Basin & Petroleum Systems Modeling Definitions Source / Reservoir / Trap / Seal Timing! Migration Petroleum Systems Model

Basin & Petroleum Systems Modeling Petroleum System – Definitions What is a 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 which includes all of the geologic elements and processes that are essential if a hydrocarbon accumulation is to exist.“ Magoon and Dow, 1994

Basin & Petroleum Systems Modeling Petroleum System – Definitions Petroleum A mineral oil occurring in subsurface rocks and at the surface which is a naturally occurring mixture of hydrocarbon and non-hydrocarbon compounds. It may occur in the gaseous, liquid, or solid state depending on the nature of these compounds and the existent conditions of temperature and pressure. Common synonyms are hydrocarbons and oil and gas. System A regularly interacting or interdependent group of items forming a unified whole whose organization forms a network for distributing something, for example; telephone, highway, blood, or petroleum. (after Magoon and Dow, 1994)

Basin & Petroleum Systems Modeling Petroleum System – Definitions Geographic Extent The area over which the petroleum system occurs, defined by a line that circumscribes the pod of active source rock as well as all the discovered petroleum shows, seeps, and accumulations that originated from that pod. The geographic extent is mapped at the critical moment. Also the known extent. Burial History Chart A burial history curve or geohistory diagram constructed to show the time over which hydrocarbon generation occurs. Depicts the essential elements and the critical moment for the petroleum system. Events Chart A chart for a petroleum system showing when the essential elements and processes took place as well as the preservation time and critical moment of the system. (after Magoon and Dow, 1994)

Basin & Petroleum Systems Modeling Petroleum System – Definitions Geograpic Extent (from Magoon and Dow, 1994) A-A’ Cross Section Pod of Active Source Rock Reservoirs Deer Boar Petroleum System @ 250 Ma -> Critical Moment: generation started traps exist migration possible

Basin & Petroleum Systems Modeling Petroleum System – Definitions Burial Chart Combined with Events Chart Events Chart Deer Boar Petroleum System @ 250 Ma -> Critical Moment: generation started traps exist migration possible (from Magoon and Dow, 1994)

Basin & Petroleum Systems Modeling Petroleum System – Source / Reservoir / Trap / Seal Source Rock A rock unit containing sufficient organic matter of suitable chemical composition to biogenically or thermally generate and expel petroleum. Pod of Active Source Rock A contiguous volume of source rock that is generating and expelling petroleum at the critical moment and is the provenance for a series of genetically related petroleum shows, seeps, and accumulations in a petroleum system. A pod of mature source rock may be active, inactive or spent. Reservoir Rock A subsurface volume of rock that has sufficient porosity and permeability to permit the migration and accumulation of petroleum under adequate trap conditions. (after Magoon and Dow, 1994)

Basin & Petroleum Systems Modeling Petroleum System – Source / Reservoir / Trap / Seal Seal A shale or other impervious rock that acts as a barrier to the passage of petroleum migrating in the sub-surface; it overlies the reservoir rock to form a trap or conduit. Also known as roof rock and cap rock. Overburden Rock The sedimentary rock above which compresses and consolidates the material below. In a petroleum system the overburden rock overlies the source rock and contributes to its thermal maturation because of higher temperatures at greater depths. (after Magoon and Dow, 1994)

Basin & Petroleum Systems Modeling Petroleum System – Exercise PARIS BASIN – Petroleum System Analysis Follow the below listed instructions to analyze the Paris Basin petroleum system Draw a line (map) around the pod of active source rock (green-colored pencil). Draw a line (map) around the geographic extent of the petroleum system (red-colored pencil). Draw a line (map) of cross-section on the map (brown-colored pencil) that would best show the relation of the pod of active source rock to the petroleum migration paths and accumulations. Draw an asterisk on the map (brown-colored pencil) where a burial history chart would best show the onset and end of petroleum generation and the critical moment. Draw a few arrows (green-colored pencil) to indicate the directions of oil and gas migration.

Basin & Petroleum Systems Modeling Petroleum System – Exercise Use the following symbols to analyze the Paris Basin Petroleum System Pod of active source rock Geographic extent Cross section location Burial history chart location Petroleum migration

Basin & Petroleum Systems Modeling Petroleum System – Exercise Paris Basin, from Tissot & Welte, 1978

Basin & Petroleum Systems Modeling Petroleum System – Exercise Paris Basin, from Tissot & Welte, 1978

Basin & Petroleum Systems Modeling Petroleum System – Timing! Critical Moment The time that best depicts the generation – migration – accumulation of hydrocarbons in a petroleum system. A map and a cross section drawn at the critical moment best shows the geographic and stratigraphic extent of the System. The four elements Source Rock, Reservoir Rock, Seal Rock and a sufficient Amount of Overburden have to be in place before the Critical Moment. Petroleum System Age The time over which the process of generation-migration accumulation of hydrocarbons in the system takes place on the events chart. Preservation Time The time after generation-migration-accumulation of petroleum takes place and encompasses any changes to the petroleum accumulations up to present day. (after Magoon and Dow, 1994)

Basin & Petroleum Systems Modeling Petroleum System – Petroleum System Elements 2 Processes are essential for a working Petroleum System Generation – Migration – Accumulation (driven by temperature) Trap Formation! (structural evolution or stratigraphic framework)

Basin & Petroleum Systems Modeling Petroleum System – Migration (Expulsion) from TISSOT & WELTE (1984)

Basin & Petroleum Systems Modeling Petroleum System – Migration Migration is the process, whereby hydrocarbons move from source rocks to traps. Migration is divided into four categories: Primary migration – The process of loss of hydrocarbons from the source rock (also Expulsion). Secondary migration – Migration from source to reservoir rock in trap configuration along a carrier system. Including the migration within the reservoir rock itself. Tertiary migration – Migration to the surface, either from the reservoir or source rock (dismigration). Re-migration – Migration from one reservoir system position through an intervening section into another reservoir position (trap) in the same or a different reservoir.

Basin & Petroleum Systems Modeling Petroleum System – Migration Why do hydrocarbons migrate? Fluids migrate along a pressure gradient  pressure driven Density contrasts between hydrocarbons and water buoyancy driven Diffusion due to concentration differences  chemical gradient driven from Hantschel & Kauerauf (2009) buoyancy driven How do hydrocarbons migrate? Hydrocarbons migrate as a separate phase from the higher potential to a lower potential on the direct way  topography driven Topography driven Generated HC Masses from Source Overpressure Buoyancy Capillary Pressure

Basin & Petroleum Systems Modeling Petroleum System – Migration Petroleum Migration Rates Migration Mechanism Migration Rate Hydrodynamic (pressure driven) 10-3 to 1000 m/a Compaction (drainage!) 10-5 to 1 m/a Buoyancy Meters per day (gas) Diffusion 1 to 10 m / Ma Diffusion Buoyancy GAS Compactionally driven flow ? ? Hydrodynamic 10-7 10-6 10-5 10-4 10-3 10-2 0.1 1 10 102 103 104 Fluid velocity [m/a]

Basin & Petroleum Systems Modeling Petroleum System – Migration Petroleum Migration Rates for a distance of 500m and a pressure gradient of 5MPa/km ( Darcy Law ) 0.01 0.1 1.0 10.0 100.0 1000.0 gas oil Viscosity [mPa s] Permeability [mD] 104 103 102 101 10-1 10-2 10-3 10-4 10-5 100 1 day 1000 years Silt @ 20% porosity 1 year Sand

Basin & Petroleum Systems Modeling Petroleum System – Migration The following main driving mechanisms can be distinguished Pressure Gradient Driven Sediment Compaction  - overpressure (grad u), compaction driven fluid movement, permeability Capillary imbibition  - capillary pressure differences between fine and coarse grained layers (leads to downward expulsion) - capillary fluid flow depends on fluid components involved, relative permeability Buoyancy Driven Fluid composition  density contrast between hydrocarbons and water Temperature  Temperature increase leads to increasing buoyancy - primary effect - the density contrast between water an HC’s increase - secondary effect - cracking to lighter HC’s Pressure  Pressure increase leads to decreasing buoyancy - primary effect - the density contrast between water an HC’s decrease - secondary effect - dissolving of lighter HC’s into the liquid phase Chemical potential  concentration differences (diffusion)

Basin & Petroleum Systems Modeling Petroleum System – Migration Sediment Compaction Pressure : Lithostatic Pressure (MPa) normal / hydrostatic pressure : Hydrostatic Pressure (MPa) : Effective Overburden Pressure (MPa) : Excess Pore Pressure (MPa) Fluidflow Overpressure Zone of Compaction overpressure Burial Depth Hydrostatic Pressure Pore Pressure Lithostatic Pressure

Basin & Petroleum Systems Modeling Petroleum System – Migration Sediment Compaction A pressure gradient dependent fluid flow can be quantified by the Darcy Law : volumetric flow [m3 / s] : permebility [ m2 ] : darcy velocity (discharge velocity) [m / s] : flow specific surface [m2] : pressure gradient [Pa / m] Q v η dp/dx : dynamic viscosity [ Pa s ] k A

Basin & Petroleum Systems Modeling Petroleum System – Migration Sediment Compaction f f Porosity-Depth Function Porosity-Effective Stress Function z s Permeabilities

Basin & Petroleum Systems Modeling Petroleum System – Migration Capillary Imbibition When a drop of one immiscible fluid is immersed in another and comes to rest on a solid surface. The shape of the resulting interface is governed by the balance of adhesive and cohesive forces. Example: Water Oil q SOLID SURFACE The surface area at the fluid-fluid contact is minimized by the interaction of these forces: cohesive forces at the fluid-fluid interface adhesive forces at the solid-fluid interface

Basin & Petroleum Systems Modeling Petroleum System – Migration Capillary pressure is the difference in pressure across the interface between two immiscible fluids, and thus defined as: Pc = Pnw - Pw Pw = wetting phase Pnw non-wetting phase In oil-water systems, water is typically the wetting phase, while for gas-oil systems, oil is typically the wetting phase.   When adhesion > cohesion, adhesive forces draw the fluid up the tube until they are balanced by the weight of the fluid column. When cohesion > adhesion, cohesive forces drag fluid down the tube until they are balanced by the weight of the head difference forcing fluid upwards.

Basin & Petroleum Systems Modeling Petroleum System – Migration Capillary Imbibition

Basin & Petroleum Systems Modeling Petroleum System – Migration drainage imbibition Oil phase As HC migrate into a water-wet rock - They first enter the pores with the largest pore throats (capillaries) leaving the wetting phase in the pores with the smaller throats (insufficient pressure). - Can also leave the wetting phase in irregular nooks and crannies. - As the hydrocarbon column rises, Pc rises (buoyancy) and forces hydrocarbons into pores with smaller and smaller throats

Basin & Petroleum Systems Modeling Petroleum System – Migration Sediment Compaction The petroleum potential up : Petroleum Potntial uw : Excess Pore Pressure (Overpressure) ρw : Water Density ρp : Petroleum Density g : acceleration due to gravity h : column height Pc : Capillary Pressure

Basin & Petroleum Systems Modeling Petroleum System – Exercise 5000m 4500m 3000m 4000m 3500m 2500m 2000m B A C A’ 1500 2000 2500 3000 3500 4000 4500 5000 A A’ Hydrocarbons migrate as a separate phase from the higher potential to a lower potential on the direct way, usually from the deepest to the shallowest part of the basin, depending on the drainage area. Identify the drainage area for trap A, B & C Draw the hydrocarbon flow lines towards each trap A

Basin & Petroleum Systems Modeling Petroleum System – Migration - Exercise 5000m 4500m 3000m 4000m 3500m 2500m 2000m B A C

Basin & Petroleum Systems Modeling Petroleum System – Migration - Solution B A C

Basin & Petroleum Systems Modeling Petroleum System – Migration There are a variety of modelling methods in computerized Basin Modelling, out of which three basic concepts can be indentified: Darcy Flow – Based on equations of flow through porous media Flow Path – Geometrical surface analysis (buoyancy driven migration) Invasion Percolation – Flow controlled by capillary forces only A combination of methods – A combination of different methods needs the introduction of threshold values to enable the program to decide when a specific method is used, advantages of each method can be combined in a time effective and accurate simulation of the migration and accumulation processes

Basin & Petroleum Systems Modeling Petroleum System – Migration Darcy Flowpath Percolation 3D Modeling Requirements: Dynamics ++ - Scaling + Processing speed -- + - Data availability Petroleum Systems Components: Source and expulsion + - Migration – low perm. units -- Migration – high perm. carriers ++ Reservoir bodies

Basin & Petroleum Systems Modeling „A Petroleum Systems Model is a digital data model of an entire petroleum system in which the interrelated processes and their results can be simulated in order to understand and predict them.“ „The model is dynamic and provides a complete record through geologic time.“ from Magoon and Dow, 1994

Basin & Petroleum Systems Modeling Key Questions and Tasks of Petroleum Systems Modeling Petroleum Generation Have hydrocarbons been generated? Resource assessment studies and initial charge risking. There are basins in which no oil and gas have been generated! Where were hydrocarbons generated? If hydrocarbons were generated, we can define their locations quite accurately. When were hydrocarbons generated? There are many clear examples of where basins/plays/prospects have failed due to timing problems. For example, when oil and gas was generated early and the structures were created much later: Petroleum Migration & Accumulation Could they have migrated to the prospect? Modeling of the dynamic process of generation, expulsion and migration makes it possible to determine if the oil and gas charge could reach the trap. What are the properties of the hydrocarbons? Modeling of the phase behaviour of the hydrocarbons during migration, accumulation and loss makes it possible to determine oil vs. gas probabilities and even predict properties such as API gravities and GORs.

Basin & Petroleum Systems Modeling Trap Risk for example: - Prospect geometry - Reservoir quality (por/perm) - Seal quality seal carrier/ reservoir Definition: Charge is the volume of hydrocarbons available for entrapment Charge Risk for example: - Source rock quality Source rock maturity Generated petroleum Timing and Migration Risk! - relates the charge to the trap ... migration! - takes dependencies and processes into account! - takes dynamics into account! carrier source This is what Petroleum Systems Modeling technology does!