Petroleum Exploration
Searching for hydrocarbons accumulation :
Where?
What Depth under the Surface?
What Quantity?
Techniques based on Geology, Geophysics and Geochemistry are utilized.
Geological Methods:
Image Processing.
Contour maps.
Geophysical Methods:
Seismic Method.
Magnetic Method.
Gravitational Method.
Electrical Method (Resistivity Survey)
Geo-Chemical Method
Soil Analysis
Water Analysis
Petroleum Exploration
1.
Geological Methods:
Methods rely on Maps in which surface and subsurface layers are Studied & Correlated.
Image processing :
photographs taken from airplanes or satellites used to make
surface and Subsurface maps of the earth.
Contour Maps: Consists of a number of Contours.
Contours are lines on which every point has the same property.
Types of Contours maps:
Structural Contour map : lines of equal Elevation measured from sea level.
Isopacheous map: lines of equal thickness of a subsurface layer.
Isobaric Map: Lines of equal Pressure.
Isothermal Map: lines equal Temperature.
Isoporosity Map: lines of equal Porosity.
Isopermeability Map: line of equal permeability.
Petroleum Exploration
Petroleum Exploration
2. Geophysical Methods: (Mostly used)
Methods involve the application of principles of physics and Rock Mechanics of the earth.
Seismic, Magnetic, gravitational & Electric
None of these methods directly detect the presence of hydrocarbons within the subsurface layers.
They outline Sedimentary layers and traps beneath the Surface.
Seismic Method
Most widely used to measure the thickness & mapping the structure of Subsurface layers.
Principle:
Generate sound waves at surface and record the time takes to
travel down to subsurface layer and reflected back to surface.
L=vt
L = travel distance, m
V= Sound Velocity, m/s
t= travel time, s
Petroleum Exploration
On-shore:
Sound waves generated by dynamite or
vibrosis this is the recent technique using hydraulic vibrator carried by a truck.
Generation points→ shot points
Receiving points→ reflected or refracted sound waves by geophones.
Reflected → ( Striking back)
Refracted
→
( Passing through)
Off-shore:
Sound waves generated by air-gun on a ship & received by hydrophones.
Petroleum Exploration
Petroleum Exploration
Petroleum Exploration
Magnetic Method
Principle: measurement of the intensity of the earth's magnetic field
The magnetic field generated at the earth's surface depends on the distribution and magnetic
properties of the rocks beneath the surface.
Igneous & Metamorphic rocks exhibit significant magnetic field (because of magnetic minerals in magma +
molten material crystallization)
Sedimentary rocks exhibit weaker magnetic characteristics.
Magnetite: the only common Strongly magnetic mineral, is commonly found in igneous & metamorphic
rocks but quite rare in Sedimentary rock.
Instrument: (Geomagnetic Gradiometers.)
by low-flying airplanes.
Petroleum Exploration
Gravitational Method
Principle: In this method, variations in the gravitational acceleration of the earth (g) are measured.
Changes in earth's gravitational force reflect variation in the density of the subsurface rocks.
Instrument: (Gravitometers)
by low-flying planes & moving Survey ships
Electrical Method (Resistivity Survey)
Used for Simple Structure 1 km in depth.
Principle: Sending electrical current into the ground & measuring the potential drop due to the
resistance of subsurface layers.
Layers containing water shows much lower electrical resistively than layers containing oil &
water.
Petroleum Exploration
3.
Geochemical Method
Involve analyses of Air, Soil Samples and Surface & ground waters.
Soil Sample analysis: May indicate the presence of hydrocarbons beneath Surface.
Surface Water: may indicate oil Seeps escaping from underground trap.
Petroleum Exploration