TECHNICAL INVESTIGATION ON CHALLENGES OF CASING WHILE DRILLING (CWD) APPLICATION IN OMAN- CASE STUDY
Mahmood Saif Mohammed Al-khanjari
International College of Engineering and Management (ICEM)
TECHNICAL INVESTIGATION ON CHALLENGES OF CASING WHILE DRILLING (CWD) APPLICATION IN OMAN- CASE STUDY
Mahmood Saif Mohammed Al-khanjari
Department of Well Engineering
International College of Engineering and Management (ICEM)
TABLE OF CONTENTS
3 METHODOLOGY 11
Casing while Drilling (CwD) or rotary drilling is a method to drill the well. Rotary drilling process is the one that has been used globally and it is more popular. In this process a sharp drill bit which is connected with dill string. On the other hand, there is other method can be used for drilling which is conventional drilling. In past, they widely used it till now. Both of methods are used in Oman. Conventional drilling is consist of drill string which is contain of drill pipe and drill collar and connecting with bit. Drill bit will drill the area until reach the specific depth, then it will remove the bit and run another bit to drill the next area. So, changing the bit depend on type of formation. After that, it will pump cementing after running the casing, Martinez (2008).
Casing while drilling (CwD) is consisting of casing that is connecting with drill bit. Which is it will drill the total depth without change or remove the bit then, it will drill next area by the same bit. The bit just adds number of joints then. Actually, casing while drilling is useful base on two an important factors. Which are non-productive time (NPT) and cost (USD). Drilling with casing method is not required to use tripping out and tripping in. So, the problems will be decreased. On the other side, conventional drilling is more problems and spend more time and cost. During tripping operation, there are many encountered problems occurs and need more time to provide it, (Limbert 2009).
In addition, hole problems are main common occurring in conventional drilling because of tripping the pipe such as, loss of circulation and cave-in. CwD is provide or prevents these problems by smearing effects. That is why most of companies use CwD more than conventional drilling in different areas of different countries. This technique has play an important role for reducing the time and cost. Moreover, casing while drilling provides performance efficiency of overall drilling by reducing time and cost around 37.5% comparing with conventional drill pipe (Karimi, 2016).
There are some limitations while use CwD method, but it is still under research and development that are improving the limitations. Casing while drilling has been used in Fiqa formation of northern Oman. It used in surface to an intermediate sections for a trail phase. It was successfully story. (Sanshez, 2010). In this project I will applied this method in north of Oman especially in intermediate section. I have trying to evaluate the challenges of this technique.
The problem of Casing while drilling (CwD) in Sultanate of Oman.
Actually, casing with drilling is new method that used for drilling well. In Sultanate of Oman, mostly they used another method, which is Conventional drilling method. A little of companies used (CwD) method because it is usually depend on geological characteristics of formations. So, it’s not easy to use Casing while drilling method around areas of Sultanate of Oman.
1.2Aims and Objectives
Nowadays, casing while drilling has become an important role in an oil field industry. Therefore, the aim of the project is to evaluate a critical analysis of the challenges of (CwD) in Sultanate of Oman.
The objectives of this study are:
1. To identify the challenges of casing while drilling.
2. To analyses the highest risk factors of (CwD).
3. To compare and contrast cost and Non-Productive Time (NPT) in both type of drilling, (CwD / conventional drilling).
4. To develop solution for optimum drilling condition on (CwD).
2. This chapter, there are several of previous researches and studies about CwD in Oman and other countries. Therefore, in the beginning is taking about the problems of two methods that are using in soft formations. Then, (CwD) methods was used in north of Oman if it is successfully or not. After that, it have been analysed of problems by comparing two methods between time and cost. I read a lot, but in this project, I chose the better studies that gave me a complete summary of CwD.
The author did this investigation to know the difference between two methods of drilling which are drilling with casing (CwD) and conventional drilling. He used these methods in soft formation to appraise which one of method is more effective drilling. In addition, the problems that are estimated for drilling completed with cost. Federer is trying to find proofs for both methods, which one is better than other. So, he did his comparison between these methods by using different factors, he got casing while drilling is able to drill any formation. In CwD, they used drive system which is connected with casing that leading to drill any formation. On the other hand, conventional drilling is difficult to drill any formation with one bit. Second point is downtime rig. He noted in casing while drilling has low risk during drilling comparing to conventional drilling. For examples of problems occur while drilling like stuck pipe and loss of circulation. Also, the number of joints that needed to make connection is less than drilling with pipe (Federer, 2014).
This research is done about case study of casing while drilling in Oman. They applied this method in shale formation in south of Oman. Which is they drilled the surface and intermediate section to see, if it can be useful or not. They found that there is reduction of risks such as, wellbore instability and pipe sticking. Moreover, this study was successfully by comparing to the several offset wells. In addition, they got improvement in this technique (CwD). Casing with drilling team used PDC bit to drill the formation then, they found that PDC bit is more performance when they comparing to the drill bit. Furthermore, cement operation in CwD is maybe avoid the problems of the hole. Also, there is no tripping condition which is delay the drilling time. Casing drilling team drilled from surface to 754 m by using PDC bit and this bit can be drill for hard formation. So, time taken to drill this section is 50 hours and by this time can be provided 40% of time comparing to the conventional drilling. They evaluate the type of formation during drilling by analyzing the formation. Fiqa formation consist of Arada formation and Fiqa sharji. Arad formation is from surface to 369 m section of limestone and Fiqa sharji is from 369 m to 689 m of shale formation. In addition, they estimated when they used large diameter od casing while drilling is better than used small diameter of drill string because, most problems coming with lower diameter like collapse formation and burst pressure. So, large diameter of casing get less vibration. Base on this research, it will evaluate technical investigation on challenges of CwD in Oman and trying to apply this method in an intermediate section (Sanchez et al. 2012).
Karunakar did his research about two methods of drilling and use them at soft to medium formation. He makes analysing for both techniques which are casing with drilling (CwD) and conventional drilling to know how stresses are affecting to their design. Also, he compared the advantages and disadvantages of using two methods by various factors. He evaluated that casing with drilling is take time less than conventional drilling to drill that formations, because CwD is no need to use tripping rather than in what it used in conventional drilling. Tripping is run the pipe and pull it up which is getting to take extra time in drilling time. In addition, there are common problems occur while drilling such as, hole instability and loss of circulation. In CwD, loss circulation is not encounters or less because of smearing effects. Smearing effects occur when there is small gap between casing and the wall of hole that lead to cuttings plasters in the wall during drilling. Most of time, loss circulation occur in conventional drilling. Moreover, CwD is giving a good hole cleaning, because of small annuals with high flow velocity allowing to give the optimum hole cleaning. On the other hand, conventional drilling is more problem than CwD in buckling pipe. That is depends on the strength of pipe or casing because while drilling will face high stresses, so casing is more strong than pipe (Karunakar et al. 2015). According to this research, the CwD has been analysed and estimated during drill soft to medium formations.
The author found out hole problems when he was used Casing while drilling method by study formation characteristics and optimize the drilling. He trying to find the pressures and stresses base on that problem. In addition, the hole instability is one of the hole problems that affecting to the non-productive time (NPT). This problem occurs when the formation is soft and easy to break and getting loss time. He also found difference between two factor of formation which are strength and elastic. Where the dynamic rock is more than static rock. Moreover, when it apply high pressures in the hole it will resulting a breaking into the formation that will take time to control the pressures or cures this problem. The cement operation that used to avoid hole problems it can be danger. So, my project is going to make evaluation of the problems that affecting to the time for different formation in Oman by using CwD method (Eric et al. 2008).
This research is toking about casing with drilling improve the stability of wellbore. So, the author is trying to obtain the advantages of CwD by compering to the conventional drilling. Elimination of the tripping is one of the advantages in drilling with casing where, there is no tripping out and tripping of casing. Which it can occur swap and surge pressures during tripping. Other advantage is plastering or smearing effects. This smearing occurs when there is small annuls between casing and the wall and during cuttings go up to surface it will plaster into the wall. Smearing effects is preventing loos circulation rather than conventional drilling. Base on this benefits it will make reduction of time with less cost. Also, it is allowing for providing more chance to improve wellbore instability. (Eric et al. 2011)
This method uses conventional surface equipment and casing accessories applied in vertical wells and also uses a retrievable BHA to steer the well. This enables changes to be made to the BHA and/or the bit without tripping the casing (Warrent et al. 2005).
Casing drilling, otherwise known as drilling with casing (CwD), is not limited to retrievable systems. It even has a simpler and less expensive application in non- retrievable systems. So, they use casing while drilling method more than conventional drilling (Rosenberg et al. 2008).
They have studied the wellbore instability improvement by drilling with casing. In this investigation, he try to estimate the benefits of drilling with casing and shows how this method different to the conventional drilling method. Elimination of tripping is one of the benefits. (Tessari et al. 2006).
2.2 Types of casing while drilling system
In casing while drilling,there are two types of drilling system which are, Non- Retrievable system and Retrievable system.
(Robinson, 2008) Non- Retrievable system is one type of casing with drilling that consist of drive system which is responsible for rotation, casing string and drill shoe. Non- Retrievable system is not retrieve of BHA after reaching casing and cementing for specific depth why, because the bit will drill out during drilling next stage. For this system, it will use drillable bit that is can be opening the cutters under pressures.
Retrievable system is consisting of a pilot bit, drill lock assembly (DLA), and an under reamer. The purpose of pilot bit is arranged base on the casing when it retrieve back. Also, the function of under reamer is allowing the casing run easily by working to increase the size of the hole. The drill lock assembly is working for make connection with conventional tools and let the casing run tools throughout casing. Also, it is providing capability to lock and unlocking bottom hole assembly for the casing.
Figure 1, Types of drilling (Robinson, 2008)
2.3 Over Drive System
(TESCO, 2008) It is an integral system that includes many conventional tools connected with a technology, such as circulation tools, clamps, handrails, elevators, and filling-up. Casing while drilling technology allows simulating circulation, rotation of casing. In addition, the reciprocating casing that leading to reach the total depth. Overdrive system tools, such as handrails is used only to lift the V-shaped door tube. The function of elevators is rising up the casing by catching it. While running the casing it allow to make rotation by using circulation tools and filling. This system provides engineering and equipment by safety through slipping design and safety interlock system. That is allowing to maintain constant control of casing string. In addition, Overdrive is strongly associated with increased torque and the ability to rotate and reverse the casing string. Casing with drilling technology is not too expensive for the equipment.
Figure 2, Overdrive Tool (TESCO, 2008)
Fig2: Overdrive Tool TESCO, ( 2008)
2.4 Internal Casing Drive Tool (ICDT)
Internal drive tool is connected to the casing in drilling with casing system. It is used to make a connection with casing to save the casing string specification and improving time connection. In addition, internal drive tool is not change while make connection with other casing string that leading to save time. On the other hand, conventional drilling used Kelly to rotate the drill string then, when it reach the total depth it will replace the Kelly to rat hole to connecting again for next joint of drill string. After that, casing joint make connection with Kelly from the top. (AAPG SU Channel, 2010).
2.5 Drillable Casing Bit
This part is specialized for drilling with casing in any formation. It is made of polycrystalline diamond (PDC). It is possible to using at high temperatures and also allows to drill formation like soft, medium and hard formation. In addition, this drill bit can be removed after reach the maximum depth, not more than half an hour with comparing to the conventional PDC drill without compromising accuracy. It have been eliminating the time required to complete drilling and also minimizing hole problems. This type of bit, after reaching full depth then string of casing slowly is rising up to allowing the cutters open while applying pressures to avoid the effect bit used in the next phase (Weather Ford, 2012).
Figure 4, Drillable bit (weather ford, 2012)
2.6 Conventional Drilling Bit
In conventional drilling or drilling with pipe, several types of drill bit are used. That is depend on type of formation properties so, each bit is used only for specific formation. Also, these types of bits can help to increase the legitimacy of bit and give improvement in hole cleaning efficiency. In soft formation, it is better to select the mild tooth Tricone bit with long teeth as shown in figure (a) because it is cheap and drilling fast. Also for hard formation, it would be chosen tungsten carbide bit or diamond bit. In hard formation is needed short teeth with strong material that will drill that formation and also giving long life as shown in figure (b) and (c) (Robinson, 2008).
(a) (b) (c)
Figure 5, Types of bit, a) Diamond bit, b) Tungsten Carbide bit and c) Milled Tooth Tricone bit.
2.7 Comparison between drillable bit and conventional drill bit
Shepard et al. 2002 used different bits for different methods of drilling in the drilling oil field. In casing while drilling method is used drillable bit and on other side used drill bit in conventional drilling. Drillable bit usually used for all environment of sections and no need to replace it which is drilling all sections without changing. For conventional drill bit. It is only for specific environment used or one section base on type of formation properties. It will replace when it start to drill next section. Also, drill bit will spend more time while pull up or replace another bit rather than drillable bit save time because it not required to replace it. For the cost, drill bit or conventional bit is cheaper than drillable bit.
2.7.1 Benefits of drilling with casing
Drilling efficiency should be increased due to the tripping elimination that will prevent many problems as well as problems on the hole instability like caving and stuck pipe because of closing the cutting passage. In casing while drilling there are no swabbing and surging pressures that leading to stuck pipe. In CwD, the swap and surge pressures are coming during tripping which is when it pulls out and pull down fast, it will be getting this problem. Furthermore, drilling with casing is not affect by loss of circulation because of smearing effects. While drilling the cutting go up to surface but because of there is small gap between wall and casing then the cuttings
3.1 Identify the challenges of casing while drilling.
a- Study on (CwD) by reading books, search on internet.
b- Prepare the data that collected from researches, and oil field books.
c- Meeting the experienced people to collect information about CwD.
3.2 Analyses the highest risk factor of (CwD).
a- Visit an oil and drilling company and collecting data then analysis these data
b- Reading more literature views about this technique and its risk
3.3 Compare and contrast cost and Non-Productive Time (NPT) in both type of drilling, (CwD / conventional drilling).
a- Going to an oil company which it use these techniques and get data for each method.
b- Making charts and diagrams to help analyzing and comparison process by using multi-software.
3.4 Develop solution for optimum drilling condition on (CwD).
a- Analyse the categorized data.
b-Evaluate the results and get the solution for this technique.
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