RRR Exam

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.

hydrocarbons it just needs to be capable of containing them.

BIG 5

• Source rock and maturation
• Migration path and timing
• Reservoir rock
• Seal rock
• Trap
• All factors MUST be present!

• Injection depth
• Migration path and potential leakage path
• Reservoir rock
• Seal rock
• Trap

All factors must be present for a viable storage site.

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.

• Things that you can physically touch, hold and manipulate. 
• Examples:
• Core - conventional and sidewall
• Cuttings

• Core - conventional and sidewall
• Cuttings

• Indirect data. 
• Examples:
• Seismic, gravity , magnetics, well logs and anologues

• Seal - fine grained (mudstones and shales)
• Reservoir - coarse grain (sandstone)

• 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

• Stratigraphic traps (deposition ordering)
• Structural traps (faults and folds)
• Potential reservoir rocks
• Potential seal rocks

• Core
• Produce/inject fluids
• Collect samples
• Get quality log data
• Get PVT data

• Circulate and lubricate
• Circulation - removes cuttings and maintains temperature
• Borehole stability - prevents collapse
• Stops fluid entering

• Mineralogy
• Microscopic k and θ
• Bedding thickness
• Grain size
• Rock type
• Discontinuities
• Stratigraphy

Order of deposition - the way strata has been laid and the associated time

• Gamma
• Sonic
• Neutron
• Density

• 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

• 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

An area which contains hydrocarbons that cannot be produced.

Exists where capillary pressure is zero. This implies there is a flat interface between the fluids.

There can only be one per reservoir.

• Surface tension (1 liquid)
• Interfacial tension (2 liquids)

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

Wetting phase  θ<90

• Non-wetting phase:
•   cohesive forces > adhesive
•   θ>90

• nw - non-wetting phase
• w - wetting phase

r_c - pore radius

• 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

• Non-wetting phase displaces the wetting phase.
• i.e. hydrocarbon migrating into a previously brine saturated rock

• The opposite to drainage.
• The wetting phase displaces the non-wetting phase.

• 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.

• 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

• Generation and migration stops
• Spill point is reached
• Seal failure

Distance between the min and max S_w (water saturation)

Seal capacity = Hmax

• One that will retain an economic volume of hydrocarbon
• A good seal will have
•   High ductility
•   High compressibility
•   Low srength
•   Low velocity

One that retains anything less than an economic volume of hydrocarbon

• Seal Capacity - H_max (max column thickness)
• Seal Geometry - thickness and areal extent

Seal Integrity - mechanical properties, ductility

A flat (planar surface) along which there is a slip

A compression fracture which causes slippage

• Fractures can be compressional or tensional
• Fault is compression
• Gap is tension

• Fault zone deformation process.
• Grey Cats Die Shamefully

• Grain sliding
• Cataclasis
• Diagenesis

Shale gouge/clay smear

• 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

• High shale/sand ration.
• Sand grinds up the shale.
• Result clay incorporated into the fault plane
• gladwrap --> higher capillary pressure required

• Shale gouge/clay smear (smallest pore throat radius)
• Cementation
• Cataclasis
• Grain sliding (greatest pore throat radius)

A visual representation of geological structures with respect to true north.

A layer of rock with seal potential laying over the reservoir rock.

• Capacity
• Geometry
• Integrity

• Risk of reactivation
• Juxtaposition relationships
• Fault zone properties

• Abundance
• Size
• Shape
• Distribution
• Interconnectivity

Diagenesis and depositional process

• Volume
• Rate
• Type

Of reservoir fluids produced of fluids injected

• Think of locked room there is space but it is NOT effective.
• Absolute porosity is the total porosity - pore space to bulk volume (%)

Effective porosity - interconnected pore space to bulk volume

• A measure of a rock's ability to allow fluid flow.
• Measure of fluid connectivity

Macro - inter and intraparticle

Micro - inter and intraparticle

Secondary - moldic and fracture

k_e= k_a x k_r

Even if you have a high water saturation it does not mean that you will produce water.

Microporosity --> VERY low permeabilities

• 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 $$$

• CONCLUSIONS
• Defined 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

Cavity in a rock, line with mineral crystals

• Type of secondary porosity.
• Caused by the dissolution of shell fragments or other particles, leaving voids

Low pore/throat ratio - lower S_r (residual saturation) HIGHER HC recovery

High pore/throat ratio - higher S_r (residual saturation) LOWER HC recovery

Estimated volumes og HCs commercially recoverable under existing economic conditions

• Proved
•   Developed   
•     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 P_r>50%
•     Possible - unproved reserves not likely to be produced Pr>10%

Simplified way of determining the area (trapezoid) or volume (slab) under a cap rock.

Therefore an approximation of the reservoir area and volume. 

• Drive mechanism
• Fluid properties
• Geological model (pore geometry)
• Relative permeability
• OOIP/OGIP
• Economics of operations

Capturing CO₂ from flue gas after a fuel has been combusted in air.

• HC fuel is gasified
• Water-gas is shifted to form a mixture of H and CO₂
• CO₂ is captured from the synthesis gas before it is combusted

• 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

• Pipeline (most common)
• Ship
• Road
• Rail

• 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

• Core plug data
• Wireline log cutoffs
• Well test and production data

• Pore geometry
• Mineralogy
• Capillary pressure
• Porosity
• Permeability

• Production methods
• Relative permeability
• Height O/W
• Continuity
• Well tests

• Analogues 
• Volumetrics
• Performance 

• Analogues - compare similar reservoirs and/or wells. Before drilling.
• Volumetrics - subsurface geological data. After discovery or during development.

Performance -  pressure and production history. After substantial production.

Having inappropriate facilities.

• Look at analogues
• Identify critical uncertainties

Plan interventions to manage uncertainty

Reduce uncertainty by collecting and analysing quality data

• Uncertainty decreases with time
• Data increases with time
• Expenditure and value increases with time

• Proven
• producing
• under development
• undeveloped

Unproven

• Increased uncertainty in reservoir
•  quality
•  variability
•  connectivity

3D seismic

• 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

When uncertainty was understood, projects were managed successfully

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

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

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.

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

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

• 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

USA then Japan then Germany

Middle East then North America

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

Russia

Indicator of how well domestic production meets demand.


Self sufficiency = (production + domestic demand)/Net domestic demand for petro products

Oil reserves to production

• Last Dirty Dancing Episode Excluded Mum
• Locate
• Detect
• Distinguish
• Evaluate
• Estimate
• Monitor

• TVT - True Vertical Thickness
• AVT - Apparent Vertical Thickness
• TST - True Stratigraphic Thickness
• MT - Measured Thickness

The compliment of the cumulative distribution.


Expectation is the area above the cumulative probability curve.

The mode is the inflection point.

• Normal (log-normal)
• Discrete
• Beta, Gamma
• Triangular (double triangular)
• Constant, Uniform
• Cumulative Frequency (expectation, step)
• Empirical (actual frequency, multimodal)

• Have two triangles of equal area and discontinuity in the middle.
• Cannot be used in Beta distribution.

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.

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

• First - mean
• Second - variance (peakedness)
• Third - skewness
• Fourth - Kurtosis (flatness) - low=fat high=skinny

• Data availability and uncertainty
• Selection of variables
• Distribution type
• Variable dependency
• Calculation procedures
• Presentation of final results

• Complete
• Partial
• Single Variable
• Multivariable
• Direct relationship
• Parametric relaionship

Scale

Uncertainty - more certain, more quality data --> steeper

Less complexity --> steeper

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.

• Large offshore gas fields
• Long term contracts
• Isolated gas projects
• Large number of participants
• Bank financing
• Extensive seismic coverage
• Few appraisal wells

Accurate - on average the correct output is achieved.

Precise - values are clustered in a particular area. All answers are very close in value.

Securities and Exchange Commission

Unidentified complex mixture

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