Employing a failure criterion with interaction terms to simulate the progressive failure of carbon-epoxy laminates

A failure criterion with the existence of coupling terms is employed to investigate the progressive failure in anisotropic laminated carbon-epoxy plates. The criterion is employed because it is developed recently. Moreover, the criterion allows interaction between fiber and matrix properties. This paper is aimed to investigate the contribution of the coupling terms and thus, to simulate the progressive failure of the carbon-epoxy plates. A mathematical model and computational model are presented for the analysis. The deformation of the plates is predicted based on higher order shear deformation theory. Variation of material properties through thickness is used and accommodated by a discrete layer approach. A program based on finite element method is developed to determine the lamina stresses. Stresses calculated are used in the present failure model to determine the first ply failure and last ply failure, by progressively reducing the stiffness of the laminas. Finally, the first ply failure and last ply failure results are used to determine the lower and upper bounds within which the true load carrying capacity lies. The numerical results obtained show some improvement compared to other failure criteria

Indirect Extrusion: A Multifaceted Approach of Sub-surface Tubular Expansion

Extrusion and indirect extrusion is a very old manufacturing process used in multitudes of applications mainly focused on transportation, household and power industries. Indirect extrusion has found an interesting application in petroleum industry, which resulted in resolving many unsolvable issues over the last few decades. The current and expected future global demand for hydrocarbons became a driving force for researchers to find new comprehensive and cheaper solutions for hydrocarbon production. The challenges faced in oil and gas fields, while drilling, constructing and operating new and old vertical/horizontal wells, are many. The use of indirect extrusion for in-situ expansion of sub-surface tubulars used in wells revolutionized the drilling and completion as opposed to one and half decade back. The emergence of solid expandable tubular technology has changed the basics of how we design and construct wells. The original development of the technology was to overcome the challenges faced by the petroleum industry to reach ultra-deep reservoirs, off-shore drilling, drilling in high-pressure/difficult zones and repair/maintenance of old/ageing wells. However, it gained significant interest of researchers and operators in providing solutions to wide-range problems. The development of a computational framework using finite element method (FEM) enabled to determine the force required for expansion and resulting dimensional changes in final product, which is of direct assistance to the field engineers. The effect of friction and stress variations along contact surface is also determined

Swelling Elastomer Applications in Petroleum Drilling and Development

Oil and gas drilling and development is witnessing new and inventive techniques targeted at increased production from difficult and aging wells. As depth of an oil or gas well increases, higher temperatures and harsher environments are encountered. Suitable elastomers can provide good sealing as they possess good resistance to heat and chemical attack, and as they are widely availability at low cost. In comparison with metals, elastomers are lighter in weight and lesser in stiffness and hardness, swell more with increasing temperature, and are usually better in corrosion resistance. Other reasons for their preference include excellent damping and energy absorption, more flexibility and longer life; good sealing even with moisture, heat, and pressure; negligible toxicity; good moldability; and flexible stiffness. As mentioned in chapter-1, swelling elastomers or gels have found extensive use in different applications including drug delivery, microfluidics, biomedical devices, scaffolds for tissue engineering, biosensors, etc. As the main focus of this book is the oil and gas industry, implementation of swelling elastomer technology and deployment in different petroleum applications are discussed below

Experimental Setup for Swellable Elastomers in Cased and Open Holes

A full scale experimental setup was designed and commissioned for testing of swelling elastomer seals against a casing (cased hole) and formation (open hole). Actual replicate of wellbore was designed with varying inside diameters and roughness to reproduce the effect of actual formation. The Dynaset packer mounted on a 7-inch tubular was allowed to swell against a 9–5/8-inch casing, while the fast swell packer mounted on a 9–5/8-inch tubular was allowed to swell against the 12–1/4-inch replicated well bore. This one-of-its-kind test setup can demonstrate the way the elastomers swell out and fill the asperities against smooth outer casing (cased hole) or against rough wellbore surface (open hole). Dismantling of the test setup midway through the testing scheme revealed a severely dimpled surface of the swelled elastomer

Swelling Elastomers and Tubular Expansion—Numerical Investigation

Swell packers were initially used for repair of old and damaged wells, but they are now increasingly used for higher productivity and profitability through developments like slim well design and reduced-cement or cementless completions. Solid expandable tubular (SET) technology has gained popularity in the petroleum development industry as it can reduce well costs and improve well performance. A conical mandrel is pushed or pulled through a petroleum tubular, either hydraulically or mechanically, to expand it (in-situ) to the desired diameter. In SET applications such as water shutoff and zonal isolation, swelling elastomers are an obvious choice as a sealing material. For proper downhole deployment of swell packers in SET applications, it is important to have a good idea about their behavior under a given set of field conditions. Design and manufacturing of SET applications using swelling elastomers as sealing elements also needs some sort of seal performance analysis

New Analytical Model for Swellable Materials

As discussed in Chapter 6, numerical prediction of swelling can be attempted using existing hyperelastic material models available in commercial finite element (FE) packages. However, none of these models can accurately represent the behavior of swelling elastomers. The major shortcoming of currently available swelling models is that they consider Gaussian statistics for mechanical contribution of configuration entropy, which is based on chains having limited extensibility. Some later models (not yet incorporated into commercial FE packages) can give a reasonable account of certain behavior patterns in swelling elastomers, but do not explain other aspects well. One of the new approaches is to treat swelling elastomers as gels. As described earlier, gels are mostly liquid, yet they behave like solids due to a three-dimensional cross-linked network within the liquid. Many authors consider gel as poro-elastic or porous and use Darcy’s law to model the amount of fluid influx. However, a swollen elastomer mostly consists of the solvent. When an external load is applied, maximum resistance comes from the solvent molecules as in diffusion. Also, most of the new models are quite complex in concept and formulation, and there is a serious need for a scientifically simpler model

Analytical Model for Seal Contact Pressure

Swellable elastomers are used for zonal isolation and as an alternate to cementing is a new approach, resulting in significant reduction in time, cost, and weight. Very large strains, flexibility, resilience, and durability are their special features. Performance analysis is important design improvement and appropriate selection of swell packers. Experimental evaluation of swelling-elastomer seal performance can be very costly, and is not even possible in many cases. Numerical simulations (Chapters 8 and 9) can be more convenient, but computational effort and cost can be high. Development of closed-form (analytical) solutions is presented in this chapter to estimate the variation of contact pressure along the length of the elastomer seal. Major relevant parameters are properties of the material elastomer, seal configuration and size, magnitude of seal compression, and differential pressure across the seal. Numerical (finite element) modeling and simulation is also performed. There was good conformity between analytical and simulation results, validating the soundness of the analytical solution, and providing assurance that it can reliably predict the sealing response of the elastomer. A comprehensive parametric study is then conducted to assess seal performance while varying different key factors. Properties of the elastomer material (as it swells with exposure time) are required to run the analytical and the FE models. A large set of experiments were therefore designed and conducted to evaluate mechanical properties (E, G, K, and v) of the elastomer with gradual swelling (Chapters 3 and 7)

Numerical Investigation of Elastomer Seal Performance

Analytical models for swelling of rubberlike materials are difficult to formulate, and restricted in actual application due to their need for simplifying assumptions. Tests conducted on laboratory size samples of swelling elastomers cannot reproduce actual oil well conditions, and cannot cover all possible variations of testing parameters. However, these laboratory tests do provide useful information about material response of swellable elastomers in various conditions, serving as a basis for analytical and numerical modeling. Properly developed and robust numerical models can be used to predict near-actual performance of elastomeric seals. The current chapter describes the use of numerical (finite element) simulation to investigate swelling elastomer seal behavior in downhole petroleum applications. Variations in sealing (contact) pressure are studied for seal length, seal thickness, compression ratio, water salinity, swelling time, and type of well completion (open-hole or cased-hole). Month-long swelling experiments on samples of two actual elastomers (Chapters 3 and 7) provide input to the numerical model in terms of real material and deformation data. On the basis of these results, petroleum engineers can make informed decisions about the selection of elastomer material and seal geometry appropriate for the well type and conditions encountered. Application developers and researchers can also find this investigation useful in performance analysis and design of swelling elastomer seals

Swelling Behavior of Elastomers under Water, Oil, and Acid

It is very important to determine the behavior of elastomer materials under realistic well conditions in order to select appropriate swelling elastomers for a particular set of field conditions, for successful modeling and simulation of various downhole processes, and for design improvement of swell packers and other sealing applications. In collaboration with national and regional petroleum development and rubber engineering companies, a series of experimental studies were therefore conducted at Sultan Qaboos University for characterization of swelling related material behavior of different elastomers. Results from some of these investigations (studies A, B, and C) are reported and discussed in this chapter

Long-Term Integrity Testing of Water-Swelling and Oil-Swelling Packers

As easy oil in many fields is dwindling, there is increasing stress worldwide on innovative enhanced oil recovery (EOR) techniques. One forward-looking EOR approach is the workover method. It tries to convert currently weak horizontal wells to maximum reservoir contact (MRC) wells, or abandoned vertical wells to horizontal ones or power water injectors. Where conventional techniques fail, swelling elastomer seals and packers provide effective water shutoff and zonal isolation in even very complex environments, resulting in significant savings in rig time and development cost. One major issue of interest is the service life of elastomer seals and packers. It can be attempted to predict the probable working life based on the theory of accelerated testing. However, this forecast will not be very dependable for swelling elastomers as the material performance is substantially different from other rubber-type polymers. A full-scale test rig (one of its kind in the world) was therefore designed and fabricated at Sultan Qaboos University (SQU), in collaboration with a regional petroleum development company, for long-term service life assessment of actual full-size water-swelling and oil-swelling packers