Predicting the exact moment to close a well is something difficult and unpredictable, but what is certain is that once the emergence of fluids to the well occurs and we cannot control the migration of these fluids to the surface is the most appropriate time to make the decision to close the well, for this there are a series of methodologies for the closing of wells, taking into consideration that for the time of closing the well can be open hole or closed. Not only the closing of the well is affected by how the well is completed, are elements such as the equipment available at the surface, the method of closure with which the work team feels comfortable to apply are parameters that determine the choice of closure method to be applied.
However, it is not necessary to leave a lot of time to close the well once the upsurge is detected, so once the upsurge is detected, the well must be controlled according to the closing procedures in a correct way. Although the closing of a well deserves knowledge whose characteristics are technical, it is pertinent to add in this article that the procedures for closing an oil well require much common sense among the people involved in the closure.
During these moments of shutdown and control of the well, many emotions arise that cause pressure, panic, and anguish, so it is recommended to the personnel involved that there be control of the emotions and that the necessary discipline be maintained on the drill platform so that the well can be shut down and controlled.
In conclusion, if there is even the slightest suspicion that fluids such as oil and natural gas are entering the well from the reservoir, the most convenient thing to do is to close the well. Closing a well will differ in technique depending on whether the work being done is open-hole drilling, or whether, for example, tubewell rehabilitation activities are being carried out.
What are the reasons for closing an oil well?
First of all the most important thing about closing an oil well is to be able to protect the personnel and the drilling equipment, once the well is closed, the influxes like oil and natural gas are left inside the well, making sure that a fluid burst does not occur that could cause material losses like all the drilling and camping equipment, and most importantly people's lives.
As secondary element of importance is to be able to give time with the closing of the well, so that in a safe way the procedure of controlling or drowning the well can be organized, for this the well is closed, with the closing we are supposed to be sure that a burst cannot happen, however we only have a short time in which the personnel must act quickly and in a controlled way.
The closing of the well is only to give time to take those influences out of the well in a controlled way, that is to say, controlling the pressures inside the well, so that the formation does not fracture, or that the gas migrates until the well head explodes.
Technical considerations before closing the well
Before closing the well, it is necessary to observe it, to know if it is flowing or if it remains static. To study this condition it is necessary to know the generalized procedures for flow control, once the procedures for flow control are understood then it is necessary to discern which of the two types of well closure is the best applicable for the operation we are performing.
It is not the same to apply a hard closure to a cased well as a bare hole well, the other thing to take into account is that the procedures for closing a well also vary according to whether it is being drilled, if a tubing trip is made among others.
Flow control procedures
Before we start explaining what flow control procedures are, it is important to know that the only way the well will flow with the mud pumps off is if an upsurge is occurring in the well.
The reason the well flows with the pumps off is that the influx of gas and oil is entering the well and pushing the drilling fluid (mud) to the surface, and it is because of this phenomenon that we observe the well flowing, otherwise the well conditions with the pumps off are static.
Considering the above arguments we can conceptualize flow control procedures as all those procedures that allow us to observe the well with the mud pumps off, and thus determine the flow rate of the well.
We do not necessarily have to use the flow control procedures only when there are indications of an upsurge, depending on the security policies of the oil company also recommend for example to observe the well every time we are at the bottom of the well and prepare to lift the string. In particular, it seems to me that it is very safe to apply this procedure every time we are going to lift the string to the surface, because if we do it continuously, it will become a habit within the drilling and rehabilitation operations of oil wells to help reduce the risks of blowouts.
The way to observe the well is varied, you can observe the well to know if it is flowing by direct observation, through the use of flow sensors, or volumetrically. After checking the flow of the well, if it is flowing, it is recommended to start the procedures of the well closure.
When we are in the field and we want to observe the well to know if it is flowing or static, we must wait enough time, since sometimes we think that in the first minutes observing the well is more than enough to analyze its flow behavior, this short time used to observe the well is incorrect, since there are certain factors such as the depth of the well, the type of drilling fluid, the permeability of the formation and other factors that affect the time of observation of the well during the flow control. It is therefore recommended that the flow control be a test that lasts long enough to determine if the well is flowing or remains static.
From my own experience I can tell you that at one time in the 21X well we found our drilling operations stopped because of a lack of chemical material to continue preparing drilling fluid for the next phase of the well, and we had our doubts as to whether the mud density was sufficient to maintain the gas and oil inflows into the formation, For this purpose the South Division Manager of Lake Trujillo ordered us to perform a flow control test to see if the well was flowing, in this particular case we were told that we should be observing the well for 2 hours, since we were in the production well phase, approximately 15000 feet deep so we needed to wait that time.
As I said at the beginning of the article, that is why there are certain parameters for the closing of the well that depend on the conditions of each well, it is not the same to perform a flow control test for a shallow well, which may require less observation time to one that is deeper and suddenly requires more observation time.
To perform a flow control the first thing the engineer must do in the drill is to alert the personnel, then give the order to the driller to stop the rotation of the drill string, from there on the other procedures must be known by the driller, so we could say that the next step to perform is to lift the drill string until it is at wedge height, then turn off the mud pumps, then divert and check flow in the travel tank and finally observe the well to see if it is flowing.
It is important to note that these considerations should only be made if you are drilling in the well under construction, because if we are in a tube hole and the techniques and considerations to apply are others, not to make this article so extensive only explain the considerations for when we are drilling.
When the well is closed it is recommended to activate the annular ball valve, as it closes at any diameter of pipe, as there are other valves that crush or cut the drill pipe, so its application is usually not recommended, here is a picture of the type of valve that is not recommended to be activated during the closing of a well:
By closing the well it could be said that it is not totally controlled, if you are in the presence of an influx or emergence in the same way it is necessary to remove the influx of gas or oil using two techniques of well control which are: the method of the driller and the method of the engineer (also called method of waiting and densify) that will be explained in the next publication. However, once the well is closed, it is a firm step to prevent an uncontrolled form of surface fluid (blowout).
There are certain points that are key to understanding how well completion procedures are executed, these points are
Know the equipment or set of preventer valves (impidereventones), also called BOP set.
Know what the maximum surface annular pressure (MAASP) is and how it is found.
I hope that this technical material and engineering features are useful for all STEMSOCIAL readers, greetings and until a next delivery.
Reference consulted and recommended