Patent Application
20180086012
In the field of offshore drilling, a landing string is composed of a number of interconnected drill pipes which can be used for drilling, landing heavy casing strings in a well, landing heavy equipment on the sea bed, and other uses. The type of drill pipe used in a landing string has a relatively heavy wall (e.g., with a 0.5″ or greater pipe wall) and is generally used where regular (e.g., more lightweight) drill pipe does not have sufficient tensile strength. Thus, landing string drill pipes are designed to resist crushing and can be relatively heavy.
For a more complete understanding of the embodiments and the advantages thereof, reference is now made to the following description, in conjunction with the accompanying figures briefly described as follows:
The drawings illustrate only example embodiments and are therefore not to be considered limiting of the scope of the embodiments described herein, as other embodiments are within the scope of this disclosure. The elements and features shown in the drawings are not necessarily drawn to scale, emphasis instead being placed upon clearly illustrating the principles of the embodiments. Additionally, certain dimensions or positionings may be exaggerated to help visually convey certain principles. In the drawings, similar reference numerals between figures designate like or corresponding, but not necessarily the same, elements.
As noted above, a landing string is composed of a number of interconnected drill pipes which can be used for drilling, landing heavy casing strings in a well, landing heavy equipment on the sea bed, and other uses. The type of drill pipe used in a landing string has a relatively heavy wall (e.g., with a 0.5″ or greater pipe wall) and is generally used where regular (e.g., more lightweight) drill pipe does not have sufficient tensile strength. Thus, landing string drill pipes are designed to resist crushing and can be relatively heavy.
While buoyancy modules can be attached to the outside of a drilling riser to reduce or eliminate its overall weight in water, the weight of the landing string, which runs inside the drilling riser, is still borne by the drilling rig as it is effectively independent of the drilling riser. The overall drilling depth (water column plus distance to well) is therefore limited by the total load that the rig can carry via the hook.
To effectively reduce the weight of the landing string, the concept of landing string buoyancy (e.g., as described in U.S. Pat. No. 7,383,885) involves the addition of buoyancy modules to landing string drill pipes. The buoyancy modules reduce the overall weight carried by a drilling rig. By adding buoyancy modules to the landing string, the overall depth capabilities can be greatly increased, effectively extending the working capacity of existing vessels with little or no upgrades.
To provide a more robust and safe solution, the following design constraints can be applied to components used in a landing string buoyancy solution: (1) no metallic components to minimize any damage caused by a component falling into the annulus and entering the well, and (2) the amount of ‘trap points’ for drilling mud should be minimized.
The environment in the annulus between the drill pipe and the drill riser is typically olefin-based drilling fluid or drilling mud. The density of the drilling mud will vary depending upon the drill depth, well characteristics, and other factors. Typical olefin-based drilling fluids that may be suitable are Novaplus® and Rheliant®, both available from MI-Swaco, among others. The typical density range for these types of synthetic muds is between about 8.0-14.0 lb/gal.
Hydrostatic pressure is built up within the drilling mud by virtue of the fact that it will effectively form a ‘column’ within the drilling annulus. The maximum operating pressure is therefore dependent upon the total length of riser deployed, the drilling rig air gap, and the density of mud used. All the components of any landing string buoyancy solution should thus be able to survive the maximum and minimum temperatures during operations, regardless of service pressure. An example of the operating conditions that all components should be able to survive are given in Error! Reference source not found. below.
Thus, example performance criteria for a landing string buoyancy solution include the ability to operate effectively in olefin-based drilling mud at temperatures from about 36-80° F. (2-27° C.) and pressures up to a maximum of about 6000 psi (equivalent to >4000 msw/13500 fsw). The complete assembled solution should be suitable for exposure to surface temperatures ranging from 23-150° F. (−5-66° C.), with the assembly hardware able to maintain functionality when mechanically loaded under these conditions.
In the context of the requirements and operating conditions for the landing string buoyancy solutions described above, landing string buoyancy hardware and a method of manufacture thereof is described herein. In one embodiment, the landing string hardware includes a stop collar to be fitted and secured around a drill pipe and stop collar hardware to secure the stop collar together around the drill pipe. The stop collar can be secured at one end of a number of buoyancy modules placed along a longitudinal length of the drill pipe to hold the buoyancy modules into place along the drill pipe. A pair of stop collars can be secured at the two ends of the buoyancy modules along a longitudinal length of the drill pipe to hold the buoyancy modules into place along the drill pipe. In one example, the stop collars and the landing string hardware can be formed from long fiber thermoplastic using extrusion-compression molding. In other examples, the stop collars and the hardware can be formed from other polymers and other fibers using other manufacturing methods, such as injection molding, injection-compression molding, and other suitable molding methods.
The hardware used to secure the stop collars in place on the drill pipe is described as stop collar hardware herein. In one example, the stop collar hardware includes a bolt having an external thread formed from long fiber thermoplastic and a nut having an internal thread formed from long fiber thermoplastic. Both the stop collar and the stop collar hardware have been tested for suitability for the application of holding the buoyancy modules in place under operating conditions.
The buoyancy modules can be embodied as cylindrical half shells assembled around the drill pipe. Each stop collar can be embodied as a single, two-piece collar that can be attached to each end of a string of buoyancy modules to restrain axial and lateral movement of the buoyancy modules. The two halves of each stop collar can be secured around and tensioned upon the drill pipe via the composite stop collar hardware, including bolts, nuts, and in some cases lock or jamb nuts if necessary. In one case, a total of four 1.125″ diameter composite bolts, along with matching composite nuts and jamb nuts, can be used to secure the two halves of each stop collar to the drill pipe.
As described in further detail below, composite bolts and nuts can be used to tension the stop collars onto the drill pipe, with sufficient tightening torque specifications to tension the stop collars such that axial motion is prevented under an axial load that is the greater of the initial buoyancy of the lightest density modules or the weight in air of the heaviest density modules. Calculations and testing demonstrate that, once tensioned, the stop collars can withstand the force of 15 buoyancy modules acting in series (e.g., in a string), multiplied by a dynamic amplification factor (DAF) of 2.5 and a safety factor (SF) against slippage of 1.5 without slipping.
During transportation, storage, and handling, the buoyancy modules, stop collars, and composite hardware will be expected to remain in operational and assembled (e.g., fully assembled and torqued) condition on landing string drill pipes. Ultraviolet (UV) exposure and ambient temperatures typical of those expected in deep water conditions can be experienced in such assembled conditions.
Turning to the drawings,
Although not visible in
Referring to
During installation and operation, the string of buoyancy modules 12 will experience external loadings due to the relative movement of raising and lowering the drill pipes 10 in the olefin mud and the buoyancy created by the string of buoyancy modules 12. Axial loads will be passed from the string of buoyancy modules 12 to the stop collars 14A and 14B. The coefficient of friction between the stop collars 14A and 14B and the drill pipe 10 can vary based on the type of material from which the stop collars 14A and 14B are formed. Thus, as described in further detail below, various prototypes of the the stop collars 14A and 14B the stop collar hardware 30 formed from different materials were tested for the suitability of holding buoyancy modules in place under operating conditions. The results of the testing is applicable to both the stop collars 14A and 14B shown in
Testing a prototype polyurethane stop collar has confirmed that 162.7 N-m of bolt torque per bolt, for example, can provide sufficient normal force to prevent slippage at the required axial load. Table 2 below provides an example of the axial load requirement and the estimated upper bolt tension value that could be generated.
1Calculated using 15 lowest density modules in 15 lb/gal olefin- based drill mud including SF and DAF.
2Measured torque at which slip load requirement was met.
3Calculated upper bound of possible tension generated by 120 lbf-ft torque, per API 6A with estimated thread friction. Actual required bolt tension to satisfy minimum slip load must be re-calculated or confirmed experimentally if friction coefficient changes.
Exact values of the frictional coefficient at the threads of the bolt and nut is unknown. Thus, only the upper bound of the bolt tension is specified. Likewise, the friction coefficient between the stop collar and drill pipe has not been established, so experimental testing was used to demonstrate adequacy. During the evaluation of the stop collar, steel bolts and nuts were used for the slip test.
One initial material selected for the stop collar was castable glass filled polyurethane. The material was evaluated for the application of the stop collar and found to be deficient with respect to certain mechanical properties, especially environmental conditions. A bulk molding compound (BMC) material of unknown composition was also evaluated and found to be unsuitable for the application with respect to its mechanical properties.
The following materials for the stop collar were evaluated for the application: 50% long glass fiber reinforced polypropylene (PPGL50), 50% long glass fiber filled nylon 6,6 (PA66GL50), and 40% thermoplastic polyurethane (TPUGL40). The stop collars can also be formed from other long fiber thermoplastic (LFT) materials formed by hot melt-impregnating continuous reinforcing fiber into a thermoplastic resin. The mixture can be cooled and formed (e.g., chopped) into discontinuous reinforcing fiber pellets. The amount of thermoplastic resin can be about 40 to 99 weight % of the LFT material, and the amount of continuous reinforcing fiber (once cut into the discontinuous reinforcing fiber) can be approximately 0.1 to 60 weight % of the LFT material. Example thermoplastic resins include polyamide, acrylonitrile butadiene styrene (ABS), polyphenylene sulfide, polypropylene, poly ether ether ketone, poly ether ketone, polyethylene, poly butylene terephthalate, poly ethylene terephthalate, polyoxymethylene, or combinations thereof. Example reinforcing fibers include carbon, glass, aramid, polypropylene, polyethylene, basalt, poly{diimidazo pyridinylene (dihydroxy) phenylene}, or combinations thereof.
As part of the evaluation, 6″×6″ plates were manufactured using extrusion-compression molding (ECM) techniques, although other molding techniques can be used. The plates were used to prepare samples for tension (ASTM D638), flexure (ASTM D790), and impact testing at room and elevated (150° F.) temperature for both the as-manufactured and exposed conditions. Due to the cost and timing of conditioning the samples, the PPGL50 material was exposed first, followed by the PA66GL50 material. The TPUGL40 material was not conditioned.
The test samples were exposed to pressurized synthetic (olefin) based mud (SBM) at 6000 psi at the maximum service temperature, followed by the testing described herein. The exposure was cyclic, consisting of 14 cycles to pressure and temperature, each cycle having a 24 hour duration according to the cycle profile for a single aging cycle shown in
Tensile testing was conducted according to ASTM D638—Standard Test Methods for Tensile Properties of Plastics. Samples were prepared according to the specification mentioned in the standard. The samples were cut from the test plaques into rectangular beams that were then routed to dog-bone shaped test specimens. First, the rectangular beams were cut with the help of a water cooled tile saw equipped with a diamond blade. The rectangular beams were then routed to dog-bone shaped specimens with a router.
The samples were prepared in two directions, namely transverse and longitudinal (to the direction of material flow). A number of the samples were conditioned and the rest tested at room and elevated temperatures. The elevated temperature tests were performed by testing the samples at 65° C. (150° F.) environment. All tensile tests were conducted on a SATEC™ load frame equipped with a 50,000 lbs-force load cell and a one inch gauge extensometer to measure the strain data. The tests were conducted on displacement control mode with a rate of 2 mm/min. Time (msec), load (Newtons), displacement (mm), and strain (mm/mm) were the variables measured for each of the tests. Results of the testing are shown in Table 6-1 through Table 6-5 for various materials. Bar charts are also shown in
Flexural testing was also conducted according to ASTM 790—Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials. Samples were prepared with the dimensions specified in the standard. Half of the samples were tested as unconditioned and the other half were conditioned prior to the flexural test. The BMC samples were prepared in two directions, Direction 1 and Direction 2. Each direction was tested under room temperature and 65° C. (150° F.). At least five samples were tested for each category. The span length for the flexural testing was 120 mm and the loading rate 5 mm/min. Results are shown in Table 6-6 through Table 6-9 for respective materials. Bar charts are shown in
Low velocity impact (LVI) testing was conducted using an instrumented drop weight impact tower. The instrument measures impact force and energy as a function of time. The force-time or energy-time curves convey information pertaining to response of the sample to impact. A 100×100 mm (4″×4″) sample is held in a fixture with a 76 mm (3″) diameter circular opening. The impact weight is 6.15 kg and the impactor has a 16 mm (⅝″) diameter hemispherical tip. Two heights were used to obtain different impact energy levels, 18 and 60 joule, respectively. The energy to maximum load and the peak force for the various materials are shown in the tables that follow. The values are normalized with respect to sample thickness. Comparative bar graphs for the different materials tested are shown in
To further analyze stop collar designs, a solid model of a prototype stop collar was constructed. Half of the assembly was used for finite element analysis as outlined in the APPENDIX attached to U.S. Provisional Application No. 62/398,736, filed Sep. 23, 2016, the entire contents of which is hereby incorporated herein by reference.
A stop collar and section of drill pipe were used to measure the slip load under simulated operating conditions. Two collar halves of a stop collar were clamped directly onto a section of drill pipe section with steel bolts and nuts as shown in
To test at 60° C., the entire clamp/pipe assembly was placed in a convection oven set to around 65° C. for at least 1 hour until equilibrium was achieved. A handheld pyrometer was used to verify temperature before and after the slip test. The mating surfaces of the clamp and pipe remained above 60° C. with the external surfaces at approximately 55° C. The assembly was loaded onto an MTS® load frame (capacity of 222 kN). Load was applied to the drill pipe at a rate of 0.01 in/min until the assembly could not resist an increasing load. A test matrix is given in Table 7-2.
Measurements were obtained of the bolt torque after the assembly was heated to operating temperature. The test assembly was removed from the oven. Torque was applied at approximately 75% of the set torque. If the bolt did not slip, the torque was increased 5 ft-lbf and re-torqued. When the bolt turned, the torque was recorded. The average of all four bolts is noted in Table 7-2 for Trials 11 and 14. The assembly was re-heated for 15 minutes before the final slip test.
Trials 11 and 14 in Table 7-2 show a drop in the apparent torque when the assembly temperature rises from room temperature to 60° C. The other elevated temperature trials were done after the assembly was re-torqued warm, immediately before the test. A typical load curve for a room temperature torque and test is shown in
Based on the testing and analysis presented above, the long glass fiber filled nylon 6,6 (PA66GL50) was found to have adequate properties to meet all the design requirements of the stop collar. FEA analysis performed on the optimized design resulted in a factor of safety of 2.61, as described in the APPENDIX, exceeding the 2.5 required. The long fiber thermoplastic (LFT) PA66 stop collar manufactured using the ECM process and tested under simulated performance condition exceeded the required slip load conditions. Even at a reduced torque of 100 ft-lbf at elevated temperature and not re-torqued, the slip load exceeded the required 40 kN.
Turning to testing for the stop collar hardware, a single hardware assembly to secure a stop collar includes 1× Stop Collar Bolt, 1× Top Stop Collar Nut (Flange Nut), QTY: 1× Bottom Stop Collar Nut (Locker Nut). For each stop collar (pair of collar halves) 4 hardware assemblies are required. Polymeric or polymer matrix composite materials, for example, are candidates for the stop collar hardware, and the stop collar hardware can be tested for compliance with requirements similar to that for the stop collars.
Additionally, the correlation between bolt torque and bolt tension can be experimentally determined and used to determine the appropriate thread friction coefficient for use in the flange clamping equations in API SPEC 6A, Annex D.
Prototype production bolts and nuts were exposed to pressurized synthetic (olefin) based mud (SBM) at 6000 psi at the maximum service temperature, followed by functionality evaluation as described above. The exposure was cyclic, consisting of 14 cycles to pressure and temperature, each cycle having a 24 hour duration as shown in
Tension testing was performed with customized fixtures that allow axial loading of the bolt to occur through the threads, head, and shaft as would be the case when in service; a similar arrangement shall be used to load the threads and face of each type of nut. Axial applied load was continuously monitored in both tests as in a normal tensile test according to ASMT D638.
Torque testing and the determination of the relationship between torque and tension was also tested via a custom fixture which utilizes load cells, strain gauges, or linear variable differential transducers (LVDTs) to determine the axial tension and/or strain in the bolt shaft. Torque testing was via a calibrated precision torque wrench of suitable size to accurately measure torques in the range of 108.5-203.4 N-m. An example of the complete testing program is given in Table 8.
To conduct the testing, composite stop collar hardware was manufactured using ECM. The material used was a pigmented (black), 50% weight long chopped glass fiber reinforced polyphenylene sulphide (PPS). The stop collar hardware can also be formed from other LFT materials formed by hot melt-impregnating continuous reinforcing fiber into a thermoplastic resin. The mixture can be cooled and formed (e.g., chopped) into discontinuous reinforcing fiber pellets. The amount of thermoplastic resin can be about 40 to 99 weight % of the LFT material, and the amount of continuous reinforcing fiber (once cut into the discontinuous reinforcing fiber) can be approximately 0.1 to 60 weight % of the LFT material. Example thermoplastic resins include polyamide, acrylonitrile butadiene styrene (ABS), polyphenylene sulfide, polypropylene, poly ether ether ketone, poly ether ketone, polyethylene, poly butylene terephthalate, poly ethylene terephthalate, polyoxymethylene, or combinations thereof. Example reinforcing fibers include carbon, glass, aramid, polypropylene, polyethylene, basalt, poly{diimidazo pyridinylene (dihydroxy) phenylene}, or combinations thereof.
The bolt shown in
The bolts from the mold tool, an example of which is shown in
100% of the stop collar hardware parts were subjected to multiple visual inspections after production. All parts that showed visual signs of voiding, incomplete part fill, cracks, chips, or thread damage were rejected and excluded from the total count.
10% of normal production part assemblies were subjected for conformance to critical dimensions. All tested parts were found to be in conformance with tolerance below ± 1/32 in (±0.8 mm). These same parts were also inspected for a complete hardware assembly fit-up. In addition, 100% of produced bolts were inspected for weight conformance. All accepted bolts are within the weight range of 227 g-230 g.
Ten (10) hardware assemblies were subjected to torque testing. The torque testing test assembly is shown in
All tested assemblies passed the torque test without failure. It is of importance to state that in order to avoid failure completely, the lock nut should be screwed into the bolt and not the opposite.
To determine the tension load on each bolt, which is equivalent to the clamping force, the following test was performed:
Table 9 shows the strain data recorded during this testing and convert theses data into tension force.
The mathematical relation between the applied torque on the bolts and the tension load on it is:
T=C
f
DF
were T is the applied torque, Cf is the coefficient of friction, D is the bolt nominal diameter, and F is the tension force on acting on the bolt.
Using this relation, it is possible to calculate the value for the coefficient of friction, Cf, based on the data obtained in Table 9.
Based on the obtained parameters, a relation between the clamping force and the applied torque can be concluded as shown in
In order to test the bolts behavior under slip conditions, four composite bolts were lubricated and torqued into the stop collar halves to 40 lb. ft. Then, a compressive load was applied into the stop collar.
Using the process 100, bolts similar the bolt 31 shown in
At step 104, the process 100 includes forming a mold assembly for the bolt. An example of such a mold assembly is shown as the mold tool 50 in
At step 106, the process 100 includes inserting the collet assembly formed at step 102 inside the mold assembly formed at step 104. The purpose of the mold assembly at this point in the process is to secure the collet assembly for the molding process steps.
At step 108, the process 100 includes inserting a thermoplastic charge into the mold assembly. In various embodiments, the thermoplastic charge can include a long fiber thermoplastic, such as long glass fiber reinforced nylon 66, or the other materials identified herein as being suitable for the intended use of the bolt.
At step 110, the process includes compressing the thermoplastic charge within the mold assembly. The compressing at step 110 can be performed using a ram to press the thermoplastic charge into the mold assembly and the collet assembly. The compressing can also be performed with the application of heat to one or more of the ram, the mold assembly, and the collet assembly to cause the thermoplastic charge to melt and flow into the collet assembly. When the thermoplastic charge flows into the collet assembly, it can cool to form a bolt similar to the bolt 31 shown in
At step 112, the process includes removing the collet assembly from the mold assembly, opening the collet assembly, and removing the bolt from the collet assembly. If necessary, the process can also include machining steps to remove excess thermoplastic material, remove rough edges, etc.
Turning to the process 200 shown in
At step 204, the process includes inserting a thermoplastic charge into the mold assembly. In various embodiments, the thermoplastic charge can include a long fiber thermoplastic, such as long glass fiber reinforced polyphenylene sulphide, or the other materials identified herein as being suitable for the intended use of the nuts and lock nuts.
At step 206, the process includes inserting one or more bolts having an external bolt thread of a predetermined thread lead for the nuts and the lock nuts into the mold assembly. The predetermined thread lead of the bolts can be the same as that formed into the collet at step 102 in
At step 208, the process includes compressing the thermoplastic charge within the mold assembly. The compressing at step 208 can be performed using a ram to press the thermoplastic charge into the mold assembly. The compressing can also be performed with the application of heat to one or both of the ram and the mold assembly to cause the thermoplastic charge to melt and flow into the form of the mold assembly. Once flowed into the form, the thermoplastic charge can cool as a molded part. Nuts and lock nuts similar to the the nut 32 and the lock or jamb nut 33 shown in
At step 210, the process includes removing the molded part from the mold assembly. As part of the removing, the bolts inserted at step 206 can be removed from the mold assembly, and the ram can be removed from the mold assembly.
At step 212, the process includes cutting the molded part removed from the mold assembly at step 210. The molded part can be cut using any suitable cutting tools and/or techniques, including saws, lathes, etc., or combinations thereof. As one example cutting sequence, step 212 can include cutting the molded part laterally through the threaded apertures. The threaded apertures are formed in the molded part around the bolts (which were inserted at step 206). Thus, the molded part can be cut laterally to form a nut molding and a lock nut molding. The nut molding can also be divided into a number of nuts, and the lock nut molding can be divided into a number of lock nuts. Thus, the process can also include dividing the nut molding between the threaded apertures to form a number of nuts, and dividing the lock nut molding between the threaded apertures to form a number of lock nuts. As an alternative cutting sequence, the molded part can be first cut between the threaded apertures to form a number of nut/lock nut molding pairs, and each nut/lock nut molding pair can then be cut laterally to separate the nut and the lock nut from each other.
At step 214, the process includes machining the nuts and/or the lock nuts, to the extent necessary. For example, the top nut upper surface can be machined to cut the circular flange. If necessary, the process can also include machining steps to remove excess thermoplastic material, remove rough edges, etc.
Although embodiments have been described herein in detail, the descriptions are by way of example. The features of the embodiments described herein are representative and, in alternative embodiments, certain features and elements may be added or omitted. Additionally, modifications to aspects of the embodiments described herein may be made by those skilled in the art without departing from the spirit and scope of the present invention defined in the following claims, the scope of which are to be accorded the broadest interpretation so as to encompass modifications and equivalent structures.
This application claims the benefit of and priority to U.S. Provisional Application No. 62/398,736, filed Sep. 23, 2016, the entire contents of which is hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62398736 | Sep 2016 | US |
