Geopressure and Prospect's Risk Assessment

by Selim S. Shaker

Duration: Two days

Intended Audience: Geophysicists, geologists, petrophysicists, drilling and reservoir engineers, geopressure modelers, hydro-geologists, rock-mechanic scientists, geosciences technicians and almost all technical personnel in the oil patch.

Prospect risk is dependent on seal integrity and hydrocarbon retention capacity of a subsurface structural closure.  These aspects are the consequence of the subsurface geopressure vertical and lateral partitions.  Moreover, successful drilling relies on accurate prediction of pore–fracture (PP-FP) pressure within the drilling tolerance window and safety limitations.

Geophysics plays an essential function in prediction and risk assessment of a prospect's geopressure compartment's profile.  2D-3D seismic mapping, velocity analysis, sequence stratigraphy and AVO appraisal are the building blocks of pre-drilling geopressure assessment.  During and post drilling, petrophysical bore-hole measurements are used to calibrate and fine-tune the prediction models.

This two day course focuses on predicting and appraising the subsurface geopressure and evaluating a prospect's risk before, during and post-drilling.  Geological, rock-mechanics, petrophysical and hydrodynamic models are used as the foundation for the prediction models, in addition to, rather than only, algorithm formulas.

Course Outline:

Introduction, Definitions and Plots

  • Explain the integrated process of prospect generation.
  • Demonstrate the four geopressure zones and their causes, models and graphic representations.
  • Discuss the measured pore (MPP) – fracture pressures (FP) tools, charts, and plots.
  • Formulate the petrophysical data needed for predicting pore (PPP) – fracture (PFP) pressures.  Focus on the effective stress- transformation models.

Geophysical Data for PPP

  • Select and QC seismic velocity for the proposed wildcat location.
  • Define the top of geopressure derived from average, stacking, RMS, PSDM velocities.
  • Design the transformation/prediction model based on seismic velocity (Vs/Vp, Poisson ratio) and the petrophysical properties (DT, R, Density, VSP…) of the offset wells.
  • Distinguish velocity trends in normally pressured vs. geopressured systems, velocity cross-over, AVO assessment.

Geopressure Applications

  • Recognize compartmentalization, transgression, regression and communication.
  • Appraise sealing vs. retention capacities of the structural closure cap in four way closure.
  • Evaluate faulted three way closure breach pressure.

Before Drilling

  • Calculate the pre-drilling mud weight and casing seats in bare dry hole vs. producer.
  • Recognize the drilling challenges due to the geological setting.

During and post drilling assessment:

  • Compare and calibrate the pre-drilling prediction seismic model with the real time data.
  • Appraise the success of finding hydrocarbon and lesson learned due to failure.
  • Assess the challenges in deep water frontier areas and salt basins.
  • Evaluate the untested offset structural segments in the prospect and play concept.

Some global case histories from the Gulf of Mexico, North America, North Sea, Mediterranean and Far East will be discussed.

Case histories and exercises follow each segment of this course in form of Q&A, charts, plots etc.

Instructor Biography:
Selim S. Shaker