Sayyad Zahid Qamar

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.

Shape Complexity, Metal Flow, and Dead Metal Zone in Cold Extrusion

Nonhomogeneous metal flow through an extrusion die can directly affect product quality, productivity, and die life. The complexity of a die profile is an indicator of how difficult it is to extrude the profile. Some investigations about the effect of die complexity on extrusion pressure, product quality, and die life can be found in the published literature. However, the effect of profile complexity on metal flow through the extrusion die has not been explored much. Such a study can directly contribute toward die design improvement and reduction of extrusion defects related to metal flow. This article investigates the effect of shape complexity on the dead metal zone (DMZ) and metal flow through cold extrusion experiments and finite element simulations on some solid profiles. Experiments were performed using flat-face dies of different complexities and different billet materials. 2D and 3D finite element simulations were carried out. One significant conclusion is that currently existing definitions of extrusion shape complexity cannot satisfactorily explain the variations in DMZ size under different conditions. Factors such as die profile symmetry and extrusion ratio may play significant roles in the formation of DMZ and distortion of metal flow through the die.

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.

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.

Finite Element Analysis of Tubular Ovality in Oil Well

This paper presents the finite element analysis of tubular expansion in oval bore holes such as those frequently observed in Upper Natih reservoirs. The minimum inner diameter of the expanded tubular must be larger than the drift diameter set by American Petroleum Institute (API) standards. If the minimum inner diameter is smaller than drift diameter, completion equipments can not be run successfully, which is necessary to complete an oil-well for production. The phenomenon of tubular ovality has been previously unknown to petroleum industry. Finite element model of tubular expansion in oval bore-holes is developed to determine the tubular ovality and compared with measured ovality. It was found that ovality increases linearly with tubular expansion ratio. With increase in expansion ratio, the tubular contact length with formation and developed contact pressure increases. Tubular ovality, if not considered in well design, may lead to premature tubular failure due to lower collapse rating and higher stresses.

Optimum Mandrel Configuration for Efficient Down-Hole Tube Expansion

In the last decade, traditional tube expansion process has found an innovative application in oil and gas wells drilling and remediation. The ultimate goal is to replace the conventional telescopic wells to monodiameter wells with minimum cost, which is still a distant reality. Further to this, large diameters are needed at terminal depths for enhanced production from a single well while keeping the power required for expansion and related costs to a minimum. Progress has been made to realize slim wells by driving a rigid mandrel of a suitable diameter through the tube either mechanically or hydraulically to attain a desirable expansion ratio. This paper presents a finite element model, which predicts the drawing force for expansion, the stress field in expanded and pre-/postexpanded zones, and the energy required for expansion. Through minimization of energy required for expansion, an optimum mandrel configuration, i.e., shape, size, and angle, was obtained, which can be used to achieve larger in situ expansion. It is found that mandrel with elliptical, hemispherical, and curved conical shapes has minimum resistance during expansion as compared to the widely used circular cross section mandrel with a cone angle of 10 deg. However, further manipulation of shape parameters of the circular cross section mandrel yielded an improved efficiency. The drawing force required for expansion reduces by 7–10% having minimum dissipated energy during expansion. It is also found that these mandrels yield less reduction in tube thickness after expansion, which results in higher postexpansion collapse strength. In addition, rotating a mandrel further reduces the energy required for expansion by another 7%.

A CVN-KIC correlation for H13 tool steels

Fracture is the most common cause of die failure in hot extrusion. Prediction of fracture life requires a reasonably accurate determination of plane-strain fracture toughness (KIC). Standard K(KIC) testing is difficult, time-consuming, and costly. Charpy impact energy (CVN) is often used as an indirect measure of fracture toughness. Published CVN-K(KIC) correlations do not generally apply to tool steels, and are not suitable for high temperature predictions. This paper is part of a study aimed at the development of a reasonable CVN-K(KIC) correlation for the hot work tool steel H13, subjected to various tempering cycles and tested at different elevated temperatures, based on hardness and impact energy data.