Well Damage Analysis and Design Optimization

 


Technology Summary

Reservoir compaction and associated bedding plane slip and overburden shear has induced damage to hundreds of wells in fields throughout the world. Through simple screening processes, or in some cases more extensive geomechanical modeling efforts, strains induced by reservoir production on specific well trajectories at specific locations in the field can be assessed. Damage risks can then be reduced by modifications in well path or by modifications in completion designs in the high risk areas.

Terralog Technologies has unique expertise and experience analyzing compaction, subsidence, and well casing damage in a variety of settings worldwide. We have analyzed a wide range of completion designs and developed damage tolerance databases for several international oil companies.

Terralog Services

Well Casing Damage Analysis

Field Observation                                                  Well Damage Model

Oil and gas production, geothermal operations, in-situ mining processes, and gas storage operations can all lead to subsurface formation movement and associated well casing damage. Reservoir compaction and associated bedding plane slip and overburden shear has induced damage to hundreds of wells in oil and gas fields throughout the world. Well casing damage can be caused by compaction in the reservoir or by overburden formation faulting and bedding plane slip. Casing damage types can include compression and buckling, shearing deformations, and tensile parting. Compression and buckling damage is most often found within compaction zones near perforations, while shear damage is most often found within the overburden and at the top of compacting or dilating formations. Shearing damage in overburden and at top of producing interval has been noted in Gulf of Mexico, North Sea, California, and Southeast Asia.

Key features include:

•   Damage localization over very short interval.
•   Damage often tied to lithology stiffness contrasts (indicating weak
     interfaces).
•   Damage wells can be distributed over large vertical and lateral extent in
     overburden.

Axial compression and buckling damage occurs most frequently near perforations due to: 1) large pressure drawdown; 2) loss of lateral support from perforations and solids production. Terralog Technologies has evaluated well casing damage in a variety of structural settings world-wide and is the industry leader in analysis of damage risk and mitigation strategies. We provide such services as:

• Analysis of casing damage risks in oil and gas production, gas
   storage, steamflood, and geothermal operations.
• Numerical simulation of coupled formation/casing
   interaction to develop optimum completion designs which
   mitigate potential well damage.
• Design and operation of a casing deformation monitoring
   programs.

Well Design and Decision Analysis

 

Most appropriate casing designs to mitigate damage depend on: well orientation, damage type, damage magnitude.

Mitigation strategies include:

•   Adjusting well trajectory.
•   Modifying hole size and cementing practices
•   Changing casing size/grad (D/t ratio)
•   Changing inner completion design (gravel
     pack properties, centralizers, screens, rings,
     shunts, etc...)

Or....

Quantify and accept casing damage risks, adjust economic forecasts appropriately, and design for easier re- drills.

Casing Damage Risks in Stacked Pays Depend on:     
                         

•    Well position within each compaction zone
•    Well orientation through each compaction zone
•    Magnitude and timing of pressure depletion in each zone                                                                         


For Gulf area, an additional risk factor is that inner completions (pre-packed screens) can not always accomodate same deformation magnitude as production casing, resulting in failure and sand production.


Shear damage to inner completion can be mitigated by: 1) accomodating external deformation with hole size and cement design, and...
2) accomodating internal deformation with casing size and gravel pack design.


Three Dimensional Numerical Models

3D geomechanical models are required to simulate vertical compression on deviated wells and lateral shear dislacements on any well trajectory. Large-strain, inelastic material models are generally required to simulate deformation and failure of various completion designs.

Decision Analysis Techniques

An economic decision tree model can be applied to compare the costs and benefits of alternative well designs, while taking into account the inherent uncertainties in geomechanical model input data, well damage location, and effectiveness of various mitigation strategies.

In some instances the appropriate action is not to change completion design and simply accept and account for damage risk in economic projections.

Sample input table for sensitivity analysis

                                                                                  Axial strain estimate sensitivity

Simplified economic decision tree example

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SFI™, Slurry Fracture Injection™, TTI™, Terralog™, and SFI-Slurry Fracture Injection™ are trademarks of Terralog Technologies Inc.

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