Casing and Screen Failure Analysis in Highly Compacting Sandstone Fields
- Kenji Furui (ConocoPhillips) | Giin-Fa Fuh (ConocoPhillips) | Nobuo Morita (Waseda U.)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 30 October-2 November, Denver, Colorado, USA
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 5.6.11 Reservoir monitoring with permanent sensors, 5.3.4 Integration of geomechanics in models, 5.2.1 Phase Behavior and PVT Measurements, 5.4.6 Thermal Methods, 2.4.6 Frac and Pack, 2.4.5 Gravel pack design & evaluation, 1.2.3 Rock properties, 1.2.2 Geomechanics, 1.10 Drilling Equipment, 5.1.2 Faults and Fracture Characterisation, 4.6 Natural Gas, 5.5.11 Formation Testing (e.g., Wireline, LWD), 2.4.3 Sand/Solids Control, 3 Production and Well Operations, 5.1.1 Exploration, Development, Structural Geology, 2 Well Completion
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Many casing and screen damage incidents have been reported in deep-water oil and gas fields in the Gulf of Mexico and other locations around the world. We reviewed historical casing/well failure events in a highly compacting sandstone field and performed a comprehensive geomechanics analysis of various casing damage mechanisms (tension, axial compression, shear, and bending) related to large reservoir depletion. Among five wells that experienced mechanical well integrity issues, two of them showed casing restrictions in the cap rock at intervals around 1,000 to 1,600 ft-TVD above the top of the depleting (main) reservoir. A multi-finger caliper log obtained from one of the wells indicates that the overburden casing failure occurred at a highly geo-pressured, thin sand layer approximately 1,100 ft-TVD above the top of the compacting reservoir. The remaining casing failure events occurred near (less than 200 ft-TVD) or within the compacting reservoir interval.
A 3D non-linear finite element model has been developed for simulating stress changes in the overburden and the reservoir intervals and evaluating the effect of lithological anomalies on casing stability. The simulation results indicate that large tensile and shear strains could develop within a thin, weak-strength layer in the overburden and at the interface between cap rock and depleting reservoir interval. Casing damage by bending/shear could also occur at these thin-layered sands saturated with overpressured gas.
In the reservoir interval, shear stresses acting on the screens can be relatively high due to the difference of the movements between the internal base pipe and the external shroud and gravel. Screen failure may also occur at the welded points. If casing failure occurs in the unperforated sand layer just above the compacting reservoir, it induces localized high velocity flow on the upper part of the screen causing potential screen erosion. Casing failure due to fault slip near the reservoir occurs only if a fault has sealing capability while maintaining a large pressure differential across the fault plane.
The numerical analysis results presented in this work help engineers understand possible casing and screen deformation and failure mechanisms experienced in highly compacting sandstone fields. Based on the study findings, we also present completion design guidelines to avoid or mitigate compaction-induced casing damage in both the overburden and reservoir intervals.
A field investigated in this study has hydrocarbon pays where both oil and gas bearing sands are present at various depths in the field, with everything from highly undersaturated, good quality crudes in the main reservoirs and saturated crudes, rich gas-condensate to dry gases in some of the shallower intervals. There is significant faulting due to deformation by an underlying salt diapir, resulting in compartmentalization of the field. The reservoirs are highly overpressured at pressure gradients of 0.68 to 0.77 psi/ft while the reservoir temperature is fairly low, typically 145 to 160 °F. The reservoirs have coarse silt to very fine-grained sands resulting in initial permeability values in the main target reservoirs from 50 to 250 md with average sand grain size in the 70 micron range. The reservoir sands are quite thick in places, resulting in relatively good k×h values between 7,500 to 50,000 md-ft in the main target reservoirs. This causes relatively large reservoir thickness to drainage radius ratios (H/rb). The reservoirs are mostly depletion drive with significant compaction due to very high compressibility of the rock.
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