overview of drilling operations may 2011 sem

Overview of Drilling Operations

PAB 2024

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LESSON OBJECTIVES

At the end of this lesson you should be able to:

1. Describe the process of rotary drilling;

2. Determine Rig Selection;

3. Describe the data Acquisition and Monitoring System

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INTRODUCTION• Drilling for oil and natural gas requires two major

constituents: manpower and hardware systems.

• The manpower encompasses a drilling-engineering group and Rig operation group.

• The first group provides engineering support for optimum drilling operations, including : rig selection and design of the mud program, casing and cementing programs, the hydraulic program, the drill bit program, the drill string program, and the well control program.

• After drilling begins, the daily operations are handled by the second group, which consists of a tool pusher and several drilling crews (derrick and motor personnel, drillers, etc.).

The hardware systems that make up a rotary drilling rig are

• A power generation system

• A hoisting system

• A drilling fluid circulating system

• A rotary system

• Well blowout control systems

• A drilling data acquisition and monitoring system

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The Process of Rotary Drilling

• several elements are needed to drill the hole successfully and economically (illustrated in fig. 1-2), including:

1. A force acting downward on a drill bit;

2. Rotation of the drill bit;

3. Circulation of fluid, called drilling fluid (liquid. gas, or gasified liquid), from the surface through the tubular called the drill string, and back to the surface through the annular space, the area between the hole wall and the outside wall of the drill string.

Fig-1: vertical and Directional drilling

Fig-2: Basic Element to Drill a Well

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The Process of Rotary DrillingA. FORCE

To drill through a rock, a force (weight on bit / WOB) of a certain magnitude has to be applied downward on a drill bit.

This force is provided by slacking off tension on the drilling line that supports the total weight of the drill string.

The amount of force varies, depending on the hardness of rock and the type of drill bit in use, and is provided by the portion of thetubular (drill string) above the bit.

Fig-3: Packed Hole Assembly

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The Process of Rotary Drilling• Drill bit rotation

In rotary drilling, the drill bit has to be rotated at a certain speed

to cut and advance through the rock. Rotation of the drill bit

may be accomplished from the surface or down hole.

Surface rotation is done through the use of a conventional rotary

table or top drive motor.

Bottom-Hole rotation is achieved by using down-hole motors

(positive-displacement mud motors or mud turbines or electric

motors) that directly rotate the drill bit without drill string

rotation.

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• Drilling Fluid Circulation

a fluid has to be continuously circulated from

the surface to the bottom and back to the

surface again to dissipate the heat and remove

cutting

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The Process of Rotary Drilling

Rotary Drilling Rigs

• The power of rotary rigs is generally generated by diesel or gas-driven engines.

• The power is transmitted to the various rig systems (hoisting, rotary, circulating, etc.) by means of mechanical or electrical drives.

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The electric drive system was introduced to rotary rigs in the mid of 50’s for use in offshore operations.

The electric drive system, requires that one or more DC generators be specifically assigned to a DC motor to meet the desired load requirement for a specific unit (pumps, rotary motor, draw-works, etc.) at a controllable desired speed.

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• The overall efficiency of power-generating systems defined as follows:

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1-1a

or

1-1b

The output power of an engine is generally expressed as a function of the engine rotary speed, N and the output torque, T:

1-2


• The input power is expressed in terms of the rate of fuel consumption, Qf, and the fuel heating value:

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1-3


• Example 1A drilling rig has three diesel engines for generating the rig power requirement.

Determine the total daily fuel consumption for an average engine running speed

of 900 rpm, average output torque of 1,610 ft-lbs, and engine efficiency of 40%.

The heating value of diesel oil is 19,000 BTU/lb.

Solution:From equations ( 1.1)-(1.3), the fuel consumption per engine can be solved

for and is given by :

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• Hence:

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For three engines, total Qf = 308 x 3 = 924 gal/day

Rig Selection

• The main objective of rig selection is to choose from the available rigs the one that will closely meet the criterion for drilling a usable hole at the lowest overall cost of the proposed well.

• The selection process is the evaluation of all of the following rig systems:

1. Power generation system2. Hoisting system3. Fluid circulation system4. Rotary system5. Well control system6. Drilling data acquisition and monitoring system

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Rotary Drilling System

• Hoisting SystemFunction: to hoist the drill and casing strings

during drilling and casing operations,

respectively.

Major components are the draw-work, the

crown block, the travelling block, the hook,

the drilling (wire) line, and the elevator.

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HOISTING SYSTEM

• Consist of :1. Draw Work

2. Crown Block

3. Dead Line anchor

4. Travelling Block

5. Hook

6. Drilling line

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• Hoisting Design ConsiderationThe procedure to carrying out hoisting design calculation are as

follow:

1. Determine the deepest hole to be drilled;

2. Determine the worst drilling loads or casing load;

3. To select drilling line and derrick capacity.

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HOISTING SYSTEM

• Example 2The following well data refer to a 1.5 inch block line with 10 lines strung of extra improved plough Steel wire rope strung to travelling block.

Table-1Hole depth = 10,000 ftDrillpipe = 5 inch OD; 4.27 inch ID, 19.5 lb/ftDrill collars = 500 ft, 8 inch / 2.825 inch, 150 lb/ftMud weight = 10 ppgLine and sheave efficiency Coefficient = 0.9616Buoyancy factor = 0.847

Determine:1. Weight of drill string in air and mud;2. Hook load, assuming weight of travelling block and hook to be 23,500 lb;3. Dead line and fast line loads, assuming an efficiency factors of 0.814. Dynamic crown load;5. Wire line design factor during drilling if breaking strengths of wire is 228,000 lb;6. Wire line design factor when running casing 7 inch of 29lb/ft.

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HOISTING SYSTEM

• Solution1. Weight drill string in air (unit in lb) :

Weight of DP and DC (unit in lb)

Weight of drill string in mud (unit in lb):

Buoyancy factor x weight drill string in air.

2. Hook Load (unit in lb):

Weight of string in the mud + weight of travelling block and hook

3. Dead line load (unit in lb) :

Where : N: number of line strung, K = Line efficiency per sheave (see Table-1)

HL : Hook Load, lb

Fast line Load (unit in lb) :

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HOISTING SYSTEM

4. Dynamind Crown Load (unit in lb) :

Dead line load + fast line load + Hook Load

5. Wire line design factor (no unit):

Breaking strength / fast line load

6. Design factor when ruuning 7 inch casing 29 lb/ft (no unit):

- calculate casing weight in mud (depth of hole x lb/ft x Buoyancy factor);

- determine hook load (weight of casing in mud + weight of block and Hook;

- calculate fast line load;

- determine wire line design factor.

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HOISTING SYSTEM


• Drawworks

1. The drowworks is an assemblage of components that provides the hoisting

and breaking power to enable the down- and up-hole movements of heavy loads of the drill

string and casings or other equipment. Its components include the drum, the brakes. the

transmission, and the cathead.

2. Drawworks rated by input horsepower. And calculated as follows:

3. To determine the drawworks horsepower required for drilling a well, the hook horsepower is first calculated using the weight of the heaviest drill string in air, along with a reasonable hoisting speed. A minimum of 100 ft/min is recommended for rating a rig.

An overall hoisting efficiency of 65% is recommended to calculate the required drawworkshorsepower rating .

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• Example 3:What minimum drawworks horsepower is required in order to drill a well

when using 10,000 ft of 16.6 lb/ft drill pipe with an outside diameter (OD) of

4 ½ inches (in.) and 50,000 lbs of drill collars? (the rotary table speed of

100 ft/min) and overall hoisting efficiency of 65%.

Solution:

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Block and drilling line. • The principle function is to provide a mechanical advantage while raising and

lowering the extremely heavy loads into the wellbore. Their efficiency is measured by equation (1-1a).

• The output power is define as follows: The input power is define :

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1-4 1-5


The magnitude of Ftp depends on the number of lines strung between the crown

Block and the traveling block and the frictional forces induced between the contact

surfaces of the lines and block sheaves. Utilizing equations (1.4) and (1.5), equation

(1.1a) becomes :

It can be easily established that,

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1-6

1-7


• Therefore ,

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1-8

where n is the number of lines strung between the crown block and the traveling block.

Example 1-4 .

A rotary rig that can handle triples is equipped with 1.200 hp draw-works and 90 ft line strung (Ls). The output of the drawwork is 927 hp and the efficiency of the hoisting system is 81%. Determine the time it takes to pull one stand at a hook load of 300,000Ibs.


• Solution:

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This method neglects the effect of buoyancy and the weight of

the block and hook. In straight holes, buoyancy can be assumed

to be offset by pipe drag. In directional holes, drag has to be

Considered.

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Mud System Evaluation

• The function of the Fluid circulating system in rotary drilling is to allow the movement of a drilling fluid from the surface to the hole bottom and back to surface again. The main components of the system include

• Mud pumps/air compressors• High-pressure surface connections• Drill string• Drill bit• Return annulus• Mud pits• Mud treatment equipment

The configuration of tanks, shakers, stirring devices, and solids control equipment is unique to each rig.

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• Mud pumpsRotary rig pumps are reciprocatingpositive-displacement units and areeither duplex or triplex pumps.Duplex pumps have two liners andmove fluid on the forward andbackward stokes (double acting).Triplex pumps have three liners andmove fluids only on the forward stoke(single acting).


Example 5 (Horse Power req. of mud Pump)Calculate the power requirement for the following pump:

Flow rate = 1200 gpm; pump pressure = 2000 psi and

mechanical efficiency = 0.85

Solution:- Determine hydraulic HP = (Flow rate (gpm) x Pressure) / 1713.6

- Power equired from motor = hydraulic HP / mechanical eff.

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Well Control System

• Primary Function??

The system requirements are to safely permit:

1) shutting in the well at the surface,

(2) controlling the removal of formation fluids from

the wellbore.

(3) pumping higher-density mud into the hole, and

(4) stripping the drill pipe in to or out of the hole.

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Well Control System• The basic components of the well control system are:• Annular preventer1. Ram preventers2. Spools3. Internal preventers4. Casing head5. Flow and choke lines and fittings6. Kill lines and connections7. Mud- and gas-handling facilities8. Accumulators

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BOP are rated by API as 3 M (3000 psi), 5 M, 10 M and 15 M. For HPHT well BOP’s are either 15 M or 20 M

Well Control System

• Ram preventerPipe ram preventers are mechanical

devices that close in the annular space

around the drill pipe or casing when they

are hydraulically activated.

There are three types of ram preventers:

• pipe ram or casing ram

• Blind ram

• Shear ram

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Well Control System

• Rams that are designed to close in the annulus when no pipe is present are called blind rams.

• Rams that are designed to shear off drill pipe while string is in hole are referred to as shear rams.

• These kind of rams are activated only if all other preventers fail to shut the well.

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Well Control System

• Annular preventer : well control devices that employ a ring of reinforced synthetic rubber as a packing unit that surround the drill string to cause the shut- off.

• These preventers will close and shut in the well regardless of the shape or diameter of the conduit that might be in the hole.

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Well Control System

• Drilling spools

• are drill-through-type fittings that are placed in the BOP stack assembly to provide space between two consecutive pipe rams for temporary storage of tool joints during stripping operations and to allow attachment of the kill and choke lines.

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Data Acquisition and Monitoring System

The data acquisition and monitoring system of a rotary drilling

rig consists of all the devices used to monitor analyze, display,

Record and retrieve information regarding drilling operations.

The parameters that are of prime concern are the following:

1. Drilling rate 6. Torque 11. Pump stroke

2. Hook Load 7. Rotary speed 12. WOB

3. Hole depth 8. Mud density, temperature, salinity

4. Pump Pressure 9. flow properties 13. Hoisting speed

5. Flow rate 10. Mud tank level

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• Drilling problems ?

• can be easily detected by the monitoring equipment.

• Drilling breaks, which are easily seen on the drilling rate chart can provide information on changes of lithology and formation pressures.

• Excessive torques may indicate a bit bearing failure or an extremely high concentration of drilled cuttings in the wellbore annulus.

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• A drastic increase in hook load or decrease in mud returning to the surface could indicate that a lost circulation zone has been encountered.

• A sudden increase in pit level indicates that formation fluids are entering the wellbore and. Hence, that blowout is eminent.

• The proper maintenance of rotary speed, weight on bit, mud properties, and now rates is of upmost importance for achieving optimum drilling conditions.

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Special Systems for Offshore Drilling

• Drilling at sea requires two special systems:

1. a motion compensating system for floating units and;

2. a marine riser system.

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• Riser system and components

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The marine riser is an extension of the wellbore from the ocean floor to the derrick floor above the water surface. Its purpose is to guide and protect the drill string and to serve as a conduit for the return of drilling fluid and cutting to the surface

It is a structure that is made of 40-50-ft-long joints. which are connected by means of rigid, pressure-tight couplings, called riser connectors.


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Large fixed-end moments are avoided by using ball joints at the riser ends. Ball joints are normally designed for rotations of up to 8-100 in any direction However, the drill string has to pass freely through the joints, which limits the drilling operation to bail joint angles of at maximum. 4-5°.

Marine Riser

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SUPPLEMENTARY PROBLEM• PROBLEM-1:

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The following well data refer to a 1.5 inch block line with 10 lines strung of extra improved plough Steel wire rope strung to travelling block.

Table-1Hole depth = 12,000 ftDrillpipe = 5 inch OD; 4.27 inch ID, 19.5 lb/ftDrill collars = 500 ft, 8 inch / 2.825 inch, 150 lb/ftMud weight = 14 ppgLine and sheave efficiency Coefficient = 0.9616Buoyancy factor = 0.847

Determine:1. Weight of drill string in air and mud;2. Hook load, assuming weight of travelling block and hook to be 23,500 lb;3. Dead line and fast line loads, assuming an efficiency factors of 0.814. Dynamic crown load;5. Wire line design factor during drilling if breaking strengths of wire is 228,000 lb;6. Wire line design factor when running casing 12,000 ft 7 inch of 29 lb/ft.

SUPPLEMENTARY PROBLEM

• PROBLEM-2: A drilling rig has three diesel engines for generating the rig

power requirement. Determine the total daily fuel consumption

for an average engine running speed of 800 rpm, average output

torque of 1,610 ft-lbs, and engine efficiency of 45%.

The heating value of diesel oil is 18,000 BTU/lb.

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• PROBLEM-3.

Compute the tension in the fast line when lifting

a 500,000 lb load for 6, 8, 10 and 12 line strung

between the crown block and travelling block.

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• PROBLEM-4.Discuss the function of this marine drilling equipment:1. Marine riser2. Ball Joint3. Pneumatic tensioning device,4. Bumper sub5. Slip joint6. Taut-line Inclinometer.

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• PROBLEM-5 : Describe how the rig can be monitor :1. Hole depth2. Penetration rate3. Rotary speed4. Rotary torque5. Pump rate6. Pump pressure7. Mud density8. Mud temperature9. Mud salinity10. Gas contents of mud11. Pit level12. Mud flow rate.

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overview of drilling operations may 2011 sem

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