Field Development Programme for Holly Field


Term Paper, 2014
29 Pages, Grade: A

Excerpt

Table of Contents

List of Figures

List of Tables

Eecutive summary

1.1 Rotary drilling
1.1.1 Hoisting system
1.1.2 Circulating system
1.1.3 Rotating system
1.2 Process of rotary drilling
1.3 Criterion for land rig selection

2.1 Well planning
2.1.1 Well kick
2.1.2 Lost circulation
2.1.3 Selecting of casing setting depths

3.1 Pore pressure gradient

4.1 Cement additives and cementing
4.1.1 Lightweight additives
4.1.2 Retarders
4.1.3 Accelerators
4.1.4 Heavyweight additives
4.2 Cementing calculations

5.1 Selection of casing setting depths
5.1.1 Bottom-top design
5.1.2 Top-bottom design

6.1 Bottom Hole Assembly (BHA)
6.1.1 Drill bit
6.1.2 Mud motor
6.1.3 Measurement while drilling (MWD)
6.1.4 Logging while drilling (LWD)
6.1.5 Non-magnetic drill collar (NMDC)
6.1.6 Drilling jars
6.1.7 Drill collars
6.1.8 Stabilizers
6.1.9 Subs
6.2 Drill collars calculation

7.0 Well completion
7.1 Objective of bottom top design

8.0 Well schematic

CONCLUSION

REFERENCES

BIBLIOGRAPHY

APPENDIX

3.1.1 Determination of pore pressure at different depths.

4.2 Cementing calculations

6.2 Drill collar calculation

List of Figures

Figure 1: A rotary rig hoisting system (Mohammed, 1992)

Figure 2: A mud circulating system (Boyun and Gefei, 2011).

Figure 3: Schematic of rotary system (Bourgoyne et al, 1984)

Figure 4: A rotary drilling process (Bourgoyne et al, 1984).

Figure 5: Basic element to drill a well (Azar and Robello, 2007).

Figure 6: Pore pressure equivalent mud weight (EMW), and mud weight versus well depth.

Figure 7: Casing setting depth-bottom-top design. (Robert, 2006)

Figure 8: Casing setting depth-top-bottom design. (Robert, 2006)

Figure 9: Schematic diagram of the well showing the casing and cementing details.

List of Tables

Table 1: Pressure gradient expressed as an equivalent mud weight, (EMW) and Depth (ft)

Table 2: Determination of pore pressure at different depths.

Table 3: The capacity of annulus and the volume of cement

Eecutive summary

This report presents the Holly field exploratory well development programme including well planning and designing which requires engineering support for optimum drilling operations. The exploratory well to be drilled lies 12,000ft (true vertical depth) relative to the ground.

The report is based on the discussion of the field development plan options considered which includes the functions of the three rotary systems (hoisting, circulating and rotating) which are required in the rotary drilling. Also, it explains the main criterion for selecting a land rig and how the accurate values of pore and fracture pressures are important for successful safe drilling of the well. The function of the additives used in Portland cement for casing cementing were stated; cementing calculation was done, determining the volume of the cement slurry and mud required to displace the cement, then differential pressure at the float collar. The methods of selecting casing setting depths were discussed. In drilling the final hole section of the well, the detail functions of various selected BHA component were stated and the calculation of the number of the drill collar required in the BHA to provide a 21,000lb weight on bit at an angle 10 degree was done. The options for completing the well and the reasons for bottom to the top design were also discussed.

1.1 Rotary drilling

Rotary drilling is any form of drilling which involves a rotary action combined with downward force to grind away the cuttings in which a hole is being formed (Azar and Robello, 2007). The three systems on a rotary drilling are the:

Hoisting system

Circulating system

Rotating system

1.1.1 Hoisting system

The hoisting system on a rotary rig consist of tools used to support a means to lower and raise the principal items of equipment such as drill strings, casing strings and other necessary subsurface equipment in and out of the well. The drilling operation involves withdrawing the drill string from the well, to change a dull drill bit and to add additional drill pipe to the drill string as the hole deepens. The major components are the draw-works, block and tackle, derrick and substructure.

Figure 1: A rotary rig hoisting system (Mohammed, 1992)

illustration not visible in this excerpt

1.1.2 Circulating system

The primary function of the fluid-circulating system in rotary drilling is to allow the movement of the mud through the well to remove the rock cuttings from the bottom hole to the surface during drilling process (Azar and Robello, 2007). It also cools and lubricates the drill bit; and in an uncased hole, it serves to support the walls of the hole. The principal components of the circulating system include mud pumps, mud pits, mud mixing and treatment equipment.

Figure 2: A mud circulating system (Boyun and Gefei, 2011).

illustration not visible in this excerpt

1.1.3 Rotating system

The rotating system on a rotary drilling rig consists of the components used to achieve bit rotation. The major function involves transmitting rotating action to the drill string and consequently the bit. The main parts include drill pipe, swivel, drill collar, Kelly, rotary table and drive. (Azar and Robello, 2007).

Figure 3: Schematic of rotary system (Bourgoyne et al, 1984)

illustration not visible in this excerpt

1.2 Process of rotary drilling

In drilling a well for the purpose of producing oil or natural gas, there are several elements involved to successfully and economically drill a well. They include:

Downward force on a drill bit

The drill bit rotation

Fluid circulation

Drilling through a rock require a force (weight of the bit) to be applied downward to the bit by the drill collars, in the drill string. The bit is rotated by drill string using the rotary table or top drive motor at the surface and the drill collar in the drilling string also applies the downward force on the bit.

During drilling process, rock cuttings and heat are being continuously generated. To remove the cuttings from the hole a drilling mud has to be continuously circulated from the surface down the drill string through the bit to the bottom, the fluid cleans the bit from the cuttings and carries the cuttings through the annular space between the drilling string and the walls of the hole to the surface again to dissipate the heat and remove cuttings and is circulated back into the drilling string. (Abdel, et al, 2003)

Figure 4: A rotary drilling process (Bourgoyne et al, 1984).

illustration not visible in this excerpt

Figure 5: Basic element to drill a well (Azar and Robello, 2007).

illustration not visible in this excerpt

1.3 Criterion for land rig selection

A rig is large complex machine design to drill a wellbore which comprises of most facilities for drilling purposes. Any choice of a rig is usually a compromise so in selecting a land rig for a particular well it is important to consider a well trajectory from the surface to total depth (TD) prior to drilling, providing expectations for the total depth of the drilling, lithology and pressure. The total depth of the well depends on the rig selection which should be capable of drilling the designed well with sufficient redundancy to handle all possible constraints.

2.1 Well planning

The purpose of good well planning (such as choice of mud weight profile and casing programs) and actual drilling operations is to avoid or minimise the dangers of lost circulation, well kicks, stuck pipe, blowout and excessive costs, if pressure is properly evaluated. The drilling mud density which is used to control the hydrocarbon pressure is determined by the pore and fracture pressure. Thus basic knowledge of the two key pressure parameters is important.

Pore pressure is the pressure exerted by the fluids (such as hydrocarbons) in the pore space of rock. Fracture pressure is the pressure at which the subsurface formation is not strong enough to withstand the pressure of the drilling mud in the well and is fractured.

In well planning pore and fracture pressure can help in the following:

2.1.1 Well kick

Kick occurs when the fluid from the formation flows into the wellbore during drilling operations. This can be prevented if the hydrostatic pressure of the drilling mud density is approximately equal or slightly higher than the pore pressure to prevent formation fluids from entering the wellbore (trip margin). If the mud weight is too low and the drillers do not balance the pressure, hydrocarbons can flows into the well bore causing kick; a blow-out could result if proper well control procedures are not followed. (Byrom, 2014).

2.1.2 Lost circulation

Lost circulation occurs when the drilling mud flows into the surrounding formation instead of returning to the surface. This is avoided if mud density is lower than the fracture pressure so that the drilling fluid does not fracture and enter the formation (kick margin). But if the mud weight is too high it can fracture the surrounding rock; when this happens the drilling mud flow out of the well bore into the formation instead of circulating back to the surface. This potentially causes lost return and circulation. This inflow can cause unprotected section of the well to collapse.

2.1.3 Selecting of casing setting depths

The changes in pore and fracture pressure gradient varies with depth. As the well is drilled, the pore pressure increases in the bottom of the open hole because the pressure difference between the mud and pore pressure gradient is decreasing which causes an exceeding fracture pressure of the formation higher up in this open hole. When this occurs, the drillers can no longer depend on the mud to control pore pressure in the wellbore because if they increase the mud density, it will fracture the relatively weak, exposed formation higher up and if they keep drilling without increasing the mud weight, hydrocarbons or other fluids in the deeper formation will flow into the well. Since the wellbore pressure must be maintained, then casing is set to help prevent the weak formation of the hole outside the casing from the pressure of the drilling mud inside and also protects high pressure fluids outside the casing from entering the well. Addition of casing string is necessary during drilling as the pore pressure in the formation approaches the fracture pressure at the last casing seat. This is done to prevent the mud weight from fracturing the formation at the last casing string depth. The accurate determination of pressure required to fracture a formation is important for selecting casing depth.

The complete well planning process with some exceptions, is based on prediction of pore and fracture pressure. The pressure is the key factor for many sectors of the well plan. If adequate concern is not shown to formation pressure, the other technical segment of the well plan may be affected.

3.1 Pore pressure gradient

The pore pressure gradient, expressed as an equivalent mud weight, is a curve that shows how the pore pressure in the well changes by depth.

Table 1: Pressure gradient expressed as an equivalent mud weight, (EMW) and Depth (ft)

illustration not visible in this excerpt

Figure 6: Pore pressure equivalent mud weight (EMW), and mud weight versus well depth.

illustration not visible in this excerpt

Table 2: Determination of pore pressure at different depths.

illustration not visible in this excerpt

4.1 Cement additives and cementing

Cement additives have been produced to enable the use of Portland cement in many oil and gas well application. These additive modifies the cement grade to suit the well being drilled. The function and example of each of the additive includes:

4.1.1 Lightweight additives

They are known as extenders or water absorbing. It reduces cement slurry density. It reduces the hydrostatic pressure during cementing, which avoids the breakdown of weak rock formations preventing induced lost circulation caused by such breakdown. It reduces the mobility of water as more water is added to lower the weight of the slurry. It increases the viscosity of the slurry, increase the permeability and reduce the final strength of the cement. One of the example of the additive is Bentonite. (Nelson, 1990).

[...]

Excerpt out of 29 pages

Details

Title
Field Development Programme for Holly Field
College
Robert Gordon University Aberdeen
Course
Wells
Grade
A
Author
Year
2014
Pages
29
Catalog Number
V300250
ISBN (eBook)
9783656978558
ISBN (Book)
9783656978565
File size
1032 KB
Language
English
Tags
field, development, programme, holly
Quote paper
Okoye Uchechukwu (Author), 2014, Field Development Programme for Holly Field, Munich, GRIN Verlag, https://www.grin.com/document/300250

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