Fig. 1. The lithology derived from a LAS file.
Payzone simulators can be used in well planning whenever the driller has sufficient information to let a well be drilled in simulation before spud. The major objective is to be able to experiment with different scenarios without incurring the costs of drilling a real well.
One possible use is illustrated in exercises DE 6 (Importing a LAS File) and DE 7 (Optimizing the LAS Well). These are found in the set of exercises on Well Design and Evaluation for Payzone J. The two exercises show schematically how, once a well has been drilled and logged in a particular area, log data and the drilling record from the first well can be used to plan an optimum set of operating conditions for subsequent wells to be drilled in the same area.
In exercise DE 6 it is shown how a set of field data in the form of a LAS file can be imported into the simulator to make a drillable lithology. The set of data channels in a LAS file is not fixed and the file may or may not contain information on the rock strength. If it does not, some means will have to be found for inferring the rock properties indirectly. When this is done and the file is converted, a Payzone lithology is otained and can be viewed (Figure 1).
Fig. 1. The lithology derived from a LAS file.
The lithology can then be incorporated into a Payzone "State" by use of the State Editor. At the same time, the State should be provided with the information on the set of bits that will be available and the various rig and other parameters that will influence the drilling operations.
Optimizing Drilling
Once the State is constructed, the optimization process can begin. The
first task is to tune the simulator so that it reproduces the drilling
response that was recorded in the original well. This is done by setting
the same bit and operating conditions as were used in the first well,
and then tuning the bit aggresivity and wear rates so that the original
drilling response is faithfully reproduced. Payzone J has the ability to
record a Depth-Time plot, so this is now done to serve as a reference.
(see Figure 2, the red plot)
Fig. 2. The original (red) and optimized(blue) Depth-Time plots.
Now the driller may re-set the simulation and try drilling with a different set of operating parameters (WOB, rotary speed, bit nozzles, mud flow rate, mud type .... ) to see if a better set of conditions can be found for that bit. If there is room for improvement, a saving in time may be found (Figure 2, the blue plot).
It is also possible to experiment with different bit types, to see if a different style of bit may do a better job, although the driller will be less confident of a prediction of this type unless he has a good knowledge of how different bits behave in the suite of rocks being drilled.
Last update 20 March 2001.