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HYDROCARBON PETROLEUM SYSTEM.  This section is based on literature review as seismic data was not provided.  Help us to know how hydrocarbons are produced.

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Presentation on theme: "HYDROCARBON PETROLEUM SYSTEM.  This section is based on literature review as seismic data was not provided.  Help us to know how hydrocarbons are produced."— Presentation transcript:


2  This section is based on literature review as seismic data was not provided.  Help us to know how hydrocarbons are produced and migrated. SOURCE ROCK  Two main sources  Oil-Prone Draupne Formation  Gas Prone Heather Formation DRAUPNE FORMATION  Main Shale rock that forms the hydrocarbon source in this field  Physical Characteristics Include  Brownish Black  Medium of Dark Olive Grey  Non- Calcareous Mudstones  Thickness of Formation typically 50- 250 m but may exceed 1200m in localized area

3 HEATHER FORMATION  Physical Characteristic  Dark grey Silty Mudstones with thin Carbonate layers  Thickness formation ranges up to 1000 m  It is typically gas prone  Total organic carbon ( TOC ) values are typically between 2-2.5 % RESERVOIR ROCK TRIASSIC AND LOWER JURASSIC  Occurs in tilted fault blocks with varying degree of Jurassic Cretaceous erosion and onlap.  The main reservoir intervals comprise of thick, fluvial channel and sheetflood deposit.  Porosity range from 20-24%  Permeability 300-2000 mD

4 MIDDLE JURASSIC  Present in the Northen Sea are arkoses and subarkoses with quartz, clay minerals and Fledspars consisting about 95 % of the total miner  Sandstones are both quartz and calcite cemented at depths exceeding 2500 m.  Reservoir form a thick clastic wedge comprising laterally extensive interconnected fluvial  Deltaic and coastal depositional systems with porosities 20-30% and permeability 50 – 500 mD. UPPER JURASSIC  Its is rarer in the Gullfaks field.

5 TRAPS AND SEALS  Most trapping mechanism is provided by rotated faults sealed by fine grained post rift sediments.  These sediments draped on to the structures to form seals Lateral trapping and sealing is formed where reservoir rocks are juxtaposed with non reservoir rocks at fault contacts  Most seals are closed to hydraulic fracture. Migration  Primary migration in the North Sea is through pressure driven flow of a discrete hydrocarbon phase through pores and micro fractures  Secondary migration is mostly by buoyancy resulting from difference in density between the hydrocarbon and water

6  Sandstones of the Brent Group provide the main conduits of migration with the study area  Three main mechanisms of primary migration as follows: (i) migration enhanced intercalation of source and reservoir (ii) migration due to juxtaposition of reservoir and source rocks across faults (iii) vertical migration across  Micro fracture systems Classification into five modes as follows 1. Short distance migration 2. Migration in rotated fault blocks 3. Migration through faults and micro fractures 4. Up-flank migration from the graben 5. Unconformity and multiple conduit migration

7 Migration in Gullfaks

8 Depositional Environment and Facies Analysis

9  Middle Jurassic deposits of the reservoirs in Gullfaks field are represented by the deltaic sediments with deposition strongly controlled by regressive/transgressive cycles and occurred during the late phase of post-rift subsidence  The thickness distribution is consequently controlled by both the thermally driven subsidence and ongoing faulting of the Late Jurassic-Early Cretaceous episode of rifting.  Basically the Gullfaks field is subdivided into 4 major stratigraphic units as Cretaceous, Tarbert,Ness and Etive formations.  This petroleum system is a sequence of sandstones, siltstones, shales and coals with maximum thickness of 300 - 400 m.

10 Cretaceous  Cretaceous sediments were deposited unconformably on late Jurassic sediments of the North Sea.  This major unconformity between the Jurassic and Cretaceous is called the Base Cretaceous Unconformity (BCU).  the Lower Cretaceous deposits comprise shallow marine mudstones,calcareous shales and some sands.  Planktonic carbonate algae then mainly dominated sedimentation Tarbert  There is controversy exists regarding the boundary between Ness and Tarbert formation and depositional environment consequently.  Consequently from that point of view the Tarbert formation is interpreted as pure controlled by the marine environment. Lithology varies from shales, siltstones and coal beds to medium-to coarse- gained sands in which calcite cementation is found.

11 Ness  Ness and Etive formation is assigned by the first occurrence of a coal bed above the clean sands.  Additionally several coarsening-upward sequences of sandstone with good reservoir quality propose the crevasse splay, crevasse channels and overbank flooding.  The Upper Ness unit might be described as domination of siltstone/claystone and coal deposits with some lacustrine deposits.

12 Etive Etive formation according to recent studies was interpreted as a barrier bar complex. On the basis of low-angle large scale cross-stratification, grain size, heavy mineral concentration and parallel lamination a high energy beach environment. Formation consisting primarily of medium-to coarse-grained sandstones varies in thickness of 15 to 40 m.

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