Tasneem Pervez

Simulation of Solid Tubular Expansion in Well Drilling Using Finite Element Method

Abstract Solid expandable tubular is an emerging and promising technology in petroleum industry. It consists of increasing the diameter of a tubular by hydraulically pushing or mechanically pulling a conical mandrel through it. In this paper, a dy namic explicit finite element analysis (FEA) has been used to study the solid tubular expansion using ABAQUS, a commercial FEA software package. The required drawing force for tubular expansion was estimated for different mandrel shapes, friction coefficients, and expansion ratios. The drawing force increases with the increase in friction coefficient and expansion ratio. It was also found that the material velocities increase on the front of the mandrel but decrease to zero in the post expansion section. Moreover, the plastic deformation shows a reduction of thickness with friction coefficient and expansion ratio. Simulation results also revealed that contact occurs at the two ends of the conical mandrel tubular interface and that the contact stress increases with friction coefficient reaches to maximum value at an expansion ratio of 20%.

Experimental and Numerical Simulation of In-Situ Tube Expansion for Deep Gas Wells

Growing energy demand is forcing the petroleum industry to reevaluate resources found in unconventional gas formations and utilizing low-production zones. Extracting oil and gas from these difficult and deep reservoirs require new knowledge which should lead to develop solutions in lifting those reserves to the surface. Centuries-old manufacturing process of tube forming has found an interesting and extended application in petroleum well drilling and delivery. The in-situ expansion of tube is aimed at expanding its diameter by pushing or pulling a mandrel through it. The expansion process is strongly nonlinear due to material and contact nonlinearities. The goal is to achieve desired tube expansion smoothly as well as maintain minimum post expansion material and mechanical properties. The objective of this research is to conduct experiments to expand the tube under simulated downhole conditions. Finite element analysis is also used to simulate the expansion process, and the results are compared with experimental data. The force required for expanding the tube, thickness reduction in tube wall thickness, and length shortening under fixed-free end condition are estimated. Good agreements were found between numerical and experimental results. Thickness reduction greater than 12% lowers collapse strength by 50% making it unsuitable for deep wells.

Mechanical Testing and Characterization of a Swelling Elastomer

Elastomers are being increasingly used for sealing and other applications in the oil and gas industry. Specifically developed elastomers possess durable properties and have the ability to withstand detrimental effects of heat, chemicals, and harsh environments. For successful modeling and simulation of various downhole processes, it is very important to determine the behavior of elastomer materials under realistic well conditions. Of special interest is the class known as swelling elastomers. This article reports some results from experiments conducted on mechanical testing and characterization of an inert (nonswelling) and a water-swelling elastomer (both belonging to the EPDM family) used for sealing purposes by a local petroleum development firm. Experiments were designed and conducted in accordance with standard ASTM test methods. Apart from regularly available testing equipment, some simple test rigs and fixtures were designed and fabricated. Elastomer behavior was tested for hardness, compression set (at different temperatures and for different periods of time), tensile set (for different periods of time), tensile properties (fracture strength and percent elongation), and swelling. In the swelling test, different sample geometries (unconfined samples and samples mounted on steel plate) were tested for a total duration of 1000 h (roughly 45 days) in salt solutions of different concentrations and at different temperatures. Results show that compression set increases with increasing temperature and testing time, while room temperature tensile set also increases with longer testing time. Compared to the inert elastomer (exhibiting nonlinear elastic behavior like normal rubbers), swelling elastomer surprisingly showed linear stress—strain response. As expected, the inert elastomer did not exhibit any change in volume, while the swelling elastomer showed significant volume/thickness increase with increasing test temperature and decreasing salt concentration.

Design and Manufacture of Swell Packers: Influence of Material Behavior

In all well completions (oil and gas fields), effective cement job is necessary for zonal isolation. Failure of cement annulus because of large stresses has been reported in various studies, requiring huge costs in remedial intervention. Swellable packers have emerged as a new manufacturing equipment/technique able to replace conventional cement completion. These packers are custom-manufactured by vulcanizing specially developed swelling elastomer elements onto petroleum pipes. Especially designed and manufactured to suit a particular set of downhole conditions, swell packers are being used in a variety of petroleum applications such as zonal isolation and water shutoff in fractured reservoirs, slimming down of oil wells through replacement of conventional cementing, sand screening, reservoir compartmentalization, etc. Performance analysis and seal design improvement is not possible without reliable information about material response of swelling elastomers. This article summarizes the results of a series of tests performed to determine the swelling behavior of a water-swelling and an oil-swelling elastomer, with and without acid induction. Experimental setup was designed in consultation with petroleum and rubber engineers. Volume, thickness, and hardness of elastomer samples were measured before swelling and periodically after swelling over a one-month period. Test conditions were chosen to replicate actual oilfield conditions.

Structural behavior of a solid tubular under large radial plastic expansion

The theory of metal forming has been used to study the mechanical response of a solid tubular under radial plastic expansion. A mathematical model of an expanded thin walled tube under compression has been developed in this paper. The study showed that as the friction coefficient and mandrel angle increase the drawing force and induced stresses increase. However, the final tube thickness and length were found to decrease with an increase in both parameters.

Comparison between fresh and exposed swelling elastomer

Last decade has seen growing use of swelling elastomers in various applications by the oil and gas industry. Elastomers with special properties have been developed to sustain the specific downhole conditions of temperature, pressure, and chemical environment in different wells. Apart from targeted short-term tests conducted by rubber developers and drilling application companies, little is known about material characterization of such elastomers. Even these test results are not generally available in the public domain due to proprietary rights. In particular, an important factor that has not been previously explored is the effect of exposure on material response of swelling elastomers. Zonal isolation packers and other forms of elastomer-mounted tubulars are often stacked in open yards for a long time before their deployment in wells. Properties of elastomers may significantly change due to their exposure to air, sunlight, and humidity. Some results from a comparative study of the behavior of fresh and exposed samples of an ethylene propylene diene monomer (EPDM)-type water-swelling elastomers are reported here. Methodology of the swelling test was developed in consultation with petroleum engineers and rubber manufacturers. Other experiments were designed and performed in line with standard ASTM test methods. Properties of elastomers that are investigated are hardness, compression set, tensile set, tensile properties, and swelling behavior. Elastomer samples were allowed to swell for a total test duration of 1000 h. Two specimen geometries were tested for swelling: unconfined disc samples to study the behavior of free elastomer and plate samples (elastomer vulcanized on steel plate) to emulate the actual seal performance. Swelling was carried out in salt solutions of different concentrations and at different temperatures. Hardness of exposed elastomer samples (EPDM1) was generally higher than that of fresh samples (EPDM2). Similarly, exposed elastomer showed significantly higher amount of compression set when compared with fresh elastomer. Short-duration tensile set values (10 min test) were almost the same for both sample types. However, tensile set results for the longer-duration tests (10 h and 20 h) were higher for exposed samples. Surprisingly, stress–strain graphs for both fresh and exposed elastomers were almost linear, while rubber-type materials typically show a highly nonlinear behavior. Values of modulus of elasticity and stress at fracture were considerably higher for exposed samples. In contrast, percentage elongation results were higher for fresh samples. Amount of swelling against swelling time showed an up-and-down trend for both the sample types. At the same temperature and under brine solution of the same concentration, fresh elastomer generally swelled far more than the exposed one. The overall observation from the variety of experimental results is that exposure to sun and moisture for extended periods of time reduces the flexibility and swelling capacity of these elastomers.

Tubular expansion in irregularly shaped boreholes - Computer simulation and field measurement

Abstract Abstract Recently, field engineers have tried to use a new technique using expandable tubular with elastomers to seal the annulus. Ultrasonic down-hole measurements carried out for evaluation of zonal isolation revealed that the tubular expanded to an oval x-section instead of the desired circular x-section at certain locations. This is a phenomenon previously unknown. It is believed to occur due to expansion in irregularly shaped boreholes. The ovalization of expanded tubular was studied to avoid such problems in future. The finite element method was used to predict tubular ovality and compare it to measured values. Results were then used to develop ready-to-use design curves in making decisions for running a completion tool in expanded tubular.

Elastomer Seals in Cold Expansion of Petroleum Tubulars: Comparison of Material Models

Because of its ability to significantly reduce well costs, together with improvement of well functionality and performance, expandable technology is becoming popular in the oil and gas industry. Based on the well-established manufacturing method of cold expansion, novel downhole applications of this technology include expandable drilling liners, expandables, and screens, expandable casing cladding systems, and expandable liner hangers. All expandable applications need an effective sealing mechanism. One of the newest developments in seal design is the use of swelling elastomers: rubber-like materials that swell upon contact with water or oil. The authors are involved in several projects targeted at improvement of seal design and manufacturing in petroleum applications. Work reported in this article focuses on experimental and numerical (FEM) investigation of the tensile behavior of two swelling elastomers. Treating swelling elastomers as a type of hyperelastic material, coefficients for the more popular hyperelastic material models (Ogden, Yeoh, Arruda–Boyce, and Neo-Hookean) are determined using curve fitting procedures available in ABAQUS. Models are compared with each other in predicting the tensile behavior for both unswelled and swelled conditions. Neo-Hookean model appears to give the overall best results for tensile behavior of the two elastomers under swelled and unswelled states.

Dynamic effects of mandrel/tubular interaction on downhole solid tubular expansion in well engineering

The expansion process subjects a solid tubular to large plastic deformations leading to variations in tubular thickness and length, which may result in premature and unexpected failures. It was noticed that the expansion process induces wall thickness imperfections due to excessive local plastic deformation as a result of mandrel sticking and slipping relative to the expanded tubular; such irregularities increase the probability of failure. Mandrel sticking may be the result of lack of enough lubrication, tubular surface irregularities, and the presence of welded and/or threaded connections, which require higher drawing force to push the mandrel forward. When the drawing force required to overcoming the maximum static friction and the mandrel forward motion is assured, the mandrel slips relative to the expanded tubular. This “stick-slip” phenomenon results in mandrel oscillations that affect the tubular response in terms of further reduction in thickness and may jeopardize the tubular capacity under normal operating field conditions. Therefore, the present work studies the mandrel dynamics and their effect on the tubular structural response. A mathematical model, which is an extension of the quasistatic tubular expansion analysis, has been developed to describe the dynamic friction effects of the stick-slip phenomenon. A special case of tubular expansion consisting of 25% expansion ratio of a 4/12 in. liner hanger was considered. It was found that the level of mandrel oscillations is in the order of 1–2 mm around its equilibrium position resulting in tubular thickness reduction of approximately 9% on top of its variation caused by the steady state expansion process. This increase in thickness reduction may affect the postexpansion collapse strength of the tubular. DOI: 10.1115/1.3066412

Defining shape complexity of extrusion dies : A reliabilistic view

Complexity of the profile being extruded plays a critical role in die design, die reliability, process aberrations, and product defects. Engineering common sense dictates that a more complex die should require a larger amount of extrusion force or pressure. This has been experimentally substantiated by the authors in a recent study. According to a basic definition, therefore, extrusion shape complexity is the ratio of the pressure required to extrude a complex profile to the pressure required for a solid circular profile of the same area. Most of the complexity definitions reported in published literature are based on this interrelationship between extrusion pressure and profile complexity. From a die reliability viewpoint, a complex profile is more difficult to extrude than a simple one, and it generates more stresses in the die. It should therefore lead to an earlier die failure. Another study by the authors confirms that the working life of hot extrusion dies is definitely affected by profile complexity. Reported complexity definitions provide some sort of index to measure extrudability, and can thus be used for pressure prediction to a certain degree. Unfortunately, none of these definitions addresses the very important issue of die reliability, and they generally yield a counterintuitive trend of increasing die life with increasing complexity. None of these definitions includes all the significant geometrical features of a die profile. This article reports the development of two new definitions of shape complexity (linear and power-law) incorporating all significant geometrical features of an extrusion die profile. Die failure data from a large commercial extrusion facility have been collected and analyzed. Regression-based models have been developed for prediction of die failure on the basis of complexity.