LOT/FIT

Introduction

While drilling a well, the rock wall are under effect of compression and tensile stress by the drilling fluid pressure. LOT/FIT are pressure tests to ensure the well safety and integrity to avoid problems such as:

• rock collapse

• lost circulation

• shear rock failure caused by compression stresses

• fracture failure of the rock by tensile stresses

LOT pressure test is used to determine the strength or fracture pressure of the open formation, usually conducted immediately after drilling below a new casing shoe. FIT pressure test is used for testing strength of formation and shoe to designed pressure, or the maximum pressure that the wellbore can withstand with regard to the casing setting depth.

To maintain a small safety factor to permit safe well control operations, the maximum operating pressure is usually slightly below the leak-off test result.

The region of the graph bounded by the fracture pressure curve on the upper side and by the pore pressure curve) on the lower side is often referred to and defined as the Drilling Operating Window :

LOT/FIT tests help to keep the well in safety region of pressure by depth and to find critical points.

Above is shown a typical pressure-volume curve with LOP (Leak-Off-Pressure) point and FIT (Formation Integrity) point. Next is shown the fracture propagation and the when the pump stops.

Understanding the implications of mud weight, pore pressure, and fracture pressure is important in pressure management and well control assurance.

How to use

Enabling LOT/FIT Add-on

LOT/FIT add-on can be added to temporal channels charts in edit mode.

Select Leak-Off / Formation Integrity Test option:

Save and go back to dashboard:

Once the LOT/FIT Add-on is enabled there will be a new action added to the widget “Automated Tests”:

Clicking it will bring up a dropdown menu

Select a test type:

Leak-off Test (LOT)

After choosing a test it is possible to select an interval to run the test on.

Simply click and drag to determine the interval:

Next it will be presented with the calculation parameters. It is possible to inform tvd casing shoe, md casing shoe, mud weight and which asset and channels the test should based on. Also it is possible to disable pressure loss calculation and configure units:

Next it is possible to select the linear portion of the interval:

Now the system is able to display the preliminary results and also the EMW :

It is possible to comment and save the test as a note.

This note will be displayed on the dashboard timeline:

The comment field can also be edited later:

It is possible to adjust the fitted line or the results by selecting the interval span or edit the calculation parameters. Adjusting the linear interval is possible by dragging or resizing the interval marker:

It is also possible to manually override some constants used by the algorithm by clicking “Edit custom parameters". It is possible to override the leak off pressure found by the algorithm, pressure loss window and deviation threshold:

Formation Integrity Test (FIT)

Another possible test is the Formation Integrity Test (FIT), the usage is similar to the previous test where it must also select a period of time over which to test then select the asset and channels to test, but this algorithm does not require to specify a linear interval.

The result is shown below:

Like in the other test this result can also be stored as an annotation:

LOT and FIT annotations differ by the shade of purple:

In the messenger global room the annotations are rendered as follows:

It is possible to view the details of each test annotation