Modeling and Analysis Techniques for Solving Mechanical Pipe Sticking Problems in Drilling Equipment

Abstract

Mechanical pipe sticking is the important reasons which has a direct impact on the drilling process efficiency. The problems of pipe sticking during drilling, and the other problems associated with this case is a crucial task that must be early identified to find the causing factors before any further action. The main objectives of this study are to predict and specify the main causes of these problems through modeling and simulation processes. Consequently, the (ANSYS Workbench/2019 R3) Commercial version has been adopted for this analysis purposes. This analysis have been carried out based on the actual interaction and contact between the active working parts to simulate the actual process. In this simulation process, the non-deformable parts like drill pipe, and wellbore sleeve are considered (Masters), while deformable parts are (slaves). Simulation results approved that the pipe stick happened due to high values of generation stresses. The plot of maximum induced stresses shows that the generated stresses in the interaction zone between the outer surface of the drilling pipe and mud are (15) % more than in the other zones. Also, the probability of sticking during drilling can be predicted according to the relation between the drill depth with time and drag forces. It’s concluded that for freeing the stuck pipe it’s very necessary to predict the problems from the beginning. This type of analysis can assure the percentage accuracy for stuck pipe prediction is more than (70) %.

1. Introduction

During drilling, the pipe is said to be stuck when the drill string cannot rotate or move. Pipe stuck is happened due to many reasons like inadequate hole cleaning, fractured and faulted formation, and junk inside the hole. There are two mechanisms of pipe sticking; mechanical sticking and differential sticking. Both mechanisms are affected by fluid design and mud cake [1]. Mechanical pipe sticking occurs due to many drilling obstructions like inclination of the well or key seat difficulty, wherefore high attention, and continuous measurement are required to prevent any changes in bore deflection [1, 2]. There are many reasons for pipes being stuck such as the inefficiency of lifting the excavated rock fragments, swelling of the shale layers, or the drilling column being lowered in narrow areas. Mechanical sticking happens when the pipe is in motion and sticks due to insufficient cutting slip velocity, poor mud properties, and Poor hole-cleaning. The friction between the tube and wall,) as the well wall generates a groove (which causes inflexibility. Well demolition or rock pieces accumulation inside the mud due to bad clay properties of viscosity also leads to bad sticking and high difficulty of pulling or lowering the pipe during connection [3, 4]. Due to rock interaction, the nature of induced drill strings will be non-smooth. The desirable response of the system is to operate in equilibrium, with a constant rotation, but permanent vibrations or permanent sticking can occur due to large perturbation in the system. Borehole instability is a problem associated with shear failure at the wellbore walls. When the mud pressure is not enough for backing the wellbore, in this case, the peripheral stresses around the wellbore will exceed the rock strength and mechanical sticking will occur. In vertical and deviated wells, the significant wellbore instability problem is a stuck pipe which causes the non-productive time for the majority field’s development [5].

The problems and challenges that result in the possibility of blockage of the drilling pipes are included a decrease in productivity, loss of time, and additional operations that lead to the cost increase [6]. All operations will temporarily stop during the nonproductive time while drilling. In addition to financial losses and lost time, there will be a possibility leading to weakening the economics of a project [7]. The mitigation of stick-slip problems via analysis is a very important step in controlling the effective parameters. The parameter combinations that are affected by the rough nature of rock interaction should be determined previously to suppress and control the stick-slip during the drilling process [8]. The main optimization drilling factors are concerned with the rate of penetration, intelligent drilling, wellbore design, and increasing drill tool life. At this point, drilling technologies start using some special analysis trajectories for implementing directional wells in hard rock, and deep well. However, these trajectories may involve some types of complex drilling and will lead to a high-cost increase [9]. Moreover, drilling performance can be limited and effect by many parameters like shocks and drill string vibrations. The mechanical sticking due to the interactions between the borehole wall, drill string, and mud cake during the drill string stopping needs to be predicted to avoid the risks. Drilling problems like loss of circulation, torque, drag, and cuttings transport can be predicted and solved by using the general scheme by utilization of effective drilling data [10]. The crucial task to preventing a stuck pipe is the early identification of the problem. Spotting oil around the pipe section is the more usual way to reduce the pressure and free the stuck pipe [11].

A theoretical evaluation method is a measurement tool used to investigate and control a drilling string. Stuck pipe occurrence is an undesirable event and leads to string failure. Consequently, the analysis and calculation of the drilling conditions are very essential. Pipe sticking that happened in some deviated wells is considered a significant drilling problem. Simulation and analysis are accurate tools for predicting and avoiding severe collapse or failure and decreasing uncertainties of nonproductive time [12]. Predicting method like Artificial Neural Network (ANN) is the most powerful tools to avoid stuck pipe risks and can be employed for modifying the drilling variables. It’s applicable whenever the relationships between parameters are complicated, and the prediction accuracy may exceed 90% [13]. The Genetic algorithm optimization-based artificial intelligence (AI) is used as an efficient predictive analytics technique for drilling pipe stuck. The key contribution was to mitigate the pipe stuck through automate pipe stuck classification by using ML algorithms. During a drilling operation, the most expensive problem that can occur is the pipe stick. Complications of this problem can account for approximately half of the total drilling cost. A genetic algorithm (GA) can optimize the drilling parameters and be used to mitigate the risk of drilling pipe stuck [14]. There are some important procedures and considerations that should follow for the best results in pipe releasing. It involves that the pipe should be free in a short time after sticking. The procedure of freeing the pipe is shown in Figure 1 [15]. Sufficient hole cleaning is one of the essential factors of a drilling operation’s success. Inadequate hole cleaning and wellbore instability are the main factors that caused the mechanical sticking. Non-sufficient hole cleaning is one of the crucial causes of non-successful drilling operations, especially in deviated wells when the inclination angle is between 30 and 60 degrees.

Figure 1.

The procedure of freeing the pipe [15].

In this chapter, the main causes of mechanical stuck pipe problems have been explained. The finite element software (ANSYS/2019 R3), has been adopted for this analysis to find some possible solutions for mitigating these effects on the drilling process. The findings of this study present the outcome analysis of mechanical stuck pipe which is summarized by dynamic analysis.

2. Materials and method

2.1 Main objectives

The main objectives of this study are to specify the main causes for mechanical stuck pipes and to provide suitable suggestions and solutions that can mitigate and eliminate this important problem through modeling and simulation processes.

2.2 Modeling and analysis process

As far as mechanical pipe sticking is concerned, determining the relationship between all effecting factors on the drill string is necessary. At this point, studying the mechanical behavior and interaction between the drilling system parts during the actual condition will lead to a better understanding and solution as well as support the decision-making. Consequently, modeling and analyzing this complex process which consists of many interaction parts with different boundary conditions like pressure, forces, stress, and others is a significant challenge in predicting and preventing or mitigating the sticking problem during drilling. Based on the foregoing information, the physical model is created to simulate the actual case with similar operating conditions. The main parts consist of the drill pipe, mud cake, wellbore housing, and the surrounding formation. Figure 2A and B illustrates these model components in (2D) and (3D).

Figure 2.

(a) The model components in (2-D); and (b) The model components in (3-D).

The interaction and constrain between these parts were defined according to their function. The drill pipe is modeled as a rigid body (non-deformable part), while the mud in contact with the outer surface of the pipe is modeled as a deformable region. Also, the wellbore sleeve is considered as a rigid body and reacts as a non-deformable part.

Figure 3 is an illustration of the contact behavior between these parts and the direction of the applied loads.

Figure 3.

Contact behavior between the interaction parts.

The boundary condition is built according to the main function of this process. The wellbore sleeve is restricted and constrained in all directions to prevent any possible movements. While the boundary condition (move down) will apply on the upper surface of the drill pipe in order to allow the pipe to move downward direction. Figure 4 shows the constraints on the wellbore, and applied pressure on the drill pipe to move down.

Figure 4.

The boundary condition includes constraining the wellbore from any movements and applying downward pressure on the drill pipe.

3. Main calculations

For a quick approximation, here below introduced some mathematical formulas for calculating the required force to free the stuck string and the depth of the stuck pipe [15].

$$\mathit{\text{Depth of stuck pipe(feet)}}=\begin{array}{l}\mathit{\text{Pipe stretch(inch)}}\\ \times \mathit{\text{Free point constant}}\left(\mathit{FPC}\right)/\mathit{\text{Pull force}}\left(k-\mathit{\text{lbs}}\right)\end{array}$$E1

$$\mathit{FPC}=\mathit{As}\times 2500$$E2

As is the pipe wall cross-sectional area (sq. inch).

$$\mathit{As}={\left(\mathit{0.5}\right)}^{\mathit{2}}\left({\mathit{OD}}^{\mathit{2}}-{\mathit{ID}}^{\mathit{2}}\right)\times \pi =\left({\mathit{OD}}^{\mathit{2}}-{\mathit{ID}}^{\mathit{2}}\right)\times 0.7854$$E3

Where;

ID is the inner diameter of the drill pipe in inches.

OD is the outer diameter of the drill pipe in inches.

Alternatively, the stuck depth can also be calculated using this approach;

$$\mathit{\text{Stuck depth}}=735.294\times E\times \mathit{\text{Drill Pipe Weigh}}/\mathit{\text{Differential Pull}}$$E4

735.294 is a constant.

$$\mathit{\text{Differential pull}}=\mathit{\text{higher pull}}\mathit{on}\left(\mathit{lb}\right)–\mathit{\text{lower pull of}}\left(\mathit{lb}\right)$$E5

$$\mathrm{E}=\mathit{\text{Higher pull pipe stretch}}\left(\mathit{\text{in}}\right)–\mathit{\text{lower pull pipe stretch}}\left(\mathit{\text{in}}\right)$$E6

$$\mathit{\text{Axial force required to free pipe}}=\mu \times \mathit{\text{Pull force}}/1000$$E7

4. Finite element analysis

The Commercial software (ANSYS/2019 R3) has been adopted for the analysis and simulation of this process.

ANSYS is a finite-element modeling package normally used for numerically solving mechanical problems such as structural analysis. There are two methods used in (ANSYS) namely; graphical user interface (GUI) and the command line interface (CLI). Factors, such as the interaction type between the contact parts, material properties, and element type according to the mesh method are the main input variables. The Mapped Face Meshing method has been used to facilitate and extracted the element size. The method-based analysis is the failure criteria that have been incorporated to predict the problems of stuck pipes. It depends on estimating the mechanical properties of formations and the state of stresses. It also depends on the effect of the intermediate principal stress component in the failure analysis. The type of contact between the interacting parts is categorized and defined according to their functions. Bonded and non-separation contact is the suitable contact type for defining the nature of contact between these parts during drilling, and the adaptive meshing technique is also used to enhance the results and findings of this analysis. Figure 5 illustrates the contact and mesh types.

Figure 5.

The contact and mesh type.

Figure 6 illustrates the nature of interaction and the applied load during the total deformation option. This type of deformation is defining the elements of the part that are subjected to deformation to be classified as (Slaves), while the non-deformable elements are classified as (Masters).

Figure 6.

The fixed support constraints and applied load.

The drill pipe displacement is assumed to be a small value at the beginning of the drilling process due to the high resistance and high frictional forces between the contact surfaces. However, displacement of the drill pipe will increase rapidly and in proportion with the applied pressure due to an increase in contact surface area between the parts.

In this analysis model, many failure criteria have been incorporated to predict the problems of stuck pipes and estimate the mechanical stability of drilling string.

During the drilling process, the total deformation interaction will impose on the contact between the formation rock and drill pipe. Consequently, a large deformation (elastic-plastic type), and a high amount of material flow will result due to severe contact and high frictional forces between these surfaces.

5. Results and discussion

The calculation of embedment drill string depth in the mud cake is a difficult process and mostly depends on the interaction between the mud cake and downhole tools. It also depends on the mechanical properties of the mud cakes.

It’s more realistic and reliable to predict and estimate the minimum and maximum stresses. The contour plot in Figure 7 indicates the values and direction of the minimum and the maximum vertical stress.

Figure 7.

Contour plot of maximum induced stresses.

In this contour, it’s clear that the maximum stresses will be concentrated at the contact surfaces between the drill pipe and the wellbore house. This is due to the high contact pressure and high friction force between the pipe and mud.

The various failure criteria are resulting during overbalance pressure conditions, which caused mechanical pipe sticking. The contour plot of total deformation shown in Figure 8 illustrates the severe deformation that happens during the downward movement of the drill pipe. In this case, the deformable part (mud cake) will deforms, while the non-deformable part (drill pipe and well bore sleeve) doesn’t.

Figure 8.

Contour plot of total deformation.

The equivalent strain in this process is illustrated in the contour plot as shown in Figure 9. The relative displacement of both drill pipe and mud cake is represented in their movement downward for drill pipe and upward for mud cake

Figure 9.

Contour plot of equivalent strain.

The overall deformation occurrence according to the relative interaction between the parts shows that high deformation values will take place around the drill pipe and will cause high mechanical sticking with time as shown in Figure 10.

Figure 10.

Total system deformation.

Regarding the high contact forces between the parts, the probability of pipe stick will become serious, and the probability of freeing the pipe against soaking with time will be very difficult. Figure 11 shows the difficulty of freeing the drill pipe with soaking time. Consequently, calculating the required time before backing off and circulating out is very essential.

Figure 11.

The probability of freeing the pipe against soaking time.

Based on the foregoing, and due to high sticking forces between the contact surfaces along the drill pipe, so the drag force will be inversely proportional to pipe drill depth. Figures 12 and 13 are an illustration of the relationship between pipe depth and both drag force and the percentage probability of getting stuck.

Figure 12.

The relation between pipe depth and drag force.

Figure 13.

The relation between pipe depth and the percentage probability of getting stuck.

6. Suggested solutions for mechanical pipe sticking

According to the foregoing, and based on a wide range of literature scanning, here below are some suggested solutions to free a stuck drill string in mechanical pipe sticking:

• Control the mud flow rate through suitable circulation.

• Control the direction of applied torque according to the stuck position

• Decrease the contact area between the pipe and formation.

• Early detection of pipe stuck.

• Adding crude oil to drilling mud in order to control the water seepage and facilities slippage.

• It’s advised to make short trip drilling withdrawals and downloads continuously.

• Reducing the thickness of the drilling cake by reducing the seepage from the drilling fluid by treating it with the appropriate additives

• Reducing the drilling speed in some areas, especially in large cavities, to offer enough time to lift the rock fragments.

• In the case of non-return drilling, a high viscosity slurry should be pumped in before attaching a new pipe to help suspend the crumbs.

7. Conclusions

This paper provided an explanation of drilling wells using some ideas to resist the mechanical pipe stuck. The following conclusions were made according to this study:

1. To prevent stuck pipes, it’s very essential in adhering to the criterion of drilling calculation and assures the efficiency of drilling system cleaning. This will reduce the possibility of sticking and collapse.

2. There’s a high indication that failure and wellbore collapse is always associated with a stuck pipe that has been drilled with low mud weight.

3. Consequently, the parameters that have a significant impact on the failure mechanisms are mechanical properties, high-stress contrast, and well trajectory design.

It’s found from some other expert literature that diesel oil pills and stuck breakers can successfully be used to release the mechanical pipe sticking if implemented accurate procedure.

Since the severity of mechanical stuck is associated with cutting head (drill collar and bit), so minimize the interaction and contact area between mud cake, drill-string, and the wellbore is important to offer sufficient exposure time with a low flow rate to ensure an effective process.

Acknowledgments

The author would like to express high appreciation to members of the IntechOpen for their valuable advice and support.

Conflict of interest

The author declares that the given time to complete this chapter was not sufficient.

Funding information

This research received no external funding.