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.

The Exploration Cycle

 There are  three   basic phases  of prospecting  in which various  mapping techniques  and methods are required . 

1. The first  is  the initial exploration phase of  a property . Generally , few , if any wells have been  drilled  on or near  the prospect  and therefore , prospect evaluation  relies on seismic data , limited well control , a good  geologic concept  , and  comparaison   or analogies  to nearby  properties .For exploration  purposes  the emphasis may be  on defining  major sand units , locating the larger potential fault  traps , and preparing  regional  subsurface maps . 

         The aim of this work is to identify  undiscovered  economic hydrocarbon accumulations .

1. The second phase of prospecting  ocurs after  a field has been  discovered  and several  wells have been drilled . Continously accumulated well log , core , seismic , and performance  data are used  to fully develop  the field  and obtain a good  estimate of  the volume  of recoverable  hydrocarbons . 

In these newly  discovered fields , the geologic study may include  the mapping  of all recognized  faults  , the preparation  of structure , contour maps , interval  isopach maps , and net sand  and net pay isopach maps  for all known  hydrocarbon bearing  reservoirs , in addition  to a variety  of cross sections . These maps and cross sections  may be used  to estimate reserves , justify  additional  development  drilling , or establish  a field depletion plan . 

1. The third  and final phase of prospecting  occurs in maturely  developed properties . With increasing amounts  of log  and performance  data , volumetrics are compared to performance  to refine the geological  maps and ultimate  reserve estimates .

  All  the geologic , geophysical , and engineering  information  is used  to help identify  any            hydrocarbons  that remain . In any   integrated study  being conducted in a mature  area  with the   purpose of identifying  economic reserves  not capable   of being  recovered  by existing                producing    wells , to identify  additional  potential overlooked  in previous studies or to plan     secondary  or  enhanced  recovery projects .

The most detailed maps  are required , as well as the analysis of  reservoir  performance  data .  This detailed  work requires   a team  effort  consisting  of team  members  experienced in      various  disciplines , including geology , gophysics , and petroleum  engineering .It is during this  final phase  of prospecting  that many companies have  failed to recognize  and approve the kind of integrated , detailed interdisciplinary  work required to find all  the remaining oil and gas . 

Exploration : 

Exploration's  mission is to acquire access to new petroleum resources .

• Identifies and evaluates new areas 
• Acquires rights to explore 
• Identifies leads 
• Matures leads to propects 
• Selects prospects for drilling 
• Drills wildcats and appraisals 
• Shares evaluation with Development on development . 

Lead & Prospect : 

Lead	Prospect
Suggests the potential for a wildcat location	Sufficiently defined to be drilled
Substantial uncertainty remains in the potential size and chance of success	Uncertainty remains in the potential size and chance of success
Key elements of the petroleum system may not be supported by any hard data	Major elements of the petroleum system are defined

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