This document provides information about geophysics and its applications in oil and gas exploration and production. It discusses how geophysics uses physical property measurements and geophysical methods like seismic, gravity, magnetic, and electromagnetic surveys to study the subsurface where rock is not directly exposed. It explains how geophysical data provides a spatially continuous understanding of the subsurface to interpret geological structures and reservoirs, while well data provides high vertical resolution calibration. The document also outlines how geophysical data aids drilling operations by identifying hazards and illuminating what lies ahead of and around the drill bit.

1. Geophysics
Department of Oil and Gas
University of Thi Qar/ College of Engineering
Ahmed Jalal Fakher Al- Bahar
2022-2023

2. Book 1 Book 2

5. Geology & Geophysics
 Geology: it is an observational science. It involves the
study of the earth by direct measurements of rock
properties, either from surface exposures (outcrops) or
from boreholes, tunnels, and mines.
 Geophysics: applies the principles of physics to the study
of the earth, for deducing physical features of the earth’s
surface and its internal structure. Geophysics involves the
study of those parts of the earth hidden from direct view,
by measuring their physical properties, with appropriate
instruments on or above the surface of the earth, remotely
from the measurement targets.

7. Suitable for
Physical property
Methods
Geological structure, spatial variation in
rock types: for example, salt domes,
shale diapers, reefs and cavities
Gravitational attraction,
Density contrast
Gravity
Magnetic ores, Geometry of basement
below the sediments, sedimentary cover
thickness,
geological structures and
archeological studies
Magnetic field variation,
Magnetic susceptibility
contrast
Magnetic & Electromagnetic
Shallow near- surface lithology changes,
Ground water, cavities
Changes in electric
conductivity and or
permittivity
Electric & Electromagnetic
Engineering problems
Travel time to acoustic
boundaries, amplitude
(elastic moduli and
density contrast),
absorption, velocity
Refraction (Shallow)
Seismic Geological structure, depositional
history, faults, rock layers, reservoir size,
shape porosity, pressure, saturation
distribution
Reflection (Deep)
Radioactive ores
Radiation intensity
Radiometric
Geological structures, Shallow salt
domes, Anticlines and Fissures
Temperature
Geothermal
Channels, Cables, Caves, Pipes,
River floor
Electromagnetic waves
intensity
Ground Penetration
Radar - GPR

9. Reservoir, drilling and production engineers
 They must be able to understand the information provided by geophysicists,
geologists, and petrophysicists so as to be able to properly utilize it. This is
particularly important because of the multidisciplinary nature of the
challenges faced in oil and gas exploration and production. The need to
integrate the data and the disciplines is important.
 As engineers become more familiar with geophysical techniques, there will
be expansion in applications of geophysical techniques in reservoir
engineering practices.
During a reservoir’s life cycle from discovery and development to production
and field maturation, the needs for reservoir description change continuously.

10. Date from geophysical tools provide coverage with a spatially
continuous high sampling density of 10-25 m and a vertical
resolution of the order of 10-20 m.
 well data such as cores and well logs provide a vertically high
resolution of the order of 0.5 m or better at the well location; however, the
distribution of wells is sparse and discontinuous. The detailed spatial
coverage from geophysical data is calibrated with analysis of well logs,
pressure tests, cores, geologic depositional knowledge, and other
information from appraisal wells.

11. Well logging
South
Rumaila
Rock
Property
Wells
R-x R-xx R-xxx
R-xxxx
EEI30 EEI40 EEI50 EEI30 EEI40 EEI50 EEI30 EEI40 EEI50 EEI30 EEI40 EEI50
Vsh Vsh
Vsh
Vsh
Package 1
Top AB – Base F
Package 2
Top L2 – Base N
Package 3
MSM10
Core

12. Seismic reflection & well log
Lithology Volume: inline 1703 through Ru-xx well location
AB - F
LMN
MSM10

13. Geophysical tools and techniques
Geophysical methods use high-precision sensors (e.g., geophone,
hydrophone, magnetometer, gravity-meter) that measure the
physical properties onshore and offshore, in wells and from air,
there are also measurements from satellites.
 Surface: seismic reflection 2D, 3D, 4D magnetics, gravity,
electromagnetics.
 Borehole: vertical seismic profiling (VSP), cross well seismic,
cross well electromagnetics, microseismic, borehole gravimeter
(BHGM), nuclear

14. Geophysics in drilling
The process of drilling an oil or gas well
requires knowledge of all geologic
features expected to be encountered along
the way- from the surface of the ground to
the target reservoir. Thus, in addition to
steering the well so as to intersect
hydrocarbon- bearing reservoirs, the
reservoir engineer must ensure that the
well drills successfully and safely to the
target formations.
Static model
Mishrif seismic surface
Update static model with structure interpreted
on 3D seismic
Seismic & model
structures don’t
match
By providing a picture of the subsurface from the surface to the target, geophysical
measurements help ensure a successful drilling program. This geophysical picture helps to:
1. Identify drilling hazards that may lead to an uncontrollable well;
2. Describe construction hazards; predict what lies ahead of and around the drill bit; and
3. Illuminate what exists above and below the well bore in a horizontal or highly
deviated well.

17. Seismic section with Interpreted Horizons
Dammam
Top Rus
Top Tayarat
Sadi
Top Mish
Top Ahmadi
Top Uppershale
Top YRB
W E
W E
N
S
peak
trough

20. Video