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Conditioning static models with connectivity information

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Production History Match optimization requires a good consistency between geological static model and reservoir model. This is the case when the wells that have been identified as connected from dynamic synthesis are really connected in the model.

Connectivity Analysis is a way to QC a static model and to check its consistency with dynamic data at a very early stage. It allows identifying potential issues before starting time consuming flow simulations. It facilitates communication between geomodelers and reservoir engineers, by defining and quantifying the impact of geological parameters on wells connection.

Connectivity Analysis also provides some solutions to fix geological model inconsistencies and to ensure that the static model honors connectivity information.

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Conditioning static models with connectivity information

  1. 1. Jean-Marc Chautru (Geovariances) * Matthieu Bourges (Geovariances) Hélène Binet (Geovariances) Renaud Meunier (Geovariances) Conditioning Static Models with Connectivity Information
  2. 2. Introduction Page 2 / 17 • Connectivity is a key characteristics for Geomodels to be used in flow simulations  Not properly captured connectivity  biased flow simulations  Journel A., Alabert F. (1990), JPT 42 • Dynamic synthesis allows defining the hydraulic connection between wells and/or stratigraphic units  Production curves shape analysis (Pressure, produced fluids)  Well tests  Tracer tests • Geomodels are expected to reproduce these connections  If not, History Match will be very difficult Connectivity is a critical parameter for flow simulations
  3. 3. How to honor wells connection? Page 3 / 17 • No geostatistical simulation method honouring connectivity data available in commercial software • Research algorithms are available  Several authors o Allard D. o Renard P. o Mariethoz G. o Straubhaar J. o Caers J. o Deutsch C. o Etc..  Different techniques. o Based on Truncated Pluri-Gaussian facies simulation method o Based on MPS facies simulation method
  4. 4. How to honor wells connection? Page 4 / 17 • In models built in commercial software • For any facies simulation method • Preserving the facies and Permeability simulation workflows Post-processing approach
  5. 5. Checking wells connection Page 5 / 17 Connections can be checked with “connected components” • Continuous geobodies made of grid cells of similar properties that are connected by one face • Similar properties = same facies or same permeability range A B 1 geobody A B 2 geobodies A 3 geobodies
  6. 6. Geomodel QC with geobodies Page 6 / 17 • Hydrocarbon volumes connected to the wells o Volume of geobody * Porosity * N/G * (1-Sw) o Must be consistent with production data • Connection between wells o Are observed connections between wells honored? o What is the degree of consistency of the model with dynamic data? o What are the characteristics of the connections in the model? Geomodel QC must be done before flow simulations
  7. 7. Checking wells connection Page 7 / 17 Connected wells Two wells intersecting the same geobody are connected
  8. 8. Consistency with connectivity data Page 8 / 17 Stochastic Connectivity Analysis 1. Test Connections on several realizations of the same model  Calculate the percentage of realizations in which wells are connected o Low percentage  model inconsistent with dynamic data o ~50%  appropriate model, but realizations have to be selected o High percentage  model consistent with dynamic data
  9. 9. Consistency with connectivity data Page 9 / 17 Stochastic Connectivity Analysis 2. Test sensitivity to model parameters  Uncertainty on model parameters  range of variation Adjusting local VPC & ranges may solve connection inconsistencies
  10. 10. Geological models enhancement Page 10 / 17 Three steps workflow 1. Calculate cells probability to be in a connecting geobody  Calculated from stochastic realizations of the geological model 2. Select cells that are often in a connecting geobody Probability of presence in connecting geobody Selection of cells with the highest Probability of Presence
  11. 11. Geological models enhancement Page 11 / 17 3. Define a random sampling in selected cells  Connecting facies is assigned to random samples  Random samples are added to well data for next model realization  Random samples are updated for each realization Cells most frequently in a connecting geobody + Additional random conditioning data (light color) Additional samples help selecting realizations that work
  12. 12. Including Faults Page 12 / 17 • If adjusting model parameters is not enough…  Some parameters critical for fluid flow are missing o Conductive faults o Fractures • Including faults and fractures in calculations 1. Calculate the distance to faults or fractures 2. Select cells close to the faults 3. Merge this new selection with the connecting “facies” 4. Re-run the connection test Distance to the closest fault
  13. 13. Dealing with complex structures Page 13 / 17 In presence of faults with high throw • Connection may exist between wells perforated in different stratigraphic units • A global structural grid must be defined  Cells on both sides of faults must be neighbours in I, J, K indexes  Populated through an upscaling operation • Connectivity calculations can be carried out within the global grid
  14. 14. Connections characterization Page 14 / 17 • Connections must be characterized  Connecting geobody shape may be regular or irregular Connecting geobody shape impacts fluid flow
  15. 15. Connections characterization Page 15 / 17 • Connections must be characterized  Use erosion to progressively reduce the size of the connecting geobody  At each iteration, recalculate connected components on the eroded geobody After erosionInitial geobody Erosions help detecting baffles and narrow throats in geobodies
  16. 16. Upscaling issues Page 16 / 17 • Connectivity check must be done on the geological model and on the reservoir model  The reservoir engineer will generally use only one realization for History Match  This realization, which has been upscaled, must preserve connections between wells observed in the geological model • In case of contradiction, revisit the upscaling process or the reservoir grid resolution
  17. 17. Conclusion Page 17 / 17 • Stochastic connectivity analysis improves Geomodels QC  Facilitates communication between geologists and engineers • Post-processing allows enhancing simulation results  Can be used with all the geostatistical simulation methods  Better calibration of geomodel parameters  Preserves existing geomodeling workflows • QC of connections to be done before any optimization process  Enhances efficiency of Assisted History Match techniques Honoring connections is required to speed-up and improve HM

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