Excerpt
3
Table of Contents
1. Introduction ... 4
2. Rotary Drilling ... 5
2.1 Introduction to Rotary Drilling ... 5
2.2 Hoisting System ... 6
2.3 Circulating System ... 6
2.4 Rotating System ... 7
2.5 System Association ... 8
2.6 Selecting a Land Rig ... 8
3. Well Planning ... 10
3.1 Well Planning ... 10
3.2 Pore Pressure ... 10
3.3 Fracture Pressure ... 10
4. Pore Pressure and Mud Weight ... 12
5. Cement ... 14
5.1 Introduction to Cement ... 14
5.2 Lightweight Additives ... 14
5.3 Retarders ... 14
5.4 Accelerators ... 14
5.5 Heavyweight Additives ... 15
5.6 Cement related calculation ... 15
6. Casing Design ... 19
6.1 Purpose of Casing ... 19
6.2 Principle of Casing Selection ... 19
7. Selection of BHA ... 21
7.1 Principle of Selecting BHA ... 21
7.2 Function of Selected BHA ... 21
7.3 Determine the number of drill collars ... 23
8. Well Completion ... 25
8.1 Options for Well Completion ... 25
8.2 BottomtoTop Design ... 26
9. A preview of the well design ... 27
10. Conclusion ... 28
References... 29
Appendix A ... 30
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1. Introduction
Well design involves drilling and mechanical engineering, geology,
hydraulics, and the physical, chemical and material sciences, all of which
epitomises hydrocarbon exploration technology. A completed well has to qualify
in several aspects such as safety, environmental protection, production efficiency
and reasonable cost. Therefore, a comprehensive construction plan has to be
carried out first, which requires practical and theoretical expertise. In addition, a
further data collection process is required to build an integral database for
design reference. However, uncertainty exists in every operation, which should
be emphasized so that the standard procedures are strictly followed.
The aim of this report is to design a new well, namely Holly Field well.
Based on the investigation, there are two reservoirs, gas and oil, located 10,500
ft. to 11,750 ft. below the surface. The main purpose of the Holly Field well is to
develop an oil reservoir, which will define which principles should be undertaken.
This report will demonstrate the basic design of Holly Field well with a brief
design principle illustrated in each section.
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2. Rotary Drilling
2.1 Introduction to Rotary Drilling
Exploration of a hydrocarbon reservoir brings uncertainty and risk to the
drilling operation such as an unforeseen formation influx. The rotary drilling
method has been chosen to implement the Holly Field development programme
because it may provide flexible solutions for unpredictable situations. Rotary
drilling developed in the early 1800s and today is the most common way of
exploring for hydrocarbon reservoirs (Bourgoyne Jr. et al. 2003). A rotary drilling
rig normally consists of hoisting, circulating and rotating systems. Each system
has a different function, and they achieve a complete cycle of drilling operation
by working in association. The following are brief introductions to each system.
Fig. 2a. The rotary drilling process (Source: Applied Drilling Engineering)
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2.2 Hoisting System
In simple terms, the hoisting system manipulates the position of the
drilling equipment, including the drill strings and casing strings. The hoisting
system not only lowers and raises the drilling equipment but also contributes to
replacing equipment or adding extended parts. The basic structure of the
hoisting system consists of a derrick (or mast), travelling block, crown block,
drill line, and hook and draw work, which are shown in Fig 2b. (Bourgoyne Jr. et
al. 2003). The derrick is the main frame of the hoisting system and provides the
working space for the hoisting operation. The travelling block, crown block, drill
line, and hook and draw work contribute to a motion system to control the
position of the drilling equipment.
Fig. 2b. Schematic of block and tackle (Source: Applied Drilling Engineering)
2.3 Circulating System
The main function of the circulating system is to keep the hole clean
during the drilling process. The circulating system cleans the hole by moving the
rock cuttings to the surface. To improve its ability to carry cuttings, drilling mud,
which is a kind of suspension clay normally mixed with water, is commonly used
in this process as a circulating fluid (Bourgoyne Jr. et al. 2003). The circulating
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system consists of mud pumps, mud pits, mud mixing equipment and
contaminant-removal equipment (see Fig 2c). In addition, the cuttings can be
flushed to the surface to provide samples for the logging geologist to analyse.
Fig. 2c, Schematic of example rig circulating system for liquid drilling fluid
(Source: Applied Drilling Engineering)
2.4 Rotating System
The rotating system is a power source that drives the drilling bit rotation.
The rotating system is mainly composed of swivel, kelly, rotary drive, rotary
table, drill pipe and drill collars (see Fig 2d) (Bourgoyne Jr. et al. 2003). The
kelly, also called the lower rotating system, is the main equipment that provides
rotating force to the drill string. In addition, there is another type of rotating
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system, namely the top rotating system (power swivel), that is attached to the
travelling block.
Fig. 2d. Schematic of rotary system (Source: Applied Drilling Engineering)
2.5 System Association
The three aforementioned systems are the basic shape of a rotary drilling
rig. First, the hoisting system puts the drill string into position. Then the rotating
system and the circulating system are activated together to execute the drilling
process and keep the path clean simultaneously (EM201 Course Note b).
However, the drilling process in exploring a hydrocarbon reservoir can be
complicated. These three systems have to cooperate and compensate for each
other for the duration of well development.
2.6 Selecting a Land Rig
The composition of a land rig depends on local circumstance. However,
several conditions could provide the primary considerations, such as the whole
budget of the exploration, the purpose of the well, the location of the well, the
formation environment of the well, the reservoir type and the depth of the well
(Aadnøy 1999). In the case of the Holly Field well, the criteria for selecting the
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rig should include following points. The Holly Field well is a land reservoir with
two kinds of reservoirs, gas and oil. Therefore, it is inevitable that the rig will
encounter gas formations during the drilling process, which means monitoring
the formation environment is crucial. In addition, the main purpose of the Holly
Field well is to produce an oil reservoir with a total depth of 12,000 ft.
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3. Well Planning
3.1 Well Planning
In planning the well, two essential factors should be taken into account:
pore pressure and fracture pressure. During the drilling process, the wellbore
pressure should be kept equal to or higher than the naturally occurring pressure
of the formation's fluids and the maximum wellbore pressure that the formation
can tolerate without breaking (Aadnøy 1999). Before the drilling operation
starts, the big picture of pore and fracture pressures should be predicted by the
evidence from previous wells, theory and field measurements.
3.2 Pore Pressure
Pore pressure, called formation pressure, is the pressure that exists in the
pore space and is revealed by the fluids contained in the pore space (King
1988). During the drilling process, the production of oil frequently changes the
reservoir pressure and influences the permeability inside the rock. If the pore
pressure is higher than the wellbore pressure, the formation fluid might enter
the drilling pipe and pollute the production oil, possibly inducing a blowout.
Therefore, monitoring pore pressure is one of the essential routines. Two
methods used to predict pore pressure before drilling are seismic data and data
from nearby wells. A geophysicist can analyse the seismic data to reveal the
formation profiles. However, the most accurate data might be directly measured
from the field. While the drilling is in progress, continuous logging procedures
are executed to ensure that pore pressure is under control.
3.3 Fracture Pressure
Fracture pressure, also called working pressure, is related to the pressure
of the drilling fluid or of the cement slurry (King 1988). During the pumping of
the drilling fluid into the well, the hydrostatic pressure of the drilling fluid may
have a detrimental effect on the formation. A formation breakdown gives rise to
an unstable environment, which may cause the drilling fluid to lose circulation.
In other words, wellbore pressure higher than the fracture pressure means that
the drilling fluid may run into the formation faults or other more penetrable
formations. As a result, the drilling fluid loses the ability to maintain constant
wellbore pressure, and the well may collapse. There are several methods of
predicting fracture pressure, but the Hubbert and Willis equation, which provides
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- Chia Lin Lin (Author), 2014, A Development Programme for the Holly Field Well, Munich, GRIN Verlag, https://www.grin.com/document/300527
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