lecture - 03 interpretation
DESCRIPTION
Lecture - 03 interpretationTRANSCRIPT
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
www.bahria.edu.pk By: M. Hammad [email protected]
3D SEISMIC INTERPRETATION (GEO3D SEISMIC INTERPRETATION (GEO--518)518)
M. S (Geophysics)M. S (Geophysics)
By InstructorBy Instructor
M. Hammad ManzoorM. Hammad Manzoor
February 23, 2015 (Monday)February 23, 2015 (Monday) Lecture # 3Lecture # 3Lecture # 3Lecture # 3
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Hydrocarbon Hydrocarbon Exploration Overview Exploration Overview
By Utilizing By Utilizing
www.bahria.edu.pk By: M. Hammad [email protected]
Geophysical MethodsGeophysical Methods
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Key elementsKey elements
Geophysical MethodsGeophysical Methods
Key to find HydrocarbonsKey to find Hydrocarbons
Subsurface Mapping TechniquesSubsurface Mapping Techniques
www.bahria.edu.pk By: M. Hammad [email protected]
The Constraints of EconomicsThe Constraints of Economics
ConclusionsConclusions
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
A Situation - Geophysical Methods
We shall find that geophysical methods sometimes do allow
this reconstruction of the geological history.
In favorable cases, we are able to establish the configuration
of the earth's surface, and of buried layers, in times past; we can
also establish the time at which particular movements occurred.
www.bahria.edu.pk By: M. Hammad [email protected]
We have identified, then, the elements of our task. We must
find geological situations which combine a source, a reservoir, a
migration path between them, a trap, and a seal.
And we must reconstruct, as far as possible, the geological
history which gave rise to each such situation.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
A Situation - Geophysical Methods
Finally, we should note that it is only in an undeveloped area
that the exploration problem is really as harsh as suggested
above.
Often we have some wells, so that the problem is mainly one
of correlating a new prospect area to those wells; this may
require no more than tracing the continuity of known rocks into
www.bahria.edu.pk By: M. Hammad [email protected]
require no more than tracing the continuity of known rocks into
the prospect area which geophysics can usually do very well.
Again, we may already have a producing field, whose
geophysical response is known; then the problem is merely to
find a geophysical analog of that field. This makes us feel more
comfortable; at least we shall succeed some of the time.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Key to Find HydrocarbonsKey to Find Hydrocarbons
By Utilizing By Utilizing
www.bahria.edu.pk By: M. Hammad [email protected]
By Utilizing By Utilizing
Geophysical MethodsGeophysical Methods
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Key to Find Hydrocarbon
Geophysical Methods
A key operation in finding oil is the mental visualization of the
geology, and of its development through time, from an array of
data.
But if it is in the mind that the critical interpretive step occurs,
www.bahria.edu.pk By: M. Hammad [email protected]
But if it is in the mind that the critical interpretive step occurs,
how are we to get the initial data into the mind? Specifically, how
should we present the data including in particular our
geophysical results to display the geological situations most
clearly?
Probably, these situations would be most easily recognized if
our geophysical work yielded an actual model of the earth, which
we could pull apart (layer by layer, or block by block) to reveal
features of interest.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Key to Find Hydrocarbon
Geophysical Methods
Ideally, indeed, we would ask for several models. First, we
would ask for one model showing the rocks as they are today;
this would demonstrate the trap and the seal, and tell us what the
drill bit will encounter on the way down.
Second, we would ask for a set of models showing the
www.bahria.edu.pk By: M. Hammad [email protected]
Second, we would ask for a set of models showing the
conditions in which each significant layer was deposited (the
depositional environments); this would demonstrate the
likelihood of source rocks, reservoir rocks, cap rocks, and lateral
seals.
Third, we would ask for a set of models representing various
stages of development between deposition and the present; this
would show the subsidence, uplift, folding, faulting and erosion
of layers, and perhaps reveal whether the trap formed before or
after the generation and migration of the petroleum.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Key to Find Hydrocarbon
Geophysical Methods
Traditionally, the most important displays for representing
the three-dimensional earth have included the following
subsurface maps :
www.bahria.edu.pk By: M. Hammad [email protected]
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Key to Find Hydrocarbon
Geophysical Methods
Vertical sections: displaying the intersection of the entire
sequence of rock layers with a vertical plane. These are valuable in
revealing structure, layer thickness, fault planes, and depositional
surfaces (geological time lines).
www.bahria.edu.pk By: M. Hammad [email protected]
Contour maps: each specific to one selected interface
between layers displaying the variations in depth to that one
interface. A contour map is valuable as a complete description of the
structure on a single interface; contour maps are structure maps.
Continued..
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Key to Find Hydrocarbon
Geophysical Methods
Interval maps: each specific to one selected layer
displaying some property of that layer. Two important such
properties are thickness (an isopach map) and porosity (a porosity
map); clearly, if we multiply the two together (a porosity-thickness
map) and then multiply by the area of the petroleum accumulation,
we have a first estimate of reserves in place. Isopach maps are also
www.bahria.edu.pk By: M. Hammad [email protected]
we have a first estimate of reserves in place. Isopach maps are also
useful in displaying features whose recognition hinges on variations
of thickness: fans, pinch-outs, and tilting during deposition.
Shape maps: displaying the areal extent of particular geologic
features. These are valuable in identifying potential reservoir bodies
recognizable by their shape: reefs, bars, beaches, deltas, river
channels and fans.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping TechniqueSubsurface Mapping Technique
By Utilizing By Utilizing
Geophysical MethodsGeophysical Methods
www.bahria.edu.pk By: M. Hammad [email protected]
By Utilizing By Utilizing
Geophysical MethodsGeophysical Methods
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping Technique
Geophysical Methods
Many three-dimensional techniques are an extension of
traditional two-dimensional methods, in which we interpret a three-
dimensional data volume either by a set of sections or by a set of
maps.
www.bahria.edu.pk By: M. Hammad [email protected]
Because sections are best for some purposes and maps are
best for others (and because some geophysical methods yield
sections and some yield maps), we should be adept at constructing
one set from the other.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping Technique
Geophysical Methods
Let us illustrate by taking a set of sections, constructing from
them a structure map, and thereby deducing the area covered by a
trap.
Let us modify a previous figure to include a datum (for
example, sea level).
www.bahria.edu.pk By: M. Hammad [email protected]
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping Technique
Geophysical Methods
Let us define this section Line 1.
We have Seismic SP map of area.
www.bahria.edu.pk By: M. Hammad [email protected]
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping Technique
Geophysical Methods
On it we draw the position of the section of Line 1; then we
post on the map the depth values from the section.
In Figure; we see a second section, along a line marked on
the map as Line 2; again we post the depth values on the map.
www.bahria.edu.pk By: M. Hammad [email protected]
the map as Line 2; again we post the depth values on the map.
Then we do the same for
the sections along Lines 3, 4 and 5.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping Technique
Geophysical Methods
Next, we contour the depth values, joining together points of
like depth in a geologically plausible manner.
Clearly, we have a closed high, whose crest (or culmination,
or apex) is slightly south of Line 1.
www.bahria.edu.pk By: M. Hammad [email protected]
or apex) is slightly south of Line 1.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping Technique
Geophysical Methods The spill point of the structure is probably just north of Line
1, just west of Line 5. If, we draw the contour which passes through
this point, we define the probable maximum extent of the trap
This maximum extent, we hope, is the oil-water contact, OWC
(or, if the trap contains only gas, the gas-water contact, GWC). If the
trap contains both oil and gas, the spill-point contour is the oil-water
www.bahria.edu.pk By: M. Hammad [email protected]
trap contains both oil and gas, the spill-point contour is the oil-water
contact, and at some higher level there is a gas-oil contact, GOC.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping Technique
Geophysical Methods
By the same techniques of posting depth values and
contouring, we can construct structure maps of each of the other
rock interfaces observed on the sections. By posting layer
thicknesses and contouring those, we can construct isopach maps.
Given the set of structure maps, we can construct very easily
www.bahria.edu.pk By: M. Hammad [email protected]
Given the set of structure maps, we can construct very easily
the section appropriate to any arbitrary line (such as Line 6). We
merely transfer to the section the depth values given by the
intersecting contours, and join them together.
In exploration, we are doing these operations all the time
from the section to the map, from the map to the section. We read
one type of message from the section, another from the map; we
absorb all the messages into the mind .. . . and in the mind we find
the oil.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping Technique
Geophysical Methods
We must always bear in mind that a good section does not
make an oilfield. For example, the attractive contour map and the
unattractive contour map of both honor the depth values observed
along the good section of Line 1.
www.bahria.edu.pk By: M. Hammad [email protected]
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Subsurface Mapping Technique
Geophysical Methods
Because exploration is expensive, we will not explore a piece
of land unless we have some sort of exclusive right to explore.
Because the usual course of exploration takes some time, with a
significant learning process along the way, that exclusive right
should apply for a period of several years.
www.bahria.edu.pk By: M. Hammad [email protected]
If the exploration fails, the exclusive right is of no value and it
can be ceded. If the exploration succeeds and a field is discovered,
the exclusive right to explore needs to be converted to an exclusive
right to produce; this right should apply for the life of the field, which
may be 10 or 20 or 30 or 40 years.
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
Constraints of EconomicsConstraints of Economics
www.bahria.edu.pk By: M. Hammad [email protected]
Constraints of EconomicsConstraints of Economics
-
Department of Earth & Environmental Sciences,
Bahria University, Karachi Campus
ThanksThanks
www.bahria.edu.pk By: M. Hammad [email protected]
ThanksThanks