Aspects to consider in the design of the construction of an petroleum well

Introduction

The program for the drilling and construction of an oil well must contain important information that helps in the orientation of the drilling of the well. For this, all the geological information must be available in order to be able to go through the different individual sections by phases of the well to be drilled.

• Among the data that must be included in the drilling program is:

• Litho-stratigraphic behavior of neighboring wells.

• Operational drilling data from other wells drilled in the area.

• Correlation and sampling geological data.

• Mud data, strands, bottom assemblies (BHA), electrical logs, cementation and recommendations, plus well chart logs in the Master Log.

• Graphs of pressures, drilling parameters and strand performance.

In general, all information from wells belonging to the same reservoir of the well to be drilled and constructed will serve to shape and continue the design of the drilling program.
In the design of a well e should consider the operational procedures that were carried out during the construction of the wells of the developing oil field.

Since the smallest details that can be expressed from the operational point of view in the operational activities of neighboring wells will help to minimize operational problems thus reducing the cost and time in the construction of the well.

Among the operational characteristics that should be included as background of the field in exploitation of the neighboring wells to be drilled are the different stages in the construction and drilling of the same:

[1] Construction of the 26-inch Diameter Conductor Hole: This hole is built from the surface (zero feet deep) to a depth of approximately 1000 feet. The construction of the conductive hole is done in two stages:

• The first stage is drilled with a 17.5-inch diameter tricone drill from the surface to approximately 1000 feet deep.

• The second stage begins with the expansion of the hole, since it is drilled with a 26-inch diameter drill hole, the drilling of the conductive hole is done in two stages with the intention of not circulating large volumes of drilling fluid in a 26-inch hole because it could handle high volumes of mud pump flow, this could erode the walls of the hole, since the lithological formation at that depth is poorly consolidated.

[2] 17-1/2 inch diameter surface hole: This hole is drilled with a 17.5 inch diameter tricone drill from 1000 feet to approximately 7000 feet deep.

[3] 12-1/4 inch diameter intermediate hole: this hole is drilled from 7000 feet to approximately 12000 feet deep with a 12.5 inch diameter PDC drill.

[4] 8-inch diameter production hole: This is the last phase of the hole, and starts drilling from 12,000 feet to approximately 18,000 feet deep with an 8-inch diameter PDC drill.

Each of these phases of these holes in the well construction must be lined with a pipe and then cemented with a specialized cement grout.
Once at the total depth of the well, the producing sand is cannoned and the accessories and equipment with which the well will be completed are lowered.

Since the construction of the oil well is the primary objective in order to design a program that contemplates all the necessary engineering aspects, we could summarize the design in what is the mechanical diagram of a well, everything previously specified as the depths and diameters of the holes can be summarized in the following diagram:

^{Author of the image: @carlos84}

In the mechanical diagram of the well it can be seen that there is a measure of casing diameter that must be smaller than the diameter of the hole, with the intention that it can enter the hole to be subsequently cemented.

This configuration of well depths in this case is a specific example, as the depths may vary depending on the designs that are made from the estimated reservoir pressures that directly impact the casing settlement depth design.

What aspects should be considered in the design of drilling and construction of an petroleum well?

The considerations that must be had for the construction of an oil well must transcend the merely geological and operational aspects, that is to say, it is also extremely important to include the design of the equipment used to carry out the design of the drilling, among these equipment to consider is that of selecting the drilling tower according to the estimated depth at which one wants to drill.

Among the design of the equipment is not only the drill but also all surface equipment, tanks, hoses, valves, mud pumps, equipment such as drill pipes, casings, circulation sleeves, among others.

^{Drilling equipment Image Image source. Pixabay}

In the previous image we can see the drill or drilling tower in conjunction with all the surface equipment such as mud pumps necessary for the construction of the well, it is necessary to include in the design what type of drilling tower is used to drill the well, because if the well is highly deep will require a drilling drill of greater energy, ie greater horsepower (HP). For example, to drill wells from 12,000 feet to 200,000 feet deep, it is advisable to use drill rigs of 3,000 HP (horsepower).

^{Relief valve systemsImage source. Pixabay}

In the previous image we can see the case of a system of valves and hoses that are installed on the surface with the intention of working as a relief of a possible flow of fluids such as gas and/or oil that can flow from the formation, so it is essential that the diameter of the hoses and the ability to withstand the pressure of a possible attack can be supported by all that set of valves at the time of diverting the influx.

The design of well drilling is a highly complex process that includes the highest standards of engineering knowledge, which is why it requires some aspects to be determined before others. For example, predicting fracture pressure requires that the formation pressure be determined beforehand.

The calculations in the design cannot be done in a disorderly manner, everything has a reason and a reason why they are being included in the drilling program.

On the basis of the justified order to be able to carry out the design in the construction of an oil well, a series of stages must be followed in an orderly manner, which leads me to present the following:

Steps to follow during the design of the program in the construction of an petroleum well

[1] Collection of available information: If the well to be built is a well within a developing field, that is to say if it is a well that is inside an petroleum field that has already been commercially exploited it is essential to collect information from the other neighboring wells, this information includes geological information, and all that contributes to facilitating well drilling operations

[2] Prediction of formation pressure and fracture pressure: It is important to perform reservoir simulation studies, electrical records, pressure tests, and anything that helps to estimate reservoir pressure values and acceptable pressure that can withstand the formation to be fractured.

[3] Determination of the settling depth of the lining pipes: to determine the settling depth of the coaters it is necessary to go into the calculations concerning the coater design, in my blog you will find the thematic series dedicated to the design of coaters with which you can complement the information.

[4] Selection of the geometry and trajectory of the well: to touch this topic I want to make relevance of the mechanical diagram proposed above, in this diagram you can see evidence of a deviated trajectory, This trajectory is called a type of directional well s, in which it is drilled vertically to a certain depth, then it begins to deviate with an angle of inclination to a certain point until it regains verticality. In conclusion we must keep in mind that for the design in the construction everything should be included regarding the part of the directional drilling according to the trajectory proposed by the drilling program:

^{Example of horizontal trajectory in drilling a well Image Image source}

Drilling fluid program: because the formation pressure increases as we advance in the depth of the well drilling it is important to increase the density of the drilling fluid, this requires a detailed programme specifying the increase in density at different depths, And even once the well is finished, you can see how far off the density curve of the actual drilling fluid was with the density curve estimated by program.
Next I want to show you a density curve of a well that was drilled in the franking field in Tomoporo State Zulia-Venezuela in which I was an engineer of drilling operations during its construction:

^{Author of the chart: @carlos84}

In the graph shown it can be observed that the programmed density curve is the one represented by the red dot curve, while the real density curve is represented by the blue dot curve. There are two depth ranges where the two curves were detected, these intervals are: [7000 ft to 10000 ft] [13000 ft to 16000 ft] The first interval shows that the actual density was above the programmed density values, This may be due to operational slippages in the supervision of sludge engineers, or it may be worth increasing density in that stretch. In the second interval you can see that the actual density was below the actual density, in this interval it is very likely that some additive was missing in the field to increase density, and in this way you decided to continue drilling.

[5] drill bit program: It is impossible to use the same drill drill from the surface to the total depth of the well, This is why it is recommended to specify in the drilling program the detailed design of the drill bits to be used in the construction of all the holes of the well to be built.

^{Vertical Drill Bit Image source}

^{Drill bit tricone worn
Image source}

[6] Lining piping design and cementing program: as it is known, for the construction of the well it is necessary to cover the walls of the well with a pipe that functions as a lining to then pump and fix a concrete slurry in the existing space between the walls of the hole and the lining pipe.
These operations of lowering the lining pipe and cementing the well require a design that involves the depth of settling of the liners, the nominal grade type of coaters to be lowered to a specified depth, the type of cement to be used, the volumetric cement capacities, the physical and chemical properties of the cement, all this and other aspects include elements to be taken into account in the design for the liner design program and the well cementation program.

[7] Design of the Drill Pipe Pan: The Drill Pipe serves to give depth to the hole as it deepens, however there is a series of tubes which together are called Pit Bottom Assembly (BHA), this pipe and it composes the collars of perforation, the heavy pipe, in short the whole strip of pipe to employ has to be designed according to the requirements of the well, Since it does not have the same configuration in the design of the drill pan a vertical well as a bypassed well, lithology influences the design of the drill pan. The design of the drill pan is very important as any design error can cause the continuity of drilling operations to be lost.

^{Drill pipe rack Image source}

Even in the design of the drill pipe pan should not only include the type of pipe and its specifications, but also the torque values that will be given to them by the time the drill workers are screwing the drill pipe, as a confusion in torque values can cause the pipe to loose and part of it to be lost in the well.

The other consideration to be taken into account in the design program of the drill pipe pan, are the values by which the pipe can be stressed for when there is a case of the pipe becoming stuck at the bottom of the well, if the permissible voltage values are exceeded, there is a risk that the pipe will rupture as a result of the voltage values being exceeded.

^{Rupture of drilling pipe due to high force values in applied strain Image source}

[8] Hydraulic Program: Everything related to the hydraulic design involves taking into account the effective cleaning of the hole, all as a result of a high power supplied by the drilling fluid, for this it is convenient that the design engineer optimally performs the selection of the jets of the bit drilling that will be used every time there is a change of bit.

[9] Drilling times and costs: Like many other parameters included in the drilling design, the scheduled times and costs are only an estimated guideline to estimate the time it will take to build a well and the estimated costs they will have during the drilling and construction of the well product of the estimated days and of all the equipment used, as well as the payment to the personnel that works. However, the estimated time and cost may vary according to the real one, the cost and time may be below the planned, being the ideal condition for the operations carried out in the execution of the drilling program, the other condition is that the real time and costs exceed those programmed, this condition is why engineers and personnel involved in these activities have to improve to reduce the real times and costs.

Conclusion

The planning that can be carried out in all aspects related to the design in the construction of an oil well must be setting goals and priorities that are aimed at reducing the days and costs in drilling and construction of the same.

The improvement made by the design engineer incorporating new studies applying scientific methods and new technologies to improve for example operational aspects such as jamming of the drill pipe can lead to time gain optimize time and costs as planned.

Reference consulted and recommended

[1] Drilling Manual. Procedures and operations in the well. Author: Datalog. David Hawker. Karen Vogt. Calgary, Alberta, Canada. July 2002.

[2] Book. Basics of Drilling Engineering. 1st edition. PDVSA 1998. Ciudad Ojeda, Edo Zulia - Venezuela. International Centre for Education and Development (CIED).

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