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Collaborating Authors
Chan, Alvin W.
Abstract Depleted Fracture Gradients have been a challenge for the oil and gas industry during drilling and cementing operations for over 30 years. Yet, year after year, problems related to lost circulation, borehole instability (low mud weight due a low fracture gradient), and losses during cementing operations leading to NPT and remedial work continue to rank as some of the top NPT events that companies face. This paper will demonstrate how the geomechanical modeling, well execution and remedial strengthening operations should be implemented to provide for a successful outcome. The use of a Fracture Gradient (FG) framework will be discussed, and the use of a negotiated fracture gradient will highlight how the fracture gradient can be changed during operations. This paper will also show actual examples from Deepwater operations that have successfully executed a detailed borehole strengthening program. Through our offset studies and operational experience, we will provide a format for navigating complex depleted drilling issues and show an example on recovering from low fracture gradients. This paper will demonstrate (1) how our framework facilitated multi-disciplinary collaborative discussion among our subsurface and well engineering communities; (2) how the impacts of drilling fluids and operational procedures can change this lost circulation threshold; and (3) how our negotiated FG approach has successfully delivered wells drilled in narrow margins.
- Europe (0.94)
- North America > United States > Texas (0.93)
- Asia (0.69)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.70)
- Europe > Norway > North Sea > Central North Sea > Central Graben > PL 018 > Block 2/4 > Greater Ekofisk Field > Ekofisk Field > Tor Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Central Graben > PL 018 > Block 2/4 > Greater Ekofisk Field > Ekofisk Field > Ekofisk Formation (0.99)
- North America > Cuba > Gulf of Mexico (0.89)
- Asia > Malaysia (0.89)
ABSTRACT Relationships between the compaction state and effective stresses are the basis for most quantitative pore-pressure and stress estimates. Common practice uses only a single element of the stress tensor, the vertical stress, for these calculations; mean stress formulations also exist, although they are less widely applied. Using simple models and field data from two distinct stress regimes, we examined the validity and limitations of the vertical-stress approach as well as a mean-stress approach, showing that in complex stress settings, both can perform very poorly. We evaluated a method for incorporating shear stresses into compaction relations by using state boundary surface (SBS) formulations from soil mechanics and demonstrated how the resulting model may be calibrated and applied to field data. This approach was found to perform much better in the complex stress environment, providing more stable calibration behavior and more reliably extrapolating to stress states beyond those present in the calibration data. Although vertical and mean stress compaction models may work well in simple stress environments, we discovered that incorporation of shear stress is necessary for models in complex stress settings. Although the addition of shear stress significantly improves agreement with field data, it also increases the complexity of the model as well as the requirements for calibration data. We therefore evaluated the settings in which each of these three approaches — vertical stress, mean stress, and SBS — may be most appropriate.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Fault > Dip-Slip Fault (0.68)