updated February 24^th 2003

This important new feature in Cerberus release 6.7 (January 2003) allows the user to analyze the forces acting on a downhole packer caused by pipe movement and the effect of temperature, pressure, fluid density and flowrate as these parameters vary as conditions in the wellbore change. The purpose is to predict movement, tension or compression at the packer to determine if the packer will be unset or if the pipe may exceed yield limits. The program also models whether the buckling may prevent a wireline or coiled tubing conveyed toolstring from passing freely through the completion in either direction. Unlike existing tube move spreadsheets, Cerberus takes into account the deviation of the well in all calculations, and is also able to handle complex well geometries if desired.

Typical questions addressed by PACA include:

• What effects do changes in the wellbore conditions have on the forces acting on the tubing and packer?

• Do the triaxial forces exerted on the tubing over the life of the well exceed its operating envelope for tension, compression, collapse and burst?

• Is the movement provided for in the seal assembly adequate to meet my design objectives?

• What effect will well deviation and metal-to-metal friction coefficient have on the forces on my tubing and packer?

• What is the differential pressure across my packer during production or stimulation treatments?

• Will the tubing-to-packer force exceed a treating packer’s shear release rating while a stimulation treatment is performed?

• Can I run a wireline-conveyed tool both in and out of my tubing even though helical buckling is present? If not, could it be run on coiled tubing?

• How much does my tubing move at the packer in response to pickup or slackoff force changes at surface in a deviated well?

Getting Started

On the introduction screen, the user can choose what type of application is to be modeled. At the moment, there are two choices, conventional packer run on tubing or drillpipe, and inflate packer run on CT.

For the well geometry and survey data, the user has the choice of configuring a basic well configuration in the Wizard, or selecting a well previously configured in Cerberus. The former is very simple and quick, but limited to vertical wells (equivalent to a spreadsheet). The latter however can be as simple or complex as required, and may be deviated. This capability is one of the key features of the Cerberus tool movement wizard. An example of each is shown below:

The following screen shows the configuration of the tubing (or workstring or drillpipe). When the panel is first viewed, the yield strength and subsequent inputs are hidden (to keep screen complexity to a minimum) and accessed by clicking an <Advanced> button. The screen capture below shows the panel after this has been done.

The packer is configured next. In the beta version only one packer is considered, but we intend to allow multiple packers in subsequent versions.

Configuring Scenarios

Once the geometry has been configured, we move to the “Scenarios”, the wellsite conditions which we want to model. We start with “Initial Conditions”, followed by “Subsequent Conditions”. The program calculates the pipe movement (if any), degree of buckling and resulting forces and stresses caused by the change of conditions between the two steps. The user can edit any of the input parameters by clicking on the item in the screen below. The diagram on the right will show the current pipe status schematically relative to the initial conditions, with data labels next to the key points of interest.

Each line item is edited on a separate panel. This allows plenty of space for advanced options. For example, temperature can be entered either as a simple linear gradient, or a complex profile can be imported from a separate spreadsheet or file. The following are cropped screen captures for three such items:

For the subsequent conditions, the user can edit any parameter, but the Scenario selection will configure the Wizard appropriately to a particular operation. You can configure up to four different scenarios, reflecting key operations during the life of the installation, and later model the effect of these scenarios occurring in sequence over time.

The results might typically look like this. The items in yellow indicate that they are different from the Initial Conditions:

Clicking on the Analysis button brings up detailed results. 

Warnings are given for pipe yield, packer unsetting or other serious conditions!

The Graphs and Tables panel will bring up several different charts of relevant data, including tubing stress, burst/collapse analysis, and temperature and pressure gradients.

Time-Lapse Calculations

Next, up to four different “scenarios” can be run in sequence, to simulate changes over time (“time-lapse”). Thus, you might model events when the packer is first set, followed by the effect of temperature and flow changes as the well produces over many months or even years. The following screen allows you to edit the order in which the scenarios are calculated, and to include or exclude a given scenario.

The results for each scenario can be viewed in the sequence they were run.

Finally, you can view how the tubing stress varies with each scenario, and make sure that it always remains within working limits. (note: following screen capture is very preliminary)

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