Petroleum Geology
The Context of Petroleum Geology
What is petroleum geology
• It is the application of geology (the study of rocks) to the exploration for and production of oil and gas.
• Geology itself is strongly based on chemistry, physics and biology, involving the application of essentially abstract concepts to data.
• In the past these data were basically observational and subjective.
• Petroleum geology, in particular still rely on value judgments based on experience and an assessment of validity among the data presented.
• Exploration had advanced over the years as various geological techniques were developed.
A History of Petroleum
Ancient: • Egypt: oil to preserve mummies• China: natural gas for fuel• Babylonia: oil to seal walls and pave streets• America: tar to seal canoes
First Drilling: • America: using cable tool: to 70’ in 1859
First Product: • Kerosene for lamps (Gasoline an unwanted by-product)
Demand: • Industrial Revolution- Internal Combustion Engine (1885)- Global Economic Growth
Natural Oil Spills
Anticlinal Theory
Gas Oil
Water
Petroleum Accumulates in Structural Closure
Drill here!
Exploration and Production : Seismic Surveys
•Seismic surveys are used to locate likely rock structures underground in which oil and gas might be found
• Shock waves are fired into the ground. These bounce off layers of rock and reveal any structural domes that might contain oil
We’ve just established what kind of structures tend to trap oil and gas in the Earth’s crust, but how do we locate potential traps underground? One technique is to use seismic surveys. In this technique, a Vibrator Truck fires shock waves into the ground. The shock waves pass through some rock layers and bounce off others. By recording how long it takes for the shock waves to arrive back at the surface allows geologist to build a picture of the internal structure of the rocks beneath their feet. An example of a seismic survey is shown in the diagram on the right. It reveals a large underground dome in the rocks. As we have seen domes often trap oil and gas so this may be a potential site to drill.
notes: The term seismic is derived from the Greek for “shake” (think earthquakes!)
Industry ‘Technological’ Milestones
1883: Anticlinal theory (where to drill)
1914: Seismograph invented (remote sensing)
2D Seismic LineGulf of Mexico (offshore)
Industry ‘Technological’ Milestones1883: Anticlinal theory (where to drill)
1914: Seismograph invented (remote sensing)
1920s: Introduction of rotary drilling (well control, environment)
Large Land Drilling RigRotary Drilling Rig Schematic
Industry ‘Technological’ Milestones
1883: Anticlinal theory (where to drill)
1914: Seismograph invented (remote sensing)
1920s: Introduction of rotary drilling (well control, environment) Start of waterflooding (improved recovery)
1924: First electrical well logging (formation evaluation)
Industry ‘Technological’ Milestones
1883: Anticlinal theory (where to drill)
1914: Seismograph invented (remote sensing)
1920s: Introduction of rotary drilling (well control, environment) Start of waterflooding (improved recovery)
1924: First electrical well logging (formation evaluation)
1930s: Offshore drilling (access to prospective areas)
Jack-Up Drilling Rig (Texas Federal Waters ~150’ water depth)
Industry ‘Technological’ Milestones
1883: Anticlinal theory (where to drill)
1914: Seismograph invented (remote sensing)
1920s: Introduction of rotary drilling (well control, environment) Start of waterflooding (improved recovery)
1924: First electrical well logging (formation evaluation)
1930s: Offshore drilling (access to prospective areas)
1960s: Digital computers (data manipulation)
1970s: Directional drilling
1980s: 3D seismic (enhanced imaging)
Relief Well Control
Petroleum System
A Petroleum System is defined as a natural system that encompasses a pod of active source rock and all related oil and gas and which includes all of the geologic elements and processes that are essential if a hydrocarbon accumulation is to exist.
(Leslie B. Magoon and Wallace G. Dow, AAPG Memoir 60)
DEFINITION
MR@Aug2008
• Source Rock - A rock with abundant hydrocarbon-prone organic matter
• Reservoir Rock - A rock in which oil and gas accumulates:- Porosity - space between rock grains in which oil
accumulates - Permeability - passage-ways between pores through which oil and gas moves
• Seal Rock - A rock through which oil and gas cannot move effectively (such as mudstone and claystone)
• Migration Route - Avenues in rock through which oil and gas moves from source rock to trap
• Trap - The structural and stratigraphic configuration that focuses oil and gas into an accumulation
Source: AAPG
PETROLEUM SYSTEM ELEMENTS - DEFINITION
MJH@Mac2007
The elements
Source rock layer
Source rock layer
Reservoir layer
Seal layer
Overburden
Overburden
Top of oil window
Top of gas window
Generation Expulsion Accumulation
GOC
OWC
Migration Preservation
The processes
Reservoir Heterogeneity in Sandstone
Heterogeneity MayResult From:
Depositional Features
Diagenetic Features
(Whole Core Photograph, MisoaSandstone, Venezuela)
Heterogeneity
Segments Reservoirs
Increases Tortuosity of Fluid Flow
Reservoir Heterogeneity in Sandstone
Heterogeneity Also MayResult From:
Faults
Fractures
Faults and Fractures maybe Open (Conduits) or Closed (Barriers) to Fluid Flow
(Whole Core Photograph, MisoaSandstone, Venezuela)
Questions?