Basin Analysis & Petroleum System QAB3033 Assoc. Prof. Dr. Swapan Kumar Bhattacharya Geoscience & Petroleum Engineering Department PAB 1023 Petroleum Geoscience

Fundamentals of Petroleum Geology Prospect & Play Analysis Petroleum System This Week Fundamentals of Petroleum Geology Source Rock Generation Elements Reservoir Rock Processes Migration Seal Rock Accumulation Overburden Rock Prospect & Play Analysis

Prospect & Play Prospect - a lead which has been fully evaluated and is ready to drill. Play - A particular combination of reservoir, seal, source and trap associated with proven hydrocarbon accumulations.

Source Rock Source Rock is defined as the rock having efficient hydrocarbon generation and expulsion capacities. Characteristically, these are fine grained sedimentary rocks with high total organic carbon (TOC), high molar H/C ratio. Their thermal maturity (Vro) need to be sufficient so that at least they cross oil or gas Window for specific oil or gas generation.

Reservoir Rock Reservoir Rock is defined as the rock having appreciable porosity to trap the hydrocarbons and sufficient permeability for the oil to flow during migration and production. Characteristically, these are coarse grained clastic sedimentary rocks or porous limestones or fractured igneous or metamorphic rocks.

Hydrocarbon Traps Hydrocarbon Traps are: Structural: If trapping is exclusively due to structural style, or Stratigraphic: If trapping is exclusively due to stratigraphic disposition, or Combination: If trapping is due to both structure & stratigraphic disposition. Structural Traps: Folds, Faults Stratigraphic Traps: Lenticular Sands, Channel fills Combination Traps: Up-dip pinchouts

PAB 1023 Petroleum Geoscience Structural Traps Structural traps are those where entrapment of hydrocarbon takes place due to structural configuration only. Structural traps form usually by tectonic forces. An anticline is where rocks are folded or bent upwards. Hydrocarbons migrate up the flanks of the anticline and are trapped in the crest. Faults occur where there is movement along a joint or fracture. Offset of the beds could result in an impermeable layer being on top of a permeable layer. PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Structural Traps : PAB 1023 Petroleum Geoscience

Structural Traps Terminology PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Six trapping and two non-trapping configurations against a fault, depending on whether the fault is normal or reverse, on the direction of dip of the beds relative to the fault plane, and on the amount of displacement of the reservoir. PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Sealing Faults An investigation into the sealing qualities of faults affecting roll-over anticlines in the Niger Delta, where the reservoirs overlie overpressured shales (bulging). Where a reservoir is full to spill-point against a fault, and where an oil-water contact is continuous across a fault, it is presumed that the fault is non-sealing; elsewhere it appears to form a trap. The difference is believed to be due to clay being smeared into the fault plane, where there is enough of it in the section, as the fault moved PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Sealing Faults PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Stratigraphic Traps Stratigraphic traps are those where entrapment of hydrocarbon takes place due to stratigraphic disposition only. Rock layers changing from a good reservoir to non-reservoir due to change in rock type (pinch-out), reservoir quality (diagenesis), or removal (erosional unconformity) PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Pinch Out Sometimes due to a lateral change in the environment of deposition a lens of permeable sand is surrounded by less permeable siltstones and shales, forming a pinch out trap. This commonly happens in stream environments where sand is deposited along the stream channel which is surrounded by a flood plain characterized by finer grained sediments. PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Channel Trap PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Unconformity Unconformities are another type of stratigraphic trap. They represent a gap in the geologic record, in other words a period of erosion and/or nondeposition. They can result in a permeable reservoir rock being truncated and overlain by an impermeable unit. PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Hydrodynamic trap Oil, attempting to escape to surface up a reservoir, is held against an unevenness of its upper surface by water flowing in the opposite direction. There is no structural or stratigraphic closure. Note that the oil-water contact is tilted down in the direction of water flow. PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Diapiric Traps Caused by upward movement of sediments that are less dense than those overlying them Salt Clay PAB 1023 Petroleum Geoscience

Salt Dome Associated Traps PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience Seal A seal is a fine-grained rock that prevents the oil migrating to the surface @ vertical migration (which happens in many parts of the world - leading to natural oil seeps). The seal is an important component in a prospect. PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience SEAL Common seals include salt evaporites, chalks provides an effective seal, but Muddy @ clay-rich rocks @ mudrock, shale represent most seals. Siltstones (very fine-grained) PAB 1023 Petroleum Geoscience

PAB 1023 Petroleum Geoscience HOW WE QUANTIFY SEAL? Analysis of seals involves assessment of their thickness and extent, such that their effectiveness can be quantified. Knowledge of sequence stratigraphy is crucial for better understanding of seal. PAB 1023 Petroleum Geoscience

Petroleum System A petroleum system includes all those geological elements & processes that are essential for an oil deposit to exist in nature. (Magoon, 1988) These basic elements are: Petroleum Source rocks Reservoir Rocks Seals Migration Paths Traps And the geological processes that created each of them Source Rock Migration Route Reservoir Rock Seal Rock Trap Generation Migration Accumulation Preservation

Petroleum System Processes Accumulation Source Rock

e.g La Luna – Misoa (!) Marcaibo Basin, Venezuela. Petroleum System The term petroleum includes high concentrations of either thermal or biogenic gas, condensates, crude oils, natural waxes, or asphalts found in both conventional & in tight reservoirs, fractured shales, gas hydrates, coal beds and bituminous sandstones. The name of a petroleum system is a combination of the source & reservoir rock names followed by a symbol indicating the level of certainty of the source – reservoir association. The symbols are: Known (!) Hypothetical (.) Speculative (?) e.g La Luna – Misoa (!) Marcaibo Basin, Venezuela.

Petroleum System Petroleum system is best described by: Table listing all the field names, year of discovery, name of producing unit, depth, reservoir seal lithology, trap type, cumulative production & reserves. A map showing the geographic extent of the system, matured source pod , location of fields & key wells etc. A burial history chart at one or more locations. A geologic cross-section drawn at the critical moment illustrating the spatial relationship of the essential elements. An event chart indicating the time intervals of the essential elements & processes including preservation time & critical moment.

Petroleum System

GEOGRAPHIC EXTENT OF PETROLEUM SYSTEM Present-Day Petroleum System GEOGRAPHIC EXTENT OF PETROLEUM SYSTEM Present-Day A Trap A’ STRATIGRAPHIC EXTENT OF PETROLEUM SYSTEM Basement Overburden Seal Petroleum accumulation Reservoir Top of oil window Source Bottom of oil window Underburden Magoon and Dow, 1994

Petroleum System

Petroleum System

Petroleum System

Petroleum System Formulae to calculate hydrocarbon generation M (g.TOC) = V (cm3) x p (g/cm3) x [TOC(wt%) /100] R (mg HC/g TOC) = HI0(mg HC/g TOC) – HIp (mg HC/g TOC) HCG (kg HC) = R xM x 10-6 Oil (bbl) = HCG / 131.15 (kg/bbl of 400 API oil)

Total Petroleum System Reasons for carrying out oil and gas related investigations in a geologic province are : To decide where to explore and / or To assess undiscovered commercial quantities of petroleum Both can be assessed by ‘Petroleum System’ In USGS World Petroleum Assessment, 2000 the term ‘Total Petroleum System’ was introduced to evaluate undiscovered oil and Gas resources that have the potential to be added within the next 30 years To reserves in the world.

Total Petroleum System The ‘Total Petroleum System is evaluated by dividing the world into eight (8) regions and 937 geological provinces. Maps were prepared for each region using GIS and each region and province is named and numbered. Each province is characteristically hundred or even thousand square kilometers encompassing a natural geological entity – a basin, a thrust belt, a delta or some combination of geological entity. These provinces are then ranked by known volume of petroleum in barrels.

Total Petroleum System The goal of ‘TPS’ investigation is to understand the geographic, stratigraphic and temporal evolution of the system so that the resource assessment can be based on sound geologic and geochemical concepts. ‘TPS’ ideally includes : Genetically related known oil and gas accumulations, shows and seeps The pod or pods of active source rocks Minimum geographic extent Maximum geographic extent. The location of the TPS cross-section and The location of the locality depicted in the burial history chart.

Total Petroleum System 1. Discovered accumulations, shows and seeps: Within a given TPS, the genetically related discovered oil and gas fields or petroleum accumulations originated from same pod of active source rock. The investigator starts with a map that shows the discovered oil and gas fields. The investigator then groups the oil and gas fields into one or more possible TPS based on their geographic and stratigraphic locations and the bulk and geochemical properties of the fluids in each accumulation. 2. Pod of active source rock: The pod of active source rock is a contiguous volume of source rock that generated and expelled petroleum at the critical moment and is the provenance for a group of genetically petroleum shows, seeps and accumulations in a TPS. A pod of active source rock may be active, inactive or spent.

Total Petroleum System 3. Minimum geographic extent: The minimum geographic extent of the TPS is a line that circumscribes the pod of active source rock and includes all the discovered Petroleum shows, seeps and accumulations that generated from this pod. This is the same line of the geographic extent of the petroleum system. 4. Maximum geographic extent: The maximum geographic extent of the TPS is line that lies beyond or coincides with minimum geographic extent. The maximum geographic extent is mapped using geological evidence, such as the geographic extent of the reservoir rock, the indicates the possibility that oil and gas migrated beyond the minimum geographic extent but no seeps, shows or accumulations are known.

Total Petroleum System

Total Petroleum System

Source Material Non-Biogenic Origins Biogenic (Kerogen Types) Type I – Algal (oil prone) sapropelic Type II – Mixed Type III – Woody (gas prone) humic Host rock (Shales and Coals)

1 2 15 10 8 9 2 7 11 12 6 3 13 4 14 5

TOC Vro Well 5.2 0.56 80 5.1 0.60 140 5.0 0.60 130 5.2 0.55 150 5.2 0.58 115 6.4 0.45 150 4.8 0.78 120 3.9 0.65 110 3.0 0.50 80 2.0 0.43 30 0.3 0.42 50 0.6 0.45 25 0.8 0.5 60 0.3 0.4 65 0.25 0.35 20 Thickness These data are available with data package. Other data you have to purchase @ USD1000 You are asked to evaluate and bid for the exploration.

Kerogen Types Type 1 Type 2 Type 3