In this opportunity I would like to present to you an analysis with engineering characteristics about the importance of applying the drillability tests regarding the operations in the drilling of oil wells.
There are certain drilling parameters that are important in order to drill and deepen the well, the driller together with the drilling crews carry out the drilling operations and in turn have the responsibility that these drilling parameters do not take deviations from the values dictated by the drilling program.
The Drilling Operations Engineer is responsible for applying drillability tests especially when there is a slight presumption that there is a drilling parameter that is outside of the drill program values.
Relevant points to be addressed in this article to give a meaningful analysis about the importance of the application of perforability testing include the following:
1] What is perforation testing?
2] Favourable perforation parameters for applying perforation testing.
3] Operational procedure for applying perforation testing.
What is the perforability test?
The perforability test is a test whose mechanism seeks to find the new values that will help optimize the penetration rate. Perhaps for many of your reading friends who read this part, you may be wondering:
When we talk about penetration it is because it is the advance that the drilling has as it gets deeper into the well, now it is called rate due to the change of rhythm that exists between the feet that is advanced for each elapsed hour, so we could say then that the penetration rate is the speed with which the drilling is penetrated
Weight over Wick (PSM): Sometimes the value of the weight over the wick indicated by the program does not turn out to be a reliable value, since that value is based on a lithology of the formation to be perforated that in reality can vary. For example, we can start drilling with a wick weight for a soft lithology, but:
It is most likely that there is a sudden change in lithology, for example a stretch of sandstone can be drilled and we will find a stretch of limestone, which means that when we find a harder formation we will need more weight on the wick.
 Revolutions per minute: one of the advantages since the emergence of the technique of rotary drilling is the ability to have a system that spins the string, the more revolutions per minute, the higher the rate of penetration, however you must find a value according to the requirements and demand that you have at the time, if there is a change in lithology, it is likely to require a readjustment in this value, so it is advisable to apply a test of perforation.
Favourable drilling parameters for applying the drillability test
It is very probable that during the application of the test of perforability there are certain parameters that must be clear in their values, since if this is not the case they can delay the time of their application:
1] It is necessary to maintain an optimum value in the test drilling speed, where preferably very low values are not handled, since this would delay the time of application of the test.
2] It is highly desirable that the perforability test be applied at a constant lithology interval, i.e. where no abrupt changes in lithology occur, as these abrupt changes could delay the test application time.
3] It is important that drilling is achieved very close to balance, i.e. that the perforability test is applied under a condition where the hydrostatic pressure of the drilling fluid is equal to the pressure exerted by the formation, i.e. that a not too high gradient is used between the mud gradient and the formation gradient.
Operational procedure for applying the perforability test
You can select an optimal wick weight to start the test, this value could be around 5000 lbs and can serve as a reference value to take the time.
The other value that should be kept fixed is the other drilling parameter on which the penetration rate depends, and this is the revolutions per minute (RPM).
While keeping the RPM values fixed, the weight values on the wick that have been previously selected for the test should be varied while noting the shortest time spent losing the 5000 pounds that were taken as a reference.
The next step is to select another fixed wick weight value which should be chosen as the one that accompanies the previous shorter time.
The RPM values must be varied and the shortest time must also be selected.
Finally, it is important to evaluate the ROP values with these last two values of PSM and RPM during a time interval. As we have already obtained a new ROP value, it is advisable to compare this new ROP with the ROP values you had before the test.
Conclusions and contributions
It is very important for the oil industry that oil engineering students are taught the basics of this perforability test, because when we are in the operational activities of drilling we often find ourselves under circumstances where the speed with which we are drilling the oil well is minimized to values that are not convenient because it will take us longer to achieve drilling and construction of an oil well.
The approach to optimize this drilling speed is to perform the drillability tests as explained in this post with the intention of correcting the values of certain drilling parameters such as the weight on the drill string and the RPM of the drill string.
I only hope that this post with unedited characteristics and loaded with engineering knowledge can be useful to the great Steem community, greetings and until a next delivery.