REFLECTIVE PRACTICE Evaluation of operational performance of workover rigs activities in oilfields Haitham Mansour, M. Munir Ahmad, Nesreddin Dhafr and Hussain Ahmed School of Science and Engineering, Teesside University, Middlesbrough, UK Abstract Purpose – This paper aims to develop a practical method to evaluate operational performance of workover rigs and present an approach to measure the overall equipment effectiveness (OEE) based on results of the evaluation method. Design/methodology/approach – The area of this study focuses on workover rigs processes in the oilfield and investigates the impact of workover activities on the production at the Sarir Oilfield in Libya. The loss of time from workover procedures and electrical submersible pumps ESP installation and pulling, which affect oil well production, should be eliminated in order to reduce the cost. Several example calculations of workover operation efficiency involving actual workover operational data are presented. The method of evaluation of workover process has been developing which were the bases of OEE calculation. Findings – The measure was developed to help support continuing efforts around process improvements and cost leadership at Oilfields. The results on the empirical findings are introducing OEE for the workover activities which will be used as a valuable indicator for workover activities improvement. Practical implications – The result of this research makes it possible to represent the OEE as a benchmark that will be used to compare the performance of workover process. Originality/value – This paper presents a successful and effective evaluation of OEE which will provide a useful observer to set of operational improvement areas and how such activities could be organised and managed more effectively. Keywords Workover activities, Benchmarking, Performance measurement, Overall equipment effectiveness (OEE), Libya, Performance management Paper type Research paper Introduction Every well in the oilfield is as a small manufacturing plant and each plant needs different equipment as the conditions for each plant are unique. Producing oil needs many procedures to keep the well running, well needs equipment to produce, equipment needs tools to install or uninstall (Ken and Stewart, 1987). These activities of develop of wells, maintenance, repair have many wastes that could affect the total production from the oil wells. The reason of selecting the oilfield operations are that the operation and the activities are continuous process and become discrete, that makes them more applicable to improvement tools (Ken and Stewart, 1987). Oil wells require maintenance and repair, from time to time, due to normal wear and tear, age and the effects of the environment to which the equipment is exposed (Ken and Stewart, 1987). Changing electrical submersible pump (ESP) failures in each well are undertaken by the workover rig, which needs to change the ESP and repair any other failures in the downhole well (Ga ´bor, 1999); workover operations include any The current issue and full text archive of this journal is available at www.emeraldinsight.com/1741-0401.htm International Journal of Productivity and Performance Management Vol. 62 No. 2, 2013 pp. 204-218 r Emerald Group Publishing Limited 1741-0401 DOI 10.1108/17410401311295740 204 IJPPM 62,2
Transcript
REFLECTIVE PRACTICE
Evaluation of operationalperformance of workover rigs
activities in oilfieldsHaitham Mansour, M. Munir Ahmad, Nesreddin Dhafr and
Hussain AhmedSchool of Science and Engineering, Teesside University, Middlesbrough, UK
Abstract
Purpose – This paper aims to develop a practical method to evaluate operational performance ofworkover rigs and present an approach to measure the overall equipment effectiveness (OEE) based onresults of the evaluation method.Design/methodology/approach – The area of this study focuses on workover rigs processes in theoilfield and investigates the impact of workover activities on the production at the Sarir Oilfield inLibya. The loss of time from workover procedures and electrical submersible pumps ESP installationand pulling, which affect oil well production, should be eliminated in order to reduce the cost. Severalexample calculations of workover operation efficiency involving actual workover operational data arepresented. The method of evaluation of workover process has been developing which were the bases ofOEE calculation.Findings – The measure was developed to help support continuing efforts around processimprovements and cost leadership at Oilfields. The results on the empirical findings are introducingOEE for the workover activities which will be used as a valuable indicator for workover activitiesimprovement.Practical implications – The result of this research makes it possible to represent the OEE as abenchmark that will be used to compare the performance of workover process.Originality/value – This paper presents a successful and effective evaluation of OEE which willprovide a useful observer to set of operational improvement areas and how such activities could beorganised and managed more effectively.
IntroductionEvery well in the oilfield is as a small manufacturing plant and each plant needsdifferent equipment as the conditions for each plant are unique. Producing oil needsmany procedures to keep the well running, well needs equipment to produce,equipment needs tools to install or uninstall (Ken and Stewart, 1987). These activitiesof develop of wells, maintenance, repair have many wastes that could affect the totalproduction from the oil wells. The reason of selecting the oilfield operations are that theoperation and the activities are continuous process and become discrete, that makesthem more applicable to improvement tools (Ken and Stewart, 1987).
Oil wells require maintenance and repair, from time to time, due to normal wear andtear, age and the effects of the environment to which the equipment is exposed(Ken and Stewart, 1987). Changing electrical submersible pump (ESP) failures in eachwell are undertaken by the workover rig, which needs to change the ESP and repairany other failures in the downhole well (Gabor, 1999); workover operations include any
The current issue and full text archive of this journal is available atwww.emeraldinsight.com/1741-0401.htm
International Journal of Productivityand Performance ManagementVol. 62 No. 2, 2013pp. 204-218r Emerald Group Publishing Limited1741-0401DOI 10.1108/17410401311295740
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number of activities performed on a well, after initial completion, includingrecompletion and remedial repair work (Ken and Stewart, 1987).
Workover operations are referred to such operations that are performed to resolvespecific problems that are found after production has started (Ken and Stewart, 1987;Gabor, 1999). Workovers usually involve a service rig; however, many types ofworkovers are performed (Ken and Stewart, 1987; Gabor, 1999):
. well completion;
. downhole equipment failure of tubing artificial lift equipment; and
. others.
Workover usually involves a service rig to solve the problems in oil wells with aproposed program. The workover program is an orderly step-by-step procedureto be followed, to achieve the required objective safely, at the minimum cost, withminimum expenditure of resources (Ken and Stewart, 1987; Spoerker and Doschek,2005).
The loss of time from workover procedures and ESP installation and pulling, whichaffect oil well production, should be eliminated in order to reduce the cost. This reducesworkover costs and increases the number of days the well can stay on productionwithout intervention.
Overall equipment effectiveness (OEE) is a basic, fundamental measurementmethod for performance measurement system. It has suggested that OEE might beused as a “benchmark” for measuring the primary performance of process (Ahmad andBenson, 1999). In this way, the primary OEE measure can be compared with futureOEE values, thus quantifying the level of improvement made (Ahmad and Benson,1999). The OEE is used to measure the effectiveness of total preventive maintenanceand improve it in individual equipment by reducing the concerned losses (Ahmad andBenson, 1999; Jeong and Phillips, 2001).
The OEE measurement is an effective way of analyzing the efficiency of a singlemachine in the system. Nakajima suggested that ideal values for the OEE componentmeasures are (Nakajima and Gabor, 1988):
. availability in excess of 90 percent;
. performance efficiency in excess of 95 percent; and
. quality in excess of 99 percent.
Purpose of OEEThe OEE measure can be applied at numerous different levels within a workoveroperation environment (Nakajima and Gabor, 1988; Anvari et al., 2010):
. First, OEE can be used as a “benchmark” for measuring the initial performanceof operation process in its totality. In this way the initial OEE measure can becompared with future OEE values (Anvari et al., 2010).
. Second, an OEE value can be used to compare activities performance across theprocess, thereby highlighting any poor activities performance (Ahmad andBenson, 1999).
. Third, if the operation procedures work individually, an OEE measure canidentify which process performance is worst (Ahmad et al., 2004).
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OEE is measured in terms of these six big losses, which are essentially a function of theavailability, performance rate, and quality rate of the machine (Ahmad and Benson,1999; Nakajima and Gabor, 1988):
MethodologyOEE is designed based on similar measures that are commonly used in amanufacturing environment. The measure was developed to help support continuingefforts around process improvements and cost leadership in the distribution operationsfunction at oilfields. Several example calculations of workover operation efficiencyinvolving actual workover operational data are presented. The method of evaluation ofworkover process has been developed which was based for OEE calculation. SarirOilfield which is owned by Arabian Gulf Oil Company in Libya has been selected ascase study to investigation of workover and ESP problem.
The workover process improvement opportunities continue to be identified basedon OEE results and new variations of this measures can be implementing for otheroilfield that using the same artificial lift method. A case study approach was adoptedfor the data collection, which was undertaken over a eight-month period, and utiliseda number of collection techniques including, participant observation, daily reportanalysis, and work experience.
Major losses in oilfieldsOilfield operations have various processes to keep producing crude oil as shownin Figure 1. The various processes are: 1. drilling, 2. well production, 3. separation, 4.water treatment, 5. maintenance, 6. workover.
2
3
4
1
5
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Figure 1.Oilfield facilities
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The procedures of the oilfield operation are normally are affected by somefactors which lead to major production losses such as downtime of the operationprocess (Sonatrach and Forage, 2007). Therefore, production losses associated to wellswaiting for maintenance services, and it is important to attend them as soon aspossible (Francis and Richard, 1995).
The major components of losses are categorised under four different headings(Arnold and Stewart, 1998-1999), as given below (Figure 2):
(1) Workover rig activity lossesWorkover rigs may lead to service delays and inactive wells, with potentiallyhigh production loss, due to time losses. The losses are comprised of rig move,rig standby, and shutdown, which are related to safety reasons, weatherconditions, and losses due to the rig on location.
(2) Artificial lift failure lossesA production loss due to failure is the major problem in oilfields; the numbersof ESPs in most oilfields are increasing, due to the increasing total oilproduction and the failure of ESP in relation to the:
. quality of the design of the ESP system; and
. problems in the ESP cables, pump, and motor.
(3) Operation losses (percent)The oilfield operation losses comprise losses due to shutdowns, pipelinepigging, inspection jobs, pipeline repair, and other engineering modifications.
(4) Other losses (percent)Due to the increased pressure on maximising oil production and change in thereservoir composition, with time, there are some losses when the facilitiesshutdown for these purposes.
The reason of focus on workover activities and ESP (artificial lift method), because theother two losses are not related to the operations on the oil wells which are not cove inthis paper.
Losses inoilfields
Other
lossesP
oliticalreasons
Reservoir
condition
Other engineeringm
odifications
Pipelinerepair
Inspectionjobs
Pipeline
pigging
Shout dow
n
Quality of E
SP
installation
ES
P problem
,cable, etc.
Failures
Location
Standby
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ove
Operationloss
Artificial
lift loss
Workover
activities
Figure 2.Major components oflosses in the oilfields
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Operationalperformance ofworkover rigs
Workover processA workover is an extensive service on an oil or gas well, requiring interventions inthe wellbore itself to correct a problem with the well (Ken and Stewart, 1987; Arnoldand Stewart, 1998-1999). Some oil and gas companies may perform this workthemselves, while others choose to contract it out to companies specialising inworkovers. The length of time required can vary, and the well will not be productiveduring the servicing. Some planning is also necessary to prepare ahead oftime, whether the event is a scheduled or emergency intervention (Sonatrach andForage, 2007).
The decision of which workover rig should be sent to do some maintenance onthe well is based on factors such as the well production, the current location of theworkover rig in relation to the demanding well, and the type of service to be completed(Sonatrach and Forage, 2007). The workover rig scheduling problem consists of findingthe best schedule for the limited number of workover rigs, minimising the productionloss associated with the wells waiting for maintenance service (Sonatrach and Forage,2007; Blikra et al., 2002).
The first step in the process is a well kill, where the workers pump heavymaterial into the well to stop production (Gabor, 1999). The material’s densityprevents oil and gas from seeping up into the wellbore, clearing it for work.Next, personnel will remove material inside the wellbore so they can access it. Theirwork may require inserting and removing various equipment such as ESP(Blikra et al., 2002).
The total cost includes the rig expenses (transport, assembly, and operation), whichare functions of time and distances, plus the losses of revenue in the wells waiting forthe rig, which are dependent of time (Sonatrach and Forage, 2007). Therefore, the totalcost depends on the ordering of the wells in the itinerary.
The actual process timeThe cycle time of processes is the time of the process from when process start untilfinished (Ahmad and Benson, 1999; Ahmad and Dhafr, 2003). The actual cycle time inthis paper refers to either the activities of the workover process to return the oil wellsto production, or the total time that the processes take. The time normally comprisesthe following:
. time for moving workover rig;
. time to kill the well;
. time for pulling downhole equipment;
. time for run in hole (RIH) with downhole equipment;
. time to return ESP to production; and
. time for preparing the wells for production.
The assessment and analysis of the workover operations activities’ performance can beintroduced. This analysis includes the main stage of workover processes, such as therig up (R/U), rig down (R/D) and ESP installation, RIH, and pull out of hole (POH) of theequipment such as ESP. The cycle time can be represented in hours, or minutes and canbe measured by adding all the planned and unplanned steps from start to finish(Ahmad and Benson, 1999; Ahmad and Dhafr, 2003).
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Evaluation of workover rig’s performanceA complete evaluation of the workover rig’s efficiency should include the effect of allplanned and unplanned operation activities on the overall workover operation(Sonatrach and Forage, 2007). The time required to perform workover activities is usedin this work for evaluating the overall workover rig’s performance. The Figures 3-6show time distribution and the best achieved time for each rig used in this study, whichwas obtained directly from the daily workover activities in the Sarir Oilfield. Rigefficiency is then a function of the rig activities. The theory implies that any workoverrig should be able to equal the fastest time. The time required to perform theseoperation activities is defined as total workover time (TWT) as Shown in Figure 7:
TWTðhoursÞ ¼ total of workover time in ðactual timeÞ
¼ ðmovingÞ þ ðrig upÞ þ ðpulling ESPÞ
þ ðRIH with equipmentÞ þ ðPOHwith equipmentÞ
þðRIH with ESPÞ þ ðfinal checkÞþðrig releaseÞ
The best total workover time (BTWT) achieved is defined as the sum of the fastesttime achieved by any workover rig. The method of calculation workover rig efficiencyprovides a relative measure of rig performance:
BTWTðhoursÞ ¼ total best ðhistoricalÞ time achieved by
workover rig ðminimum timeÞ in
¼ ðmovingÞ þ ðrig upÞ þ ðpulling ESPÞ
þ ðRIH with equipmentÞ þ ðPOHwith equipmentÞ
þðRIH with ESPÞ þ ðfinal checkÞþðrig releaseÞ
Figure 3 shows the operation activities of the workover rig number (1). The orange linepoints to the best time achieved by the same rig.
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Move Rig up POH w/ESP
RIH wtools
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Workover well 1Workover well 2Workover well 3
Workover well 4Workover well 5
Best time achieved
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king
hou
rs (
hour
s)
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34
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Figure 3.Rig (1) workover hours
for five wells
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Operationalperformance ofworkover rigs
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RIH wtools
POH w/same
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Workover well 1Workover well 2
Workover well 3
Workover well 4
Workover well 5
Best time achieved
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king
hou
rs (
hour
s)
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Figure 5.Rig (3) workover hoursfor five wells
0
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RIH wtools
POH w/same
RIH w/ESP
Finalcheck
Rigrelease
Workover well 1
Workover well 2
Workover well 3Workover well 4
Workover well 5
Best time achieved
Wor
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hou
rs (
hour
s)
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Figure 6.Rig (4) workover hoursfor five wells
0
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RIH wtools
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Workover well 1
Workover well 2
Workover well 3
Workover well 4
Workover well 5
Best time achieved
Wor
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rs (
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s)1
2 345
Figure 4.Rig (2) workover hoursfor five wells
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Figure 4 shows the operation activities of the workover rig number (2). The orangeline points to the best time achieved by the same rig. It can be seen that ESP takesa long time to finish the process that affect the overall efficiency.
The POH with ESP, RIH with ESP, and final check are required more time toreturn the well to production. The time required to finish the process is important timeto keep the well running in the future.
The time required to perform these operation activities is defined as TWT as in:The BTWT is defined as the sum of the fastest time achieved by any workover
rig. The method of calculation workover rig efficiency provides a relative measureof rig performance (Figure 7).
Rig efficiencyThe efficiency measures can cover time, distance, performance, productivity, andfinancial parameters. The analyses of these processes are essential in identifying themain causes that affect the overall performance of processes (Ahmad and Dhafr, 2003).Efficiency is defined as a metric of productive output for a given set of inputs (Ahmadand Dhafr, 2002; Dal et al., 2006). Reduced workover costs are one of the implications ofimproved efficiency (Spoerker and Doschek, 2005).
Data from four workover rigs’ activities for eight months, obtained directly from thedaily workover activities in the Sarir Oilfield which have been used in this study. Rigefficiency for each job (well) in each rig is calculated in Table I.
After the concept of TWT had been developed, the workover rig efficiency iscalculated by the use of relationship as shown below:
Efficiency¼ ðhistorical best time achieved ðBTWTÞÞ=ðactual time ðTWTÞÞ
The efficiencies of the workover are based on the historical data that can be used topredict future performance in each rig. The reason of the different efficiency for thesame rig is that the rig has working to nearby best time that achieved duringthe working days at the same rig, or workover procedures have delay for finished them.
Effective daily rig costIt is simply the actual workover price divided by its efficiency for the particularworkover area. It can be a useful tool in rig selection.
0
1
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Rig 1 Rig 2 Rig 3 Rig 4
Move
Rig up
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RIH w/ESP
Final check
Rig release
Bes
t tim
e ac
hiev
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s)
Mov
eR
ig u
pP
OH
w/E
SP
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w/to
ols
PO
H w
/sam
eR
IH w
/ES
PF
inal
che
ckR
ig r
elea
seFigure 7.
Best time achievedfor activities by
workover rigs
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Operationalperformance ofworkover rigs
Effective daily fixed costThe daily fixed cost includes the cost of the fuel, water, rental equipment, labor, andother daily expense. The effective daily fixed cost therefore represent the real fixed costassociated with the rig’s overall workover efficiency:
Effective daily workover costThe bottom line in evaluating the workover rig performance is the overall cost to job(well). It is the summation of effective daily rig cost and effective daily fixed cost. Thesecosts are summarised in Table II.
Initial development of OEEIn order to start the OEE measurement process, operational performance datacollection of the three OEE variables, availability, performance, and quality (Ahmadand Benson, 1999; Nakajima and Gabor, 1988; Reyes et al., 2010), were carried outduring a period of eight months.
Calculation of OEE componentsThe OEE is using the same loss categorisation as in Nakajima’s (Nakajima and Gabor,1988) approach which is using the Equation (1) as above. Each element of the OEE
The second element is “performance rate.” This measures the ratio of the best timeachieved to the actual time. That has been calculated in the method of evaluation of theworkover:
Performance % ¼ best time achieved (BTWT)/actual time (TWT)where,
TWTðhoursÞ ¼ total of workover time in ðactual timeÞ¼ ðmovingÞ þ ðrig upÞ þ ðpulling ESPÞþ ðRIHwith equipmentÞ þ ðPOHwith equipmentÞþðRIH with ESPÞ þ ðfinal checkÞ þðrig releaseÞ
BTWTðhoursÞ¼ total best time achieved byworkoverrig ðminimum timeÞ in ¼ ðmovingÞþðrig upÞ þ ðpulling ESPÞ þ ðRIHwithequipmentÞ þ ðPOHwith equipmentÞþðRIHwith ESPÞ þ ðfinal checkÞþðrig releaseÞ
The third element of the OEE calculation is the “quality rate,” and is used to indicatethe proportion of defective time for good workover to the TWT:
Quality% ¼ time for goodworkover=time for total workover
Investigation of resultsFrom the data analyses in the above, the practical method for evaluating theoperational performance of workover activities in Sarir Oilfield varies greatly. The rigsefficiencies remain relatively constant when they are operated in the differentlocations. Table II shows the combined effect of rig efficiency and the efficiency toperform all other workover operations as the effective daily workover cost, which is apractical measure of the overall workover performance. It can be seen in Figure 6 theimprovement in each rig can be performed and the improvement of the efficiencyof the rigs can be maintained. Each rig has target obtained hours in each steps of theworkover operation.
Table II shows many examples of results obtained with this method of evaluation ofthe workover rig efficiency.
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The effective daily workover cost can give a good display to see the impact ofthe rig efficiency on the cost of operation ( Jeong and Phillips, 2001). Figure 8 showsthe oilfield will have useful method to select and evaluate the rig efficiency. Theimprovement in workover procedures greatly could reduce the downtime caused byincorrect operating procedures while a good workover program reduces downtimecaused by worse workover procedures could be achieved.
The minimum cost is another performance objective in the company (Ahmad andBenson, 1999; (Tsarouhas, 2007). Costs in this case is associated with workoverprocedures, resource utilisation, and ESP pulling and installation.
The optimum workover procedures of each rig gives the lowest total cost. The fixedoperating costs are directly proportional to output, such as fuel, power, water, wastetreatment, and rental special equipment.
OEE results for workover rigsThe construction of this initial OEE measure as in Table III was undertaken byutilising existing workover performance data as in the above. While most ofthe existing measurement data already collected was of a suitable basis to develop theOEE measure.
The actual availability, performance rate, and quality measures, together with thecomplete OEE figure are shown in Table III. In order to add more meaning tothe bare percentage figures histograms were also plotted to visualise these values.The conclusion of this process resulted in an average OEE measure beingcalculated which was used to indicate the current performance of the workover rigas a whole.
The main causes for low OEEs (Figure 9), were lack of workover procedures,ESP pulling and installation, and the location of the oil well. The lack of ESPprocedures was considered to be a problem that is depend on the numberof the technical and the helper at same time, and the type of equipment used to finishthe job.
The proposed method of evaluation the workover rig is measured overalleffectiveness. The calculation is based on results of this evaluation. The drop in OEEreflects a change in the quality and the procedures time of the workover activitiesin each well (Figure 8). While the efficiency gave the clear points to evaluation the
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Rig 1 Rig 4Rig 3Rig 2
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effi
cien
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%)
Figure 8.The overall workover
job performance inSarir Oilfield
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workover rig. The OEE and efficiency have different impact on the cost as inFigures 8 and 10. The costs associated with workover procedures, resource utilisation,and ESP pulling and installation. The quality of workover has major impact on the OEEresult which is basis of OEE calculation (Table III). The quality is affected by the workingdays that each rig takes them to complete the workover job and return the oil wellto production. Monitoring the process and precise measurement of its main aspects isthe key step to workover plan and to manage improvement for the procedures.
ConclusionsThe main purpose of an OEE results is to present essential data against where decisionsmay be made. It based on the results of method of evaluation of the workover rig. Thismethod of calculating rig efficiency provides the practical measure of the workoverperformance which can aid in rig procedures negotiation and rig selection.
A case study approach was adopted for the data collection, which was undertakenover eight-month period, and utilised a number of collection techniques including,participant observation, daily report analysis, and work experience.
The concept discussed in this paper is providing the basis for developing a moreuniform method of evaluating rig performance. It should result in more efficient rigoperations. The OEE monitors the actual performance of workover relative to itsperformance capabilities under optimal workover conditions.
Numerous factors impacting performance can vary from location to locationand from rig to rig. Improved efficiency can be achieved through the effectivemanagement of effort to improve productivity. An attempt could be made to theprocedures of the workover activities to enhance the efficiencies of the workoverrigs in the Sarir Oilfield. The workover process improvement opportunities continue tobe identified based on OEE results and new variations of these measures can beimplementing for other workover at oilfields that using them artificial lift method.
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0
5
10
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25
30
35
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45
0
20,000
40,000
60,000
80,000Effective daily workover cost (£)
OEEC
ost (
£)
Rig 1 Rig 4Rig 3Rig 2
OE
E (
%)
Wel
l 1
Wel
l 2
Wel
l 3
Wel
l 4
Wel
l 5
Wel
l 1
Wel
l 2
Wel
l 3
Wel
l 4
Wel
l 5
Wel
l 1
Wel
l 2
Wel
l 3
Wel
l 4
Wel
l 5
Wel
l 1
Wel
l 2
Wel
l 3
Wel
l 4
Wel
l 5 Figure 10.The OEE workover
activities
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Tsarouhas, P. (2007), “Implementation of total productive maintenance in food industry: acase study”, Journal of Quality in Maintenance Engineering, Vol. 13 No. 1, pp. 5-18.
Further reading
Anupindi, R., Chopra, S., Deshmukh, S.D., Van Meighem, J.A. and Zemel, E. (1999), ManagingBusiness Process Flows – Principles of Operations Management, Pearson Prentice Hall,Upper Saddle River, NJ.
Jonsson, P. and Lesshammar, M. (1999), “Evaluation and improvement of manufacturingperformance measurement systems: the role of OEE”, International Journal of Operations& Production Management, Vol. 19 No. 1, pp. 55-78.
Norton, J. (2002), Formulas and Calculations for Drilling, Production and Workover, ISBN:0750674520, Gulf Professional, Burlington.
Pintelon, L., Pinjala, S.K. and Vereecke, A. (2006), “Evaluating the effectiveness of maintenancestrategies”, Journal of Quality in Maintenance Engineering, Vol. 12 No. 1, pp. 7-20.
van der Leij, E. and Zuidema, F. (1999), “Theoretical maximum performance”, Working PaperNo. 57557, ProStar Rig 2000, Society of Petroleum Engineer (SPE), Abu Dhabi.
Corresponding authorM. Munir Ahmad can be contacted at: [email protected]
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