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Chapter 4 Life of Well Operations
CHAPTER 4
Life of Well Operations
Well interventions such as wireline or coiled tubing are common and important operations. It is not possible to provide the space in this book for the details of such post-construction activities. However, it is important that all possible well interventions are analysed as part of the completion design to ensure that the design takes their requirements into account. For example, if through tubing sidetracks are planned, there are a number of steps that can be taken during the well design phase to make these sidetracks easier and safer to perform at a later stage. Alternatives to well interventions are also considered during the design phase, for example smart wells or through tubing interventions for water and gas shutoff. Therefore, knowledge of the opportunities for, and the risks of, well interventions is required. Many completions will be constructed using a variety of through tubing well interventions, for example running a plug for pressure testing or electric line perforating through the completion. Again, an understanding of intervention techniques and risks is essential. This book deliberately avoids detailing specific vendor’s equipment, preferring to remain generic. However, a detailed knowledge of the application range and components of your vendors’ equipment is fundamental to the success of any well intervention (and completion).
4.1. Types and Methods of Intervening It is useful to look ahead during the design phase to try to foresee what may happen to the well throughout its life. Table 4.1 details some of the events that are possible and the main methods of achieving them.
4.2. Impact on Completion Design There is tendency in the completion design phase to under assess the number and variety of interventions that a well could undergo. Table 4.1 gives some ideas of the possibilities. For any of these (and other) possibilities, it is worth asking how to enhance the completion design to improve the chances of successful interventions. It is quite possible to design an ‘intervention-free well,’ that is a completion that you believe is reliable and can cope with any probable eventuality. The reality is that, sooner or later, even for subsea wells, some form of well intervention is likely. Even small changes in the well design can improve the chances of successful well interventions. Figure 4.1 highlights a selection of well intervention issues. 241
242
Table 4.1
Impact on Completion Design
Well operations through the life of a well
Opportunity
Data acquisition
Integrity monitoring and repair
Water or gas shut-off
Debris removal and sand control
Reason
Main Methods
All data acquisition must be Much data can be acquired without interventions through continuous in support of a decision. pressure and temperature The decision may measurements (surface or involve the current well bottomhole), well sampling and (e.g. production log to well tests. Some wells are hard to determine the test (e.g. many subsea wells), and opportunity for water downhole meters/gauges may assist. shut-off ) or the field in Interventions for data acquisition general (e.g. measure include production logs, cased hole reservoir pressure decline formation logs and downhole to determine if water sampling. injection is required). Maintaining integrity of Monitoring integrity primarily the well is essential. involves measuring annulus pressures. Some well designs make this harder (subsea or gas lift). Supplementing pressure monitoring are calipers. Repairing of the well may be performed with straddles or expandable tubing/patches or by replacing the tubing. Safety valves may be repaired with insert valves or ‘‘storm’’ chokes used (Section 10.2, Chapter 10). Excess water or gas reduces Through tubing interventions include cement and gel squeezes, plugs, tubing performance straddles, patches and mechanical and may constrain closing of sleeves. production due to Interventionless techniques primarily surface processing require smart wells. limitations. Debris can be removed by slickline Many wells fill up with (bailing), which is slow. Coiled debris (perforating tubing and jointed pipe (hydraulic debris, sand or chalk, workover unit) are more effective corrosion products, and can incorporate mills and drilling materials, junk jetting. Reverse circulation can and proppant). This be more effective than forward debris can cover circulation but requires the well production/injection to be overbalanced. intervals. Remedial sand control is difficult; techniques include sand consolidation, insert screens and sidetracks (especially with total screen failure).
243
Life of Well Operations
Table 4.1. (Continued ) Opportunity
Sidetracks and well deepening
Tubing replacements
Flow assurance
Stimulation
Perforating
Reason
Main Methods
Completion sidetracks are Through tubing sidetracks and well deepening using through tubing to replace a failed rotary drilling (TTRD) may be reservoir completion and possible depending on the are often located close completion design. Sidetracks are to the existing wellbore. made easier by reduced numbers Geological sidetracks of casing/tubing strings to mill and move the wellbore by these strings being cemented. to access new reserves. Conventional sidetracks require the removal of the upper completion. Top hole workover (reservoir remains Replacing failed tubing isolated) or full workover (entire or components. Different completion pulled). tubing sizes or adding artificial lift may enhance Techniques include straight pull (e.g. above a tubing disconnect) or a performance. chemical/mechanical cut. Packers may need to be milled. Prevention methods include inhibitor The prevention of squeezes (bullheading, coiled tubing restrictions to flow or jointed pipe) and batch caused by scale, wax, treatments. Removal techniques asphaltene, etc. can involve bullheading or (Chapter 7). If circulation of chemicals from prevention is surface (e.g. acids or hot oiling), unsuccessful, deposits pipe operations ( jetting, washing, may be removed. milling, pulsation) or mechanical removal with wireline (blasting, cutting, reperforating). Most stimulations can be performed Stimulation can be through tubing either by performed during well bullheading or with coiled tubing. construction or post well Proppant fracturing (Section 2.4, construction. Many Chapter 2) will require extensive stimulations have to be clean-up operations. Chemical periodically repeated. treatments (Section 2.5, Chapter 2) require compatible materials (e.g. elastomers) (Chapter 8). Most perforating, post well This can be to add new construction will be through completion intervals tubing (wireline or coiled (e.g. identified from tubing/jointed pipe). production logs) or to reperforate existing intervals that are performing badly (poor initial perforating, scaled up, etc.)
244
Impact on Completion Design
Table 4.1. (Continued ) Opportunity
Tubing performance enhancement
Retrofit artificial lift
Conversion of duty
Reason
Main Methods
Lift problems are common Velocity strings can be hung off the existing completion. in late life (Sections 5.6 Deliquification includes plungers, and 5.7, Chapter 5). This surfactant injection and pumping. can be due to excess water or gas or declining rates. Artificial lift can be added by Many wells benefit from through tubing interventions artificial lift late in field (gas lift, jet pumps, some rod pumps life when pressures and hydraulic submersible are lower and water pumps) (Chapter 6). If the well cuts higher. design is correct, electrical submersible pumps can be retrofitted through tubing. Other techniques require a tubing replacement. Depending on the well design, no As wells mature, they are downhole intervention may be frequently converted required. The production intervals from oil/gas production may require reconfiguring (shutting to some other duty off some intervals, opening up (especially injection). others). If the tubing metallurgy or Injection options include size is not suitable for the new duty, water (including it may need replacing (Chapter 8). produced water), gas, water alternating gas (WAG), carbon dioxide and other waste streams.
One of the concepts promoted in Figure 4.1 is the monobore completion. A monobore completion has the same internal diameter for the tubing and liner/ screens. This can be unduly restrictive and limits the use of nipple profiles. Nipple profiles can be useful during the completion phase and for the life of the well (if they do not scale up or corrode). Nipples are easier to use than the alternative of tubing set bridge plugs. Instead of using a strict monobore completion, a ‘‘working monobore’’ concept simply ensures that non-inflating bridge plugs are deployable to the reservoir section. This can be achieved with tubing of the same size as the liner and a small number of nipple profiles or with liner slightly smaller than the tubing. A common offshore configuration is 5½ in. tubing and a 5 in. liner or screen. Such a configuration is also beneficial for flow performance. Tubing sizing (covering flow performance and clearances) is in Section 5.8, Chapter 5.
245
Life of Well Operations
Is there space above the tree (platform wells) for rig independent, through tubing well interventions. Can you influence the wellbay design?
Is a tree saver required and deployable to allow fracturing to take place during the life of the well.
What is the system for measuring annulus pressure and assessing integrity of tubing and casing?
How easy is the deployment of a velocity string?
P
Is the metallurgy suitable for conversion to injection duty? Large tubing diameter at intermediate hole inclinations (40-60°) provide areas for debris to accumulate.
Are elastomers suitable for well interventions/ inhibitors, acids, methanol, solvents, etc.? Can the safety valve be maintained open during all operations e.g. stimulation or conversion to water injection?
Reverse tapers like this give debris hold up (clean out) and wireline fishing problems. Will packer need to be pulled or milled?
Position of gauge relative to reservoir - too far and the value of data reduces. Ease of pulling/cutting tubing (clearance and metallurgy dependent). Can a top hole workover be performed by setting a deepset barrier? Are there contingencies for debris on plugs?
A gap between the tailpipe and liner/screens can be awkward to traverse with wireline/coiled tubing toolstrings. Centralised, non sealing connector preferred.
Figure 4.1
Position of packer and liner hanger relative to through tubing sidetracks - easier to sidetrack below packer through a single, cemented casing string. Consider tractor access with changing wellbore internal diameters. A “working monobore” completion improves chances for plug setting, cleanouts, through tubing sidetracks, etc.
Perforated wells suitable locations for setting plugs?
Can the toe of the well be accessed through tubing?
Well operations in£uencing completion design.
It is inevitable that some types of wells will have increased well intervention frequency. Subsea wells, for example, are always costly to enter. Any opportunities that can replace routine well interventions should be investigated. Examples include downhole gauges, smart wells and multipurpose downhole chemical injection lines.
Life of Well Operations
Well interventions such as wireline or coiled tubing are common and important operations. It is not possible to provide the space in this book for the details of such post-construction activities. However, it is important that all possible well interventions are analysed as part of the completion design to ensure that the design takes their requirements into account. For example, if through tubing sidetracks are planned, there are a number of steps that can be taken during the well design phase to make these sidetracks easier and safer to perform at a later stage. Alternatives to well interventions are also considered during the design phase, for example smart wells or through tubing interventions for water and gas shutoff. Therefore, knowledge of the opportunities for, and the risks of, well interventions is required. Many completions will be constructed using a variety of through tubing well interventions, for example running a plug for pressure testing or electric line perforating through the completion. Again, an understanding of intervention techniques and risks is essential. This book deliberately avoids detailing specific vendor’s equipment, preferring to remain generic. However, a detailed knowledge of the application range and components of your vendors’ equipment is fundamental to the success of any well intervention (and completion).
4.1. Types and Methods of Intervening It is useful to look ahead during the design phase to try to foresee what may happen to the well throughout its life. Table 4.1 details some of the events that are possible and the main methods of achieving them.
4.2. Impact on Completion Design There is tendency in the completion design phase to under assess the number and variety of interventions that a well could undergo. Table 4.1 gives some ideas of the possibilities. For any of these (and other) possibilities, it is worth asking how to enhance the completion design to improve the chances of successful interventions. It is quite possible to design an ‘intervention-free well,’ that is a completion that you believe is reliable and can cope with any probable eventuality. The reality is that, sooner or later, even for subsea wells, some form of well intervention is likely. Even small changes in the well design can improve the chances of successful well interventions. Figure 4.1 highlights a selection of well intervention issues. 241
242
Table 4.1
Impact on Completion Design
Well operations through the life of a well
Opportunity
Data acquisition
Integrity monitoring and repair
Water or gas shut-off
Debris removal and sand control
Reason
Main Methods
All data acquisition must be Much data can be acquired without interventions through continuous in support of a decision. pressure and temperature The decision may measurements (surface or involve the current well bottomhole), well sampling and (e.g. production log to well tests. Some wells are hard to determine the test (e.g. many subsea wells), and opportunity for water downhole meters/gauges may assist. shut-off ) or the field in Interventions for data acquisition general (e.g. measure include production logs, cased hole reservoir pressure decline formation logs and downhole to determine if water sampling. injection is required). Maintaining integrity of Monitoring integrity primarily the well is essential. involves measuring annulus pressures. Some well designs make this harder (subsea or gas lift). Supplementing pressure monitoring are calipers. Repairing of the well may be performed with straddles or expandable tubing/patches or by replacing the tubing. Safety valves may be repaired with insert valves or ‘‘storm’’ chokes used (Section 10.2, Chapter 10). Excess water or gas reduces Through tubing interventions include cement and gel squeezes, plugs, tubing performance straddles, patches and mechanical and may constrain closing of sleeves. production due to Interventionless techniques primarily surface processing require smart wells. limitations. Debris can be removed by slickline Many wells fill up with (bailing), which is slow. Coiled debris (perforating tubing and jointed pipe (hydraulic debris, sand or chalk, workover unit) are more effective corrosion products, and can incorporate mills and drilling materials, junk jetting. Reverse circulation can and proppant). This be more effective than forward debris can cover circulation but requires the well production/injection to be overbalanced. intervals. Remedial sand control is difficult; techniques include sand consolidation, insert screens and sidetracks (especially with total screen failure).
243
Life of Well Operations
Table 4.1. (Continued ) Opportunity
Sidetracks and well deepening
Tubing replacements
Flow assurance
Stimulation
Perforating
Reason
Main Methods
Completion sidetracks are Through tubing sidetracks and well deepening using through tubing to replace a failed rotary drilling (TTRD) may be reservoir completion and possible depending on the are often located close completion design. Sidetracks are to the existing wellbore. made easier by reduced numbers Geological sidetracks of casing/tubing strings to mill and move the wellbore by these strings being cemented. to access new reserves. Conventional sidetracks require the removal of the upper completion. Top hole workover (reservoir remains Replacing failed tubing isolated) or full workover (entire or components. Different completion pulled). tubing sizes or adding artificial lift may enhance Techniques include straight pull (e.g. above a tubing disconnect) or a performance. chemical/mechanical cut. Packers may need to be milled. Prevention methods include inhibitor The prevention of squeezes (bullheading, coiled tubing restrictions to flow or jointed pipe) and batch caused by scale, wax, treatments. Removal techniques asphaltene, etc. can involve bullheading or (Chapter 7). If circulation of chemicals from prevention is surface (e.g. acids or hot oiling), unsuccessful, deposits pipe operations ( jetting, washing, may be removed. milling, pulsation) or mechanical removal with wireline (blasting, cutting, reperforating). Most stimulations can be performed Stimulation can be through tubing either by performed during well bullheading or with coiled tubing. construction or post well Proppant fracturing (Section 2.4, construction. Many Chapter 2) will require extensive stimulations have to be clean-up operations. Chemical periodically repeated. treatments (Section 2.5, Chapter 2) require compatible materials (e.g. elastomers) (Chapter 8). Most perforating, post well This can be to add new construction will be through completion intervals tubing (wireline or coiled (e.g. identified from tubing/jointed pipe). production logs) or to reperforate existing intervals that are performing badly (poor initial perforating, scaled up, etc.)
244
Impact on Completion Design
Table 4.1. (Continued ) Opportunity
Tubing performance enhancement
Retrofit artificial lift
Conversion of duty
Reason
Main Methods
Lift problems are common Velocity strings can be hung off the existing completion. in late life (Sections 5.6 Deliquification includes plungers, and 5.7, Chapter 5). This surfactant injection and pumping. can be due to excess water or gas or declining rates. Artificial lift can be added by Many wells benefit from through tubing interventions artificial lift late in field (gas lift, jet pumps, some rod pumps life when pressures and hydraulic submersible are lower and water pumps) (Chapter 6). If the well cuts higher. design is correct, electrical submersible pumps can be retrofitted through tubing. Other techniques require a tubing replacement. Depending on the well design, no As wells mature, they are downhole intervention may be frequently converted required. The production intervals from oil/gas production may require reconfiguring (shutting to some other duty off some intervals, opening up (especially injection). others). If the tubing metallurgy or Injection options include size is not suitable for the new duty, water (including it may need replacing (Chapter 8). produced water), gas, water alternating gas (WAG), carbon dioxide and other waste streams.
One of the concepts promoted in Figure 4.1 is the monobore completion. A monobore completion has the same internal diameter for the tubing and liner/ screens. This can be unduly restrictive and limits the use of nipple profiles. Nipple profiles can be useful during the completion phase and for the life of the well (if they do not scale up or corrode). Nipples are easier to use than the alternative of tubing set bridge plugs. Instead of using a strict monobore completion, a ‘‘working monobore’’ concept simply ensures that non-inflating bridge plugs are deployable to the reservoir section. This can be achieved with tubing of the same size as the liner and a small number of nipple profiles or with liner slightly smaller than the tubing. A common offshore configuration is 5½ in. tubing and a 5 in. liner or screen. Such a configuration is also beneficial for flow performance. Tubing sizing (covering flow performance and clearances) is in Section 5.8, Chapter 5.
245
Life of Well Operations
Is there space above the tree (platform wells) for rig independent, through tubing well interventions. Can you influence the wellbay design?
Is a tree saver required and deployable to allow fracturing to take place during the life of the well.
What is the system for measuring annulus pressure and assessing integrity of tubing and casing?
How easy is the deployment of a velocity string?
P
Is the metallurgy suitable for conversion to injection duty? Large tubing diameter at intermediate hole inclinations (40-60°) provide areas for debris to accumulate.
Are elastomers suitable for well interventions/ inhibitors, acids, methanol, solvents, etc.? Can the safety valve be maintained open during all operations e.g. stimulation or conversion to water injection?
Reverse tapers like this give debris hold up (clean out) and wireline fishing problems. Will packer need to be pulled or milled?
Position of gauge relative to reservoir - too far and the value of data reduces. Ease of pulling/cutting tubing (clearance and metallurgy dependent). Can a top hole workover be performed by setting a deepset barrier? Are there contingencies for debris on plugs?
A gap between the tailpipe and liner/screens can be awkward to traverse with wireline/coiled tubing toolstrings. Centralised, non sealing connector preferred.
Figure 4.1
Position of packer and liner hanger relative to through tubing sidetracks - easier to sidetrack below packer through a single, cemented casing string. Consider tractor access with changing wellbore internal diameters. A “working monobore” completion improves chances for plug setting, cleanouts, through tubing sidetracks, etc.
Perforated wells suitable locations for setting plugs?
Can the toe of the well be accessed through tubing?
Well operations in£uencing completion design.
It is inevitable that some types of wells will have increased well intervention frequency. Subsea wells, for example, are always costly to enter. Any opportunities that can replace routine well interventions should be investigated. Examples include downhole gauges, smart wells and multipurpose downhole chemical injection lines.