Maaz Akhtar

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

Part of the book: Swelling Elastomers in Petroleum Drilling and Development

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

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.

Part of the book: Swelling Elastomers in Petroleum Drilling and Development

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

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.

Part of the book: Swelling Elastomers in Petroleum Drilling and Development

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

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).

Part of the book: Swelling Elastomers in Petroleum Drilling and Development

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

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.

Part of the book: Swelling Elastomers in Petroleum Drilling and Development

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

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.

Part of the book: Swelling Elastomers in Petroleum Drilling and Development

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

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.

Part of the book: Swelling Elastomers in Petroleum Drilling and Development

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

Little data is available about the material properties and swelling response of the elsatomers used in swell packers. This information is necessary for modeling and simulation of these elastomers in different petroleum applications. An experimental setup was therefore designed and implemented at Sultan Qaboos University (SQU) to investigate the material behavior of these elastomers under tension and compression, so that these properties could be used for different simulations. Before developing a finite element model (FEM) of elastomer seal performance, it was felt that a thorough evaluation needs to be carried out to decide which of the currently available material models is most suitable for swelling elastomers. This comparison translates into the selection of the correct strain energy function for accurate determination of material coefficients. Different hyperelastic material models are compared here. Experimental investigations under tensile and compressive loads, along with their numerical analysis are presented in detail in this chapter.

Part of the book: Swelling Elastomers in Petroleum Drilling and Development

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

Swelling elastomers are a new breed of advanced polymers, and found increasing use in drilling of difficult oil and gas wells. It is important to know how an elastomer will behave under a given set of well conditions, especially after the initial quick-swell period. Good design depends on appropriate material selection. Results are presented in this chapter from experimental and numerical studies conducted to analyze how compressive and bulk behavior of actual oilfield elastomers changes due to swelling. Six key attributes of swelling elastomers needed for design improvement and performance analysis of elastomer seals are discussed: four mechanical properties (elastic modulus E, bulk modulus K, shear modulus G, and Poisson’s ratio ν), and two polymer structure characteristics (cross-link chain density NC, and average molecular weight MC). These parameters were experimentally determined before and after various stages of swelling for two different swelling elastomers being currently used by the regional petroleum industry, in low and high salinity brines. To strengthen the experimental results, and to be able to forecast for other elastomer materials and well conditions, tests were also simulated using the commercial FEM package ABAQUS, using the best available hyperelastic material models.

Part of the book: Swelling Elastomers in Petroleum Drilling and Development

By Sayyad Zahid Qamar, Maaz Akhtar and Tasneem Pervez

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.

Part of the book: Swelling Elastomers in Petroleum Drilling and Development