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A rock capable of containing and producing hydrocarbon.
A rock capable of retaining a column (thickness) of hydrocarbon.
The formation thickness of reservoir rock within the hydrocarbon column that can be produced economically.
Reservoir DOES NOT need to contain...
hydrocarbons it just needs to be capable of containing them.
List the requirements for a petroleum accumulation.
- Source rock and maturation
- Migration path and timing
- Reservoir rock
- Seal rock
- All factors MUST be present!
List the requirements for a CO2 storage system.
All factors must be present for a viable storage site.
- Injection depth
- Migration path and potential leakage path
- Reservoir rock
- Seal rock
What is exploration?
The use of scientific principles to locate areas in which the probability of 'THE BIG 5' occurring is greater than the company's risk threshold.
What is hard data?
- Things that you can physically touch, hold and manipulate.
- Core - conventional and sidewall
Where can hard data be obtained?
- Core - conventional and sidewall
What is soft data?
- Indirect data.
- Seismic, gravity , magnetics, well logs and anologues
Difference in seal and reservoir rock geology..
- Seal - fine grained (mudstones and shales)
- Reservoir - coarse grain (sandstone)
Explain the seismic process.
- Source - sound/vibration
- Sound waves penetrate through the subsurface
- Receiver records the travel time
- From travel time and depth density and hence rock type can be determined
What can seismic data tell us?
- Stratigraphic traps (deposition ordering)
- Structural traps (faults and folds)
- Potential reservoir rocks
- Potential seal rocks
Why do we drill wells?
- Produce/inject fluids
- Collect samples
- Get quality log data
- Get PVT data
Why is drilling mud important?
- Circulate and lubricate
- Circulation - removes cuttings and maintains temperature
- Borehole stability - prevents collapse
- Stops fluid entering
What information can we get from core?
- Microscopic k and θ
- Bedding thickness
- Grain size
- Rock type
What is stratigraphy?
Order of deposition - the way strata has been laid and the associated time
List the types of wireline well logging
Describe the types of wireline well logging.
- Gamma - measures radioactivity and therefore shale presence can be determined
- Sonic - emits a sound wave and measures trave time to determine density
- Neutron - bombards rock with neutrons to get porosity
- Density - bombards rock with radiation, records gamma ray count and density is calculated
List the stages of the E & P process
- 1. Permit evaluation/bid
- 2. Exploration
- 3. Discovery and initial appraisal
- 4. Full appraisal
- 5. Primary development
- 6. Enhanced recovery
- 7. Abandonment
An area in which hydrocarbon accumulations or prospects of a given type occur.
Trend along which a particular geological feature is likely.
- Actual mapable area of the play.
- If you can map it, it is a prospect
What is a waste zone?
An area which contains hydrocarbons that cannot be produced.
What is a free water level?
Exists where capillary pressure is zero. This implies there is a flat interface between the fluids.
There can only be one per reservoir.
What are the two cohesive forces?
- Surface tension (1 liquid)
- Interfacial tension (2 liquids)
What is miscibility?
Miscibility is controlled by interfacial tension. It is the ability of two liquids when mixed to form a homogeneous solution.
- Miscible - low IFT
- Immiscible - High IFT
What phase exists when the adhesive forces are greater than the cohesive?
Wetting phase θ<90
- Non-wetting phase:
- cohesive forces > adhesive
Write the capillary pressure equation.
- nw - non-wetting phase
- w - wetting phase
- pore radius
If two immiscible fluids are in a tube...
- Meniscus separates the the two.
- The non-wetting phase is on top and the wetting phase at the bottom.
Non-wetting phase has greater pressure
What is the drainage case?
- Non-wetting phase displaces the wetting phase.
- i.e. hydrocarbon migrating into a previously brine saturated rock
What is imbibition?
- The opposite to drainage.
- The wetting phase displaces the non-wetting phase.
What is the difference between drainage and imbibition?
- They are opposites.
- Drainage refers to the non-wetting phase displacing the wetting phase.
Imbibition is when the wetting phase displaces the non-wetting phase.
Narrow test tube versus wide test tube. Explain the difference in terms of capillary pressure.
- Two immiscible fluids present implies a meniscus separates them.
- Wetting fluid at the bottom non-wetting on top.
- Narrow test tube - higher capillary pressure therefore meniscus is higher. Greater adhesive force.
- Wide test tube - lower capillary pressure required to force wetting phase out. Therefore lower height achieved. Lower adhesive forces
A trap will continue to fill until...
- Generation and migration stops
- Spill point is reached
- Seal failure
Define the transition zone (TZ).
Distance between the min and max Sw (water saturation)
What is the seal capacity equation?
What is a good seal?
- One that will retain an economic volume of hydrocarbon
- A good seal will have
- High ductility
- High compressibility
- Low srength
- Low velocity
What is a poor seal?
One that retains anything less than an economic volume of hydrocarbon
What is seal potential dependent upon?
- Seal Capacity - Hmax (max column thickness)
- Seal Geometry - thickness and areal extent
Seal Integrity - mechanical properties, ductility
What is a fault plane?
A flat (planar surface) along which there is a slip
What is a fault?
A compression fracture which causes slippage
- Fractures can be compressional or tensional
- Fault is compression
- Gap is tension
What is FZDP? What are they?
- Fault zone deformation process.
- Grey Cats Die Shamefully
- Grain sliding
Shale gouge/clay smear
Explain grain sliding.
- Grain slippage along a fault plane
- due to minor fault movement or high pore pressure
- Grain breakage and crushing
- Causes fine grained gouge along faul
Preferential cementation along permeable fault plane
- The process of changing a sediment into a sedimentory rock via chemical and physical processes
- i.e. changing a sand into a sandstone
Explain shale gouge/clay smear.
- High shale/sand ration.
- Sand grinds up the shale.
- Result clay incorporated into the fault plane
- gladwrap --> higher capillary pressure required
Rank the FZSP in order of seal potential.
- Shale gouge/clay smear (smallest pore throat radius)CementationCataclasis
- Grain sliding (greatest pore throat radius)
What is a stereonet?
A visual representation of geological structures with respect to true north.
What is a cap rock seal?
A layer of rock with seal potential laying over the reservoir rock.
What is caprock seal potential a function of?
What is a fault seal controlled by?
- Risk of reactivation
- Juxtaposition relationships
- Fault zone properties
What is pore geometry dependent on?
What controls pore geometry?
Diagenesis and depositional process
What does pore geometry control?
Of reservoir fluids produced of fluids injected
What is the difference between absolute and effective porosity.
- Think of locked room there is space but it is NOT effective.
- Absolute porosity is the total porosity - pore space to bulk volume (%)
porosity - interconnected pore space to bulk volume
- A measure of a rock's ability to allow fluid flow.
- Measure of fluid connectivity
List the three pore types.
Macro - inter and intraparticle
Micro - inter and intraparticle
Secondary - moldic and fracture
Equation for effective permeability.
ke= ka x kr
What should be noted when dealing with microporosity?
Even if you have a high water saturation it does not mean that you will produce water.
Microporosity --> VERY low permeabilities
Briefly summarise what occurred in the Lisburne Field, Alaska.
- There was a microporosity issue.
- Production increased rapidly then plateaued and dropped right off.
- Had a cutoff porosity of 8%, critical permeability of 0.5 md
- There was much less dolomite intercrystal + vugs than estimated --> less k
- Engineer a solution?
- Couldn't acidise because of $$$
- CONCLUSIONSDefined by 4 reservoir rock types
- Microporosity --> low k, high
- Most of HC bearing rock NOT pay
- Highly fracture dolomites main contribution to flow in short term but have a rapid decline
- LESSONS Engineering solutions may not be economically feasible
Be aware of microporosity
Delay calcs/facility planning until SS evaluation complete
If fractures are present --> long term DSTs required
What is a vug?
Cavity in a rock, line with mineral crystals
What is moldic porosity?
- Type of secondary porosity.
- Caused by the dissolution of shell fragments or other particles, leaving voids
Explain the difference between a low pore/throat ration and a high pore/throat ratio.
Low pore/throat ratio - lower Sr (residual saturation) HIGHER HC recovery
High pore/throat ratio - higher Sr (residual saturation) LOWER HC recovery
Estimated volumes og HCs commercially recoverable under existing economic conditions
Explain the types of reserves.
- Producing - actual production info
- Non-producing - shut-in or awaiting completion
- Undeveloped - undrilled areas of producing reservoir with reasonable engineering and geological data to expect production
- Unproved - HC volumes supported by geo and eng data BUT economic and/or other uncertainties don't allow it to be classified as proved
- Probable - unproved reserves likely to be recovered Pr>50%
- Possible - unproved reserves not likely to be produced Pr>10%
What is trapezoid and slab integration used for?
Simplified way of determining the area (trapezoid) or volume (slab) under a cap rock.
Therefore an approximation of the reservoir area and volume.
What are the key elements for estimating recovery factor?
- Drive mechanism
- Fluid properties
- Geological model (pore geometry)Relative permeability
- Economics of operations
What is post combustion capture?
Capturing CO2 from flue gas after a fuel has been combusted in air.
Describe pre-combustion capture.
- HC fuel is gasified
- Water-gas is shifted to form a mixture of H and CO2CO2 is captured from the synthesis gas before it is combusted
What is oxyfuel capture?
- Conventional power station boilers burn pulverised coal in pure oxygen.
- to fuel a steam generator
creates an exhaust mixture of high concentration CO2
and water vapor
high concentration of CO2
easier and cheaper to capture
Means of transporting CO2
- Pipeline (most common)
What are the key criteria for storage site selection?
- Capacity - what volume of CO2 the rock can hold?
- Containment - can we keep the CO2 in the rock?
- Injectivity - can we put CO2 in the rock?
- Other - economics, risk, legal, community
How is net pay determined?
- Core plug data
- Wireline log cutoffs
- Well test and production data
What factors determine a reservoir rock?
- Pore geometry
- Capillary pressure
Net pay depends on...
- Production methods
- Relative permeability
- Height O/W
- Well tests
List the reserves estimating techniques in order of uncertainty.
- Analogues - compare similar reservoirs and/or wells. Before drilling.
- Volumetrics - subsurface geological data. After discovery or during development.
pressure and production history. After substantial production.
What causes all failures offshore?
Having inappropriate facilities.
Best appraisal practices...
- Look at analogues
- Identify critical uncertainties
Plan interventions to manage uncertainty
Reduce uncertainty by collecting
and analysing quality data
Describe the change in uncertainty during field development.
- Uncertainty decreases with time
- Data increases with time
- Expenditure and value increases with time
Reserves are classified as...
- under development
What attributes are generally associated with a heterogeneous reservoir?
- Increased uncertainty in reservoir
What is a 'must' for expensive (offshore) field development?
Conclusions drawn from reserves histories.
When uncertainty was understood, projects were managed successfully
- Mistakes have been repeated
- 3D seismic is a MUST for expensive field development
- Underestimate uncertainty and reserves at sanction
- Must consider more than one reservoir model
What are the criteria for proved reserves estimations?
Must be supported by actual production or formation tests and refer to actual reserve quantities
Based on well log data and/or core analysis
Analogous reservoirs for estimating reserves must be productive or potentially productive
What are the criteria for proved reserves reservoir areas and limits?
Areas are delineated by drilling and defined by fluid contacts
Undrilled reservoir areas should be judged as commercially productive based on geo and eng data
When fluid contact data unavailable, lowest known HC occurrence controls the proved reservoir limit
What are the criteria for proved reserves production facilities?
Reserves can be classified as proved if operational facilities to process and transport the HCs to market are currently installed.
Reserves can also be classified as proved if there is reasonable expectation that facilities will be installed.
Criteria for proved reserves classification, undeveloped locations.
Locations directly offsetting wells, indicative if commercial production
Locations are within the known proved productive limits
Locations conform to exisiting well spacing
Locations will be developed in future
Summarise the criteria required for proved reserves.
Production and transport systems must be installed or have reasonable expectation they will be.
Reserves estimations must be supported by actual production or formation tests.
- Reserves estimations must be based on well log data or core analysis.
- Analogous reservoirs must be productive or potentially productive.
- Area and limits must be delineated by drilling and defined by fluid contacts.
If fluid contact data is unavailable lowest known HC show used.
Undeveloped locations will be developed in the future.
Undeveloped locations are directly offsetting wells indicative of commercial production
Undeveloped locations are within the proved productive limits
What is the difference between EOR and IOR?
- IOR is used to recover the remaining mobile and immobile oil. Using techniques such as EOR.
- i.e. horizontal wells and fracturing
- EOR is specifically designed to recover the immobile oil.
- i.e. water flooding
What country has the highest oil consumption?
USA then Japan then Germany
Which area has the greatest proved oil reserves?
Middle East then North America
Describe the 'Hubbert Curve', peak production.
Developed by Hubbert to predict peak oil production
Based on oil discoveries over time
Assumed that everything remained constant therefore didn't account for improved technology
Where are the greatest Natural gas reserves and resources?
What is estimated self sufficiency?
Indicator of how well domestic production meets demand.
Self sufficiency = (production + domestic demand)/Net domestic demand for petro products
What is a R/P Ratio?
Oil reserves to production
What is the petrophysics workflow?
- Last Dirty Dancing Episode Excluded Mum
List the four types of interval thickness
- TVT - True Vertical Thickness
- AVT - Apparent Vertical Thickness
- TST - True Stratigraphic Thickness
- MT - Measured Thickness
What is the expectation curve?
The compliment of the cumulative distribution.
Expectation is the area above the cumulative probability curve.
The mode is the inflection point.
List the probability distribution types
- Normal (log-normal)
- Beta, Gamma
- Triangular (double triangular)
- Constant, Uniform
- Cumulative Frequency (expectation, step)
- Empirical (actual frequency, multimodal)
Describe double triangular distribution.
- Have two triangles of equal area and discontinuity in the middle.
- Cannot be used in Beta distribution.
Describe wedge error.
Error encountered due to erosion or weathering of bedding causing uneven surface and decreased thickness of layer and hence volume of rock. Overestimating as assuming more volume than there actually is.
Describe the Beta distribution.
Defined by two positive shape parameters, α and β
- Has to be differentiable across the whole function therefore cant include discontinuities.
- Therefore triangular or double triangular distributions cannot be represented by the Beta distributions
List the moments of distributions.
- First - mean
- Second - variance (peakedness)
- Third - skewness
- Fourth - Kurtosis (flatness) - low=fat high=skinny
List statistical considerations.
- Data availability and uncertainty
- Selection of variables
- Distribution type
- Variable dependency
- Calculation procedures
- Presentation of final results
List the types of dependencies.
- Single Variable
- Direct relationship
- Parametric relaionship
What determines the steepness of the expectation curve?
Uncertainty - more certain, more quality data --> steeper
Less complexity --> steeper
Explain the Latin Hypercube Method.
Is a method used to reduce the number of iterations required by Monte Carlo process.
- Form of stratified sampling.
- Breaks the distribution up into sections and takes samples from each section. This reduces clustering around particular values.
Ensures the distribution function is sampled evenly.
List the reasons for sophisticated reserves simulation.
- Large offshore gas fields
- Long term contracts
- Isolated gas projects
- Large number of participants
- Bank financing
- Extensive seismic coverage
- Few appraisal wells
Explain the difference between accurate and precise.
Accurate - on average the correct output is achieved.
Precise - values are clustered in a particular area. All answers are very close in value.
What does SEC stand for?
Securities and Exchange Commission
What is UCM?
Unidentified complex mixture
Summarise the Multiple Realisation Approach method for managing uncertainty
Identifies and captures all key uncertainties
Reconciles production data with multiple realisations
Reconciles probabilistic GIIP distributions with actual production data
Objectively assigns probabilities
Preserves clearly identifiable sub-surface realisations
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