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Project Topic:

COMPARATIVE STUDY BETWEEN OVERBALANCED AND UNDERBALANCED OIL DRILLING METHODS

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 Format: MS WORD ::   Chapters: 1-5 ::   Pages: 60 ::   Attributes: DOCUMENTATION ::   13,286 people found this useful

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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 Underbalance Drilling Operation: 3

1.4 Underbalance 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 DIFFRENCES BETWEEN OVERBALANCE AND UNDERBALANCE 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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  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.


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Paper Information

Format:MS WORD
Chapter:1-5
Pages:60
Attribute:DOCUMENTATION
Price:₦3,000
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