Omar S. Al-Abri

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.

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%.

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 well drilling and remediation. The ultimate goal is to replace the conventional telescopic wells to mono-diameter 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/post expanded 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 have minimum resistance during expansion as compared to the widely used circular cross section mandrel with a cone angle of 10°. However, further manipulation of shape parameters of the circular cross section mandrel revealed an improved efficiency. The drawing force required for expansion reduces by 7% to 10% having minimum dissipated energy during expansion. It is also found that these cones yield less reduction in tube thickness after expansion, which results in higher post-expansion collapse strength. In addition, rotating a mandrel further reduces the energy required for expansion by 7%.Copyright

Modeling and Simulations of Transformation and Twinning Induced Plasticity in Advanced High Strength Austenitic Steels

The current research work is focused on the development of a combined micromechanical model of transformation and twinning induced plasticity mechanisms in austenite based high Mn steels. Both mechanisms are combined by incorporating transformation in twinning based crystal plasticity model. Initially, mechanical twinning is incorporated in slip based crystal plasticity model. Afterwards, transformation phenomenon (austenite to martensite) is included in the developed slip and twin based crystal plasticity model. The kinematics of the mechanisms is developed by defining elastic, plastic, and transformation deformation gradients. These deformation gradients are then used to calculate stress tensors. The constitutive equations in terms of integration algorithm are implemented in ABAQUS as a user-defined subroutine. Three dimensional finite element model of single and polycrystal austenite are developed. Single austenite crystal is represented by one finite element while the behavior of polycrystal austenite is estimated through 500 grains. The orientation of each grain is defined through Euler angles. The performance of the model is evaluated through finite element simulations in order to predict the elastic-plastic and transformation behaviors of single and polycrystal austenite under different loading conditions i.e. uniaxial tension and simple shear. The developed model is in good agreement with published literature. In simple shear, prominent difference in stress magnitude is found once twinning mode is incorporated in slip and transformation. This difference has significant magnitude in case of polycrystal austenite. This shows substantial advantage (in terms of strength and formability) of incorporating mechanical twinning along with slip and transformation.Copyright

Minimization of Pop-Out Phenomenon Effect in Down-Hole Tubular Expansion

In published literature, Solid Expandable Tubular (SET) is defined as a down-hole cold work process to expand a tubular to attain desired inner diameter. Tubular expansion process is a complicated process and a number of challenges are associated with its usage. However, proper planning before execution may lead the operators for more options that can affect important parameters such as; tubular length after expansion, hole diameter, expansion force, tubular structural integrity, post expansion properties, suitable material for tubular, selection or design of associated tools for expansion, and optimal selection of system components based on formation type, to name a few. Further studies are needed to overcome the challenges of these problems. Most of the published materials in this area mainly present the experience of using the technology without pointing directly to the technical challenges and understanding the fundamentals behind it. The successful expansion process shall make sure of no fracture, burst, collapse or any damage in the tubular; constant tubular diameter along the tubular; and the structural integrity of tubular and tubular connections.In general, expansion process involves placing a cone inside tubular and through the application of force at one end of the cone tubular expands. The sudden release of energy, at the end of expansion process, acts as a dynamic excitation to the tubular-fluid-formation system, which may affect tubular material properties and geometry, and is termed as pop-out phenomenon. The dynamics of problem is solved by considering inner/outer fluids and tubular itself. The forward and backward movement of pressure waves in inner and outer fluid and the stress wave in tubular is solved analytically as a coupled problem. It is assumed that the three mediums are uniform in nature, formation is isotropic, damping is negligible, fluid velocity behind cone is low and wave lengths are large compared to borehole diameter. It was found that the fluctuating stress levels at the fixed end of the tubular causes permanent ripples, which will increase tubular diameter beyond allowable limit and/or will cause converging and diverging sections within the tubular resulting from constructive or destructive interference of stress wave originating after pop-out. In order to limit the number of runs for computer simulation, particular type of tubular and well are chosen, hence keeping the geometrical parameters constant for all simulation. Other parameters are changed and their effects on pop-out phenomenon are determined. The results show that changing the formations, inner and outer fluid densities have no effect on the inner fluid pressure and axial stress for specific tubular materials. However, significant variations occur in outer fluid pressure. Among all tubular materials high Mn steel alloy experiences lower stress values. The current study can be used to aid in selection of reliable materials for SET system to minimize the affect of pop-out phenomenon. Also, formations variation varies outer fluid pressure. In addition, all expansion ratios follow the same pattern in parameters variation.Copyright

Mechanical and Microstructural changes of fine GRAINED C-Mn steel tubular undergoing down-hole cold expansion process

As easily recoverable hydrocarbon resources are depleting, the oil and gas industry focuses more on producing oil and gas from ultra-deep, tight and scattered pockets of reserves. However, these recoveries are not only difficult and expensive, but also require the development of new technologies and materials that can meet stringent requirements regarding operation in sub-surface environment. The emergence of expandable tubular in the late 1990s has opened a new avenue for oil and gas wells design and remediation processes. However, these tubular go through large expansion in diameter at kilometers depths in onshore and offshore wells. This alters the post expansion mechanical and microstructural properties of the tubular that may lead to premature failure during operation. The idea of understanding such variations revolve around complex mechanisms occurring at micro level including multiphase microstructure, grains sizes and morphology, and crystallographic orientations. Initial grains morphology and distribution of phases, and the subsequent changes due to the expansion process lead to significant variations in material properties at macro level. Optical micrographs showed that the expandable tubular material is composed of fine grained microstructure of ferrite phase with some traces of martensite and plate-like structures. Induced martensite results from the phase transformation of metastable austenite induced by thermomechanical processing applied during the manufacturing stage. A reasonable presence of martensite phase in the tubular material enhances its structural integrity, collapse and burst strengths, as well as provides a safeguard against possible mechanical failures such as buckling. On the other hand, the ferrite phase is a soft phase and its presence improves the formability of the tubular resulting in higher expansion ratio. It was also observed that the grains size is affected by the tubular expansion. The presence of elongated grains in the microstructure is due to the excessive deformation as well as the crystallographic reorientation of grains due to the course of tubular expansion. However, no strong texture has been found in the expanded tubular material, which may be attributed to the complex nature of loadings induced during the expansion process. In order to understand the influence of tubular expansion process on mechanical properties of tubular, samples from un-expanded and expanded sections of the tubular (expanded at 16%, 20% and 24% of the tubular original inner diameter) are investigated using standard mechanical testing procedures. Mechanical testing results revealed an increase in yield strength, ultimate tensile strength and hardness, whereas ductility and impact toughness tend to decrease. Fracture surface analysis of fractured tensile samples has also been done using scanning electron microscope (SEM). At lower expansion ratio, fracture surface micrographs revealed a predominantly ductile nature of failure with clusters of fine microscopic dimples intermingled with voids. However, at higher expansion ratio, the test specimens revealed a mixed mode of failure with both brittle and ductile features.Copyright

Modeling of Twinning Based Plasticity Phenomenon in Austenite Dominated Steels Under Combined Loading

Advanced high strength steels cover a vast range of applications more specifically in aerospace and oil industry where large deformation of a material is desired in order to attain a specified shape and geometry of the product. The main reason behind their successful implementation is having an optimum combination of strength and formability. Austenite based twinning induced plasticity steel lies in the second generation and has excellent strength-cum-formability combination among the group of advanced high strength steels. The stress assisted phase transformation from austenite to martensite, which is known as twinning, found to be principal reason behind an enhancement of these properties. This work is aimed to investigate an elastic-plastic behavior of an austenite dominated steel, which undergoes slip and mechanical twinning modes of deformation. Initially, a micromechanical model of twining induced plasticity phenomenon is developed using crystal plasticity theory. Then, the developed model is numerically implemented into finite element software ABAQUS through a user-defined material sub-routine. Finally, finite element simulations are done for single and poly-crystal austenite subjected to combined load. This replicates the complex loading condition which exists in material forming processes like pipe expansion, extrusion, rolling. The variation in stress-strain response, magnitude of shear strain, and volume fraction of twinned martensite are plotted and analyzed.Copyright