Basics of Petroleum Geology Presented By: Shahnawaz Mustafa
The science of petroleum geology• Chemistry Geochemistry is a major component of petroleum geology • Detailed knowledge of the mineralogical composition of rocks – reservoir quality. • Pore-fluid chemistry Pore-• Physics Geophysics contributes to: • Understanding the structures involved in trapping: folds, faults • Understanding the wells: wireline logs, lithology, porosity
• Biology • Biochemistry: transformation of plant and animal tissues into kerogen and through to oil and gas. • Study of fossil life: Paleontology
Formation of an oil accumulationBurial of adequate organic source material. most petroleum is derived from the accumulation of trillions of individual micro-organisms. micro-Burial to the appropriate depths. depths of 2-6 km and temperatures of 60-160º C. 2- 60-Presence of a reservoir-quality rock. reservoir- a porous storage space. Sandstone and limestones are the most common reservoir rocks. To be a reservoir they must have: Porosity, Porosity, to hold the hydrocarbons Permeability, Permeability, to allow fluid flow
Presence of an adequate seal A seal is an impermeable bed (such as a shale or a bed of salt) that sits on top of the trap and prevents the hydrocarbons rising any further.Presence of a trap In order to prevent the hydrocarbons rising to the surface and escaping they must be caught in a confined space, termed a trap. i.e. the source, reservoir and seal must be arranged in such a way that the petroleum is trapped.
Organic MatterWhen an organism (plant or animal) dies, it isnormally oxidizedUnder exceptional conditions: organic matter is buriedand preserved in sedimentsThe composition of the organic matter strongly influences whether the organic matter can produce coal, oil or gas.
Basic components of organic matter in sediments• PROTEINS• CARBOHYDRATES• LIPIDS (Fats)• LIGNINAll of these + Time + Temperature + Pressure = KEROGEN
Types of Kerogen• Type I : algal kerogen – “best” oil source – Lipid-rich Lipid-• Type II: herbaceous II: kerogen – Good oil source – Includes zooplankton (sapropelic)• Type III: woody III: kerogen (coaly) – Good gas source
The Source Rock • A type of rock which contains organic matter and is capable to generate the hydrocarbons. • Best example of source rock is shale.
The Reservoir Rock • A reservoir rock is that kind of rock which can hold the hydrocarbons. • Most common examples of reservoir rocks are sandstone and Carbonates (limestone and dolomite).
The Reservoir Rock: Dolomite • This is an example of an important reservoir rock type. • Fossils have been hollowed out by the chemical conversion of limestone to dolomite, creating pore spaces so large that they are sometimes called “cavernous porosity” porosity”
The Seal• The seal or cap rock is an impermeable rock which don’t allow the hydrocarbons to escape from the reservoir rock.• Common examples of cap rocks are, chalks , shales, clays etc.
The Trap• A subsurface obstacle to flow of petroleum to the earth’s surface.• Classified (broadly) into Structural Traps Examples: folds and faults. Stratigraphic Traps Examples: pinch out and unconformity traps
Migration Processes• Primary Migration: involves the expulsion of petroleum from the source rocks to reservoir rock.• Secondary Migration: involves the movement of petroleum through permeable layers (carrier beds) to the trap. trap.
Reservoir Porosity and PermeabilityThere are two fundamental physical properties that a good reservoir must have: (1) porosity, or sufficient void space to contain significant petroleum. petroleum. (2) permeability, the ability of petroleum to flow through these voids. voids.