4. Petroleum appraisal Flashcards
What are the aims of the petroleum appraisal phase?
Assess whether to develop
Develop optimized production strategy
What is involved in the appraisal?
Reservior description
- depositional environment
- diagenesis and structure
- distribution of porosity and permeability
- reservoir architecture
- reservoir fluids
Volumetrics
Cost/benefit analysis
What information is collected for a reservoir description?
Spatial and temporal distribution of depositional environments and their constituent lithologies
Correlation across several wells- biostratigraphy, log character, gamma
Correlation will depend on depositional model being used
Net/Gross
Diagenesis - impact on porosity and permeability
Heterogeneity
Reservoir fluids
volumetrics
What data sources are used for a reservoir description?
Seismic
core
wireline logs
analogs
conceptual models
How is fluid property data used?
- Calculate in-place volumes of hydrocarbons and recovery rates
- Accurately design production strategies and facilities
- Implement HSE protocols
- Plan processing and marketing
- Is it corrosive
Why do we need to estimate the volumes in an accumulation?
- As a basis for reserves estimation -> value of company
- As a basis for development plan scenarios and reservoir management
- As a basis for well planning
- Large uncertainty and will change over time
What is STOIIP?
Stock Tank Oil Initially In Place (STOIIP)
GRV: gross rock volume - from seismic
N/G: for seismic, core, logs
Porosity: for core, logs
Sw: water saturation - from logs, core
FVF: formation volume factor - from fluid samples
What tools are used for appraisal?
- Appraisal wells
- Well tests, fluid pressure (rate of flow)
- Well bore sampling
- Logs (contrain architecture)
- Core
- Seismic
Describe the drilling process
drilling mud lubricates the drill and stabilises the well
What are the purposes of drilling?
data gathering, production, injection, alternating use
Done in stages for control of subsurface pressure - each stage is cased
cases can be perforated after drilling to allow hydrocarbons to flow into the well during production
What is mudlogging and why is it done?
Drill mud brings up small cuttings which can be logged
Aims:
- well status vs well objectives
- well safety (subsurface pressure)
- drillling optimisation
- oil and gas shows
- initial geological and petrophysical description
What are drilling data types
STATIC DATA (does not involve flow)
* mudlogs - ‘‘while drilling’’ data
* wireline logs - measured in open hole after drilling
* LWD - ‘‘logging while drilling’’ - logging tools attatched to drill string behind bit
* Core
* Fluid samples
* borehole seismic - min-seismic survey shot using the borehole
DYNAMIC DATA (involves flow)
* Well tests via temporary and permanent production systems
* Production data
Describe coring and its limitations
- Provides only physical measurement of reservoir characteristics
- Rotary cpre and sidewall cores (SWC)
- Expensive : slow drilling rate to [reserve rock, extra ‘trips’
- Plugged at 1ft intervals: core plugs for conventional geological and petrophysical analysis
- Sections are also preserved in wax or vacuum for special core analyis (SCAL)
Why is wireline logging used in the petroleum appraisal phase?
colect in-situ data about lithology, porosity, fluid types in absence of core data
much cheaper than coreing and covers entire well
What log types can wireline logging produce?
- Gamma ray/spectral gamma ray
- Sonic logs
- Neutron family of tools (needs radioactive source)
- Resistivity family of tools
- Caliper/diametre
