论文部分内容阅读
Received 8 May 2012； accepted 14 June 2012
Abstract
There are abundant shallow heavy oil resources in Shengli Oilfield， heavy oil reservoirs in the oil field have soft formation and shallow burial depth which ranges from 800 m to 1200 m in most blocks， fishbone wells are used to develop heavy oil fields by increasing the reservoir contact and thermal efficiency and thus getting high production. In order to drill the fishbone wells in shallow heavy oil field， some problems should be solved： the technology of big hole trajectory control in soft formation， big diameter casing run in high dogleg hole， avoiding the wall collapse between main bore and branches and running drill pipe or casing into main bore easily. In this paper， the technology of big hole trajectory control in soft formation， the suspended sidetracking technology in loose formation， and the drill pipe or casing design optimization are introduced. In order to increase the measurement accuracy of the well trajectory， the effect of different mud motor conditions on the measurement accuracy is analyzed and the formula for calculating the measurement error is obtained. Drilling technology in this paper was applied in Zhan 18 — P1 well， which provides good experience for heavy oil thermal recovery in Shengli oilfield.
Key words： Fishbone wells； Shallow heavy oil； Trajectory control； Wall collapse； Production
Dong， Z. G.， & Zhang， C. L. （2012）. Fishbone Wells Drilling Technology in Shallow Heavy Oil Field：A Case of Zhan 18—P1 Well in Shengli Oilfield in China. Advances in Petroleum Exploration and Development， 3（2）， xx—xx. Available from： URL： http：//www.cscanada.net/index.php/aped/article/view/j.aped.1925543820120302.589
DOI： http：//dx.doi.org/10.3968/j.aped.1925543820120302.589
NOMENCLATURE
=deviation of the mud motor bend point from its axis， mm
=distance between the mud motor bend point and the bit， mm
=distance of the tangential point and the bit， mm
σ =gap between the tool and the hole wall， mm
γ =angle of the mud motor， °
θ =tool face angle， °
=measurement error， °
INTRODUCTION
It is a major way to develop the heavy oil reservoir by the injecting steam. In the common horizontal well， the teaming can not be injected to all horizontal sections. Thus at the end of horizontal section， it can not get good steaming result， and can not get high heavy oil production in the common horizontal well[1—2]. The practice shows： it is difficult to greatly improve the developing effect by simply increasing the length of the horizontal section during the heavy oil development. Fishbone well is a technology that further extension and development of horizontal well. It has become an important way to improve the development effectiveness and enhanced oil recovery in Shallow Heavy Oil Field over the last ten years[3—4]. Since 2006， fishbone wells have been drilled to develop heavy oil in Shengli oil field and good results have been achieved. Shengli heavy oil reservoir is shallow with the soft formation and composed of the loose rock. The reservoir is made up of the sand or gravel. According to its formation characters， the structure of the fishbone wells was： to run in the Φ339.70 mm surface casing to seal the upper loose surface formation and to setup the well head， to use Φ311 mm drill bits to drill the build up section to A point， and to run in the Φ245 mm technical casing. The technical casing shoe was set on the shale rock below the target point of the horizontal section to improve the well cementing quality. Φ215.9 mm bits were used to drill the main bore and branches， which were up to the oil zone from the low shale section. The process was： When drilling to the deviation point， the branch hole was begun to drill. Then， the drill bit were pulled to the deviation point to drill the next section of the main bore to the next deviation point and to drill the second branch till the main bore and branches were completed. This is called “go forward” drilling technology. Φ168.3mm screen casing was run into the main bore after the well completion and the open hole completion method for the branches were used.
1. THE KEY PROBLEMS IN THE PROJECT
1.1 The Trajectory Control in the Big Diameter Hole
Because the viscosity of the heavy oil is very high， the big diameter casing should be run into the hole for the thermal production. With the limit of the layer condition and the reservoir situation， the hole from the vertical section to the horizontal section should be drilled in Φ311.2 mm well bore， which needs a high build angle rate. The drilling tools used in big well bore have a big diameter with the big rigidity and strong anti—bending ability. Comparing with the common￠215.9 mm well bore， their build rate will have a big discount for the same structure parameter， which would affect the efficiency. In addition， the bigger freedom of the drilling tools in the large well bore， the more serious measurement error would take place. So it is important to analyze the measurement error.
1.2 Avoiding the Wall Collapse Between the Main Bore and the Branch in the Loose Formation As Shengli heavy oil reservoir is shallow with the soft formation and composed of loose rock， it was an important technology in fishbone wells drilling to avoid the collapse of the wall between the main bore and the branch. While sidetracking， the wall should be build up as soon as possible.The branch should be separated from main bore both in plane and in perpendicular direction to avoid the wall collapse under its gravity.
1.3 The Re—Entry Problem of the Drilling Tools or the Screen Casing
During the drilling of a branch， if a bit changing or short trip was needed， it is should be ensured that the drilling string should be smoothly run into the branch hole again. the drilling tools from can not go into a finished brunch hole while drilling the other next main bore hole or next branches. After the fishbone wells completion， it should be ensured that the screen pipe run into the main bore instead of the branches.
1.4 The Big Diameter Casing String Run in the High Curvature Well Bore
Because of the high well bore curvature， it was difficult to run the ￠244.5mm casing into the ￠311.2mm well bore. As the casing load was little in shallow well， running the strings became more difficult. In the implementation， the work of analyzing the casing mathematical model， calculating the casing friction， optimization casing structure and preparing convenient surface pressure should be done unit to ensure running of the casing.
2. The Key Technology Used in the Project
2.1 The Trajectory Control and Measurement Technology
There are many factors affecting the well trajectory control such as the structure parameter of mud motor， the accuracy control of the tool face while drilling， the drilling parameters， the formation drill ability and the anisotropism， in which the structure parameter of the mud motor is the key part[5—6].
While drilling the build up section， the double bending mud motor as the kick—off tool was selected. As the penetration rate fluctuation can produce the build angle rate fluctuation， in order to keep stable build up rate， the “time—control drilling technology” to drill the soft formation section was used to avoid the fluctuation of the build up rate. With the increased well depth and the increased deviation angle， the WOB was increased properly to offset the friction on drilling pipe. According to the measurement result， the drilling software was used to calculate and predict the path. If the measurement result was not consistent with the designed trajectory， the drilling parameters or the tool structure should be changed in time. While drilling the horizontal section， the gliding and rotating ways and monitored the well path with the instruments of MWD were adopted. We increased the measurement frequency to improve the controlling accuracy. To decrease the tool condition influence on the measurement accuracy， a Φ205 mm stabilizer was linked at the end of the mud motor to ensure the drilling tool to stay in the center of the hole.
2.2 To Calculate Measurement Error
The mud motor condition would affect the MWD measurement accuracy. The more freedom of the drilling tools in hole， the more serious the measurement error. So it is important to calculate the measurement error of the big angle mud motor in the big diameter well bore. The formula is obtained according to some relative materials. Assuming that the measurement instrument was aligned with the drilling tool axis， the inclination difference of the drilling tool axis from hole axis is the measurement error at the survey point. If the hole axis is X—axis and the high side of well bottom is Y—axis， the initial crooked formula of the mud motor is：
（1）
During the measurement， the mud motor condition accorded with the above initial crooked formula. In the formula， e is the deviation of the mud motor bend point from its axis； c is the distance between the mud motor bend point and the bit； l is the distance of the tangential point and the bit. The tangential point is the contact point between drilling tool and the hole wall， about at the end of non—magnetic drill collar， σ is the gap between the tool and the hole wall， it can be obtained from above formula：
（2）
According to the definition of the derivative， the derivative is slope of the curve.
If the angle of the mud motor is， the relational expression as follow：
（3）
If the tool face angle is q， the bend angle of mud motor is ， the angle deviation between the tool axis and the well axis at the survey point is：
（4）
2.3 Suspended Sidetracking Technology in the Loose Formation
Suspended sidetracking technique is a key technique in drilling the fishbone wells. It is a key technique of avoiding the wall collapse and ensuring the drilling pipe or casing re—entry into the hole. In order to ensure that the drilling tools or the completion casing were ran into the main bore smoothly after the suspended sidetracking， the path of main bore must be assured at the lower part of the branch. That is， at the branched point， the main bore should gradually deviate from the branch hole not only at the plane direction， but also at the perpendicular direction. The re—entry tools or the completion casing can be run into the main bore smoothly under the effect of its gravity. Because of the loose formation of the shallow heavy oil reservoir， the wall between the main bore and the branch hole was easy to collapse[7—8]. To form a stable wall is a key technology during the sidetrack. The form of the wall should deviate not only at the plane direction， but also at the perpendicular direction to avoid the wall to collapse under its gravity. If the tool face is 140owhen drilling the branch hole， the tool face should be about 320owhen drilling the main hole. When drilling about 20～30 m， the tool face should be regulated according to the MWD data as the well inclination， azimuth and the vertical depth. The main hole climbing should be finished before drilling to the next deviation point.
During the suspended sidetracking for the loose formation， there are 3 steps： “slotting”， “making nest” and “controlling the penetration rate”. It should not ream again and again while suspended sidetracking in the soft formation to avoid the lose control of the trajectory. The drilling parameters， especially the hydraulic parameter， are very important during the sidetrack. The hydraulic parameter should be optimized to decrease the erosion of the hydraulic horsepower to the formation.
2.4 The Optimization of the Drill String and Casing Structure
In the drill string design of the fishbone wells， the drill string or the screen casing rigidity should be considered in accordance with the well bore. According to the mechanics analyzing result， the drilling tools structure were designed the rigidity of the kick off tool was kept from becoming bigger than that of screen casing’s to ensure that the screen casing be run into the main bore smoothly.
The drilling software was used to analyze the consistence of the drilling string， the screen casing and the main bore to optimize the best tool structure and well completion string. The process was as follows： （1） according to tool structure and trajectory parameters to analyze it’s stress， （2） to analyze the calculating result， （3） if the result could not meet the requirement， the drill string should be designed again.
3. THE CASE
Zhan 18 — P1 well is the first fishbone well in Shallow Heavy Oil Field in Shengli Oilfield， Its purpose was to increase the heavy oil production， the technical specification are shown in Table 1. its initial production is 62 ton， which is three times of the horizontal well’s production and 17 times of the vertical well’s production in the same block， its development shows great application prospect of this technology in heavy oil recovery. CONCLUSION
Using the fishbone wells to develop heavy oil can increase the reservoir contact and thermal efficiency and thus get the high production. we successfully finished the fishbone wells in shallow heavy oil field which provide good experiences for the similar area.
This paper provided certain knowledge about the big size well trajectory control in the loose formation， and proposed a formula to calculate the measurement error. We should continue to approach the relationship between the mud motor structure、drilling parameters、formation property and the build up rate in order to improve the drilling efficiency.
Suspended sidetracking is a key technology in the fishbone wells project. In the distribution design of the main bore and branches， we must ensure to avoid the wall collapse between the main bore and branches and to assure the smooth re—entry of the drilling pipe or casing.
REFERENCES
[1] Yeten， B.， & Durlofsky， L. J. （2003）. Optimization of Nonconventional Well Type， Location， and Trajectory. SPEJ， 8（3）， 200—210.
[2] Brister， R.， & Oberkircher， J. （2000）. The Optimum Junction Depth for Multilateral Well. Paper 64699—MS Presented at the International Oil and Gas Conference and Exhibition， 7—10 November， 2000， Beijing， China. New York： SPE， 2000.
[3] Gipson， L. J.， Owen， R.， & Robertson， C. R.， et al. （2002）. Hamaca Heavy Oil Project： Lessons Learned and an Evolving Development Strategy. SPE 78990.
[4] Liu， S.， Li， J. P.， & Lü， D. Y. （2007）. Succeeding with Multilateral Wells in Complex Channel Sands. SPE 110240.
[5] Cavender， T. （2004）. Summary of Multilateral Completion Strategies Used in Heavy Oil Field Development. SPE 86926.
[6] Zhou， Y. J. （2008）. Advances on Special Structure Drilling Development Techniques in Shengli Oilfield. Petroleum Exploration and Development， 35（3）， 318—329.
[7] Xu， H.， Yan， Z. L.， Niu， H. B.， et al. （2010）. DRILLING PRACTice of Heavy Oil Thermal Recovery Fish—Bone Shaped Horizontal Branch Well. Petroleum Geology and Engineering， 24（1）， 98—100.
[8] Geng， Y. C.， Hai， L. J.， Wang， A. G.， et al. （2007）. Technique of Horizontal Multilateral Well CB26B—ZP1 in Shengli Oilfield. Petroleum Drilling Techniques， 35（5）， 52—54.
Abstract
There are abundant shallow heavy oil resources in Shengli Oilfield， heavy oil reservoirs in the oil field have soft formation and shallow burial depth which ranges from 800 m to 1200 m in most blocks， fishbone wells are used to develop heavy oil fields by increasing the reservoir contact and thermal efficiency and thus getting high production. In order to drill the fishbone wells in shallow heavy oil field， some problems should be solved： the technology of big hole trajectory control in soft formation， big diameter casing run in high dogleg hole， avoiding the wall collapse between main bore and branches and running drill pipe or casing into main bore easily. In this paper， the technology of big hole trajectory control in soft formation， the suspended sidetracking technology in loose formation， and the drill pipe or casing design optimization are introduced. In order to increase the measurement accuracy of the well trajectory， the effect of different mud motor conditions on the measurement accuracy is analyzed and the formula for calculating the measurement error is obtained. Drilling technology in this paper was applied in Zhan 18 — P1 well， which provides good experience for heavy oil thermal recovery in Shengli oilfield.
Key words： Fishbone wells； Shallow heavy oil； Trajectory control； Wall collapse； Production
Dong， Z. G.， & Zhang， C. L. （2012）. Fishbone Wells Drilling Technology in Shallow Heavy Oil Field：A Case of Zhan 18—P1 Well in Shengli Oilfield in China. Advances in Petroleum Exploration and Development， 3（2）， xx—xx. Available from： URL： http：//www.cscanada.net/index.php/aped/article/view/j.aped.1925543820120302.589
DOI： http：//dx.doi.org/10.3968/j.aped.1925543820120302.589
NOMENCLATURE
=deviation of the mud motor bend point from its axis， mm
=distance between the mud motor bend point and the bit， mm
=distance of the tangential point and the bit， mm
σ =gap between the tool and the hole wall， mm
γ =angle of the mud motor， °
θ =tool face angle， °
=measurement error， °
INTRODUCTION
It is a major way to develop the heavy oil reservoir by the injecting steam. In the common horizontal well， the teaming can not be injected to all horizontal sections. Thus at the end of horizontal section， it can not get good steaming result， and can not get high heavy oil production in the common horizontal well[1—2]. The practice shows： it is difficult to greatly improve the developing effect by simply increasing the length of the horizontal section during the heavy oil development. Fishbone well is a technology that further extension and development of horizontal well. It has become an important way to improve the development effectiveness and enhanced oil recovery in Shallow Heavy Oil Field over the last ten years[3—4]. Since 2006， fishbone wells have been drilled to develop heavy oil in Shengli oil field and good results have been achieved. Shengli heavy oil reservoir is shallow with the soft formation and composed of the loose rock. The reservoir is made up of the sand or gravel. According to its formation characters， the structure of the fishbone wells was： to run in the Φ339.70 mm surface casing to seal the upper loose surface formation and to setup the well head， to use Φ311 mm drill bits to drill the build up section to A point， and to run in the Φ245 mm technical casing. The technical casing shoe was set on the shale rock below the target point of the horizontal section to improve the well cementing quality. Φ215.9 mm bits were used to drill the main bore and branches， which were up to the oil zone from the low shale section. The process was： When drilling to the deviation point， the branch hole was begun to drill. Then， the drill bit were pulled to the deviation point to drill the next section of the main bore to the next deviation point and to drill the second branch till the main bore and branches were completed. This is called “go forward” drilling technology. Φ168.3mm screen casing was run into the main bore after the well completion and the open hole completion method for the branches were used.
1. THE KEY PROBLEMS IN THE PROJECT
1.1 The Trajectory Control in the Big Diameter Hole
Because the viscosity of the heavy oil is very high， the big diameter casing should be run into the hole for the thermal production. With the limit of the layer condition and the reservoir situation， the hole from the vertical section to the horizontal section should be drilled in Φ311.2 mm well bore， which needs a high build angle rate. The drilling tools used in big well bore have a big diameter with the big rigidity and strong anti—bending ability. Comparing with the common￠215.9 mm well bore， their build rate will have a big discount for the same structure parameter， which would affect the efficiency. In addition， the bigger freedom of the drilling tools in the large well bore， the more serious measurement error would take place. So it is important to analyze the measurement error.
1.2 Avoiding the Wall Collapse Between the Main Bore and the Branch in the Loose Formation As Shengli heavy oil reservoir is shallow with the soft formation and composed of loose rock， it was an important technology in fishbone wells drilling to avoid the collapse of the wall between the main bore and the branch. While sidetracking， the wall should be build up as soon as possible.The branch should be separated from main bore both in plane and in perpendicular direction to avoid the wall collapse under its gravity.
1.3 The Re—Entry Problem of the Drilling Tools or the Screen Casing
During the drilling of a branch， if a bit changing or short trip was needed， it is should be ensured that the drilling string should be smoothly run into the branch hole again. the drilling tools from can not go into a finished brunch hole while drilling the other next main bore hole or next branches. After the fishbone wells completion， it should be ensured that the screen pipe run into the main bore instead of the branches.
1.4 The Big Diameter Casing String Run in the High Curvature Well Bore
Because of the high well bore curvature， it was difficult to run the ￠244.5mm casing into the ￠311.2mm well bore. As the casing load was little in shallow well， running the strings became more difficult. In the implementation， the work of analyzing the casing mathematical model， calculating the casing friction， optimization casing structure and preparing convenient surface pressure should be done unit to ensure running of the casing.
2. The Key Technology Used in the Project
2.1 The Trajectory Control and Measurement Technology
There are many factors affecting the well trajectory control such as the structure parameter of mud motor， the accuracy control of the tool face while drilling， the drilling parameters， the formation drill ability and the anisotropism， in which the structure parameter of the mud motor is the key part[5—6].
While drilling the build up section， the double bending mud motor as the kick—off tool was selected. As the penetration rate fluctuation can produce the build angle rate fluctuation， in order to keep stable build up rate， the “time—control drilling technology” to drill the soft formation section was used to avoid the fluctuation of the build up rate. With the increased well depth and the increased deviation angle， the WOB was increased properly to offset the friction on drilling pipe. According to the measurement result， the drilling software was used to calculate and predict the path. If the measurement result was not consistent with the designed trajectory， the drilling parameters or the tool structure should be changed in time. While drilling the horizontal section， the gliding and rotating ways and monitored the well path with the instruments of MWD were adopted. We increased the measurement frequency to improve the controlling accuracy. To decrease the tool condition influence on the measurement accuracy， a Φ205 mm stabilizer was linked at the end of the mud motor to ensure the drilling tool to stay in the center of the hole.
2.2 To Calculate Measurement Error
The mud motor condition would affect the MWD measurement accuracy. The more freedom of the drilling tools in hole， the more serious the measurement error. So it is important to calculate the measurement error of the big angle mud motor in the big diameter well bore. The formula is obtained according to some relative materials. Assuming that the measurement instrument was aligned with the drilling tool axis， the inclination difference of the drilling tool axis from hole axis is the measurement error at the survey point. If the hole axis is X—axis and the high side of well bottom is Y—axis， the initial crooked formula of the mud motor is：
（1）
During the measurement， the mud motor condition accorded with the above initial crooked formula. In the formula， e is the deviation of the mud motor bend point from its axis； c is the distance between the mud motor bend point and the bit； l is the distance of the tangential point and the bit. The tangential point is the contact point between drilling tool and the hole wall， about at the end of non—magnetic drill collar， σ is the gap between the tool and the hole wall， it can be obtained from above formula：
（2）
According to the definition of the derivative， the derivative is slope of the curve.
If the angle of the mud motor is， the relational expression as follow：
（3）
If the tool face angle is q， the bend angle of mud motor is ， the angle deviation between the tool axis and the well axis at the survey point is：
（4）
2.3 Suspended Sidetracking Technology in the Loose Formation
Suspended sidetracking technique is a key technique in drilling the fishbone wells. It is a key technique of avoiding the wall collapse and ensuring the drilling pipe or casing re—entry into the hole. In order to ensure that the drilling tools or the completion casing were ran into the main bore smoothly after the suspended sidetracking， the path of main bore must be assured at the lower part of the branch. That is， at the branched point， the main bore should gradually deviate from the branch hole not only at the plane direction， but also at the perpendicular direction. The re—entry tools or the completion casing can be run into the main bore smoothly under the effect of its gravity. Because of the loose formation of the shallow heavy oil reservoir， the wall between the main bore and the branch hole was easy to collapse[7—8]. To form a stable wall is a key technology during the sidetrack. The form of the wall should deviate not only at the plane direction， but also at the perpendicular direction to avoid the wall to collapse under its gravity. If the tool face is 140owhen drilling the branch hole， the tool face should be about 320owhen drilling the main hole. When drilling about 20～30 m， the tool face should be regulated according to the MWD data as the well inclination， azimuth and the vertical depth. The main hole climbing should be finished before drilling to the next deviation point.
During the suspended sidetracking for the loose formation， there are 3 steps： “slotting”， “making nest” and “controlling the penetration rate”. It should not ream again and again while suspended sidetracking in the soft formation to avoid the lose control of the trajectory. The drilling parameters， especially the hydraulic parameter， are very important during the sidetrack. The hydraulic parameter should be optimized to decrease the erosion of the hydraulic horsepower to the formation.
2.4 The Optimization of the Drill String and Casing Structure
In the drill string design of the fishbone wells， the drill string or the screen casing rigidity should be considered in accordance with the well bore. According to the mechanics analyzing result， the drilling tools structure were designed the rigidity of the kick off tool was kept from becoming bigger than that of screen casing’s to ensure that the screen casing be run into the main bore smoothly.
The drilling software was used to analyze the consistence of the drilling string， the screen casing and the main bore to optimize the best tool structure and well completion string. The process was as follows： （1） according to tool structure and trajectory parameters to analyze it’s stress， （2） to analyze the calculating result， （3） if the result could not meet the requirement， the drill string should be designed again.
3. THE CASE
Zhan 18 — P1 well is the first fishbone well in Shallow Heavy Oil Field in Shengli Oilfield， Its purpose was to increase the heavy oil production， the technical specification are shown in Table 1. its initial production is 62 ton， which is three times of the horizontal well’s production and 17 times of the vertical well’s production in the same block， its development shows great application prospect of this technology in heavy oil recovery. CONCLUSION
Using the fishbone wells to develop heavy oil can increase the reservoir contact and thermal efficiency and thus get the high production. we successfully finished the fishbone wells in shallow heavy oil field which provide good experiences for the similar area.
This paper provided certain knowledge about the big size well trajectory control in the loose formation， and proposed a formula to calculate the measurement error. We should continue to approach the relationship between the mud motor structure、drilling parameters、formation property and the build up rate in order to improve the drilling efficiency.
Suspended sidetracking is a key technology in the fishbone wells project. In the distribution design of the main bore and branches， we must ensure to avoid the wall collapse between the main bore and branches and to assure the smooth re—entry of the drilling pipe or casing.
REFERENCES
[1] Yeten， B.， & Durlofsky， L. J. （2003）. Optimization of Nonconventional Well Type， Location， and Trajectory. SPEJ， 8（3）， 200—210.
[2] Brister， R.， & Oberkircher， J. （2000）. The Optimum Junction Depth for Multilateral Well. Paper 64699—MS Presented at the International Oil and Gas Conference and Exhibition， 7—10 November， 2000， Beijing， China. New York： SPE， 2000.
[3] Gipson， L. J.， Owen， R.， & Robertson， C. R.， et al. （2002）. Hamaca Heavy Oil Project： Lessons Learned and an Evolving Development Strategy. SPE 78990.
[4] Liu， S.， Li， J. P.， & Lü， D. Y. （2007）. Succeeding with Multilateral Wells in Complex Channel Sands. SPE 110240.
[5] Cavender， T. （2004）. Summary of Multilateral Completion Strategies Used in Heavy Oil Field Development. SPE 86926.
[6] Zhou， Y. J. （2008）. Advances on Special Structure Drilling Development Techniques in Shengli Oilfield. Petroleum Exploration and Development， 35（3）， 318—329.
[7] Xu， H.， Yan， Z. L.， Niu， H. B.， et al. （2010）. DRILLING PRACTice of Heavy Oil Thermal Recovery Fish—Bone Shaped Horizontal Branch Well. Petroleum Geology and Engineering， 24（1）， 98—100.
[8] Geng， Y. C.， Hai， L. J.， Wang， A. G.， et al. （2007）. Technique of Horizontal Multilateral Well CB26B—ZP1 in Shengli Oilfield. Petroleum Drilling Techniques， 35（5）， 52—54.