area with the reservoir. However, formation damage is more critical to horizontal wells because these wells have such long exposed interval that stimulation jobs are not efficient and feasible. (S.Z. Jilani et al.)

Drilling operation is considered as the primary initiator of formation impairment as virgin formation comes first time in contact with a foreign fluid, i.e. drilling mud, which invades the formation and plugs the pores around the well bore. Although drilling fluids are presently being designed in such a way to minimize solid and fluid invasion into the formation.

In this project we would be taking a look at some comparative analysis done between two drilling operational techniques; the conventional Overbalance drilling technique (OBD) and the Underbalance drilling technique (UBD).   1.2 Overbalance Drilling Operation:

Many definitions have been laid down for a conventional overbalance drilling operation usually referred to as conventional drilling. These definitions categorize the drilling fluid design used for an overbalance drilling operation.

The amount of pressure (or force per unit area) in the wellbore that exceeds the pressure of fluids in the formation is also considered as overbalance.This excess pressure is needed to prevent reservoir fluids (oil, gas, water) from entering the wellbore.. However, excessive overbalance can dramatically slow the drilling process by effectively strengthening the near-wellbore rock and limiting removal of drilled cuttings under the bit.

In conventional overbalanced drilling operations, the hydrostatic pressure exerted by the drilling fluid in the well is designed to exceed the pressure of the hydrocarbon fluids in the reservoir. Since the pressure in the hole is higher than the pressure in the rock fluid therefore drilling fluid can lose into the formation. These losses cause damage to the near well-wall area resulting in reduced production, experience show that even a short exposure to overbalanced conditions can severely impair the productivity of the well.

In addition, high overbalance pressures coupled with poor mud properties can cause differential sticking problems in which the drill pipe is pressed against the wellbore wall and as a result the pipe becomes stuck to the wall. Because reservoir pressures vary from one formation to another, while the mud is relatively constant density, overbalance varies from one zone to another. (Schlumberger Oilfield Glossary, 2014)

Figure 1.1 illustrates an overbalance drilling operation. As we can see, the drilling fluid being circulated plugs the pores causing drilling fines to migrate and invade the formation.

A simple equation to illustrate this condition of drilling can be given as:

Pm ˃ Pf

Figure 1.1 : Conventional overbalance drilling

1.3 Underbalanced Drilling Operation:

The growing number of depleted reservoirs around the world and the increasing necessity to recover hydrocarbons more efficiently has been forcing the oil and gas industry to continuously improve its drilling technology. Currently, the combination of drilling techniques that were conceptualized more than 100 years ago, have with recent technological innovations ended up in specialized drilling techniques. These techniques, when properly designed and executed, allow drilling a well more economically, safely, and successfully in almost any given environment. One such technique is called underbalanced drilling (UBD).

Underbalanced drilling, or UBD, is a procedure used to drill oil and gas wells where the pressure in the wellbore is kept lower than the fluid pressure in the formation being drilled. As the well is being drilled, formation fluid flows into the wellbore and up to the surface. This is the opposite of the usual situation, where the wellbore is kept at a pressure above the formation to prevent formation fluid entering the well. In such a conventional "overbalanced" well, the invasion of fluid is considered a kick, and if the well is not shut-in it can lead to a blowout, a dangerous situation. In underbalanced drilling, however, there is a "rotating head" at the surface - essentially a seal that diverts produced fluids to a separator while allowing the drill string to continue rotating guaranteeing safety. (Wikipedia.org)

Though not as common as overbalanced drilling, underbalanced drilling is achieved when the pressure exerted on the well is less than or equal to that of the reservoir. Performed with a light-weight drilling mud that applies less pressure than formation pressure, underbalanced drilling prevents formation damage that can occur during conventional or overbalanced drilling processes.

The negative differential pressure obtained during underbalanced drilling between the reservoir and the wellbore encourages production of formation fluids and gases. In contrast to conventional drilling, flow from the reservoir is driven into the wellbore during underbalanced drilling, rather than away from it.

Figure 1.2 describes an underbalance drilling operation showing less hydrostatic drilling fluid being circulated and we can see flow from the reservoir as well as formation fines into the wellbore as drilling operation is carried out.

A simple equation to illustrate the condition of drilling can be given as:

Pf > Pm

Figure 1.2 : Underbalanced Drilling

Although initially more costly, underbalanced drilling, also known as managed-pressure drilling, reduces common conventional drilling problems, such as lost circulation, differential sticking, minimal drilling rates and formation damage.  Additionally, underbalanced drilling extends the life of the drill bit because the drilling gases cool the bit while quickly removing cuttings.

To establish pressure control, a rotating control head with a rotating inner seal assembly is used in conjunction with the rotating table. An important factor to successful underbalanced drilling, drilling and completion operations must remain underbalanced at all times during operations. To accomplish this, pre-planning and onsite engineering are critical to the success of underbalanced drilling procedures.

Typically used for only a section of the entire drilling process, underbalanced drilling cannot be used in most shale environments.   1.4 Underbalanced Gases

Gases used for underbalance include air, nitrogen and natural gas. Although it is not typical, if natural gas is recovered from the well, it can be reinjected into the well to establish underbalance, resulting in the most cost-effective solution for underbalanced drilling.

Commonly used in underbalance operations, nitrogen is preferred for its somewhat low cost of generation, scale of control and minimal potential for downhole fires. While pure nitrogen can be purchased, it is cost-prohibitive. Therefore, nitrogen is more commonly produced onsite with a membrane unit, resulting in a 95% level of purity.   1.5 Underbalance Techniques

There are four main techniques to achieve underbalance, including using lightweight drilling fluids, gas injection down the drill pipe, gas injection through a parasite string and foam injection.

Using lightweight drilling fluids, such as fresh water, diesel and lease crude, is the simplest way to reduce wellbore pressure.

The method of injecting gas down the drillpipe involves adding air or nitrogen to the drilling fluid that is pumped directly down the drillpipe. Advantages to this technique include improved penetration, decreased amount of gas required, and that the wellbore does not have to be designed specifically for underbalanced drilling.

In performing the gas injection via parasite string, a second pipe is run outside of the intermediate casing. While the cost of drilling increases, as does the time it takes, this technique applies constant bottom hole pressure and requires no operational differences or unique MWD systems. Figure 1.3 shows a pictorial representation of the above procedure.   Figure 1.3 : Gas injection via parasite string

A less common underbalanced application, nitrogen foam is less damaging to reserves that exhibit water sensitivities. While the margin of safety is increased using foams, the additional nitrogen needed to generate stable foam makes this technique cost-prohibitive. Additionally, there are temperature limits to using foam in underbalanced drilling, limiting using the technique to wells measuring less than 12,000 feet deep.   1.6 Statement of the problem

Due to the growing technologies associated with drilling operations, it is pertinent to look for affordable, convenient and more productive alternatives. In this project, we would analyze both drilling techniques and see its effect on various formations to be able to make a better choice for each drilling scenario.   1.7 Aims and Objectives

In view of the comparative analysis of overbalance and underbalance drilling operations in the Oil and Gas industry, this project work seeks to investigate the following:

(i)    To have an understanding of both the underbalance and overbalance drilling operations.

(ii)    To know reservoirs suitable for either underbalance or overbalance drilling operations.

(iii)    To also know the various effects and challenges associated with these operations.

1.8 Scope and Limitation

The scope of this study is to comparatively analyze underbalance and overbalance drilling operations with emphasis on reservoir types.

1.9 Methodology

In the course of the project, vital information was obtained from the library, review of related literatures, internet surfing, textbooks, petroleum journals and these formed the basis for analysis of both underbalance and overbalance drilling operations.

.

COMPARATIVE STUDY BETWEEN OVERBALANCED AND UNDERBALANCED OIL DRILLING METHODS.



TYPE IN YOUR TOPIC AND CLICK SEARCH.






RESEARCHWAP.ORG
Researchwap.org is an online repository for free project topics and research materials, articles and custom writing of research works. We’re an online resource centre that provides a vast database for students to access numerous research project topics and materials. Researchwap.org guides and assist Postgraduate, Undergraduate and Final Year Students with well researched and quality project topics, topic ideas, research guides and project materials. We’re reliable and trustworthy, and we really understand what is called “time factor”, that is why we’ve simplified the process so that students can get their research projects ready on time. Our platform provides more educational services, such as hiring a writer, research analysis, and software for computer science research and we also seriously adhere to a timely delivery.

TESTIMONIES FROM OUR CLIENTS


Please feel free to carefully review some written and captured responses from our satisfied clients.

  • "Exceptionally outstanding. Highly recommend for all who wish to have effective and excellent project defence. Easily Accessable, Affordable, Effective and effective."

    Debby Henry George, Massachusetts Institute of Technology (MIT), Cambridge, USA.
  • "I saw this website on facebook page and I did not even bother since I was in a hurry to complete my project. But I am totally amazed that when I visited the website and saw the topic I was looking for and I decided to give a try and now I have received it within an hour after ordering the material. Am grateful guys!"

    Hilary Yusuf, United States International University Africa, Nairobi, Kenya.
  • "Researchwap.org is a website I recommend to all student and researchers within and outside the country. The web owners are doing great job and I appreciate them for that. Once again, thank you very much "researchwap.org" and God bless you and your business! ."

    Debby Henry George, Massachusetts Institute of Technology (MIT), Cambridge, USA.
  • "Great User Experience, Nice flows and Superb functionalities.The app is indeed a great tech innovation for greasing the wheels of final year, research and other pedagogical related project works. A trial would definitely convince you."

    Lamilare Valentine, Kwame Nkrumah University, Kumasi, Ghana.
  • "I love what you guys are doing, your material guided me well through my research. Thank you for helping me achieve academic success."

    Sampson, University of Nigeria, Nsukka.
  • "researchwap.com is God-sent! I got good grades in my seminar and project with the help of your service, thank you soooooo much."

    Cynthia, Akwa Ibom State University .
  • "Sorry, it was in my spam folder all along, I should have looked it up properly first. Please keep up the good work, your team is quite commited. Am grateful...I will certainly refer my friends too."

    Elizabeth, Obafemi Awolowo University
  • "Am happy the defense went well, thanks to your articles. I may not be able to express how grateful I am for all your assistance, but on my honour, I owe you guys a good number of referrals. Thank you once again."

    Ali Olanrewaju, Lagos State University.
  • "My Dear Researchwap, initially I never believed one can actually do honest business transactions with Nigerians online until i stumbled into your website. You have broken a new legacy of record as far as am concerned. Keep up the good work!"

    Willie Ekereobong, University of Port Harcourt.
  • "WOW, SO IT'S TRUE??!! I can't believe I got this quality work for just 3k...I thought it was scam ooo. I wouldn't mind if it goes for over 5k, its worth it. Thank you!"

    Theressa, Igbinedion University.
  • "I did not see my project topic on your website so I decided to call your customer care number, the attention I got was epic! I got help from the beginning to the end of my project in just 3 days, they even taught me how to defend my project and I got a 'B' at the end. Thank you so much researchwap.com, infact, I owe my graduating well today to you guys...."

    Joseph, Abia state Polytechnic.
  • "My friend told me about ResearchWap website, I doubted her until I saw her receive her full project in less than 15 miniutes, I tried mine too and got it same, right now, am telling everyone in my school about researchwap.com, no one has to suffer any more writing their project. Thank you for making life easy for me and my fellow students... Keep up the good work"

    Christiana, Landmark University .
  • "I wish I knew you guys when I wrote my first degree project, it took so much time and effort then. Now, with just a click of a button, I got my complete project in less than 15 minutes. You guys are too amazing!."

    Musa, Federal University of Technology Minna
  • "I was scared at first when I saw your website but I decided to risk my last 3k and surprisingly I got my complete project in my email box instantly. This is so nice!!!."

    Ali Obafemi, Ibrahim Badamasi Babangida University, Niger State.
  • To contribute to our success story, send us a feedback or please kindly call 2348037664978.
    Then your comment and contact will be published here also with your consent.

    Thank you for choosing researchwap.com.