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OIL WELL INTEGRITY ISSUES: CRITICAL QUESTIONS BOTH ON ONSHORE &

OFFSHORE OPERATIONS

Andreia Filipa Coutinho Pereira

Instituto Superior Técnico, Universidade Técnica de Lisboa

December, 2014

ABSTRACT

The oil wells integrity has attracted, in the recent years, a growing interest by the oil industry.

The equipment, techniques and the operational proceedings had improved with the purpose of

minimizing risks, identifying potential hazards, reducing the environmental impact and even

improving the industry reputation. Nevertheless, it still occur several disasters related with the

integrity of the oil well, like the ones seen in the Gulf of Mexico, Australia and Brazil. These are

clear evidences that the investment in the stabilization of the oil wells shouldn’t be despised.

In order to decrease both the operational and financial risks, firms implemented management

systems that cover the entire life cycle of an oil well, from the conception of the project to the

construction, maintenance and exit. Thus, it is possible to drill and to operate with safety and

with fewer costs in the oil wells, meeting the predefined goals for the production.

In this work the entire process of drilling is described, being exposed the major differences

between onshore and offshore operations and the main risks in these drilling operations. As a

complement, two case-study in onshore and offshore systems are analyzed.

Keywords: Oil industry; Drilling industry; Onshore Drilling; Offshore Drilling; Stability; Safety.

1. INTRODUCTION

A great technological evolution in the drilling industry has occurred over the last 30 years.

Nevertheless, it was simultaneously responsible for an increase of the failure risk levels, since

the drilling depth was expanded. Considering the large number of variables involved, analyzes

have become more complicated.

Furthermore, the concerns regarding the environmental impact of these operations grew, being

considered as the main challenge, for the oil industry, not only to overweight the structural

complexity of the explored areas, but also to operate in a sustainable way (Torbergsen, 2012).

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The loss of integrity of an oil well can be caused by several factors, such as a mechanical,

hydraulic or electrical failure, or even by the inadequate application of a device. Several

accidents are, sometimes, aggravated by human failures, making of fundamental importance

the processes of training and practice in every oil company. In this sense, the stabilization of an

oil well is considered as: “application of technical, operational and organizational solutions to

reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well ” (Norsok

D-010). Thus, it is possible to prove that the oil well integrity does not only depend of the

equipment robustness, but of all processes, competence and resources of the company, and

mainly of the professional competence of each employee.

2. HYDROCARBON EXPLORATION

The exploration activity begins when an oil company requests to a national government the

research rights over a given concession. The main goal is to find an underground structure

containing levels of hydrocarbons in sufficient order for the production to be profitable. The

exploration is based in the acquisition and analysis of geological and geophysical data of the

formations, being followed by the drill of a research well, designated of wildcat.

The exploration well enables the validation of a conceptual model of exploration, being the only

way to confirm if there exists oil in commercial quantities. This will help to define how many oil

wells will be necessary to be made in order to drain the reservoir. In onshore operations, the

wells are made with rigs transported in trucks, while in offshore operations these are drilled

through semi-submersible platforms with telescopic pillars fixed in the bottom of the sea

(Gomes, 2011).

3. DRILLING OPERATIONS

The only available and direct method to confirm the existence of viable economic oil reserves is

to drill a well. This process is performed by a sequence of several operations. This will enable,

considering safety issues and the stability of the well, the creation of a link between the

reservoir and the surface. These operations are done through the application of a drilling rig or

platform, and can be made by choosing one of these methods: percussive and rotary

(Bourgoyne, 1986; Gatlin, 1960).

The percussive method was the first to be applied in the well drilling, being also known as cable

tool drilling. It consists in the successive tapping of the rock by the drill bit, which will fragment it

by the crush. The cleaning of the well occurs after the clearance of the bit with a bailer

responsible for taking out of its interior the cuttings generated earlier.

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Since 1900, with exception of some special cases, the rotary method is used (Figure 1). The

drill is made through the application over the drill bit of rotary and weighted movements, applied

in the drill string extremity. The fragments are taken out successively through drilling or mud

fluids that are injected by pumping them into the interior of the drill string. Then, they will get

back into the surface by the annular space existent between the walls of well and the drill string.

Figure 1 – Rotary system. (Adapted from: Lake, 2006)

3.1 Basic rig components

The drilling rigs, of land or maritime nature, have the same basic drilling equipment, which can

be grouped in seven major systems: load sustaining system, load movement system, rotary

system, fluid circulation system, monitoring system, control and security system, and the energy

generation and transmission system (Thomas, 2001). The running of these systems, together,

makes possible to drill an oil well, and should enable:

The storage of drill pipes;

The elevation and the positioning of the drill pipes;

The rotation of the drill string;

The energy management.

The drill string is composed by the drill bit and the drill pipes, and is directly responsible for the

drilling of the well. The drill pipes are linked between them through a tool joint located in one of

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the extremities and a bolt threaded on the other one. There are three types of drill pipes applied

in a drill string, namely, the drill collars, heavy-weighted drill pipes and drill pipes. They enable

the sprain of drilling fluids, playing each one a specific role in the running of the drill string.

The drill bits, putted in the end of the drill string, have the function of fragmenting the rock, using

weight and rotation over it, in a rotary movement that is induced by the rotation of the drill string

over the rotary table, or a top drive, or a high pressure mud circulation engine, if there exists

one.

3.2 Drilling Fluids

The drilling fluids are an element of major importance in the process of drilling an oil well. It is

possible to say that the success of the drilling operation will significantly depend of the fluids

that are pumped. The removal and the transportation of the well cuttings, generated by the drill

bit, to the surface is one the main roles of the drilling fluids. However, it is important to take into

consideration other important functions, such as: ensuring the cuttings suspension during the

interrupting of the circulation; supporting and stabilizing the well walls; coating the walls of the

well with a mud cake that will isolate the more permeable areas of the reservoir; avoid, or at

least, minimize the damage in the formations; cold off and lubricate the dril l bit and the drill

string; enabling the acquisition of the biggest volume of information about the crossed

formations (Drilling Fluid Processing Handbook, 2005).

A drilling fluid is generally classified in function of its composition. According to this criterion,

fluids are classified concerning their continuous basis in: water based fluids, oil based fluids, air

based fluids, and synthetic based fluids.

3.3 Casing Design and Cementation

One of the most important stages during a drilling operation is the introduction of a casings

cementation with different diameters and several depth gaps. The casing of the well enables:

the return of the drilling fluid to the surface and the pressure control; prevents the collapse of

the walls; avoids the groundwater contamination; and sustains the drill equipment’s.

Considering the descent order of the casings and their role, it is possible to identify four types of

casings strings: conductor; of surface; intermediary; and of production (Figure 2).

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Figure 2 – Casing design. (http://fracfocus.ca/groundwater-protection/drilling-and-production)

The oil industry classifies the cementation operation in two types: primary cementation and

secondary cementation, corrective or complementary. The primary cementation corresponds to

the work of cementation for each casing string, after their descent to the well. It is the main

operation of the well structuration. The secondary cementation is an emergency operation,

which has the objective of correcting errors or deficiencies resulted from a poorly executed

primary cementation.

4. ONSHORE DRILLING VS OFFSHORE DRILLING

For the oil to achieve the surface, it is inevitable to drill an oil well, onshore or offshore, that

reaches the reservoir. Actually, the land or maritime rotary drilling rigs (Figure 3) are used in

almost all the drilling works.

Figure 3 – Types of drilling rigs.

Rotary Dri l ling Rigs

Marine Rigs

Floating Rigs

Semi-submersible

Dri l lship

JackupFixed

Platform

Sel f Contained

Tendered

Land Rigs

Mobi le

Jackknife

Portable-Masts

Conventional

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The land platforms are characterized by their portability and maximum depth of operation.

(Bourgoyne, 1986) The infrastructure in onshore environment is moved to the local, and then

mounted on the ground over the oil well. The land is previously prepared, including the sizing of

the foundations, the equipment layout, the drainage and the mud tanks. Considerations about

the ground stability and the accessibilities (logistics, road conditions and possible obstructions)

must be taken.

The operations of control and safety on onshore are more facilitated that in offshore because,

beyond being the BOP (blowout preventer) at sight, it is also very close, meaning that the

valves can be operated manually in a situation of failure of the automatism.

The first maritime rigs were operated as land rigs, mounted in shallow waters. The necessity to

drill in more deep waters justified the arising of new techniques and specific equipment’s to drill

in the sea. These maritime rigs are exposed to drives due to the wave’s action, maritime

currents and the winds. Because of that, they possess positioning systems that guarantee their

stability. They can be classified in: fixed platforms, jackups, and floating platforms.

In offshore, the BOP may be located on the surface, when using fixed platforms or jackups, or

at the bottom of the sea, like in the case of floating platforms. The success of the well control

depends equally from the quickness in detecting the kick, and the efficiency and suit ability of the

procedure used.

5. CASE STUDIES

During the drilling process, the diameter of the well will decrease with the increase in depth. The

final depth for each segment of the well is defined by three criteria: costs, geology and

production objectives.

5.1 Onshore Well

For this case-study it was determined one main objective and three secondary objectives.

These objectives were defined because of the possibility of finding hydrocarbons in economic

viable quantities. The water to be used during the drilling will be provided from a water well,

previously made for the effect.

An onshore well (vertical well) was chosen for exploration, with a depth of 2918 meters. It

assumes as expected problems:

Excessive vibrations in the drilling of the well top;

Total loss of circulation until the 290 meters;

Influx of saltwater in the 2500 meters.

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In table 1 it is exposed a general summary of the drilling program and the coatings used, which

is divided in five main phases:

Table 1 – The drilling and casing design program of an onshore well.

Diameter of

the hole

(inches)

Depth (m) Bit drill

type

Casing

(inches)

Types of

casing

Dimension of

the casing (m)

Phase 1 36’’ ± 80 TCI 30‘’ Conductor ± 77

Phase 2 26’’ ± 300 TCI 20’’ Surface ± 297

Phase 3 16’’ ± 1700 PDC 13 3/8‘’ Intermediary ± 1697

Phase 4 12 ¼‘’ ± 2500 PDC/TCI 9 5/8’’ Intermediary ± 2497

Phase 5 8 ½‘’ ± 2918 PDC/TCI 7’’ Production ± 2915

The BOP (blowout preventer) to be used in this case-study will include a void and three

drawers.

5.2 Offshore Well

For this case-study it was determined two main objectives and two secondary objectives. The

offshore well was defined as for exploration, with an overall depth of 5100 meters. It presents a

sensible status and do not exhibits H2S or shallow gas risk.

The type of platform to be used will be a semi-submersible floating platform. A semi-

submersible platform has exposure to strong winds and to maritime currents, but not to the

ripple, since the floaters are located below the wave area.

In table 2 it is presented a brief summary of the drilling and the coatings to be used, divided in

five parts. It is important to notice that the mud line reaches a depth of 1002 mMD/RT

(measured depth/rotary table).

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Table 2 – The drilling and casing design program of an offshore well .

Diameter of

the hole

(inches)

Depth (m) Bit drill

type

Casing

(inches)

Types of

casing

Dimension of

the casing (m)

Phase 1 42’’ 1002 ± 1067 PDC 36‘’ Conductor 1002 ± 1067

Phase 2 26’’ ± 1887 PDC 20’’ Surface ± 1887

Phase 3 17 ½’’ ± 3203 PDC 13 3/8‘’ Intermediary ± 3193

Phase 4 12 ¼‘’ ± 4286 PDC 9 5/8’’ Production ± 4276

Phase 5 8 ½‘’ ± 5102 PDC - - -

The BOP (blowout preventer) to be used in this case-study will include two voids and four

drawers.

6. IDENTIFICATION OF MAIN RISKS

The main risks that affect the integrity of an oil well are:

1. The stability of the drill string;

2. The maneuver of the drill string;

3. Mud losses;

4. The losses of material in the bottom of the well and “fishing”;

5. The integrity of the materials and the equipment’s;

6. Human factor.

7. HEALTH, SECURITY AND ENVIRONMENT

The HSE (Health, Safety and Environment) component is a relevant concern for any industrial

operation. However, it was developed in such a way on oil projects, that the policy and the

procedures has become an integrant part of the company management. One company that

takes into consideration ethical and moral features is likewise investing in its reputation, and

generally, the oil companies with higher HSE are the ones with better economic results.

This industry is more susceptible to problems due to its history and to the difficulties inherent to

exploration and production projects. Normally, these projects occupy large areas and require a

large quantity of equipment’s (Gomes, 2011).

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8. OIL RIG DISASTERS AND THE MACONDO BLOWOUT

The images of the first explorations and production projects in the United States of America and

in the Azerbaijan show a high environmental impact. It follows the environmental problems

created by the oil camps in the Western Siberia during the Soviet regime, the contamination of

aquifers in Equator due to oil residuals that were not properly isolated from the soils, the

accidents in maritime platforms, and the spills of oil tankers.

In 2002, the wreck of the Prestige caused an oil spill of more than 500 000 barrels along the

Portuguese and Spanish coast. The accident in the Piper Alpha platform, which was not

evaluated seriously in environmentally terms, was considered as the biggest accident in the oil

industry, causing the death of 167 people. In 1979, the blowout of the well located in Campeche

basin, in the Mexico Gulf, was also very harmful for the environment.

The largest maritime oil spill in the oil industry history occurred in the April 20, 2010, in a deep

offshore in the Mexico Gulf, on the Macondo well. It was a well of exploration that aimed to

detect hydrocarbons in viable economic quantities. In the April 16 was approved the temporary

shut-down of the well, since the exploratory objectives had been achieved. The process of

cementation began. It was during this process that the Macondo accident occurred.

The blowout was the result of several operational, technical and regulatory problems, causing

an explosion and the death of 11 people. The platform sank 36 hours after the blowout. After 87

days of uncontrolled production of an estimated volume of 4.9 million of oil barrels into the sea,

it was finally constructed two relief wells in order to intercept the well and block his flux.

9. EMERGENCY RESPONSE PLAN

The oil companies follow very rigorous operational proceedings, which intend to minimize the

risk of accidents. However, these procedures must be recurrently updated and improved in

order to avoid accidents. It is obvious that this risk will never disappear, and is exactly because

of this that the necessity of defining good plans of response, with the higher efficiency and

quickness possible, arises.

The emergency plan directed to accidents resulting from the maritime drilling activity involves

the drilling platforms and the accidents where the sea is polluted by oil. In case of leakage, this

is done in boats. In onshore it is defined one meeting point for which every worker must go in

case of emergency, being on that location that the response to the incident is made.

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10. CONCLUSION

A good project of an oil well is essential to ensure the maintenance of his integrity during the

expected life cycle. For each well, it is necessary to take into consideration the detailed geology,

the environmental conditions and the operational requirements of the location where the wel l is.

Despite some differences in the development process of a well, each one is projected with the

purpose of being maintained stable during its life.

The existence of good work practices, that protects the environment, employees, contractors

and all the community around, is considered of great importance. Also the existence of a

virtuous chain of communication between the community and the company is an asset that

ensures that the needs of both are perceived. The alarms and the emergency systems are

usually verified and the workers are properly trained to operate in the well and the local

facilities.

REFERENCES

Bourgoyne Jr., A. T., Millheim, K. K., Chenevert, M. E., & Young Jr., F. S. – Applied

Drilling Engineering. USA: Society of Petroleum Engineering, 1986.

BP – British Petroleum. Relatório final da comissão de investigação (2010).

Costa Silva, A.J. – Apontamentos de Petróleo e Gás. Instituto Superior Técnico, Lisboa,

2004.

Drilling Fluid Processing Handbook. Gulf Professional Publishing, USA: Elsevier INC, 2005.

Gatlin, C. – Petroleum Engineering, Drilling and Well Completions. Englewoodwood

Clifs, N.J., USA: Prentice-Hall, 1960.

Gomes, J., Alves, F. – O Universo da Indústria Petrolífera . Lisboa: Fundação Calouste

Gulbenkian, 2011.

Lake, L. W. – Petroleum Engineering Handbook, Vol. II . USA: Society of Petroleum

Engineers, 2006.

Thomas, J., et al. – Fundamentos de Engenharia de Petróleo. Rio de Janeiro:

Interciência. Petrobras, 2001. ISBN 85-713-046-5.

Torbergsen, H., et al. – An Introduction to Well Integrity. Norwegian Oil and Gas

Association’s Well Integrity Forum (WIF), Norwegian University of Science and Technology

(NTNU), Universitet i Stavanger (UIS), 2012.