Exploration methods, techniques

1. Introduction to
Geophysical Exploration

2. Geophysical + Exploration
is a subject of natural
science concerned with
the physical processes
and physical properties
of the Earth and its
surrounding space
environment, and the use
of quantitative methods
for their analysis.
is the search by petroleum
geologists and geophysicists for
hydrocarbon deposits beneath
the Earth's surface, such
as oil and natural gas. Oil and
gas exploration are grouped
under the science of petroleum
geology.

3. Introduction
The objective of any exploration venture is to
 find new volumes of hydrocarbons at a low cost
 and in a short period of time. Time increases , costs increases
Exploration budgets are in direct competition with acquisition opportunities.
If a company spends more money finding oil than it would have had to spend buying the
equivalent amount "in the market place" there is little incentive to continue exploration.
Conversely, a company which manages to find new reserves at low cost has a significant
competitive edge since it can afford more exploration, find and develop reservoirs more
profitably, and can target and develop smaller prospects.

4. Definition
Geophysical methods are the systematic collection of geophysical data for delineating the
Earth's interior hold essential information.
Or
Is an applied branch of geophysics, which uses physical methods at the surface of the Earth to
measure the physical properties of the subsurface, along with the anomalies in those properties.

5. Continued
These methods identify resources without the need for sampling.
Usually undertaken with minimal surface disturbance.
The survey used in these methods is called Geophysical survey.
Geophysical surveys can be conducted either from ;
The air
On the ground
Down drill holes.

6. HISTORICAL VIEW OF PETROLEUM EXPLORATION
AROUND THE WORLD

7. The Bible contains many references to the use of asphalt collects from the natural seepages
with which the Middle East abounds.
Throughout the first millennium A.D, Oil and Asphalt were gathered from natural seepages in
many parts of the world.
The early uses of oil were for
 medication,
 waterproofing
 and warfare.
When Alexander invaded India, he used the burning Asphalt to scattered
the elephant corps.

8. Nadir shah employed the similar device in 1739.
Until mid-nineteenth century oil, asphalt and there by-products were produced only from
 seepages,
 shallow pits,
 and hand-dug shafts.
In 1694 the British crown issued a patient to Masters Eele, Hancock, and Portlock to make great
quantities of Asphalt out of a kind of stone.

9. The first well in the search of oil appears to have been at Pechelbronn, France in 1745.
The birth of oil shale industry is credited to James Young, who began retorting oil from the
carboniferous shale Torbon, Scotland in 1847.
The first well to produce oil intentionally in the western world was drilled at Oil Creek,
Pennsylvania, by Colonel Drake in 1859.
Previously water wells produced oil as a contaminant.
Cable-tool drilling has been used in which drilling tool being suspended from bamboo towers up
to 60 m high.

10. In 1882, Baker Brothers drilled first well with rotary equipment, pumped water with wind mill.
By the 1920’s the oil industry was dominated by seven major companies, termed the SEVEN
SISTERS, these companies included:
EUROPEAN:
 British petroleum
 Shell
AMERICAN:
 EXXON
 Gulf
 Texaco
 Mobil
 Chevron

11. European companies found their oil reserves abroad thus involved early in long-distance
transport, measuring their oil by seagoing tonne (ton).
American companies with shorter transportation distances measured their oil in barrels.
The American companies began overseas ventures in 1920’s.
In 1960 the Organization of Petroleum Exporting Companies (OPEC) was founded in Baghdad.
OPEC was consisted initially of Iran, Iraq, Kuwait, Saudi Arabia, & Venezuela.
It later expanded to include many other countries.

12. TYPES OF GEOPHYSICAL SURVEYS

14. TYPES OF GEOPHYSICAL SURVEYS
1. PASSIVE GEOPHYSICAL SURVEY
a) Gravity
b) Magnetic
c) Electrical
2. ACTIVE GEOPHYSICAL SURVEY
a) SEISMIC SURVEY:

16. PASSIVE GEOPHYSICAL SURVEY
Geophysical exploration methods which records the naturally occurring fields of the Earth.
For example
 the gravitational,
 magnetic
 and electrical fields of the Earth.
Generally, natural field methods can provide
 information on Earth properties to significantly greater depths
 and are logistically simpler to carry out than artificial source methods.

17. a. Gravity Survey
 In gravity surveying, subsurface geology is investigated on the basis of variations in the Earth’s
gravitational field arising from differences of density between subsurface rocks.
Gravity measurements made in exploration work show only variation in gravity from one place
to another.
Any variation in gravity is a positive gravity anomaly if it is higher than from that over the area
surrounding it and negative when lower.
Gravity high over a mass
Gravity low over a valley

18. Key facts
The gravity method measures small (~10−6 g) variations of the earth's gravity field caused by
density variations in geological structures.
The sensing element is a sophisticated form of spring balance.
Variations in the earth's gravity field cause changes in the length of the spring, which are
measured (shown on next slide)
Measurements must be corrected for the elevation of the recording station.

20. Contd.
Basic theory
The basis of the gravity survey method is Newton’s Law of Gravitation, which states that the
force of attraction F between two masses m1 and m2, whose dimensions are small with respect
to the distance r between them is given by
Measurement
In this method micro variation in gravitating field of the earth due to the density difference is
measured by areal-based or ground-based instrument.
These instruments have gravitometers which works by recording the downward acceleration of
mass from the minute fluctuations of a spring.

21. Cont.
Interpretation
 Geological interpretation of gravity data is not easy
as it involves more uncertainties than interpretation
of seismic data.
 Gravity maps resemble so much to structural maps
that one can wrongly identify gravity contours as
indicative of structure.

22. Contd.
Applications
 Gravity studies are used extensively in the investigation of large and medium scale geological
structures.
 Gravity surveys are useful in initial exploration in areas where no geological information is
available at all.
 Gravity method provides presence of sediments in a basin rapidly and economically.
 Mainly use for
 mineral,
 coal
 and oil & gas exploration.

23. Magnetic Survey
In magnetic surveying, subsurface geology is investigated on the basis of variations in the Earth’s
magnetic field result from lithlogic changes associated with the basement or from igneous
intrusive.
OR
The magnetic method detects changes in the earth's magnetic field caused by variations in the
magnetic properties of rocks.

24. In particular basement and igneous rocks are relatively highly magnetic and if close to the
surface give rise to short wavelength, high amplitude anomalies in the earth's magnetic field (
Diagram on next slide)
The method is airborne (plane or satellite) which permits rapid surveying and mapping with
good areal coverage.
Like the gravity technique this survey is often employed at the beginning of an exploration
venture.
In geology, basement and crystalline basement are
the rocks below a sedimentary platform or cover,
or more generally any rock below
sedimentary rocks or sedimentary basins that are
metamorphic or igneous in origin.

26. Gravitational and Magnetic
Both survey methods are mainly employed to define large scale structures such as basins.
Based on the resulting maps, seismic surveys are then carried out.

27. Contd.
Basic Theory
Magnetic field strength at a point is defined as the magnetic force exerted on a pole of unit
strength placed at that point.
If two poles of strength Po and P are placed at a distance r apart, the magnetic force between
them will be,
Measurement
In this method micro variation in existing magnetic field of the earth due to the lithology and
minrology difference is measured by areal-based or ground-based magnetometer.
Today, all magnetic surveys are done from air or from ships due to speed, economy and
convenience.

28. Interpretation
 Sedimentary rocks exert a very small magnetic effect compared to igneous rocks.
 In magnetic survey the objective is to ascertain the presence of sedimentary basins and to map
their approximate boundaries.
Applications
 Magnetic prospecting is used to explore for both oil and minerals.
 It gives information to determine depth to basement rocks.
 To locate and define the extent of sedimentary basins.
 Magnetic information is of importance in previously unexplored areas.

29. 2. ACTIVE GEOPHYSICAL SURVEY:
Geophysical exploration methods which require an artificial signal to be generated.
For example,
 seismic exploration
 and electromagnetic techniques.
These are capable of producing a more detailed and better resolved picture of the subsurface
geology.

32. SEISMIC SURVEY
Seismic waves
Seismic waves are sound waves that travel through the Earth or other elastic bodies, for
example as a result of an earthquake or explosion or vibration.

33. Types of seismic waves
1. Body waves
A wave that propagates through a medium rather than along an interface.
It is faster than Surface waves
OR
Body waves travel through the interior of the Earth

34. P-wave
 A body wave in which particles motions are parallel to the
direction the wave propagates.
 It’s velocity is faster than S-wave.
 P waves are compression waves.
 They can propagate in solid or liquid material.
S-wave
A body wave in which particles motions are perpendicular to the
direction the wave propagates.
S-waves are generated by most land seismic sources, but not by air
guns.
S-waves are shear waves.
They only propagate in solid material.

35. 2. Surface waves: A wave that propagates at the
interface between two media.
 Love wave
 It is a surface wave in which particles oscillate
horizontally and perpendicularly to the direction
of wave propagation.
 Rayleigh wave
 It is a surface wave in which particles move in an
elliptical path.
 They travel at different velocities.
 They are also called Ground Roll in seismic
exploration.

36. Mediums affect on seismic waves
1. Geometrical spreading: The energy intensity decreases when wave front gets farther from
the source.
2. Absorption: Transformation of energy to heat as seismic wave passes through a medium,
causes amplitude to decrease.
3. Interface-related effects: when a wave finds an abrupt change in rock properties, some of
energy reflected & some of energy refracted.

37. Seismic noises
It is anything other than desired signal. Noise includes disturbances in seismic data caused by
any unwanted seismic energy.
 Random noise: Random on all traces & includes wind, rain, human & machines (Environment
noise)
 Coherent noise: Include surface waves, refractions, diffractions & multiples.

38. Seismic trace
 It is the seismic data recorded for one channel.
 A seismic trace represents the response of the wave field to
• velocity
• and density
contrasts across interfaces of
• layers of rock
• or sediments
as energy travels from a source through the subsurface to a receiver.
Seismic Resolution
 It is the ability to distinguish between separate points or objects, such as
sedimentary sequences in a seismic section.
High frequency and short wavelengths provide better vertical and lateral
resolution.

39. Seismic equipments
Seismic sources:
 Land Sources
a) Impulsive sources: It is explosive sources such as Dynamite.
b) Non impulsive sources: It isn’t explosive the common is Vibroseis which is a designed
vehicle lift its weight on large plate in contact with ground surface in sweeps.
Marine sources
 Air gun:
 It is common in offshore survey.
 This gun releases highly compressed air into water.
 It uses a compressed air at 2000‐ 5000PSI to produce an explosive blast of air.
 Several air guns with different sizes are fired to enhance their initial pulses & reduce
their bubble effects.

40. Seismic detectors
Land detectors (Geophone):
 It is a device is used to detect the sound waves.
 It consists of coil of wire suspended from spring and surrounded
by (W) shaped magnet.
 Upward energy from seismic source is recorded as electrical
current generated by movement of coil.
Marine detectors (Hydrophone):
 It is a device used to detect the pressure waves.
 Upward pressure is recorded as electrical current.

41. Land Survey
Two-dimensional survey (2-D)
 Seismic data or a group of seismic lines acquired individually such that there
typically are significant gaps (commonly 1 km or more) between adjacent
lines.
 A 2D survey typically contains numerous lines acquired to the strike of
geological structures. The seismic data recorded by 2-D survey is seismic line.
Three-dimensional survey (3-D)
 The acquisition of seismic data as closely spaced receiver and shot lines such
that there typically are no significant gaps in the subsurface coverage.
 The seismic data recorded by 3-D survey is seismic cube.

42. Marine Survey:
2-D and 3-D survey in marine differ from land survey due to the different seismic equipments.
Tail buoy:
 A floating device used in marine seismic acquisition.
 It allows the seismic acquisition crew to monitor location and direction of
equipments.

43. Seismic Data Processing
Seismic processing involves lots of techniques, some most important are as follows:
Demultiplex
Gain Recovery
Deconvolution
Filtering
Stacking
Static correction
Migration

44. Seismic Data Interpretation
Interpreting seismic data requires an understanding of the subsurface formations and how they
may affect by source wave.
The original use of seismic reflection data was to create maps delineating the geometry of a
subsurface structure. Some of the maps are;
Time slice
Chair display

45. Petroleum Engineering Remarks
Explosive seismic source 10-25 kg or more in a distributed pattern
in deep holes 20 to 50 g, single shot To increase frequency
content
Mechanical seismic source
1-7 vibrators
5-15,000 kg peak force
10-100 Hz sweep
Hammer and Plates, guns Cost, increased
frequency
Geophones
Arrays of 12-48 phones; 25-40 Hz
fundamental frequency;
3-20 m spacing
Single or 3-5 geophones
50-100 Hz fundamental
frequency; 1-3 m spacing
To preserve frequency
content
Recorders Instantaneous floating point, 48-1,000
channels
Instantaneous floating point, 24-96
channels Cost
Passband analog filters 10-110 Hz 100-500 Hz To increase frequency
content
Sample interval 1-2 ms 1/4-1/8 ms Higher frequencies

46. History of Exploration in
Pakistan

47. 1866 First well drilled by Punjab Govt. at Kundal seepage (Khisor Range).
1885-1892, 13 wells were drilled near Khattan Oil Seepage (SE-Quetta) [25000bbl].
1912 Attock Oil Company (A.O.C.) of UK surveyed Potwar Area.
1915 First oil discovery at Khaur (Miocene & Eocene Reservoir) Produced oil upto 1990.
1916 Burma Oil Company (B.O.C) drilled Chandragup#1 near Mud Volcano Makran.
B.O.C./A.O.C. Joint venture discovered number of fields in Potwar Region in upper Indus Basin
such as Dhulian-1936, Joya Mair-1944 and Balkasar-1946 (Reservoir-Eocene Limestone).

48. After independence of Pakistan BOC  PPL AOC POL
PPL discovered first GAS Field at Sui (L.I.B. Eoc.Lst Reservoir)original recoverable reserves 8.624
TCF=1 Billion bbl Oil.
First boom in Petroleum Exploration in Pakistan after discovery of Sui Gas Field.
Petroleum Concession Agreements in 1954-59 with following companies
 1.Standard Vacum Oil company
 2.Hunt International Oil Company
 3.Shell Oil Company
 4.Sun oil Company
 5.Tide Water
 ( All companies from USA)

49. SVOC -1954
HIOC-1955
S.O.C.-1957
Shell Oil Company-1956
Tide Water-1958.

50. 1954 Discovery of Mari-GAS field by SVOC at Mari-Kandhkot High (H.R.L.)
During 1954-1959 PPL discovered gas fields ZIN, UCH, MAZARANI, KHAIRPUR and KANDHKOT in
Lower Indus Basin.
1956 PPL/POL discovered KARSAL oil field in Potwar Area (Upper Indus Basin).
During 1956-1959 nearly 35 exploratory wells were drilled (1 oil & 6 gas fields).
1961 OGDC founded by government of Pakistan (Russian Aids & Technology).
1961-1970 discoveries
 SAR-SINGH gas 1965,
 TOOT oil 1968,
 HUNDI gas 1970 by OGDC
MEYAL oil discovered by POL 1968.

51. 1971-1980 OGDC. discovered RHODHO gas 1972, KOTHAR gas 1973 and first considerate gas
field at DHODAK 1977.
1975 AMOCO discovered a gas field at JANDRAN 1975.
1977 PIRKOH gas field discovered by OGDC. (Resr. PAB Ss. Cret. New Resr.)
Upto 1980 Lower Indus Basin was totally GAS Prone Area.
2nd Milestone in the history of petroleum exploration of Pakistan in L.I.B. (Sindh).
1980 discovery of KHASKHAILI oil field in Badin area by UTP ( Badin block).
Boom in exploration in S. Indus Basin. Now sharing 50% in total production.

52. 1981 new reservoirs discoveries Tobra Fm.& Khewra Ss. In U.I.B Adhi oil field.
Third Milestone discovery of gas fields NANDPUR-1984, PAGPIR-1985 were discovered by
O.G.D.C. in PUNJAB PLATEFORM area (Cret./Jur. Reservoirs).
First Natural Gas discovery in Punjab was done by OGDC ( Nandpur 1984) ( Punjpir 1985) in
Jurassic/ Cretaceous reservoirs.
1981-1990 decade 55 oil, condensate & gas fields discovered mostly in L.I.B.
LASMO oil discovered gas field at Kadanwari (Khaipur-Jaccobabad High).
1991-2000 decade 50 oil,condensate & gas fields were discovered.
At present more than 130 oil, condensate & gas fields have been discovered.

53. OFF-SHORE exploration Indus Mouth & Makran Coast.
 1961 S.O.C. Daboo creek (1963), Patiani creek & Korangi creek (1964).
 1972-1973 WINTER SHELL drilled INDUS MARINE A-1, B-1 & C-1 Wells.
 1976-1977 HUSKEY OIL drilled KARACHI South-A. MARATHON JALPARI#1.
 1986 O.G.D.C./Canada drilled PAK-CAN#1 1989 OCCIDENTAL SADAF#1.
 1999-2000 U.M.C.PAK Corp. drilled two wells.
Total 450 exploratory wells Success Ratio 1:4 World Ratio 1:9. (1995 BOOK)
2018 , NO ANY DATA IS AVAILABLE
In my own perspective ?