drilling & well completion-an introduction

8/3/2019 Drilling & Well Completion-An Introduction

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Drilling & Well Completion-An

Introduction


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Geological studies and seismic surveys can

point the way to a hydrocarbon prospect. But

there is only one way to know if that prospect

contains oil or gas, and that is to drill a well.


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Joint Venture

Drilling projects are team undertakings. They encompass a widerange of disciplines and job functions, from geology, geophysics andengineering to operations, support and logistics, safety andregulatory compliance, management and administration. Projectteams are often part of alliances that include:

The oil or gas company (also known as the operating company oroperator), along with any joint venture partners having an interestin the well;

An outside drilling contractor who provides the drilling rig and thepersonnel to run it; and

One or more service companies that provide specialized equipmentand expertise at various stages of the project. The largest of theseservice companies may offer integrated project managementservices that include contract drilling.


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Well Location

The working relationships that characterize a drillingproject depend on the well's location, thearrangements between the companies involved in theproject and the number of personnel involved.

A small onshore rig may be crewed by no more thanfive contractor employees and managed by just one ortwo contractor and operator representatives, whilesome large offshore drilling operations may have

several rig crews and groups of specialists totaling 50or more persons, along with dozens of land-basedtechnical and support personnel.


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Drilling Objectives

All drilling operations have three basic objectives:

Drill safely. Health, safety and environmental (HSE) considerations supersede allother goals, even if they require changing plans, delaying operations or incurring

extra costs.

Provide a fit-for-use well. Whether it is drilled for exploration, prospect appraisal

or field development, a well must meet the needs that led to it being proposed in

the first place. As a minimum standard, it should be drilled without damaging the

borehole or any potential producing formations, and it should satisfy the design

requirements for formation testing, data gathering, oil and gas production or other

post-drilling activities.

Minimize overall well cost. It is therefore in everyone's interest to control well

costs. In this context, it is important to consider the total cost over the life of the

well, and to balance this cost against the first two objectives of safety and wellusability. An offshore well in West Coast of Africa may cost up to 30 times higher

than an average onshore well in the US. Since drilling is the most expensive

component of the entire exploration and field development process, the oil&gas

industry pays a lot of attention to improve drilling efficiency and cut drilling time in

order to control well costs.


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While drilling rigs often work in remote locations, they may also

be found in settled or even urban areas, as shown in Figure 2.


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Drilling Rigs

Most drilling rigs operate 24 hours per day, 7 days per week. Rig crews work 8 or 12-hour

shifts or tours (pronounced towers), in rotations that last anywhere from one to four weeks

or more, depending on the location.

The subsurface conditions that drilling crews encounter are as varied as their hours and work

locations. The total depth (TD) of a well may be anywhere from a few hundred to more than

20,000 feet. It may be possible to reach TD by drilling straight down, or it may be necessary--

and sometimes beneficialto drill part of the well at an angle or even horizontally. Along theway, there might be any number of rock types, including loose gravel, soft, sticky clay or

shale, abrasive sandstone, hard carbonates and even salt. Each rock type presents its own set

of challenges. Subsurface pressures may range from a few hundred at the surface to 5000,

10,000 or even 20,000 pounds per square inch ("psi") at deeper depths. In some wells it is

not always easy to predict the expected pressure level. Temperatures may likewise range

from near-surface conditions to 400 F [200 C] or more. And there is often a good chanceof encountering toxic or corrosive gases.

Before drilling even begins, a project team has to plan what will happen after TD is reached

whether it will be completed as a producing well or abandoned and how the well will fit into

overall reservoir management objectives. These and other considerations will affect project

planning, well design and drilling operations.


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Rig Counts When business analysts want to get a feel for the oil and gas industry, they often

look at rig counts such as the ones published weekly and monthly by Baker Hughes

(http://www.bakerhughes.com/investor/rig/). These provide current and historicaldata on the number of drilling rigs working in various parts of the world. This

information is valuable because the drilling sector, being at the leading edge of oil

and gas development activity, is particularly sensitive to such factors as oil price

fluctuations and economic conditions of the industry (Figure 3).
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Drilling Technology

Virtually all oil and gas wells today are drilled using the rotary method, in

which rock is broken into small particles or cuttings under the weightapplied to a rotating drill bit (Figure 5).

The bit is made up on (i.e., screwed into) the end of a drill string, which consists of

individual lengths orjoints of hollow steel pipe about 30 feet long (Figure 5). The drilling

rig, acting as a type of hoist, lowers the pipe into the well. Each time the bit drills the

equivalent of one pipe length, drilling is stopped while another joint of pipe is added to

the stringa procedure is known as making a connection. In this way, the well iseventually drilled to TD.


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As the bit drills ahead, a specially formulated drilling fluid or mudis

continually pumped or circulatedfrom the surface, to the bottom of the well,

and then back to surface to cool the bit and remove the cuttings (Figure 6).


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Phases of Well Construction

Well drilling and completion involves a number ofdistinct project functions. Companies may differ as towho is primarily responsible for each function, andwhere one function ends and another begins, but one

good breakdown would be as follows: Well Planning

Well Design

Drilling Operations

Formation Evaluation and Testing

Well Completion


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Resource

http://www.petroleumonline.com/content/ov

erview.asp?mod=4

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