In this opportunity I want to present you this post where I explain the importance in the interpretation of the drilling parameters of petroleum Wells.
It is a topic I thought about with the intention of developing some ideas that complement the academic, but of course also focused on some operational experiences when I participated as a drilling operations engineer in the drilling and construction of some wells in the Tomoporo petroleum field (Venezuela).
The teaching that I have been giving in the diverse topics treated in my articles has provided a development in all the aspects referring to the drilling and construction of petroleum wells, that is why the best way to give continuity to the teaching on the petroleum aspects could not be other than the interpretation and evaluation of the drilling parameters, always focused on the engineering and the examples and field experiences.
Within the study of oil engineering and the contribution it gives to the development of the oil industry has led me to develop for you the importance of drilling parameters in the construction of an oil well, that is why my main objective is to inform the audience present and active on the platform live all the basic concepts relating to the parameters of drilling, so they can become familiar with all the parameters of drilling that will be explained in this post.
Now the purpose of presenting this article is to make a complete summary of the theoretical aspects that involve drilling parameters and perhaps give answers to many of the questions and concerns that may be developed by some trainees who want to expand their knowledge in well drilling.
The structure will be carried out under the following order of ideas:
1] Objectives of well drilling.
2] Analysis of the conceptualization of drilling parameters.
3] The most important parameters involved in well drilling.
4] Obtaining and reading of the drilling parameters
5] Optimization of Drilling Parameters to reduce drilling costs
Objective of well drillings
A well is basically drilled to meet two main objectives:
1] To drill an exploratory well, in which it can be checked if there are mineral resources such as petroleum and/or natural gas.
2] To drill a well in development, a well is drilled in which it is certain that there is petroleum and/or natural gas, for this purpose a hole is constructed where a communication system is established between the subsoil and the surface to extract petroleum and/or natural gas.
It is important for the study and understanding of the parameters involved in drilling wells that the reasons for drilling an oil well are clearly understood.
When the reasons for drilling a well are clear, then the need to know the drilling parameters and a correct reading of them when the well is being drilled arises.
Among the drilling parameters in which you must establish a correct supervision are
1] Penetration rate (ROP),
2] RPM (drill string rotation)
3] Pump flow rate (measured in gallons per minute, GPM).
4] Pump pressure (measured in psi).
5] Weight over wick (WOB) measured in lb.
6] Torque (lbs-ft),
Other parameters may be important, but those listed above are the most important when monitoring drilling continuity.
Analysis on the conceptualization of drilling parameters
The drilling parameters are all those measurable elements under which we can take the execution of the drilling and construction of a well, these parameters must be monitored so that there is the possibility of evaluating the deviations of these parameters during drilling and compare them with the parameters according to the drilling program.
In Venezuela the oil industry and in particular the drilling processes handle the supervision of the drilling parameters in units of the English system, it is important to mention that many of these parameters can be studied in the international system, however all the equations involved for certain drilling parameters use English measurement system such as: inches, feet, barrels, gallons, pounds over square inches (Psi), pounds, among others.
The recommendation is that if many of these parameters are obtained in the international system, a conversion factor is made to bring them into the English system. Even many tools and equipment involved in the drilling measure parameters in the international system of measures, from experience I can tell you that many drilling fluid engineers measure the density of mud in grams / cubic centimeters, these fluid personnel take these mud balance density readings in that measurement system, however then perform a conversion system to bring them to pounds / gallon or in its absence to pounds / cubic foot.
It is necessary that the mud density is measured in English units of measurement, as for example the hydrostatic pressure of the drilling fluid = 0.052 x fluid density x true vertical depth.
This conversion factor of 0.052 means that the hydrostatic pressure of the mud can be expressed in PSI, as long as the fluid density in pounds/gallon and the true vertical depth in feet are entered.
The execution of the perforation could not be carried out without the evaluation and supervision of the parameters of perforation, this means that as we go deeper in the perforation we must compare the values for example of penetration rate (Drilling speed (ROP)), Rotation (RPM) Wick weight (WOB) with the values given in the drill program, if, in the event, these parameters are not monitored, multiple drilling problems could occur which would make it impossible to drill.
The conclusion of the case is that if we had the density and depth in units of the international system, we could not replace them in the equation proposed for the calculation of hydrostatic pressure of drilling fluid.
Parameters involved in well drilling
It is very important to know the current depth of the drill wick, this depth must be known at all times, this information of the depth of the wick is a data under which all other values are referenced.
During drilling we must know the depth of the wick, since it provides us with an estimate to know the depth of the well, this allows us to determine precisely the changes in the well and in the formation, it also allows to carry out precisely the pressure calculations, The change in the drilling rate (ROP) allows to identify lithological and drilling conditions changes.
In this respect, it can be concluded that if the depth of the wick is erroneous, erroneous estimates of the penetration rate (ROP) and interpretations of lithological changes in the perforated formations are most likely to be made.
During pipe travel manoeuvres, knowing the depth and speed of movement (ROP) allows precisely to determine and monitor the displacement volumes and the induced pressures. This also allows the laying of the casing strands at specified points in the well to precisely locate and test the production areas of the reservoir.
The penetration rate provides one of the main parameters recorded during the drilling operation. The units of measurement of the penetration rate can be in terms of the depth gained over a given time interval, usually expressed in feet/hour.
There are several factors that may affect the ROP, including:
Correct selection of the drill wick: if a wick is not selected according to the hardness of the lithological formation to be cut, the penetration rate is most likely very low, to the point where maybe the drilling stops at some point.
There are other parameters of perforation that when altered can vary the penetration rate, these parameters are: rotaria speed (RPM), weight on the wick (WOB), not only rotaria and weight on the wick affects a controlled penetration rate, if not, conditions such as differential pressure, hydraulic well cleaning, increase in well depth, lithology changes, wear of the wick teeth and other conditions may affect the penetration speed of the well.
Using the figure above we can analyze the behavior of the penetration rate (ROP): There in the graph we see how a constant ROP value is maintained, but when passing through the area whose lithological formation is a packet of limestone, ROP decreases considerably, this is because limestone is a very hard rock, which makes the ROP decreases considerably.
After drilling, the ROP is kept constant again. When passing through the lithological formation whose rocky area is sandstone, in this area the ROP increases because the sandstone is a soft rock and easy to drill.
The conclusion of the case is that if there is a sudden change of the ROP, it is most likely that there is a change of lithology from a soft formation to a hard formation and vice versa, that is why you have to be sure of the formation that you are, this with the intention of being able to rule out that a sudden change of the ROP has to do with a wear of the teeth of the drill wick.
One of the key elements of drilling is the rotation of the strand, actually when you switched from drilling wells to percussion by rotating drilling, you started to introduce some essential elements so that the strand of pipe had rotation. The first incorporated element was the quadrant joint or Kelly, however as time went by this element was replaced by a less complex and easy-to-use element to rotate the strand, this element is the top drive, Below I show you a public domain image of pixabay, in which you can see the component: Top drive.
The top drive provides power to the drilling strand by turning it, when the strand rotates, the drill wick at the bottom of the well also rotates, thus facilitating the drilling process, that is why one of the elements that influence the rate of penetration is the rotation of the strand.
The rotation of the drilling strand is a drill parameter that is measured in revolutions per minute, that is the turns that the strand gives in one minute (RPM). Therefore we can say that one of the simple rules within well drilling is that if the RPMs are increased, then the ROP will increase. In soft formations, the ROP is directly proportional to the RPM, resulting in a linear increase in the penetration rate, whereas for hard formations, an increase in the rpm provides a decrease in the ROP.
So we can conclude that for soft formations it is advisable to use high RPM, while for hard formations it is recommended to use low revolutions per minute to significantly increase the penetration rate (ROP), however for the use of PDC or diamond drill wicks, it is advisable to increase the RPM, as an increase in the RPM using these drill wicks will provide an increase in the penetration rate (ROP).
This is a drilling parameter in which the driller is heavily involved as an operator, since when drilling is started the mud pump parameters that are adjusted from the driller's cabin are: the pump speed (strokes/minute) and the pump pressure the parameters initially involved when the mud pumps are turned on.
The drilling fluid circulation system can be considered a closed system, and to move large volumes of mud from the storage tanks to the bottom of the well, it is necessary to apply a fairly considerable initial force, a force that translates into pressure throughout the circulation system, this force required to move the fluid is provided by the mud pumps.
The measurement of the pump pressure is performed by a pressure transducer that is placed at the base of the stand pipe (vertical pipe), which in the figure above would be point No. 8, this valve is known as a shock valve or pressure cell, and is tightened with hammers. As we all know the units of measurement of pressure in the international system are pascals, however the measurement is made in PSI in units of the English system.
There are many parameters that depend on the mud pump pressure varies, most of these parameters that influence the pump pressure are properties of the drilling fluid, in this case I can mention some as: density, viscosity, speed, however other factors such as: depth of the well, hole geometry, size of the drill string nozzles and pump efficiency can alter the value of the pump pressure.
The speed with which the pump pistons work is very important, especially for the calculation and estimation of the flow rate, in the drill's cabin there are the commands to adjust the speed of the pump. The pump speed is no more than the strokes the pump piston gives in one minute, in English it is said strokes/minute, or better known also as stroke/minute (SPM).
It is very important to keep track of this parameter, since with the pump speed (SPM) you can estimate the flow rate value in gallons per minute (GPM).
Knowing the weight of the drill string, which in turn is supported by the hook and the traveling block, allows us to determine important information when drilling or running pipe. The weight of the tubing string is the entire weight supported by the hook, and is obtained by multiplying the nominal weight of the tubing in pounds/foot by the total length of the tubing string. A sensor placed by hugging the drill string that supports the traveling block and the hook measures this weight, which is known as the load or hook weight.
When the string is off the bottom and not moving, the hook load is equal to the effective weight of the string when the block supports the entire weight of the string. The effective string weight will be slightly different from the calculated or theoretical weight because it is due to a buoyancy factor in the mud. When the drill string touches the bottom of the hole, the load on the hook will decrease, part of the weight of the string will be supported by the bottom of the hole, this is known as the weight on the drill string, so the following equation can be defined:
Weight of the drill string = Load of the hook + Weight on the wick, so if we clear the weight on the wick we get that:
Weight over Wick (WOB) = Weight of Drill String - Hook Load.
Example of obtaining and reading a drilling parameter
The unit of measure of the rotary torque is the force that is applied against a moved distance, for example pounds per foot (Lbs-ft).
If an electrical measurement is obtained, the torque can be expressed in terms of current (Amps), or can be converted to a unit of force per distance. However, this conversion is not linear, and will vary in each piece of equipment depending on the power and the rotating equipment. A conversion chart, or graph, can be obtained from the equipment manager or mechanic.
Here is an example chart for converting from amps to pound-feet:
Optimization of Drilling Parameters to reduce costs associated with drilling an petroleum well
Optimizing the drilling parameters, means that parameters such as ROP, RPM, pump pressure, gallonage, torque, weight over the wick work in appropriate units so that the drilling and construction of an oil well is executed in the shortest possible time and generates the lowest economic costs.
In this case among the variety of drilling parameters, I want to evaluate and analyze the incidence of having a correct supervision, control and monitoring of the ROP. We must study all the parameters that affect the abrupt changes of the ROP, so that in this way we can guarantee a completed well in the best of times and with the lowest possible cost.
To optimize the ROP, all decisions must be taken that result in drilling a well with the highest possible ROP, without these high ROP rates having a negative influence on drilling operations.
By not negatively influencing, I mean that even though a high ROP is considered, it is still the case to maintain a controlled rate because of all the factors that have an influence on the ROP control.
To complete the drilling of the well in less time, means that the completion of the well together with the drilling will be done in less time than estimated according to the drilling program, this results in a reduction of the drilling costs due to the drill rate, since the simple fact of having the drill string upright means having a drill rate for example expressed in Bs/day or $/day, if this drill rate is multiplied by the days that the drill has been drilling and performing the construction operations of the well, the costs associated to the drill rate will increase.
The conclusion of the case is that if the higher ROP is achieved without negatively influencing the drilling operations, the drilling time will be reduced, and therefore the drilling costs will decrease.
Conclusion and contributions
Perhaps many of those who read this post know that all operational activity involves a strict control of the most important parameters of the operation being executed.
Drilling wells adds to that list of operations where engineering makes its considerable contribution, in this post you will be able to find and analyze the multiple reasons why drilling parameters are important in drilling and that the personnel who supervise the activities must be very alert to any sudden change and any of these parameters, since any deviation implies additional costs in the drilling and construction of an petroleum well.
Recommended references to expand knowledge