Premium Connections Research Articles

Economy and Reliability Selection of Production Casing Thread Connections For Low pressure and Low permeability Gas Field

Abstract At present it is widely accepted that if gas reservoir pressure is more than 28 MPa, premium connections in production casing should be selected. However, the price of premium connections is about 1.5 to 2 times than traditional API round thread connections. Therefore, economy and reliability selection of casing thread connections type is one of effective measures to reduce development costs in low –potential gas field. Economy and reliability selection of casing thread connections type in sulige gas field (in China,Well depth at 3550 m, Gas reservoir pressure 35 MPa) was study. Through ϕ 139.7×9.17/7.72 mm N80/J55 LC casing gas-tight test under complex loads and statistical casing full-scale test data in past were analyzed, a minimum safety factor for casing string gas-tight design was determined by casing strength margin and reliability analysis method. Gas-tight reliability effect of load variability on casing was validated by Monte Carlo method. Two sets of casing string were successfully designed and applied to over 800 wells in the gas field, and all wells were reported running well until now. Over 4 hundred million Yuan(RMB) investment was reduced in developing these wells. Following conclusions were achieved by practice: Casing string of production using API long round thread and CATTS101 compound instead of premium connection was economical and feasible for low-pressure and low-permeability gas field development. Main effect factors on gas-tight with standoff and pitch were discoverer in full-scale test, which was different from the current standards on taper in evaluation of gas-tight performance. By statistics of full-scale test data in past, the casing string of design and check is a reliability method with advantage of economic and universal applicability.

Fatigue behaviour of threaded couplings – experimental research

In this article the fatigue behaviour of threaded connections is studied, as used in oil country tubular goods (OCTG). Some manufacturers have designed their own couplings (so called „premium connections‟) and they claim having an improved fatigue life or better sealability. This study will compare different coupling designs with the standard API connection. The methods used to compare the different designs are based on two-dimensional finite element analyses. Experimental research is conducted to validate the results of the FEA. The experimental research consists of a 4-point bending fatigue test, which will result in a SN-curve for the threaded connection. Based on numerical and experimental results a performance factor is deduced for the particular connection design. This factor will be used to find the best design of threaded couplings. As eventual goal of this study, with the insights gained, a threadedconnection with optimized fatigue life and sealability will be designed.

Increasing Sucker Rods' Working Capacities

Technology Update Artificial lifting systems are being pushed to their operational limits, given the more demanding field operating conditions that require deeper wells and higher production flows. Over the years, the number of secondary-recovery and nonconventional oil projects has increased, and more is being asked of rod pumping (RP) and progressive-cavity pumping (PCP) systems. Both pumping systems have found the sucker-rod string to be one of their weakest links. Stress analysis and failure statistics for different parts of sucker rods have found the weakest point to be located in its coupled connection. Rod-pin and coupling failures have become common problems in fields, making it clear that the fatigue resistance of the connection is inferior to the fatigue resistance of the rod body. Several potential solutions designed to increase rods’ working capacities have been attempted, but none of them attacked the problem genesis: the connection. Recently, however, a premium-connection rod has been developed with a new thread design that has demonstrated very positive results in reducing connection fatigue (Fig. 1). Design Process Finite element analysis (FEA) is a numerical tool used to verify designs before field testing can be performed, and with FEA, the most significant design constraints of conventional rod connections were analyzed as a basis for developing the new premium connection design. The main points addressed in the development of the new design were the following: Loosening tendency of the connection because of a gap between threads. This gap allows movement between coupling and pin threads when rods undergo compression and/or shocks. Permanent deformations of the thread (as verified by FEA) during makeup and well operations. These deformations make crack propagation more likely. They also result in a difficult makeup operation when repeating displacements. Nonuniform stress distribution in thread profile generates regions of high stress concentration and, as a result, makes the pin and coupling more susceptible to the appearance of cracks (also verified with FEA). High reliance on the makeup operation because both overtorque (increase in the stress level) and undertorque (stress concentration during well operation) are harmful for the connection and produce failures in sucker-rod pins and couplings. In conventional design, thread effectiveness is highly dependent on the cleaning operation before the string is run into the well and an inefficient makeup can easily result and later produce failures.

Using Ultrasonic Techniques to Accurately Examine Seal-Surface-Contact Stress in Premium Connections

Summary One of the most important functions of a tubular connection is sealability. This is especially the case for premium connections that are commonly used in the demanding conditions of high-pressure/high-temperature (HP/HT) and thermal-well applications. Sealability, therefore, also is one of the most important criteria used during connection qualification in which the capability of the connection is verified for the characteristics of the application. During qualification tests, it has been found that breakdown in connection sealability can be traced to damage on the primary seal surface, which can eventually develop into a leak path. Ultrasonic-inspection technology can be used to provide a means to obtain nonintrusive measurements of contact stress between two mating metal surfaces separated by a thin lubricating film. While the technology has a wide scope of potential applications in this respect, the technology has been specifically developed to measure seal-surface-contact stresses inside oilfield tubular premium connections. This application of ultrasonic technology has been used numerous times during connection-qualification programs to assess the quality of the contact-stress band in premium connections. During these analyses, the technology has been able to detect seal-surface damage in premium connections. This paper will cover the basic concepts of premium connection design, along with some of the issues that can affect the sealability of premium connections. As well, this paper will include an overview of the use of ultrasonic technology as a technique to assess the contact stress along the metal-to-metal seal band of a premium connection and methods used to monitor changes in the contactstress profile induced by many installation and service loads.

Dry dope-free premium connections: a zero discharge technology validated through laboratory and field testing and usage

Dope-free alternatives to standard thread compounds used for casing and tubing connections became commercially available around 2003. The challenges from galling resistance needs and handling and storage requirements were addressed. The lessons learnt from the initial uses and experiences with the dope-free solution were incorporated into products that are reliable and have proven their suitability in environments that vary from the extremely humid and cold North and Barents Seas to the sandy and hot environment of the Middle East. The experiences to date not only confirm the validity of initial drivers —mainly related to the environmental care—for the development of these alternatives, but also open up the possibility of the complete elimination of thread compound from the casing and tubing installation and storage processes. The dope-free solution has demonstrated suitability for application in all tubing and casing dimensional size ranges including: all type of steels (such as common carbon steel—both API grades and proprietary), 13Cr, and corrosion resistance alloys (CRA), premium connections with metal-to-metal seal both threaded and coupled (T&C), as well as integral connections. Experience with large outside diameter (OD) semi-premium connections indicates that this can be another area of application for dope-free solutions. This paper describes the different experiences related to the field use of dry, dope-free solutions, the improvements and adjustments incorporated after initial experiences and operators feedback and the verification activities in laboratory and especially in experimental rigs under actual field conditions. The intention of this presentation is to present the advantages and the value obtained through the use of this technology.

A game theoretic analysis of service competition and pricing in heterogeneous wireless access networks

Next generation wireless systems will provide highspeed wireless connectivity and seamless mobility through the provisioning of heterogeneous wireless access. In such a heterogeneous wireless access environment, mobile users will be able to connect to multiple wireless networks (e.g., IEEE 802.16, cellular, and IEEE 802.11-based networks) operated by different service providers, simultaneously. We address the problem of competitive pricing in such a heterogeneous wireless access network. Each of the wireless access networks is assumed to support two types of connections, namely, premium and best-effort connections. For the premium connections, the price is fixed, while for the best effort connections it is dynamic and depends on the competitive or cooperative behavior of the service providers. A competitive pricing model for best-effort connections is developed based on a noncooperative game formulation. We first consider the case where the prices are offered to the users at the same time (i.e., a simultaneous-play game). Nash equilibrium is considered as the solution of this game. Afterwards, we consider the case where a service provider can offer its price before other providers. This is referred to as a leader-follower game for which Stackelberg equilibrium is considered as the solution. We also consider a cooperative pricing model which maximizes the total revenue of the service providers. A method for revenue sharing is presented for this cooperative pricing model. Numerical studies are carried out to evaluate the performances of the different pricing models.

Ultrasonic Techniques Accurately Examine Seal-Surface Contact Stress in Premium Connections

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 110675, "Using Ultrasonic Techniques To Accurately Examine Seal-Surface Contact Stress in Premium Connections," by Kirk Hamilton, SPE, Brian Wagg, SPE, and Tim Roth, CFER Technologies, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11–14 November. The paper has not been peer reviewed. One of the most important functions of a tubular connection is sealability. This is especially the case for premium connections commonly used in the demanding conditions of high-pressure/high-temperature (HP/HT) and thermal-well applications. Sealability also is one of the most important criteria used during connection qualification. Ultrasonic inspection technology provides a means to obtain nonintrusive measurements of contact stress between two mating metal surfaces separated by a thin lubricating film. Introduction Resources thought unrecoverable only a few years ago now are being targeted by operators, however, the extreme environments where many of these resources are located pose unprecedented operational and technical challenges. As a result, wellbore-integrity-management (WIM) systems have become important components in well design for many operators. Critical well designs include premium connections, which generally offer better sealability compared with standard American Petroleum Inst. (API) connections. However, the sealing systems in premium connections can be damaged either during makeup or as a result of exposure to the service environment. Current connection-makeup acceptance criteria are based primarily on makeup torques (shoulder and final), which may not be associated directly with connection seal integrity and overall sealability. Wellbore Integrity Wellbore integrity is an important component of current well-design practices. WIM and WIM programs focus on prevention of uncontrolled fluids releases across well barriers including tubing, casing, packer elements, and cement sheaths over the full construction, service, and operational life of the well for worker safety, environmental protection, and well-production efficiency. Connections in casing and tubing strings play a critical role in preventing fluid loss and maintaining wellbore integrity. Two areas of concern for connections are leakage to the environment and sustained casing pressure. In both cases, an accumulation of fluid in the ground around the well, in the annular space between casing strings, or between casing and tubing strings can lead to contamination, corrosion, and even in some cases, loss of the well and catastrophic blowout situations. Operators have recognized these issues, and considerable efforts have been made to mitigate them through proper well design and construction techniques, equipment selection and installation techniques, and safe operating procedures. Proper tubing- and casing-connection selection is a very important step that operators need to take to ensure that risk of leakage past connections is minimized. It is estimated that approximately 90% of all tubing and casing leakage failures are attributed to connections. This percentage is high, but it takes into account the large number of casing and tubing connections relative to other potential downhole leak paths (e.g., packer elements and pipe-body failures).

Evaluating Pressure Integrity of Polymer Ring Seals for Threaded Connections in HP/HT Wells and Expandable Casing

Summary This paper presents new technology for evaluating high-pressure gas-seal integrity of polymer ring seals used as secondary or backup pressure seals in casing and tubing threaded connections. This new technology may also enable the further consideration of API connections with ring seals, as an alternative to premium connections, for appropriate applications. A nonlinear elasto-viscoplastic constitutive model for the behavior of polymers and elastomers has been developed and extended to the specific application of analysis of casing and tubing connections with fiberglass-filled polytetrafluoroethylene (PTFE) ring seals. Procedures for modeling makeup of a connection including a fiberglass-filled PTFE ring seal have been developed using a finite-element model (FEM) of 10¾-in. OD, 45.5 lb/ft, P-110 API buttress thread casing-seal ring groove (BTC-SRG). The results of finite-element analysis (FEA) of makeup, followed by the application of thermal, axial, and internal pressure loads are presented in this paper. In addition, based on the interest in the development of gas-tight threaded connections for expandable casing, the FEM was subjected to a radial expansion of a 20% increase in the outside diameter. In this paper, the theory of the constitutive model is summarized and calibration of the model with experimental test and published data are presented. The focus of the FEA results is on the contact pressures between the ring seal, coupling groove, and pin threads. Historical Perspective FEA of threaded connections has been used for overcoming challenging well-design problems for many years (Crose et al. 1976). FEA has become an important part of the validation and service evaluation process of API and proprietary casing and tubing threaded connection designs, along with the physical testing procedures documented in API RP 5C5 (1996) and ISO 13679: 2002 (2002). Major advances have been achieved in design of premium connections through analysis of metal-to-metal seal contact stresses computed from FEM (Hilbert and Kalil 1992). Analysis and verification of the performance of threaded connections that include polymeric or elastomeric ring seals has been limited to full-scale physical testing (Payne 1988). Until now, only costly full-scale gas pressure tests have been used to evaluate ring seal integrity. Ring-seal design has been a trial and error process, with new ring-seal or pin and coupling dimensions prescribed only after failure of the seal in a proof test. In some cases, ring design or the effects of ring dimensions have been based on analytical calculations, relying on the bulk modulus of the material. When more advanced design tools, such as FEA, have been used, the pressure generated by entrapment of the ring seal has been estimated and then these pressures have been applied to the groove and pin thread surfaces to simulate the effect of the actual ring seal. The developments in the paper were motivated by a need to reduce the cost of connection qualification by reducing the number of tests and to improve the process of ring-seal design. Properties of PTFE PTFE is a thermoplastic fluorocarbon derived from the monomer tetrafluoroethylene (TFE). PTFE is a semi-crystalline polymer composed of crystalline and amorphous regions. Its molecular structure, shown in Fig. 1, consists of long chains of carbon atoms symmetrically surrounded by fluorine atoms. This structure imbues PTFE with unique mechanical and chemical properties. The straight "backbone" of carbon atoms provides PTFE with a high degree of chemical inertness, stability, and one of the lowest coefficients of friction of any commonly used material. PTFE is more commonly known by the trade name Teflon. In a moment of pure serendipity, in 1938 Roy Plunckett of DuPont discovered TFE when he was conducting experiments to develop nonflammable, nontoxic, colorless, and odorless refrigerants (Ebnesajjad 2000).

Technology Update: Top-Drive Casing-Running Tool Solves Tough ERD Problems

Over the past 15 to 20 years, top-drive technology has brought substantial improvements in efficiency and safety to drilling operations. However, casing-running methods have evolved more slowly and have not taken advantage of all the potential offered by top-drive drilling. Weatherford International has designed its new Overdrive system for running casing and drilling with casing to make full use of the weight and power of top drives (Fig. 1). The system won a Spotlight on New Technology Award at the 2007 Offshore Technology Conference. This top-drive casing-running system was used recently by Shell to land casing on bottom at more than 18,200 ft depth on a troublesome North Sea extended-reach-drilling (ERD) well with hole restrictions caused by inability to clean the hole completely. Torque-Drive Tool The centerpiece of the technology is the torque-drive tool that combines several conventional casing-running tools into one—power tongs, main hoisting elevators, bails and single-joint elevators, a fill-up/circulation tool, and a weight compensator. All system operations are remote so that no personnel are required in the derrick or on the rig floor, resulting in a significantly lower safety risk (Fig. 2). The removal of equipment and scaffolding from the rig floor also creates a safer work environment. The torque-drive tool is connected below the rig's top drive and can be run with any topdrive system. To run casing, the tool's integral bails and single-joint elevators are used to retrieve each joint or stand of casing, lift it into the derrick, and lower it into position for makeup. The torque-drive tool is then hydraulically clamped onto the casing, and the connection is made up using the rotational power of the top drive to transfer the torque through the torque-drive tool and casing connections. A key component used in conjunction with the torque-drive tool is an integral electronic-load cell called the torque sub, mounted at the top of the torque-drive tool and used to measure the makeup torque of the casing connections. The sub is independent of the top drive and measures true torque, as opposed to conventional techniques that calibrate torque from the voltage that supplies rotational power to the top drive. This new level of accuracy is especially important when making up premium connections, which require torque-turn monitoring and a very low margin of torque-measurement error. Once the connection is made up, the driller can instantly perform a number of operations as needed, including fill-up of the casing string while lowering, and simultaneous circulation, rotation, and reciprocation of the entire casing string. This combination enables the driller to overcome virtually any unexpected hole problems, such as ledges, lost-circulation zones, shallow-water flows, and swelling formations. This greatly enhances the ability to run the casing string to bottom in a predrilled well.

Development of Dope-Free Premium Connections For Casing and Tubing

Summary Removing API dope from the makeup process of threaded premium connections during casing and tubing operations not only reduces the risk of contamination of the local environment but also provides a cleaner and safer working area. Conversely, the removal of the antigalling property inherent in API dope greatly increases the risk of galling damage to connections during power-tight makeup. This paper describes various tests carried out to evaluate manufacturers' claims of having successfully improved the galling resistance of premium connections by electro-depositing a white bronze (45%Cu-55%Sn) alloy onto couplings manufactured from high-chrome materials. Galling resistance was measured by subjecting several test coupons plated with copper and various alloy compositions to a series of tests designed to generate high stresses to threaded surfaces. The paper also shows through experimentation how the correct amount of preload was achieved in a premium connection's gas-tight seal by applying a thin lubricating layer (also referred to as a protective film) to both pin and box threads.

Experimental and numerical study of expandable threaded connections and proposal of a new design

This paper investigates the behaviour of a flush oilfield premium connection during the cold expansion process. The objective has been to validate, through experimental tests of make up and expansion on prototypes designed traditionally, the numerical simulation generated to reproduce and interpret the mechanism that occurs during the whole process. A finite element model, able to understand the expansion mechanics, to explain the damages caused on the expanded prototypes and to define design changes in order to improve the mechanical strength and hydraulic seal, has been set up. Taking advantage of the calculation procedure, a new expandable connection has been developed, at first on the basis of numerical simulation, then assessed by means of experimental tests. The new connection has shown definitely better behaviour about the hydraulic seal, withstanding the maximum internal pressure of 5050 psi.

Next-Generation Expandable-Completion Systems

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 97281, "Next-Generation Expandable-Completion Systems," by Gareth Innes, SPE, Quentin Morgan, SPE, Ally Macarthur, SPE, and Annabel Green, SPE, Weatherford, prepared for the 2005 SPE/IADC Middle East Drilling Technology Conference and Exhibition, Dubai, UAE, 12–14 September. In many cases, openhole completions could provide maximum well productivity. However, use of the method has been impeded by the inability to achieve effective zonal isolation. An expandable completion that combines slotted- and solid-expandable technology and uses conventional unexpanded premium connections can deliver freely configurable completion architecture. Introduction Expandable sand screens provide direct contact of the screen with the formation as a means of reducing completion skin and improving sand-retention characteristics. The base technology is being integrated with new and conventional downhole technologies to enable multizone completions. A common conventional approach used to complete and commingle multizone unconsolidated reservoirs has been to, first, set and cement casing in the wellbore to isolate zones. The zones of interest then would be perforated before installation of a screen and placing gravel to control solids migration. This cased-hole sand-control technique has worked reasonably well but has a history of high completion skins. Also, the resulting smaller inside diameter makes the subsequent design and installation of selective-production upper-completion strings difficult, limiting the overall achievable functionality. In many cases, emulating an openhole high-deviation or horizontal completion strategy can increase well productivity. To enable these productivity gains and facilitate selective production handling, zonal-isolation technologies were combined with compliantly expanded screens to create a sandface completion with cased-hole functionality. Zonal-isolation technologies that satisfy functionality and expandable performance criteria include swelling elastomers and solid expandables. Expandable-Completion Development An expandable screen comprises three sandwiched layers: the base pipe, filter media, and outer protective shroud. The base pipe is slotted, as is the outer shroud. These slots open during expansion to accommodate the change in diameter, while overlapped layers of filter media slide across each other to maintain sand-retention integrity. The use of slots allows expansion ratios up to 80% greater than the original diameter. The entire length of the original design was expanded, including the connectors. The original expandable screen was designed for use in single-zone openhole applications. Large exposed filter area and variable borehole contact (known as compliant expansion) provide gravel-pack functionality. The design premise was that a compliantly expanded filter that could eliminate as much of the annular gap as practicable would promote rapid formation stabilization and minimize the movement of sand particles around the screen during the transient sand-production period. The large, directly exposed filter surface was designed to minimize pressure drops in the screen and sandpack composite caused by mud particles and formation fines.

Premium-Connection Design

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 17221, "Premium & Semi-Premium Drilling-With-Casing Applications," by N.J. Santi and G.E. Carcagno, SPE, Tenaris, and R. Toscano, Centro Investigation Industrial, prepared for the 2005 Offshore Technology Conference, Houston, 2-5 May. High resistance to fatigue loading together with high torque and compression capacities is necessary for connections used for drilling with casing. On the other hand, cost-effective solutions must be found to provide connections for shallow wells for which sophisticated premium connections are not economical. The full-length paper describes the development and evaluation of premium and semipremium connections for tubing/casing. Introduction Drilling with casing originally was used for nondemanding vertical wells where, in almost all cases, American Petroleum Inst. (API) connections (sometimes with modifications to improve torque capacity) were used. As drilling with casing was used in more demanding and critical applications such as horizontal, deviated, and offshore wells where most wells are drilled directionally, new connection types were needed. Requirements for these connections include reliability, sealability, high overtorque capacity, and ultrahigh fatigue resistance because the stresses produced by bending and vibrations while rotating can reduce connection life. Considerations Use of oil-country-tubular-goods (OCTG) connections for drilling began as an attempt to reduce costs. Standard OCTG casing connections are designed to withstand static loads of tension and compression, internal and external pressure, and bending. Torque requirements for these connections are low. However, for drilling with casing, some critical issues that become important for drilling directional and deviated wells include the following.Wear protection.High torque and compression resistance.High fatigue resistance.Cost effectiveness. Wear protection is provided by means of centralizers or other hardened surfaces located close to the pipe end to avoid damage to the connection. Higher torque and compression requirements are met by designs that include robust torque shoulders, thread interferences, and reduced gaps between mating threads. Fatigue resistance is a very important issue for drilling with casing and perhaps the most difficult challenge to address. Fatigue Response of OCTG Connections. Fatigue is a complex process that affects mechanical components subjected to cyclic loads. Fatigue failure is not a sudden crack, instead it involves different failure phases that occur until component failure becomes evident. This failure occurs at stress levels much less than the elastic limit of the material. When subjected to cyclic loading, ordinary OCTG connections are weaker than drillpipe connectors that are designed to work with alternating stresses. The fatigue-failure location of threaded connections is in the area with the highest stress-concentration factor (SCF). Location of the SCF can be estimated with finite-element analysis (FEA), which also can yield a numerical value of the SCF. For standard premium OCTG connections with loads expected in drilling with casing applications, the SCF normally is greater than 2. However, from a fatigue perspective, it is desirable that the SCF be as low as possible. Threaded-connection response to fatigue loads can be plotted as a stress vs. number-of-cycles-to-failure curve.

Production Casing Performance In a Thermal Field

Abstract High temperature steaming of wells can cause plastic yielding of the production casing. However, when properly designed and installed these casing strings will last the full life of a thermal project. Inferior designs or installations can cause significant well problems ranging from wellhead growth and settling to buckled or parted casing. Since 1979, Shell Canada limited has been operating a thermal project in the Peace River/Cadotte Lake area. Steam injection temperatures have been as high as 335 ° C, but only two of the 286 steamed wells have incurred thermal induced casing failures. Three additional casing failures were caused by corrosion. Some 10 to 15 other wells have experienced wellhead settling (casing contraction). Several wellheads have gone down 25 to 50 cm, requiring wellhead and piping modifications but casing integrity has been maintained. This paper discusses the casing and cement designs used historically, field observations and explanations for the casing "shrinking" phenomena and the field testing of K-55 grade casing. Shell Canada Limited's current design utilizes K-55 premium connection casing with class G thermal 1,880 kg/m3 and 1,400 kg/m3 weight cements. Introduction Shell Canada Limited has operated a steam injection project at Peace River since 1979. The production zone is an unconsolidated sandstone of the Lower Cretaceous Gething formation. This bitumen reservoir is 550 m from surface with an average pay thickness of 25 m. The bitumen gravity is 8 - 10 ° API with a viscosity at reservoir conditions of 200 Pa.s. The bitumen saturation decreases with depth in the zone. At bitumen saturations below 65%, the water phase is mobile and allows steam injection below fracture pressures. Most, but not all the wells drilled have a mobile bottom water layer. The primary recovery process has been a pattern steam drive. Dedicated injection wells were utilized, however all wells were initially steamed and produced to establish bitumen mobility and communication between wells. In 1993, four horizontal wells were drilled to evaluate the Enhanced Steam Assisted Gravity Drainage Process (ESAGD). Since then, 25 horizontal wells have been drilled for ESAGD or cyclic steaming bitumen recovery. All of these wells have used K-55 casing with premium connections. Casing designs have varied from NM-80 LT&C, L-80 VAM, L-80 OBTC (oversize buttress threaded and coupled), and most recently K-55 NS-CC premium connection. Between 1979 and 1997, there were five casing failures at the Peace River complex. One was a buckled casing string, another was a parted connection and the remaining three were due to corrosion. Ten to 15 wells have had casing "contraction," causing the wellhead to settle 10 to 50 cm. The casing/wellhead movement is not a failure but can impose additional operating expenses and difficulty. In general, the casing performance has been satisfactory, as the above failures can be explained and continued reliability from the existing casing strings is anticipated. Casing Design An understanding of the stresses imposed on the casing during thermal operations is needed to properly design the casing and evaluate its performance.

Criterion for Gas Seal Tightness of Premium Connection of Oil Country Tubular Goods

Criterion for Gas Seal Tightness of Premium Connection of Oil Country Tubular Goods

Performance of Tubular Connections Under the Loading Conditions of Horizontal Wells

Summary This study deals with the negative effects of bending stress and casing wear on tubular connections. The joint strength of three connection types, API long round thread (LTC), API buttress thread (BTC), and typical premium joint (PJ), was measured with a full-size combined loading tester. Measurements were also made for the connections simulating wear induced by drilling operations. The sealing ability of the connections was evaluated under bending and wearing conditions. Numerical simulations were undertaken to investigate the failure mechanism of the connections. The results indicate that LTC joint strength is lowered by bending, though that of BTC and PJ is not degraded. Joint strength is reduced in direct proportion to the wear area ratio of the pipe body. In sealing ability, only the premium connection maintained leak resistance under combined loading with bending. Axial loading is more detrimental to sealing integrity than the bending moment. In conclusion, the connection performance data can be useful in designing safer horizontal well casings.

Optimum Application of Environmentally Safe Compound Greases for Casing and Tubing

Summary It is now expected to prevent the contamination of the environment from the use of pipe dope or compound grease in oilfield drilling operations. Recently, some environmentally safe compound greases have been commercially developed and are available, but it is not generally known what effect they will have on the connection performance. This paper will discuss a detailed experimental study of the performance of these greases to investigate the galling tendency and sealing capability of American Petroleum Inst. (API) buttressthread connections (BTC) and metal/metal seal premium connections. It is already known that greases without both lead and zinc can be used for a single makeup of these connections, but some improvements were expected in the antigalling performance for multiple makeups. Greases without lead or without both lead and zinc are not satisfactory for preventing hydrostatic leakage in buttress connections because of the lack of buildup of powders for thread clearance, and the addition of graphite in substituting for these metal powders tends to produce galling. Thus, the ratio of solid/liquid elements and the roughness of the graphite grain will be important in the improvement of existing greases.

苛酷な坑井条件下における油井管ねじ継手の使用性能とその最適メークアップ方法

With hostile drilling environment, multi-performance has been required for tubular connections in addition to conventional performance, so premium connection with metal-to-metal seal has become popular. This paper deals with the performance properties of tubular connections used in typical oil and gas wells, and describes the appropriate make-up operation and the torque resistance of the connections.The make-up torque was measured in the laboratory under the simulated field operations. The connection performance was evaluated using the full-size combined loading tester under the simulated conditions of hostile wells such as horizontal wells, sour service wells, and steam injection wells.As for the results of the test, the make-up torque increases when the grease quantity is small and the temperature is low. In wells, the torque resistance of the connection improves under axial loading, pressurizing, and bending. The joint strength of Round connection is lowered by bending, though that of Buttress and premium connection is not degraded. However, the joint strength decreases in direct proportion to the wear area ratio of the pipe body. Bending moment is not more detrimental to sealing integrity than the axial loading. In sour service wells, there are some possibilities of SSC occurrence at the coupling, so the casing design is required to control the hoop stress on the coupling less than the threshold stress. In steam injection wells, the casing pipe is deformed by the excessive axial load due to the thermal expansion and only the premium connection can maintain the gas tightness.In conclusion, the make-up torque can be stabilized by solving the effects of operation factors, and the connection performance described in this paper may be effective for planning a more economical and reliable casing design in oil wells. Dope of the sufficient compound grease, avoidance of the low temperature make-up, and usage of the weight compensator are recommended to avert some make-up troubles.

Unraveling the Mysteries of Proprietary Connections

The purpose of this article is to provide some insight into the potential users of proprietary connections and to facilitate a rational selection process and procurement procedure. First, it must be noted that the standard and commonly used API casing connections [short, round thread casing and coupling (STC); long, round thread casing and coupling (LTC); buttress thread casing and coupling (BTC)] and API tubing connection EUE-8R (external upset ends, eight round thread tubing and coupling) can provide reliable service for the vast majority of well drilled and completed. Proprietary connections can and have been misapplied at considerable expense; for example, 9 5/8 drilling (intermediate/protective) casing. API BTC works more than adequately in drilling-mud environments. There is no need to use a proprietary connection for such service. In fact, pin nose metal-to-metal seal proprietary connections in this type of service can be less reliable than the API BTC connection since the metal-to-metal seal is much more damage prone than the thread seal of API BTC. Also, very reliable leak resistance, even to gas, is obtained with tin plated BTC couplings.

Calculation Method of Make-up Torque of Premium Connections for Oil or Gas Wells.

The making-up process of the premium connections for oil or gas wells is generally controlled by the recommended make-up torque. In order to determine the recommended torque, an analysis method for the make-up torque with short computing time and good accuracy is required. In this paper, so as to obtain the contact load at the metal-sealed portion of the connection, the connection model of combined cylindrical shells was analyzed, considering the shrink-fit values at the threaded portion and the metal-sealed one of the connection. Then, the calculation method of the make-up torque just before the contact of the torque shoulder was obtained. As the torques calculated by the calculation method agreed well with those by FEM and actual tests, this method can be applied to determine the make-up torque of premium connections.