Getting results is made easy in Cerberus by the Question & Answer Wizard.  The main calculation tasks are presented as questions, and you simply click on the one you are interested in. The symbols on the left indicate the type of result or calculation you will see, for example a numerical result, a graph or a calculation wizard. The questions are divided into four logical sections, as shown below. [Note that some of the questions are different for jointed pipe and coiled tubing, click on the links to see those versions]

• Selecting the toolstring

• Getting into and out of the well

• Performing the job at depth

• Other calculations

What is the best weak point selection for the job? - the Weak Point Wizard helps you chose the optimum weak point to ensure you can achieve maximum overpull if you get stuck, yet still break the weak point if you need to without risk of breaking the cable first. Incorrect selection of weak point for a job in a deviated well is a major cause of lost tools, because many engineers tend to underestimate the effect of the additional drag caused by the bends in the well.  Example

How much weight do I need to get down? - the program calculates the weight required to overcome wellhead pressure and stuffing box friction to get into the well at surface, then determines if additional weight is required to overcome fluid drag if the well is producing.

What toolstring geometry will be able to navigate the bends in the well? - the Toolfit Wizard will tell you what tool dimensions (length and diameter) will fit in a given well size and dogleg severity. If it is necessary to bend the toolstring to get around the corner, the Wizard will tell you how much force is needed.

These questions concern the process of getting the tools to the required depth and out again. Several of the results involve graphs of key properties plotted against depth.

Can I reach the target depth and return to surface safely? - can you reach the target depth without cable compression, and then return to surface without breaking the cable or weak point. This gives you a quick answer to one of the most important questions.  Example

Plot a graph of surface weight against depth - this essential graph shows you what the surface weight readings should be while running into and out of the well. Print this graph and give it to the winchman for comparison with actual measurements. The same graph displays the weak point and cable breaking strength limits, and hence what your available overpull is at each depth if you should get stuck. [Note: this is especially useful when run in real-time with the Orion data acquisition system]  Example

Plot a graph of cable head tension against depth - this graph shows you how the tension at the cable head, or weak point, will vary while running into and out of the well relative to the cable breaking strength and weak point rating. This graph is essential for correct selection of the weak point.  Example

Plot a graph of maximum set-down force against depth - how much force can you set down at the end of the toolstring (by slacking off at surface) for each depth. This has limited applications for wireline, because in most cases the available set-down weight is too small to do much work, and unlike pipe the cable is unable to support compression so you can’t push. However, the calculation may be helpful when running heavy tool strings, and for applications like moving sliding sleeves or setting gas lift mandrels.  Example

Plot a graph of maximum pick-up force against depth - this very important graph shows you how much pull you can apply at the end of the toolstring for each depth before you break the cable or weak point.  Example

Plot a graph of stretch against depth (not shown on graphic) - the program can calculate what the stretch is at each depth, and hence the “true” depth. Some customers use this feature for depth correction, particularly when running depth-critical applications on slickline, for example perforating.  Example

What production flowrate would prevent the tools getting downhole? - if the well is flowing, the tools may be stopped before they reach the target, especially in the production tubing where the fluid velocity and hence drag is highest.  Example

What downward flowrate would push the tools to the target depth? - it may be possible to pump the tools to the target depth. This feature calculates the flowrate required at each depth. Care is required because the required rate will vary with depth, but pumping at a high rate at all depths may break the weak point or even the cable itself. [note: feature under development, scheduled release Q2 2002]

How fast can I run in hole without risking compression and birdcaging? - generates a graph of maximum speed vs depth to determine if fluid drag on the tool and cable will cause the tool to go down slower than you are spooling the cable into the hole, resulting in bird-caging and potentially serious damage to the cable. This is most often a problem when running into a viscous fluid in small diameter production tubing.

If the production tubing is buckled, will I be able to pull out? - buckled, or corkscrewed, production tubing can present a major problem. Going into such tubing may pose no difficulty as the tools drop under gravity, but as soon as you reverse direction and try to come out, the cable pulls against the helical tubing and the greatly increased drag may make it impossible to pull out without exceeding the cable breaking strength. This Wizard enables you to estimate the degree of buckling, and then superimpose this profile on the well geometry when performing the regular calculations. This feature is unique to Cerberus.  Example

If I need a tractor to reach TD, what is the maximum pull required? - this graph of how much tractor pull is required at each depth to overcome drag is useful for two reasons. First, you can ensure that the tractor under consideration is capable of performing the job (we recommend SmarTract), and secondly you can optimize the tractor pull at each depth to avoid running it unnecessarily at full power all the time.

This group of questions concerns the ability of the tools to do the required job once at the desired depth. Most of the results involve specific numbers, rather than graphs.

How much force can I set down at this depth? - the program calculates the maximum set down force, and the corresponding surface weight.

How much pull can I apply at this depth? - the program calculates the maximum pull, and the corresponding surface weight.

What will the depth counter read, correcting for stretch? - the program calculates the stretch at each depth, which can used to correct your measured depth at the wellsite.

What are the forces acting on the tool string and cable at this depth? - this feature gives a detailed break-down of the component forces which are contributing to the net situation. This can be useful to understand if difficulty reaching depth is due to frictional forces (using rollers may help) or fluid effects (choking the well or circulating out to a different fluid may help).

What flow rate could push the tool string back up the hole? - for example after perforating? [This calculation assumes steady-state conditions, it does not consider the initial shock wave immediately after perforating]

What pump-down rate could risk breaking the weak-point or cable? - pumping too hard may break the cable or weak point.

Plot a 2D graph of cable tension vs Depth - this is one of a family of graphs which display the conditions along the tool and cable with the toolstring fixed at a particular depth. The other graphs include hydrostatic pressure and wall contact force.

View a 3D animation of cable tension vs depth - this diagram shows the status (tension/compression/yield) of the tools and cable relative to the well geometry. You can animate the diagram in order to view how the status changes with depth. This is particularly useful when demonstrating a difficult point to a client.

Calculations and features which don’t fall into the previous three categories can be found here.

Use the Report Wizard to generate a full analysis and print a report - this Wizard allows you to perform all the key calculations and print a summary in one step, rather than do each one separately. This task is usually done last, after a detailed analysis has been completed manually.

Run a sensitivity analysis of key parameters - this task is extremely important, in order to assess whether the job is marginal or straightforward. Running the project for only one set of input parameters runs the risk that slightly different conditions encountered during the job may produce a different result. The user should test the robustness of the results by trying a range of parameters. The Analysis Wizard automates this task.  Example

The tool or cable is stuck. Perform a pull test and estimate the stuck depth - the Stuck Point Wizard allows you to perform a pull test to determine where the cable or tool is stuck downhole. This calculation is relatively simple in a vertical well, but in deviated conditions only this program can account for all the downhole forces when answering this question.  Example

If the well continued on the same trajectory, how much further could I go? - results may indicate that you can do the required job at the current depth, but if the well were to be extended a little further would this change matters? This is particularly useful for operators who are considering re-entry and well deepenings. Also, this result is a qualitative indicator of the difficulty of the present job - if a hypothetically deeper well can be entered successfully, the current well will most likely pose few problems.  Example

What is the risk of differential sticking? - this Wizard allows you to specify downhole conditions which can potentially lead to differential sticking, and then estimate the effect of this sticking on the surface weight and the ability to pull hard enough to get free should it occur.  Example

Find the friction coefficients which give the best match to observed data - this Wizard automates the task of finding what the friction coefficients should be to match measured data to model predictions. Previously, this involved a trial-and-error approach of manually changing the friction coefficients and generating the surface weight graph, noting the offset and going through the process again with slightly modified coefficients until a match is obtained.  Example

Is there a risk of drum crush? (not shown on graphic) - Cerberus can warn you if there is a significant difference between the run-in and pull-out cable tension (such as might happen if the cable speed is excessively high) with the consequent risk of drum crush.