Lecture 2 con't

2.1.3 Sedimentary rock types

In order to differentiate between the various rock types, several classifications are

structured either on the basis of the grain size or on the fundamental mineralogy. The

sedimentary processes which have formed the rock can as well be invoked into the

classification.

When it comes to classifying rocks seen at the well site, we stick to a descriptive

classification and leave environmental factors alone. This simplifies matters a great deal.

We will now go on to look at the main rock types encountered in the drilling of oil wells

and how these rocks can induce the drilling process.

2.1.4 Terrigenous sediments (clastic)

These are land derived sediments and are represented by the clay minerals that coarser

material formed from the fragmentation of silicate rocks. They have been sub-divided

further on the basis of their grain size.

·  Group A - Clays (particles with a diameter less than 0.004 mm)

·  Group B - Silts (particle diameter 0.004 to 0.06 mm)

·  Group C - Sands (particle diameter 0.06 mm to 2 mm)

·  Group D - Rudites (coarser rock fragments).

2.1.4.1 Clays

Clay minerals are hydrous platy aluminosilicates. They form a complex and extensive

series due not only to variations in ordering of the sheet-like crystal lattices, but also to

the presence of different cations between the lattices.

Clay minerals can be subdivided into five important groups with different chemical and

physical characteristics; kaolinite, illites, smectites, chlorites and glauconites.

The term “shale", generally used to name those argillaceous sediments, mostly describes

the tendency of those materials to split, especially when they have been exposed to high

compactions and pressures. Soft clays which are encountered in the topmost sections of

wells usually drill fine unless their affinity to water causes them to form so-called gumbo

formations.

Gumbo is a term used to describe claystone formations which absorb water, hence,

hydrating shales tend to expand. Sticking mechanisms are associated with such

formations:

·  Contraction of the wellbore behind the BHA makes it difficult to trip out.

·  Large clumps of gumbo will fall into the wellbore and will eventually stick to the

BHA. Chemical inhibitors can be added to the drilling fluid in order to restrict or

avoid such phenomenon.

Kaolinite clays generally form by sub-aerial weathering of granites: rocks with a low

proportion of iron or magnesium rich minerals. The clay particles may be washed out as

colloids or formed in situ. When they come in contact with water rich in potassium ions

(for instance sea water) they slowly alter to illite.

Illites are the dominant clay mineral group. They are formed by the direct weathering of

feldspars or by alteration of kaolinite and montmorillonite under marine or later

post-depositional conditions.

Montmorillonites form by the alteration of minerals rich in iron and magnesium. For

instance, certain types of volcanic ash. They too gradually change to illite when

transported into sea water.

Clays may also be the subsidiary minerals of other sedimentary rocks. Their origin

(petrogenesis) may be primary in that they were deposited at the same time as other

major constituents. Alternatively, they may have formed as a later alteration product of

those less stable minerals in the original sediment, their origin in this case being

secondary or diagenetic.

2.1.4.2 Silts

Silts are clastic sediments, intermediate in size between clays and fine sands (particle

diameter 0.004 to 0.06 mm). They are derived from fragmented rocks or minerals and are

called clastic or detrital sediments. Silt size particles are generally the result of extreme

abrasion (mechanical wearing down), and therefore all the minerals found in that size

range may also be found as sand-grade particles. They consist of quartz, feldspar, heavy

minerals, iron ores and phosphates. While sand may be silt free, most clays and

claystones contain about 35% silt or more (thus named silty claystones or argilaceous

siltstones). Very abrasive siltstones can be encountered in the drilling processes and,

therefore, frequent bit changes become necessary.

2.1.4.3 Sands

Sands, like silts, are defined by their grain size (0.062mm) and not by their mineralogy.

Terrigenous or siliclastic sands are of prime, economic importance because they are

often of wide lateral extent and are frequently porous and permeable, thereby satisfying

three basic requirements for major aquifers and hydrocarbon reservoirs.

Quartz, feldspar, lithic fragments, micas and heavy minerals are the major mineralogical

groups found in detrital sands.

2.1.4.4 Rudites

These are sediments whose grain size exceed 2 mm in diameter. This coarse rock

fraction is not unique to terrigenous deposits, and rudite grade particles are common in

both the carbonate and pyroclastic groups.

The shape of the class is also important. Rounded rock fragments which have undergone

physical abrasion are called conglomerates. Angular ones, physically as well as

chemically immature, are termed breccias.

2.1.5 Pyroclastic sediments

These are derived by volcanic eruption into the air. They may be chemically weathered

or physically reworked to closely resemble terrigenous deposits. This is because they

may have similar mineralogies, and the range of grain sizes are comparable.

Volcanic ash or tuff can fall as clay, silt or sand grade particles whereas the still coarser

agglomerate is the direct equivalent of conglomerate.

While traces of volcanic ash are common in most deep sea sediments, pyroclastic

deposits are generally rare within sedimentary sequences.

2.1.6 Carbonates

This major group of sediments is fundamentally different to the terrigenous (or

siliclastic) and pyroclastic rocks just discussed. In these clastic groups, the mineralogy of

the deposits is largely controlled by the processes of weathering and erosion of the

bedrock in the area of the sediment source; namely outside the basin. In carbonate rocks,

however, it is the depositional environment within the basin which exerts the prime

control on the mineralogy and sediment type. In this respect carbonates have closer

affinities to the evaporite and carbonaceous rocks.

Biological activity around the area of deposition is of prime importance in generating the

basic particles of carbonate sediments.

In order to determine the depositional environment and the genesis of carbonate rocks, a

fairly precise description of the chemical and physical components is required.

2.1.6.1 The Chemical Components of Carbonates

The chemical components are:

·  Aragonite

·  Magnesian

·  Calcite

·  Dolomite

All these minerals, know as polymorphs of calcium carbonate (CaC03), present different

degrees of chemical stability depending on the environmental characteristics of the

depositional basin.

2.1.6.2 The physical components of carbonates

Four basic physical components are taken into account for the description of carbonates:

The grain types either mineral or biological.

The matrix which consists of the fine material.

The cement which grows in the pore spaces of the sediment after it deposition.

The pore space remaining after cement has taken place.

2.1.6.3 The Classification of Limestone Rocks

In an essentially monomineralogical calcium carbonate system, there is apparently as

wide a range of particle type as there is in the multi-mineral terrigenous group. The most

successful attempts to solve the nomenclature problem are those of Folk, in which the

basic components of the rock are described, and of Dunham where the basic fabric is

described.

Four more terms are frequently used to describe grain size in carbonate rocks.

·  Group A - Calcilutite up to 0.004 mm grain diameter

·  Group B - Calcisiltite 0.004 to 0.065 mm

·  Group C - Calcarenite 0.065 to 2 mm

·  Group D - Calcirudite above 2 mm grain diameter

Certain specific types of limestones like chalk, marl, bituminous limestones and dolomite

can be as well mentioned at this stage.

·  Chalk This is a soft white limestone composed of the tests (or skeletons) of once

floating micro-organisms.

·  Marl This is a calcareous clay - generally an intermediate mixture of terrigenous

clay and micrite.

·  Bituminous Limestones These are micrites which contain much organic or

carbonaceous matter, mostly in the form of tarry hydrocarbons which are usually

described as bitumen.

·  Dolomite This term is applied to limestones where the calcium carbonate has

been completely replaced by the mineral dolomite.

2.1.7 Evaporites

These sediments, which include mineral salts such as anhydrite. gypsum and rock salt

(halite), are believed to form by precipitation from brines (waters concentrated in salt by

evaporation processes).

They are important as mineral deposits sometimes occurring in thick, relatively pure

mono-mineralogic sequences. They play an important role in petroleum geology, being

excellent cap rocks for oil or gas reservoirs. They are also very plastic and thick salt

sequences deform and flow to produce salt domes. Salt movements frequently produce

hydrocarbon traps.

The more frequently encountered evaporate minerals are listed Table 2-2.

2.1.8 Carbonaceous rocks

Small traces of organic material are present in most sedimentary deposits with the

notable exception of desert red-beds where it has been entirely destroyed by oxidation.

However, in certain very reducing anaerobic (oxygen free) environments it may form an

appreciable proportion of the sediment.

2.1.8.1 Coal

Coals are formed by the action of fungi and anaerobic (oxygen hating) bacteria on

decaying vegetal or “humic" matter in a reducing environment. Compaction by deep

burial is an important agent in reducing the volatile content of the rock. The series

PEAT, LIGNITE, HUMIC COAL, ANTHRACITE expresses the increase in the carbon

content as oxygen and hydrogen are progressively driven off.

2.1.8.2 Oil Shale

This is more an economic rather than geological term, and refers to argillaceous

sediments with an organic content of at least 5%, but generally meaning considerably

higher (20 to 50%). They must be sufficiently rich in organic matter to yield free oil on

heating.

They generally form in lakes where algae matter decays in a strongly reducing (or

anaerobic) environment, thereby preserving the organic material. This is referred to as

"sapropelic" matter and is a good source for oil. Marine equivalents are also known.

2.1.8.3 Bituminous Limestone

This is again an economic rather than geological concept being the direct carbonate

equivalent of terrigenous oil shales. Such sediments may form in lagoons behind a reef.

Lecture 2

2 Fundamentals
About this chapter
A solid foundation in geology as well as algebra and trigonometry is essential to
understanding directional drilling techniques and procedures. Geology, a science based
on the history and structure of the earth, combined with a thorough knowledge of
mathematics, forms the core discipline necessary for proficiency in this complex
business. Although it is far beyond the scope of this manual to completely describe the
total essence of geology and mathematics, this chapter is designed to refresh any
knowledge that should already be a part of the directional drilling trainee.
Objectives of this Chapter
On completing this chapter the directional driller should be able to do the following
exercises:
Part A/Petroleum Geology
1. Describe the phases that occurred during the formation of the earth that resulted in the
various features of its surface and inner structures.
2. Be prepared to explain the several terrigenous sediments (clastic) that can found
under the Earth’s surface.
3. Be prepared to describe the four general classes of sedimentary materials and how
they are categorized by relative size.
4. Be prepared to define pyroclastic sediments and explain the various of sub-groups.
5. Describe the basic concepts of structural geology and how the various elements are
related to exploration and production of petroleum.
Part B/Algebra and Trigonometry
1. Observe and explain miscellaneous equations of algebraic and trigonometric
mathematics.
2. Be prepared to describe geometric descriptions of a circle.
3. Understand and solve equations applicable to various straight line problems.
4. Demonstrate an understanding of angles resulting from intersecting lines.
5. Demonstrate an understanding of circles and parts of circles resulting from
intersecting lines.
6. Demonstrate an understanding of the trigonometric quadrants identified by sine,
cosine and tangent; solve various equations using these quadrants.
2.1 Petroleum Geology
Rock is a natural substance composed of a mineral or group of minerals which lead to the
formation of rocks and to accumulations of hydrocarbons. A study of this phenomenon is
aimed to help directional drillers in understanding of geological environments. Geology
is so essential to the petroleum industry that a knowledge of the basic principles of this
science is desirable for anyone associated with oil or gas.

Geological information is acquired by observing rocks and their relationship to each
other as they were formed in the layers of the earth. Chronological events can then be
reconstructed in order to understand rock formations and, in the particular field of
petroleum geology, to be able to predict where oil accumulations might occur.
2.1.1 Basic concepts of geology
2.1.1.1 Early History of the Earth
The earth is thought to have originated some 4 to 5 billion years ago out of a condensing
cloud of cosmic dust. During its early life, the earth passed through a molten or partially
molten stage induced by gravitational compression or the release of energy by
radioactive elements. During this stage, the components of the earth separated to produce
a heavy core 4,400 miles in diameter, a mantle of lighter material some 1,800 miles thick
and a crust of the lightest materials some 10 to 30 miles thick (Figure 2-1). At the same
time, large amounts of water vapor and gases erupted to form the primeval atmosphere.

A second stage can be considered as the atmosphere developed and the earth cooled, rain
began to fall. Water coming down from the heights and flowing to the valleys eroded the
surface of the earth by removing particles of rocks whereas sedimentary accumulations
deposited in the lower reliefs.
The tectonic activity resulting from the internal adjustments led to the formation of
horsts and grabens filled with sedimentary deposits (Figure 2-2), as it is attested by the
Red Sea between Asia and Africa.

Life began in the oceans sometime in the Precambrian period and eventually spread onto
the land during the Devonian period (about 350 million years ago).
Fossils preserved in deposits attest to the progressive evolution of the fauna and flora
and enabled the succession of rocks to be subdivided into eras and smaller subdivisions.
The more important ones are shown in Table 2-1.

2.1.1.2 How is the duration of eras and subdivisions measured?
Absolute ages for these subdivisions were determined from studies of radioactive
minerals.
2.1.2 The Sedimentary Cycle
The classic cycle is one of uplift, weathering, erosion, transportation, deposition,
lithification and renewed uplift.

2.1.2.1 Weathering
Weathering can be either a physical process, a biological process or a chemical process
which all result in the breakup and the decay of rocks at the earth’s surface. Erosion is the
process or removing newly formed sediments and is caused by four agents which are also
responsible for the subsequent transportation of the sediment. This sediment
transportation can be achieved through the action of gravity, water, glaciers or wind.
2.1.2.2 Erosion and deposition
Erosion results from the action of many agents such as wind, freezing water, waves and
moving ice, which remove particles from the surface of the earth (Figure 2-3).
Unconsolidated deposits (A) resulting from the accumulation of those particles were
compacted by the weight of the overlying sediments (B) and, under the action of pressure
and heat, were transformed into metamorphic rocks. Most oil and gas accumulations
occur in sedimentary rocks.

2.1.2.3 Diagenesis
A name given to the processes which change sediments to a rock. As the energy of the
transporting agent slows down, removed sediments will deposit; the coarsest part would
drop first whereas the fine fraction (such as clay) might then be slowly deposited further
away. This natural segregation of coarse materials from fine, and the soluble from
insoluble, form the basis for the classification of sedimentary rocks.
Diagenesis occurs under the effects of compaction, dewatering (water squeezed out of
the sediments) or cementation (chemical processes). All these mechanisms can be
combined over a certain period of time.

Lecture 1 con't

1.1.3 Applications of Directional Drilling
1. Sidetracking: Side-tracking was the original directional drilling technique. Initially,
sidetracks were “blind". The objective was simply to get past a fish. Oriented
sidetracks are most common. They are performed when, for example, there are
unexpected changes in geological configuration (Figure 1-1).

2. Inaccessible Locations: Targets located beneath a city, a river or in environmentally
sensitive areas make it necessary to locate the drilling rig some distance away. A
directional well is drilled to reach the target (Figure 1-2).

3. Salt Dome Drilling: Salt domes have been found to be natural traps of oil
accumulating in strata beneath the overhanging hard cap. There are severe drilling
problems associated with drilling a well through salt formations. These can be
somewhat alleviated by using a salt-saturated mud. Another solution is to drill a
directional well to reach the reservoir (Figure 1-3), thus avoiding the problem of
drilling through the salt.

4. Fault Controlling: Crooked holes are common when drilling nominally vertical. This
is often due to faulted sub-surface formations. It is often easier to drill a directional
well into such formations without crossing the fault lines (Figure 1-4).

5. Multiple Exploration Wells from a Single Well-bore: A single well bore can be
plugged back at a certain depth and deviated to make a new well. A single well bore
is sometimes used as a point of departure to drill others (Figure 1-5). It allows
exploration of structural locations without drilling other complete wells.

6. Onshore Drilling: Reservoirs located below large bodies of water which are within
drilling reach of land are being tapped by locating the wellheads on land and drilling
directionally underneath the water (Figure 1-6). This saves money-land rigs are much
cheaper

7. Offshore Multiwell Drilling: Directional drilling from a multiwell offshore platform
is the most economic way to develop offshore oil fields (Figure 1-7). Onshore, a
similar method is used where there are space restrictions e.g. jungle, swamp. Here,
the rig is skidded on a pad and the wells are drilled in “clusters".

8. Multiple Sands from a Single Well-bore: In this application, a well is drilled
directionally to intersect several inclined oil reservoirs (Figure 1-8). This allows
completion of the well using a multiple completion system. The well may have to
enter the targets at a specific angle to ensure maximum penetration of the reservoirs.

9. Relief Well: The objective of a directional relief well is to intercept the bore hole of a
well which is blowing and allow it to be “killed" (Figure 1-9). The bore hole causing
the problem is the size of the target. To locate and intercept the blowing well at a
certain depth, a carefully planned directional well must be drilled with great
precision.

10. Horizontal Wells: Reduced production in a field may be due to many factors,
including gas and water coning or formations with good but vertical permeability.
Engineers can then plan and drill a horizontal drainhole. It is a special type of
directional well (Figure 1-10). Horizontal wells are divided into long, medium and
short-radius designs, based on the buildup rates used. Other applications of
directional drilling are in developing geothermal fields and in mining.

Lecture 1

Directional Drilling Training Manual

1 Introduction
1.1 History and Applications of Directional Drilling
Controlled directional drilling is the science of deviating a well bore along a planned
course to a subsurface target whose location is a given lateral distance and direction from
the vertical. At a specified vertical depth, this definition is the fundamental concept of
controlled directional drilling even in a well bore which is held as close to vertical as
possible as well as a deliberately planned deviation from the vertical.
1.1.1 Historical Background
In earlier times, directional drilling was used primarily as a remedial operation, either to
sidetrack around stuck tools, bring the well bore back to vertical, or in drilling relief
wells to kill blowouts. Interests in controlled directional drilling began about 1929 after
new and rather accurate means of measuring hole angle was introduced during the
development of Seminole, Oklahoma field.
The first application of oil well surveying occurred in the Seminole field of Oklahoma
during the late 1920’s. A subsurface geologist found it extremely difficult to develop
logical contour maps on the oil sands or other deep key beds. The acid bottle
inclinometer was introduced into the area and disclosed the reason for the problem;
almost all the holes were crooked, having as much as 50 degrees inclination at some
check points.
In the spring of 1929 a directional inclinometer with a magnetic needle was brought into
the field. Holes that indicated an inclination of 45 degrees with the acid bottle were
actually 10 or 11 degrees less in deviation. The reason was that the acid bottle reading
chart had not been corrected for the meniscus distortion caused by capillary pull. Thus
better and more accurate survey instruments were developed over the following years.
The use of these inclination instruments and the results obtained showed that in most of
the wells surveyed, drill stem measurements had very little relation to the true vertical
depth reached, and that the majority of the wells were "crooked". Some of the wells were
inclined as much as 38 degrees off vertical. Directional drilling was employed to
straighten crooked holes.
In the early 1930’s the first controlled directional well was drilled in Huntington Beach,
California. The well was drilled from an onshore location into offshore oil sands using
whipstocks, knuckle joints and spudding bits. An early version of the single shot
instrument was used to orient the whipstock.
Controlled directional drilling was initially used in California for unethical purposes, that
is, to intentionally cross property lines. In the development of Huntington Beach Field,
two mystery wells completed in 1930 were considerably deeper and yielded more oil
than other producers in the field which by that time had to be pumped. The obvious
conclusion was that these wells had been deviated and bottomed under the ocean. This
was acknowledged in 1932, when drilling was done on town lots for the asserted purpose
of extending the producing area of the field by tapping oil reserves beneath the ocean
along the beach front.

Many legal entanglements developed when it was established through directional surveys
that oil was being removed from a productive zone under the tidelands, the ownership of
which was claimed by both the town of Huntington Beach and the State of California.
The state now supervises the Huntington Beach operations, and subsequently the art of
cylinder drilling or drilling a prescribed “right of way" was developed .
In 1933, during the development of the Signal Hill field in Long Beach, California,
several wells were drilled under the Sunnyside Cemetery from locations across the
streets surrounding the cemetery and even from more distant points to tap a productive
zone underlying the cemetery.
Controlled directional drilling had received rather unfavorable publicity until it was used
in 1934 to kill a wild well near Conroe, Texas. The Madeley No.1 had been spudded a
few weeks earlier and, for a while, everything had been going normally. But on a cold,
wet, dreary day the well developed a high pressure leak in its casing, and before long, the
escaping pressure created a monstrous crater that swallowed up the drilling rig. The
crater, approximately 170 feet in diameter and of unknown depth, filled with oil mixed
with sand in which oil boiled up constantly at the rate of 6000 barrels per day. As if that
were not enough, the pressure began to channel through upper formations and started
coming to the surface around neighboring wells, creating a very bad situation indeed.
Many people felt that there was nothing to do except let the well blow and hope that it
would eventually bridge itself over, and pray that it would do it soon so everyone could
get back to work.
In the meantime, however, a bright young engineer working for one of the major oil
companies in Conroe suggested that an offset well be drilled and deviated so that it
would bottom out near the borehole of the cratered well. Then mud under high pressure
could be pumped down this offset well so that it would channel through the formation to
the cratered well and thus control the blow out. The suggestion was approved and the
project was completed successfully, to the gratification of all concerned. As a result,
directional drilling became established as one way to overcome wild wells, and it
subsequently gained favorable recognition from both companies and contractors. With
typical oilfield ingenuity, drilling engineers and contractors began applying the
principles of controlled directional drilling whenever such techniques appeared to be the
best solution to a particular problem.
Current expenditures for hydrocarbon production have dictated the necessity of
controlled directional drilling, and today it is no longer the dreaded operation that it once
was. Probably the most important aspect of controlled directional drilling is that it
enables producers all over the world to develop subsurface deposits that could never be
reached economically in any other manner.
1.1.2 Technology Advances
The development of reliable mud motors was probably the single most important
advance in directional drilling technology. Surveying technology also has advanced in
great strides. The technologies complement each other.
The development of the steering tool replaced the magnetic single shot instrument as a
means of orienting a mud motor with a bent sub or housing. The tool was lowered by a
wireline unit and seated in the muleshoe orienting sleeve. The wireline was passed
through a circulating head mounted on a drill pipe and had to be retrieved every 90 feet.

Data sent to the surface by the wireline was processed by a surface computer.
Continuous updates were given on azimuth, inclination, temperature and tool face. With
the advent of the side-entry sub, the wireline was passed through the side of the sub thus
eliminating the need to pull the wireline every 90 feet. However, no rotary drilling was
possible with the steering tool.
In the early 1980’s ANADRILL MWD started to gain widespread acceptance as an
accurate and cost-effective surveying tool. Today the MWD has virtually replaced the
steering tool on kick-offs and is used exclusively with the steerable mud motor. A newgeneration
MWD has been developed with the additions of gamma ray, resistivity, and
DWOB/DTOR giving the MWD real time formation evaluation capabilities. Surveys
obtained with the MWD are now widely accepted by both oil industry and regulatory
agencies.
Gyro technology has also progressed. The SRG (Surface Readout Gyro) is the latest
addition to the survey line. It provides fast and accurate surveys electronically,
eliminating the need to read a film base system. Many surveying companies provide their
own tool: "FINDER", "SEEKER”, "GCT”, “FINDS", etc.

Lecture 1 con't