Analysis of Salt Creep and Well Casing Damage in High Pressure and High Temperature Environments
- Khang Lao (Terralog Technologies USA Inc.) | Michael S. Bruno (Terralog Technologies USA Inc.) | Vahid Serajian (Texas A&M University)
- Document ID
- Offshore Technology Conference
- Offshore Technology Conference, 30 April-3 May, Houston, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Offshore Technology Conference
- 1.2.2 Geomechanics, 1.13 Casing and Cementing, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 2 Well Completion, 5.3.4 Integration of geomechanics in models, 1.6 Drilling Operations, 1.13.1 Casing Design, 7.1.9 Project Economic Analysis, 4.3.4 Scale, 7.2.1 Risk, Uncertainty and Risk Assessment, 7.1.10 Field Economic Analysis
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Drilling and completing wells through deep thick salt formations is technicallychallenging and costly. Salt material flows over time whenever a stressdifference, or shear stress, is induced. The rate of deformation primarilydepends on the stress difference, and on the temperature. Both of these factorsincrease with increasing depth, often leading to severe loading and deformationof wells, and sometimes severe damage and loss of functionality. Geomechanicalanalysis can be applied to estimate such loading, to estimate damage risks, andto optimize well designs for these challenging conditions. We describe herein aprocess to evaluate salt creep and casing damage risk for high pressure andhigh temperature conditions typically encountered in deep salt formations.Because well costs often exceed 50 million dollars each, appropriate welldesign and risk analysis, supported by geomechanical modeling of salt andcasing behavior, is critical to project economics.
To simulate the visco-elasto-plastic behavior of salt, we apply thetime-dependent constitutive framework available in FLAC3D. The availableformulation is modified by Terralog to account for damage accumulation duringprimary loading, associated strength degradation, compaction-dilationtransition based on the Drucker-Prager yield criterion, and loading-unloadingresponse.
We provide an illustrative example for a deepwater Gulf of Mexico field, inwhich a multi-string casing-in-casing design was considered to resist long-termcreep. Laboratory creep data was used to calibrate the constitutive model,which was then applied to a near wellbore scale geomechanical model thatincluded the casing strings, cement, mud pressure, and 10ft of surroundingsalt. The simulation results indicate that the for the design configurationsconsidered, the minimum time for salt to contact the outer casing was on theorder of 2 years for the most severe scenarios (lowest annulus pressure), andmore than 20 years for the strongest configurations. Geomechanical analysis ofthis type provides a relatively low cost approach to quantify casing damagerisks and to optimize casing designs for completions in high stress and hightemperature environments.
Increasing exploration and production from deep regions around the worldrequire drilling through and completing wells in thick salt formations, leadingto very high well costs. Appropriate designs are required to withstand creepinduced loads during drilling and after completion. The introduction of awellbore in a salt formation changes the existing local stress field, inducinga stress difference between the borehole and surrounding salt, and resultingtime-dependent (creep) loading on well casings. Production of hot fluids fromsubsalt formations adds additional thermal strains to the wellbore andthermally induced creep acceleration.
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