Common open-hole tools and their uses

Tool Physical Measurement Use Comments Logging Conditions Temperature (BHT)     Temperature Borehole temperature for resistivity calculations . Corrected with Horner plot  Pressure (PRESS) Fluid Pressure   Fluid pressure for formation volume factor calculations . Incorporated in RFT Borehole diameter   Borehole diameter Data quality, in situ stress tensor, lithology and permeability indicator. Available in 2.4. or multi-arm versions Lithology Gamma Ray (GR) Natural radioactivity  of the formation. Shale indicator and depth matching Can read through casing.   Spontaneous Potential (SP) Sand/Shale interface potential . Permeable beds Resistivity of formation water Does not work in conductive muds, or offshore. Porosity Sonic (BHC, LSS ) Velocity of an elastic wave in the formation. Effective (connected ) porosity . Compaction gas and vugs, calibration of seismic data. Density (FDC , LDT ) Bulk density of the formation. Total porosity . Used to calculate synthetic seismograms . Neutron (SNP, CNL ) Hydrogen concentration in the formation. Total porosity (shale increases measured porosity , gas reduces measured porosity ) Can read through casing Resistivity Simple electric log (SN, LN ,Lat ) Resistivity of flushed , shallow and deep zones respectively . Used in water saturation calculations. Now obsolete, not focused, can’t be used in oil based muds, prone to invasion. Induction Logs (IES , ISF, DIL, DISF, ILm, ILd ) Conductivity of the formation. Conductivity and resistivity in oil based muds, and hence calculation of water saturation. Focused devices. Use in oil based and fresh water muds. Range of depths of investigation. (Vertical resolution 5-10 ft.) Laterolog (LL3, LL7, DLL, LLs, LLd) Resistivity of the formation. Resistivity in water based muds, and hence calculation of water saturation Focused devices. Use in salt water based muds. Range of depths of investigation. (Vertical resolution 2-4 ft.) Microlog (ML) Resistivity of mudcake and flushed zone . Indicator of permeability. Detector of thin beds. (vertical resolution about 1 ft.) Micro-laterolog (MLL) Resistivity of flushed zone. Measures RXO Not good with thick mudcakes. Proximity Log (PL) Resistivity of flushed zone . Measures RXO Not good if invasion is small. Micro-spherically focused log (MSFL) Resistivity of flushed zone . Measures RXO Part of DLL-RXO tool.

Geological model vs. Reservoir model

What is model ?

• A model is a representation of some aspect of reality.
• The Purpose of creting a model is to help understand, describe , or predict how things work in the real world by exploring  a simplified representation of a particular object or setting .

 

Cellular  models : 

A cellular model is a schematic description of a reservoir that represents its properties. 

·         Geological model =Geomodel =Static model

·         Reservoir model =Dynamic model 

   A Cellular Model is required:

·         To understand the complexity of reality

·         To quantify reality

 

®     Modeling objectives: Simplify to Quantify

Geological Model vs. Reservoir Model : 

Reservoir model definition: 

Reservoir model construction is the main objective of an integrated reservoir study. It is a grid of cells which allows manage.

Geomodel represents one of the most important phases in an integrated reservoir study workflow, because : 

• It integrates reservoir geometry, Lithofacies and petrophysical properties distribution consistency.
• It takes into account dynamic information.
• It provides key heterogeneity modeling (main flow units ).

Upscaling : a challenge for information integration.  

A Reservoir model : what for ? 

It is used to simulate the evolution of a field throughout time.

• Well production
• Fluid movements within the reservoir
• Pressure evolution 

A good Reservoir Model is strongly constrained by the Geological Model:

·         Fluid flow simulation is more realistic and more reliable.

A reliable Geological Model takes into account dynamic data:

·         Identification of main faults which impact fluid flow (either permeability barrier or conductive faults).

·         Stratigraphic barriers or multiple reservoirs.

 

®     Need strong integration between geo-disciplines (Geophysicist, Geologist, Reservoir engineers) to ensure final model consistency  (Volume , pressure , rates ) 

Use of geologic model data in reservoir simulation

 

Use of geologic model data in reservoir simulation
Property	Use in Simulation	Status
Structure top	Reservoir depth       Initial reservoir pressure       Original oil in place (OOIP ) and original   gas in place (OGIP) calculations	Required for top layer
Net reservoir thikness,hn	Assignment of cell net thikness values       Horizontal –transmissibility calculations      Pore volume calculations      Calculation of well geometric factors, Gw       OOIP and OGIP calculations	Required
Gross reservoir thikness, hg	Assignment of cell gross thikness values       Gravity head calculations        Initial reservoir pressures Transition-zone calculations. Initial saturation distributions. Vertical-transmissibility calculations	Optional (default may be obtained from net thikness)
Net-to-gross ratio	Assignment to cell hn/hg values	Optional (default may equal 1, hn/hg =1 )
Porosity	Assignment of cell Ⴔ values     Development of porosity /permeability transforms.     Pore volume (PV) calculations.     OOIP and OGIP calculations.	Required for all layers
Horizontal permeability	Assignment of cell permeability values     Horizontal –transmissibility calculations.     Development of porosity /permeability transforms.     Calculation of well geometric factors , Gw  .	Required for all layers
Vertical permeability	Assignment of cell permeability values.     Vertical –transmissibility calculations.	Optional (default may  be obtained from Kv /kh=1)
Initial saturations	Initial saturations distributions.     Transition –zone heights.     OOIP and OGIP calculations.	Optional (default may be obtained from Pc data )
End point saturations	Saturation normalization.     Assignment of cell critical saturation values for saturatioun normalization.	Optional (default may be obtained from kr curves )
Fluid Contacts	OOIP and OGIP calculations.     Initial saturation distributions.     Initial reservoir pressures.	Required

Reservoir Challenges VS Solutions

 

Challenges	Solutions
ü Reservoir Heterogeneity :           -   Lateral and vertical facies changes     -    Depositionnel environnements modelling.	Reservoirs Characterization using integrated seismic interpretation, inversion, geologic modelling with sedimentological studies.
ü  Structure Complexity -    Structural pattern is very complex, especially in the deeper Paleozoic section. -          Multi tectonic phases. -          Seismic data mask by multiples.	Ø  Overcome by sophisticated structural seismic attributes (faults likelihood as example) to detect most of faults trends. Ø  Understanding the geologic and structure setting. Ø  Structure restoration.
ü  Defining potential blocks. ü  Defining the reservoir quality.	Ø  Integrating structural interpretation with seismic attributes, available petrophysical and Engineering data.
ü  Compartimentalization	Ø  Optimized structural configuration. Ø  PVT @Pressure Analysis. Ø  Fault seal Analysis.
ü  Low resistivity pays	Ø  Conductivity of clay and minerals. Ø  Micro porosity and high irreducible water saturation. Ø  Deep invasion of high salinity filtrate.