ABSTRACT
Drilling is a process that involves the procurement of natural resources such as oil and gas which holds prime importance in today’s world, Drilling practices abounds with a number of complications and an efficient way of dealing with such problems is key to the continuity of the process.
One of such problems is stuck pipe, stuck pipe is a common problem in the industry and it accounts for major rig time loss known as Non Productive Time (NPT) and also accounts for billions of dollars wasted annually in the petroleum industry.
The purpose of this project to implement a powerful machine learning tool known as the Artificial Neural Network in the prediction of stuck pipe using Niger Delta fields as a case study,
The ANN is a Matlab built in function and computational system inspired by the structure, processing method and learning ability of the human brain.
The ANN has the ability to take multiple inputs ( plastic viscosity, yield point and gel strength at 10 seconds and 10 minutes), a target ( mud weight ) to produce a single output which is the prediction of the occurrence of stuck pipe. This was successfully carried in this research study. It is therefore shown in this study that the ANN can be successfully used to predict the occurrence of stuck pipe. Thus, they can be utilized with real-time data representing the results on a log viewer which can help reduce the occurrence of getting stuck while drilling and all the complications that comes with this occurrence.
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TABLES OF CONTENT
TITLE PAGE ………………………………………………………………………………………………………………….. i
CERTIFICATION ………………………………………………………………………………………………………….. ii
DEDICATION ………………………………………………………………………………………………………………. iii
ACKNOWLEDGEMENT ………………………………………………………………………………………………. iii
ABSTRACT …………………………………………………………………………………………………………………… v
LIST OF FIGURES ……………………………………………………………………………………………………….. ix
LIST OF TABLES ………………………………………………………………………………………………………….. x
CHAPTER ONE …………………………………………………………………………………………………………….. 1
1.0 INTRODUCTION ……………………………………………………………………………………………… 1
1.1.1 Mechanical sticking: ……………………………………………………………………………………. 2
1.1.2 Differential sticking …………………………………………………………………………………….. 3
1.1.3 Freeing stuck pipe ……………………………………………………………………………………….. 6
1.2 Background of Study ………………………………………………………………………………………….. 7
1.3 Aims and Objective ……………………………………………………………………………………………. 8
1.5 Scope of Study ………………………………………………………………………………………………… 10
1.6 Justification …………………………………………………………………………………………………….. 10
1.7 Materials and Methodology ………………………………………………………………………………. 10
CHAPTER TWO ………………………………………………………………………………………………………….. 12
2.0 LITERATUE REVIEW AND THEORITICAL FRAMEWORK …………………………… 12
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2.1 Artificial Neural Network …………………………………………………………………………………. 12
2.2 Literature Review …………………………………………………………………………………………….. 16
2.2.1 Stuck pipe prediction using ANN ………………………………………………………………… 16
2.2.2 Analysis and prevention of stuck pipe ………………………………………………………….. 17
2.2.3 Stuck pipe prediction using other tools …………………………………………………………. 19
2.2.4 Stuck Pipe in Niger Delta ……………………………………………………………………………. 20
CHAPTER THREE ………………………………………………………………………………………………………. 21
3.0 MATERIALS AND METHODOLOGY …………………………………………………………….. 21
3.1 Introduction …………………………………………………………………………………………………. 21
3.2 Data Acquisition …………………………………………………………………………………………… 21
3.3 Selection of the parameters …………………………………………………………………………….. 22
3.4 ANN Training ………………………………………………………………………………………………. 24
CHAPTER FOUR …………………………………………………………………………………………………………. 27
4.0 RESULT AND DISCUSSION…………………………………………………………………………… 27
4.1 Experimental Data ………………………………………………………………………………………… 28
CHAPTER FIVE ………………………………………………………………………………………………………….. 36
5.0 CONCLUSION AND RECOMMENDATION ……………………………………………………. 36
5.1 Conclusion ……………………………………………………………………………………………………….. 36
5.2 Recommendation ………………………………………………………………………………………………. 36
STUCK PIPE PREDICION SIMULATIONAND PREDICTION CODES USING ANN …… 41
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APPENDIX 2 ……………………………………………………………………………………………………………….. 53
STUCK PIPE PREDICION EXPRIMENTAL GRAPHS FOR INPUT AND OUTPUT …….. 53
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LIST OF FIGURES
Figure 1: Cross sectional view of differentially stuck pipe (http://www.drillingformulas.com). …………….. 4
Figure 2: Top view of a differentially stuck pipe (1997 Drillers Stuck pipe Handbook) ……………………….. 4
Figure 3 : schematic of the ANN system ………………………………………………………………………………………. 14
Figure 4 : Workspace for inputting time series ………………………………………………………………………………. 24
Figure 5: Interface for making network architecture choices. ………………………………………………………….. 25
Figure 6: Interface for choosing training algorithm ………………………………………………………………………… 25
Figure 7: Interface for choosing validation and testing data. ……………………………………………………………. 26
Figure 8: Graph of Experimental value of plastic viscosity versus number of runs …………………………….. 29
Figure 9: Graph of experimental value of yield point versus number of runs …………………………………….. 30
Figure 10:Graph of experimntal value of gel (10 secs) versus number of runs …………………………………… 30
Figure 11:Graph of experimental value of gel (10 mins) versus number of runs ………………………………… 31
Figure 12: Graph of experimental value of mud weight versus number of runs …………………………………. 32
Figure 13: A graph showing variation between the experimented and simulated value for NARX ……….. 33
Figure 14: A graph showing variation between the experimented and predicted value for NARX ……….. 33
Figure 15: A graph showing variation between the experimented and simulated value for NAR ………….. 34
Figure 16: A graph showing variation between the experimented and simulated value for NAR ………….. 34
Figure 17: A graph showing variation between the experimented and simulated value for NOI …………… 35
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LIST OF TABLES
Table 2.1: Input and output data for parameter selection………………………………..22
Table 4.1: MSE for Levenberg Marquadt………………………………………………..27
Table 4.2: MSE for Bayesian Regularization ……………………………………………27
Table 4.3: MSE for scaled Conjugate Gradient…………………………………………..28
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CHAPTER ONE
1.0 INTRODUCTION
Over several years the petroleum industry has been facing challenges associated with stuck pipe. Stuck pipe has caused a major drilling cost for the drilling industry worldwide and various cost estimates carried out have indicated that the cost of fixing stuck pipe issues exceeds $250 million per year (Bradley et al., 1991).
Problems of stuck pipe can range from minor inconveniences to increase in drilling cost up to major complications which will lead to altered drilling due to the inability to drill when this occurs resulting in major time loss.
A major key to the reduction of this phenomenon is the ability to correctly or even better, accurately predict the occurrence of stuck pipe.
Generally, stuck pipe is described as any restriction of upward or downward movement of drill string and/or pipe rotation and leads to a situation where the pipe cannot be freed from the hole without damaging the pipe, and without exceeding the drill rigs maximum allowed hook load. The portion of the drill string that cannot be rotated or moved vertically is known as the stuck pipe.
There are several causes of stuck pipe which include poor hole cleaning, key sitting, collapsed casing, junk, cement related problems, mobile formation, geo-pressured formation, fractured formation. However, the causes of stuck pipe can be classified under two broad categories which are mechanical and differential sticking.
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1.1.1 Mechanical sticking:
This is the limiting or prevention of motion of the drill string by anything other than differential pressure sticking. According to drillers stuck pipe handbook (1997) by Schlumberger, Mechanical Sticking can be caused by the following:
1. Inadequate hole cleaning
2. Formation instability (brittle, sloughing, or swelling shales)
3. Key seating
4. Under gauge hole
5. Tectonically stressed formations
6. Plastic or mobile formations
7. Under pressured formations
8. Junk
9. Ledges and doglegs
10. Collapsed casing/tubing
11. Unconsolidated formations
12. Large boulders falling into the hole
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13. Running large gauge tools
14. Cement blocks
15. Green cement
However, most cases of mechanical sticking can be avoided by proper well planning, optimal mud design and right directional planning.
1.1.2 Differential sticking
Differential pipe sticking is one of the stuck pipe mechanisms that have had a major impact on drilling efficiency and well costs (Adams, 1977; Weakley, 1990; Wisnie and Zheiwei, 1994); it is in most drilling organization, the greatest drilling problem worldwide in terms of time and financial cost.
This is a condition whereby the drill string cannot be moved (rotate or reciprocated) along the axis of the wellbore. Differential sticking occurs when high contact force caused by low reservoir pressure, high wellbore pressures, or both, are exerted over a sufficiently large area of the drill string. It is important to note that the sticking force is a product of the differential pressure between the wellbore and the reservoir and the area that the differential pressure is acting upon, this means that a relative low differential pressure (δp) applied over a large working area can be effective in sticking the pipe as can a high differential pressure applied over a small area.
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Figure 1: Cross sectional view of differentially stuck pipe (http://www.drillingformulas.com).
Figure 2: Top view of a differentially stuck pipe (1997 Drillers Stuck pipe Handbook)
The figures simply means that there is a pressure difference between the mud and the formation
which can cause the drill collar and the drill pipe to be pushed against the borehole wall therefore
it becomes impossible for the draw work to pull the pipe free.
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Differential pipe sticking occurs when a part of the drill string, casing, or logging tool becomes embedded in a mud solids filter cake and is held there by a significant amount of differential pressure. This differential pressure is the pressure difference between the hydrostatic pressure of mud and the formation pore pressure. Usually, because of the excessive differential pressure, the sticking takes place across porous and permeable formations such as sandstone or limestone, where a mud filter cake builds up during drilling. It does not occur in very low permeability formations such as shale’s, where mud filter cakes normally do not form. Although these symptoms are similar to Key Seat sticking, they usually occur under different drilling conditions.
Significant mud overbalance, as well as an exposed permeable section, must also exist for differential sticking to occur. It is clear that as many reservoirs become depleted, a significant number of wells will be drilled with high overbalance pressures, thereby maintaining the industry’s concerns over differential sticking (Miri et al., 2007). The likelihood of differential sticking is increased further with the length of the permeable section that is open to the drilling fluid. The continued trend towards extended reach and horizontal drilling means that increasing lengths of permeable formations are exposed. Clearly, the nature of the rock formations encountered certainly cannot be altered. Therefore, if those formations carry a high risk of differential sticking, this has to be accepted. Also, high overbalance pressures may be unavoidable if they are needed to maintain well control or wellbore stability in other parts of the open hole section. However, mud composition and properties can be modified, within limits, in the prevention of differential sticking.
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Differential pipe sticking problems generally result in the significant amount of downtime and remedial costs and well cost overruns and time overruns as a non-productive time in terms of loss of rig days either due to stopping of drilling operations or in an attempt to free the stuck pipe
1.1.3 Freeing stuck pipe
Several approaches have been developed to avoid or prevent stuck pipe, proactive approaches which utilize effective techniques to predict or detect stuck pipe before it occurs one of which is discussed in this literature. However it is important to know measures taken to free stuck pipe when stuck pipe incidences occur i.e. the actions made after the pipe gets stuck.
Pipe sticking is said to be a very bad surprise when drilling because once it occurs it automatically alters every operation and it is impossible to estimate how long it will take to pull out free, it can last for seconds, hours, days or even months and can even cause abandonments depending on the magnitude.
Usually when the pipe suddenly gets stuck, the first action is how to get it free as quickly as possible. Regardless of the cause of sticking, the most common action in drilling industry to free the pipe is to work it out by firing the jars, which are parts of drilling assembly. Jars exert huge amount of energy on drill string, which can be transferred to an impact force that may be able to free the pipe. Depending on the cause of the sticking, jars may be applied downwards or upwards. However, Jars sometimes are ineffective especially when they are placed below stuck point, which can be due to poor estimation of stuck zone or lacking of proper field experience. In addition the hydrostatic pressure can also be reduced by pumping low weight mud/pill, ensuring that the overall hydrostatic pressure is still able to control reservoir fluid from accidentally
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entering the wellbore. Continue jarring down with maximum trip load and apply torque into drill string.
However if all attempts to free the stuck pipe prove abortive, the next option is to retrieve he stuck pipe using special tools designed for this purpose, this tools are known as Fishing assemblies, they are a wide variety of equipment and tools used in retrieving down hole equipment, BHAs that get lost in the hole.
Depending on their functionality and the requirement in hand, we can classify them as the following:
External Catch Fishing tools
Internal Catch Fishing tools
Junk Catch Fishing tools
Milling and Cutting tools
Each of the above stated set of tools has their own specifications and are very handy in fishing operations.
1.2 Background of Study
Since the commencement of drilling operation in the petroleum industries stuck pipe has been a common problem with tremendous impact on drilling efficiency and cost among other problems. Industry statistics gathered since 1989 show the relative cost of nonproductive time. Stuck pipe is still the drilling industry’s most costly unscheduled event (SPE, 2013). This occurrence can be said to be caused by different conditions, which have been narrowed down to two categories; mechanical and differential sticking and has been said to have cost the petroleum industry millions of dollars annually.
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Different approaches have been adopted in an attempt to reduce the cost and rig time wasted on pipe sticking by predicting the occurrence, analyzing the causes, methods to prevent the occurrence, immediate actions to carry out when differential pipe sticking occurs and even methods of predicting the occurrence of stuck pipe.
Miri et al., (2007) implemented the Artificial Neural Network (ANN) to predict pipe sticking in Iranian Fields, Mustafa Moradi Nehzad et al., (2012), also did a study on a Maroon field were stuck pipe was predicted using the ANN.
Stuck pipe prediction approaches have also been carried out for the Niger Delta fields by M.A Magaji et al., (Shell Petroleum Development Company, 2002), their paper reviewed the implementation of the stuck pipe factor prediction tool which was developed based on prevailing occurrence and existing data, however the tool can only be used to predict the inherent risk of getting stuck in well planning and designing stage.
Therefore, this research study is aimed at predicting stuck pipe using the using the Niger Delta Field as a case study.
1.3 Aims and Objective
This aim of this research project is
To predict occurrence of stuck pipe in the Niger Delta by examining, analyzing drilling parameters gotten from some daily drilling reports within the Niger Delta fields using the Artificial Neural Network.
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To achieve this aim, my objectives include to:
Identify, study, analyze and understand the causes the causes of stuck pipe
Analyze the difference between drilling parameters of stuck and non- stuck wells to enable proper prediction of probability of getting stuck
Implement the ANN in predicting pipe sticking in Niger Delta fields.
1.4 Problem Statement
The purpose of his project is to utilize a powerful machine learning tool, i.e. the ANN to predict the occurrence of stuck pipe which has been a problem in the petroleum industry since the inception of drilling and has led to a lot of cost due fishing operation and time lost in addressing stuck pipe incidences.
This research intends to:
analyze the importance of each mud parameter to determine their contribution to pipe sticking to aid in stuck pipe prediction
predict the occurrence of stuck pipe to eschew the risk associated with drilling and excessive drilling.
avoid or reduce to the barest minimum the amount of money used in drilling.
avoid cost spent on fishing lost down hole tools.
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1.5 Scope of Study
There are several causes of pipe sticking, however this project will be narrowed down to differential sticking, and how ANN can be used to predict its occurrence using data acquired from Niger Delta Fields.
1.6 Justification
The technique of stuck pipe prediction using ANN can be utilized for calculating the risk of stuck pipe either mechanically or differentially before the operation. It is therefore very essential to predict the occurrence of getting stuck because if the drilling personnel know that the parameters used for drilling can cause pipes to get stuck, the parameters will be adjusted and that will result in a smooth operation.
In the comparison between wells that were drilled successfully without getting stuck and wells that had pipe sticking problem, it was clear that some parameters clearly different, therefore this research entails analyzing those differences and using them to predict the occurrence of stuck pipe.
This project will help the petroleum industry and the economy to reduce the amount spent on the already very expensive drilling operations. This will be done by reducing the need for retrieving lost down hole tools to due to stuck pipe which is a very expensive operation known as fishing, and will also reduce the Non Productive Time (NPT) spent of suck pipe problems.
1.7 Materials and Methodology
For the purpose of this project, a reliable approach for prediction of pipe sticking which is based on ANN is presented. In this method, our system possesses multiple inputs which include the plastic viscosity of the mud, the yield point, the mud weight and the gel strength, etc., and one output, which is the probability of pipe sticking.
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Furthermore to aid this research, raw data, resources from oil companies which have had incidences of stuck pipe and successful drilling (non- stuck pipe) operations will be widely consulted alongside materials from the internet and the library.
The materials for my research will majorly be raw data from daily drilling reports from oil companies comprising of the reports of stuck and non-stuck pipe. Other sources for my research will include text books, articles written by scholars on the field of study, materials from the internet and the library material shall also be widely utilized.
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