Frequently Asked Questions About STABView

1. How does STABView differ from other commercial borehole stability programs available on the market today?
2. How does STABView evaluate the risk of borehole collapse while drilling?
3. How will STABView help me determine drilling parameters that will result in a more stable well?
4. What choices do I have for units in STABView?
5. Can I use STABView to assess borehole collapse risks for underbalanced wells?
6. Can I use STABView to assess borehole instability risks for directional and horizontal wells?
7. How does STABView evaluate sand production risks?
8. What well completions options are available for sand production analyses?
9. What options are available for reservoir fluid types and properties?
10. How does STABView evaluate fracture breakdown risks?
11. What features are available for assessing failure risks on weak planes such as faults or natural fractures?
12. How much does it cost to license STABView?
13. What is the technical support policy for licensed users of STABView?

Q1: How does STABView differ from other commercial borehole stability programs available on the market today?
A: Drawing on a combined total of more than 35 years of experience in solving industry geomechanics problems, Weatherford Geomechanics Services has developed several unique approaches to borehole stability, lost circulation and sand production risk assessment. STABView was primarily designed for technical drilling, completion and production engineers, and not research scientists with advanced degrees in geophysics or rock mechanics. We have evaluated and tested many approaches to integrating the theoretical and practical aspects of well construction, drilling engineering, mud engineering, production optimization and oilfield operations. STABView combines the best of these approaches into a user-friendly interface.

The following are some of the unique features developed for STABView:

• mud-shale physico-chemical interaction
• capillary threshold pressure model for oil-based muds
• filter cake and wall coating effects
• 2D elastoplasticity with pore pressures
• modified 3D Lade failure criterion
• non-linear Hoek-Brown failure criterion
• field calibration procedures for stability analyses
• kinematic considerations for failed rock detachment
• prediction of the size and shape of the zone of rock yielding
• in-situ stress changes due to reservoir depletion or injection
• flexible output graphics designed for rapid sensitivity analyses

Q2: How does STABView evaluate the risk of borehole collapse while drilling?

A: STABView has two primary models for evaluating borehole collapse risk. Both of these models assess the mechanical integrity of the rock around the circumference of the borehole. STABView's 2D model evaluates the size of the zone of yielded rock around the borehole using the theory of elastoplasticity, including pore pressures effects during over- or underbalanced drilling. This model is useful for vertical wells, or for horizontal wells that are approximately parallel to either the maximum or minimum horizontal in-situ stress. STABView's elastic 3D model evaluates the bottomhole pressure or equivalent circulating density (ECD) at which shear yielding initiates on the borehole wall using linear elastic theory. When calibrated based on drilling experience for offset wells, this model has been shown to reliably predict the bottomhole pressure (or ECD) at which catastrophic hole collapse will occur.

Q3: How will STABView help me determine drilling parameters that will result in a more stable well?

A: STABView can evaluate the sensitivity of borehole instability risks to a large number of input parameters. Of the parameters that can be controlled in the drilling operation, the most notable are the mud equivalent circulating density or bottomhole pressure, the effectiveness of filter cake or wall coating additives for preventing mud pressure penetration into the formation, and the trajectory of the wellbore relative to the principal in-situ stresses and weak bedding or fracture planes. Other controllable factors which can be assessed include capillary threshold pressure effects for oil-based or pseudo oil-based drilling muds, the effects of high salinity muds for shale inhibition, and the consequences of sudden decreases in bottomhole pressures due to swab or surge effects. Casing setting depths may also be optimized with STABView.

Q4: What choices do I have for units in STABView?

A: The user can select from Modified SI, U.S. Oilfield or customizable units. It is possible to switch from one unit system to another at any point in the program. Higher precision unit sets are also available for shallow wells and pipeline directional drilling problems.

Q5: Can I use STABView to assess borehole collapse risks for underbalanced wells?

A: Yes. Both the 2D and 3D models in STABView are capable of assessing borehole collapse risks for conditions where the bottomhole pressure is less than the pore pressure of the formation being drilled.

Q6: Can I use STABView to assess borehole instability risks for directional and horizontal wells?

A:  Yes. The 3D linear elastic model in STABView is capable of assessing borehole instability risks for all possible well trajectories. The 2D elastoplastic model is capable of assessing borehole instability risks for wells that are within 10 to 15° of a principal in-situ stress orientation. As such, slightly deviated wells and horizontal wells that are sub-parallel to the horizontal in-situ stresses can be simulated using the 2D model.

Q7: How does STABView evaluate sand production risks?

A: STABView has two different models for evaluating sand production and openhole collapse risks. Both of these models assess the mechanical integrity of the rock around the circumference of the borehole or a perforation tunnel. The 2D model evaluates the size of the zone of yielded rock around the borehole or perforation as a function of drawdown pressure using the theory of elastoplasticity with steady-state pore pressure effects. It is this yielded material that is most susceptible to detaching from the borehole or perforation wall and falling into the well. The 3D model evaluates the bottomhole pressure at which shear yielding initiates on the borehole or perforation wall using linear elastic theory. When calibrated based on production experience for offset wells, this model can predict the bottomhole or drawdown pressure at which unacceptable sand production or catastrophic hole collapse will occur.

Q8: Which well completions options are available for sand production analyses?

A: Different modeling options are available, including openhole completions with or without a slotted liner or screen, expandables and perforated completions with cylindrical or hemispherical perforation cavities.

Q9: What options are available for reservoir fluid types and properties?

A: Steady-state fluid flow solutions are available in STABView for liquid-saturated and gas saturated reservoirs. The algorithms used for gas reservoirs account for non-ideal gas behavior and non-Darcy flow effects.

Q10: How does STABView evaluate fracture breakdown risks?

A: The primary 3D fracture breakdown model in STABView is based on linear elastic theory and calculates the bottomhole pressure (or ECD) at which a tensile fracture develops at the borehole wall. Fluid penetration, thermal stress, capillary pressure and osmotic pressure effects can be assessed with this model. Models for the initiation of passive shear failure and fracture toughness based breakdown are also available.

Q11: What features are available for assessing risk of movement on weak planes such as faults weak bedding planes, or natural fractures?

A: Two models are available for assessing these risks. One model predicts the bottomhole pressure at which shear failure will occur on weak planes. The second model predicts the pressure at which tensile failure occurs on weak planes. These models are useful for identifying the maximum pressure in disposal, waterflood, injection or gas storage wells.

Q12: How much does it cost to license STABView?

A: Contact us at stabview@advgeotech.com
for current pricing information.

Q13: What is the technical support policy for licensed users of STABView?

Companies who purchase STABView without a maintenance and support agreement will have access to technical support for problems pertaining to the installation of the software, as well as any technical problems related to the software encountered when initially running the program. Companies who purchase STABView are strongly urged to purchase a support and maintenance option for the software. These companies will receive a higher priority for assistance, and extensive technical support when addressing problems or bugs in STABView. The maintenance option also entitles such companies to intermediate upgraded versions of STABView as they become available, including code improvements, bug fixes and new features. New releases of STABView with major additions will be available for an upgrade price. Companies purchasing the maintenance option will also receive a discount on in-house or external short courses on borehole stability and sand production offered by Weatherford Geomechanics Services. Contact STABView Technical Support at software@advgeotech.com to receive a current list of software purchase, maintenance and training options.