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Formation and Discovery

  1. 1. SESSION 1: FORMATION & DISCOVERY
  2. 2. 2 2.15 km 7.4 km 500 km Session 1 – Formation and DiscoverySession 1 – Formation and Discovery
  3. 3. 3 Learning Objectives To appreciate: Where we find oil and gas deposits Characteristics of oil and gas reservoirs How we identify possible reservoirs How the size and productivity of a reservoir is estimated
  4. 4. 4 Oil and Gas Deposition Periods Tertiary: 2­65 million years ago Cretaceous: 65­136 million years ago Jurassic: 136­190 million years ago Triassic: 190­225 million years ago
  5. 5. 5 -163mil -135mil
  6. 6. 6 For Oil and Gas to be Recovered from the Earth There must have been an organic­rich source rock to generate the oil and/or gas AND the source rock must have been cooked enough (approx 120 degC) AND the hydrocarbons must have migrated to a reservoir rock formation AND the reservoir and seal must be arranged in such a way as to trap the hydrocarbon. AND an impermeable cap rock must seal the reservoir AND the reservoir must have porosity and permeability
  7. 7. 7 Porosity & Permeability A porous rock is one which is full of small pours or holes which contain the reservoir fluids A permeable rock is a porous rock in which the pours are interconnected, allowing the hydrocarbon to ‘migrate’ through the rock
  8. 8. 8 Traps We need to find the places in the Earth’s crust where hydrocarbons have not been able to rise to the surface and escape Trap requirements: Impermeable upper barrier Structure to prevent further upward movement of the hydrocarbons
  9. 9. 9 Two types of rock are necessary to form a hydrocarbon trap…… Reservoir rock ­ porous rock containing hydrocarbon fluid Sandstones (90% of reservoirs) Carbonates Cap rock ­ Non porous / Impermeable Seal Clay shales (90% or reservoirs) Evaporites e.g. salt crystals
  10. 10. 10 Three types of Trap Structural Trap - Reverse Fault Structural Trap - Anticline Stratigraphic Trap
  11. 11. 11 Reverse Fault Oil (black) in the permeable reservoir rock (green) is trapped by the upper and adjacent sealing rock (red and white) of zero permeability
  12. 12. 12 Anticline Impermeable Barrier
  13. 13. 13 Stratigraphic Trap - River Channel Sand Oil and gas are trapped in the permeable sands which were deposited in the impermeable river bed and covered by impermeable sediments
  14. 14. 14 Gas, oil and water is trapped and layered inside reservoir rock according to fluid density.
  15. 15. 15 Oil reservoirs are layers of sedimentary rocks which contain microscopic globules of oil and gas, and not underground lakes…………
  16. 16. 16 DISTRIBUTION OF PETROLEUM
  17. 17. 17 Permits and Legislation Governments allow companies to explore and produce oil and gas under strict conditions and in return receive all the information collected about the resources and a large share of the pre-tax profits. Permits are issued which regulate all activities associated with petroleum exploration and production in specifically defined areas, or ‘license blocks’. Oil companies then ‘bid’ for the license to explore and /or produce in these areas In the case of Bayu Undan, the license areas are 91-12 & 91-13 of the joint zone of co-operation (JDA) which is equally administered by Australian and East Timorese governments.
  18. 18. 18 Surveys Essentially, the task in oil and gas exploration is to locate sites where there are geological structures in which oil or gas might have been trapped, in order to minimise the risk of the high cost of drilling a ‘dry hole’. The two types of survey are: •Geological •Seismic
  19. 19. 19 Geological Surveys The first step for the survey team is to study all the available geological and geographical information about the area under investigation Aerial photographic surveys are often undertaken, especially in remote areas. Today, increasing use is made of satellite images taken from several hundred kilometres up in space which are able to show features only a few metres in size.
  20. 20. 20 N-S Trending Fault Separating Geological Regions e.g. Darling Fault Separates ‘the hills’ granites from the sandy Swan River Plain Present day drainage System Colour change Indicates Change in Vegetation/Rock Type Subsidiary Faulting Relating to Shear along Major N-S trending Fault
  21. 21. 21 Potential areas are then chosen for more detailed survey. •Geological study of formation •Analysis of rock samples and fossils for clues as to their origins and ages. Much more important these days, however, is the seismic survey……..
  22. 22. 22 Seismic Surveys In this type of survey, sound waves are sent into the earth where they become reflected by the different rock layers present. Seismic surveys can be carried out without disturbing people or damaging the environment and indicate what kinds of rock lie beneath the surface, and their depth.
  23. 23. 23 Before any drilling, a seismic survey is the only way to gather detailed information from areas lying below water. The survey is conducted using purpose built ships towing a number of air operated devices at depth of 6 - 10 metres. These generate sound waves by releasing large bubbles of compressed air below the water surface and are directed at the ocean bed. Offshore Seismic
  24. 24. 24 Seismic Results The most sophisticated seismic surveys are three-dimensional, in which the recorded data is processed in advanced computers to give a very accurate, 3-D picture of the formations and structures below the survey area.
  25. 25. 25 N
  26. 26. 26 The next step is to interpret the data to identify possible reservoir locations The process is very expensive, @ AU$15,000 per square kilometre, but time and money spent on accurate surveys are good investments, since they help to locate the wells correctly and minimise the risk of dry holes. The only sure way to test for oil and gas is to drill an exploration well into the formation……….
  27. 27. 27
  28. 28. 28 Purpose of Drilling Exploration (Wildcat Well) To determine the contents of the underlying rock structure Appraisal To determine the physical extent, reserves and likely production rate of the field Development To provide a conduit for extracting oil and gas from a reservoir
  29. 29. 29 Data Required Even if the well does not encounter hydrocarbons important information can be gained from the well which can aid further exploration: Permeability Porosity Lithology ( Types of rock layers in Formation) Water Saturation Downhole Seismic Survey
  30. 30. 30 Cuttings Analysis Sample cuttings are routinely taken (recorded against depth) from the mud returns and analysed for: • Formation lithology • Rock dating ( by examining fossils etc) • Hydrocarbon presence
  31. 31. 31 Cuttings Analysis The well site geologist utilises a fluoroscope which uses ultra violet light to check cuttings for signs of hydrocarbons which will glow brightly
  32. 32. 32 Core Analysis A cylindrical rod of the well bore or reservoir rock is cut and brought to the surface either by: Using a hollow diamond drill bit to retrieve a 9m to 50 m section of 50mm diameter core Using a logging tool with a rotary sidewall coring attachment to retrieve a 75mm long 25mm diameter slug Sidewall coring gun to fire catchers into formation 10mm diameter by 20mm long
  33. 33. 33 Well Logging By utilising acoustic, electrical, radioactive and electromagnetic logging tools in the well bore it is possible to: Determine lithology Determine important reservoir parameters • Porosity • Permeability • Reservoir depth (hydrocarbon column) Determine the reservoir fluid composition
  34. 34. 34 Well Testing Purpose - to determine the productivity of the well and reservoir size by flowing the well through a fixed choke for a period of time and monitoring flowrate and pressure decay. Fluids sampling and analysis – downhole and surface samples of the reservoir fluids are taken to the lab for chemical, thermodynamic and physical property analysis.
  35. 35. 35 Well Testing Pressure buildup test Produce well for around 12 hours at a high flow rate Measure • Stabilised flow rate • Total production Shut well in and measure wellbore pressure increase for an equal period Can repeat at an increased flow rate for establishing maximum flow rate
  36. 36. 36 Summary In this session we have covered: Where we find oil and gas deposits Characteristics of oil and gas reservoirs How we identify possible reservoirs How the size and productivity of a reservoir is estimated.

Editor's Notes

  • WHERE IS THE OIL? (BRING ALONG SOME CORE PLUGS TO HAND OUT)
    IT EXISTS IN THE MICORSCOPIC PORE SPACES IN BETWEEN THE SAND GRAINS
    THIS PICTURE REPRESENTS A MICROSCOPIC CROSS SECTION OF A CORE - POINT OUT SAND GRAINS AND PORE SPACE
    PORE SPACE IS SHARED WITH HYDROCARBON & WATER
    GEOLOGISTS DESCRIBE THIS BUT THE ENGINEERS NEED TO KNOW WHAT THE FLOW PROPERTIES ARE AND HOW EFFECIVELY WE CAN RECOVER OIL OR GAS FROM THESE SMALL SPACES
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