Detonation of shaped charges carried by a perforating gun creates a complex physical and chemical process that occurs within a very short time. During the process the shaped charge case usually disintegrates and is partially oxidized. The oxidization emits heat in addition to that of the explosive detonation and hence could eventually affect the post-detonation condition of the perforating gun. Zinc and steel are common materials used in the manufacture of shaped charge cases, but their physical and chemical properties result in quite different impacts on the performance of the perforating gun and on its survivability. About 1,000 ms after detonation, a charge with a zinc case generates a pressure approximately 50% higher than one with a steel case. The zinc case creates an impulse about 30% higher and a temperature about 220°F higher. It results in more than 45% oxidation; for the steel case oxidation is less than 5%. Conversely, the zinc and steel case contributions to the detonation process are quantifiable in terms of energy. Such a quantified study is first reported in respect to perforating. Details can be incorporated into a recently developed gun survivability model for risk management in both new perforating product development and job execution. In field operations it can be used in post-perforating evaluation of formation damage.

The bottom hole assembly (BHA) of a drill string consists of various components and tools such as a drill bit, a mud motor, a directional drilling tool, measurement-while-drilling tools, and logging-while-drilling tools. It operates at the bottom of the wellbore and physically drills the formation. A rotary shouldered threaded connection is composed of a pin element and a box element and serves as a critical component to screw the tools and subs used on the BHA together. Functionally, the rotary shouldered connection upon makeup must be able to maintain sealability between internal and annular pressures at the seal face, while transmitting torque and withstanding bending loads when drilling through a curved well section. Leaks of these connections while drilling can be catastrophic. The drilling and measurement tools could be flooded with invasion of drilling mud into the inside, which could result in severe damage of the expensive measurement devices, sensors, and electronics inside the tools as well as a significant amount of nonproductive time. Hence, sealability assurance of the connections subjected to combined loads in difficult drilling conditions is essential for qualification of advanced rotary shouldered connections. In this study, a numerical model based on three-dimensional finite element analysis (FEA) of the threads is developed for numerically qualifying the seal integrity of the connection. Specifically, the FEA model can describe the nonlinear interactions between the pin and box threads and on the seal face subjected to combined loads of preload, pressure, and bending. The resulting contact pressure distribution on the seal face predicted by the FEA model can be utilized as a performance metric for evaluating the risk of leaking. A full-scale sealability test rig with three-point bending configuration is also developed for validating the prediction from the numerical model. In the test, the test sample is held at its two ends onto a rigid beam with holding chains. A remotely controlled hydraulic jack is placed between the beam and the connection to generate the bending moment. It is observed in the test that the pressure drop after shutting down the pump is less than 1% within the last 15 minutes and there is no fluid leaking out of the connection after the pressure is released, which favorably agrees with the FEA prediction. Once validated, the numerical modeling method has been successfully applied to virtually qualify the sealing capacity of advanced rotary shouldered connections of various sizes without performing physical tests, which has resulted in a tremendous amount of cost and time savings for advanced rotary shouldered connection development.

Summary A detonated shaped charge fired from a perforating string or perforating gun will not only perforate its targets, but also possibly cause excessive damage or swell to its carrier. Comprehensive understanding of the post-perforating conditions of the perforator or perforator system is required if such damage and potential retrievability risks are to be avoided. In practice, the perforating design engineers do not have a well-established analytical tool to help them understand post-perforating behavior of perforators. They have to rely on their own experiences and previous perforating histories to roughly estimate the swell or damage conditions of similar perforators. In this paper the failure modes of continuously phased perforators for both gas well and oilwell applications are analyzed. Important factors concerning carrier serviceability are discussed. A method based on energy conservation is used to establish a swell model to predict the post-detonation conditions of the perforator. The model takes the total expendable energy from the explosives into account, relates it to the energy consumed by the functional and nonfunctional processes, and describes the relationship of energy distribution among them. A criterion is proposed to establish the serviceability of the perforators. Analytical results from the model are compared with the data collected from surface tests. The results indicate that the model can reasonably predict the perforator swell and damage after detonation, and as such will be a useful tool that shortens the required time to develop future perforators. Introduction A perforating project manager has to carefully plan a perforating job for both maximized system performance and minimized risk associated with incidents such as perforating gun carriers stuck downhole. Maximized performance usually requires use of more powerful shaped charges or higher shot density of shaped charges, which consequently inflicts more damage to the perforator carrier or gun. Examples of serious damages are over swollen or split guns. It is true that all guns will swell after shaped charges are detonated. However, an over-swollen gun refers to the swell of the gun that exceeds the specified diametric tolerances and thus cannot be retrieved from the well without costly intervention operations. A split gun is one that is fractured, with a crack extending from one shot exit hole to adjacent shot exit holes, which is also unacceptable. The risk associated with either an over-swollen or split gun is extremely high and should be avoided during perforating job planning and system development. A validated analytical model for predicting perforating gun swell can certainly enhance the effectiveness of both job risk management and system development. An analytical model of perforating gun swell can help risk management in at least two respects. First, analytical tools such as swell modeling can serve as a supplemental measure to further verify whether existing guns are adequately qualified within their respective ratings, and therefore, will be useful to both perforating job planners and perforating system developers. A second application is to special perforating jobs that may require some alterations to an existing perforating system in order to meet a specific technical requirement. If the job is imminent with little time for engineers to run another round of full qualification tests, the engineers or project managers can decide whether the gun will survive (be retrievable) by using the modeling tool, instead of merely relying on their experiences to make the tough decision.

While viscous flows in curved pipes are often encountered in industrial and biological applications, the effect of pipe streamwise curvature on the flow characteristics is not fully understood under the general conditions of strong curvature and large flow Reynolds numbers. In this paper, direct numerical simulation of three-dimensional viscous flow in a wavy pipe is performed using the lattice Boltzmann approach, as a first step in developing a general methodology and some understanding of the three-dimensional features of the flows in a curved pipe of nonuniform curvature. We first validate the lattice Boltzmann approach by simulating a transient flow in a straight pipe and comparing the numerical solution with the analytical solution. In a wavy pipe, it is shown that the pressure gradient necessary to drive the flow depends more strongly on the flow Reynolds number (Re), due to the effect of curvature-induced fluid inertial force and the transverse secondary flows. The secondary flow pattern changes with Re, from a single pair of primary Görtler vortices to multiple pairs of smaller vortices, which could trigger transition to a turbulent flow. The wavy pipe could provide a simple design for enhancing mixing and heat transfer in pipes.

To mitigate the risk of twistoff during high dogleg-severity (DLS) drilling and to reduce cost of service delivery induced by frequent recuts, an advanced rotary shouldered threaded connection design with significantly enhanced fatigue life over existing API connections has recently been developed and released for field operation. Modeling and simulation techniques had been extensively used to drive the design and qualification processes. In this paper, an overview of the numerical modeling methodology and its experimental validation is presented with an emphasis on the key functional requirements of the design. The newly developed connection design involves an optimized thread form and an advanced manufacturing process. Finite element analysis (FEA) was heavily used to optimize the design prior to physical prototyping and testing. High-fidelity modeling methods were developed, and comprehensive numerical analyses were performed to digitally evaluate the performance of the new design, including fatigue resistance, galling resistance, combined load capacity, sealability, and so on. The FEA models had very well predicted the performance of the new design, which was later validated through full-scale experimental tests. Several qualification tests, such as torsional yield limit test and tensile capacity test, were carried out completely digitally. As a result of the extensive modeling and simulation work conducted, the connection design met all requirements in one iteration. The work presented in this paper represents a successful example of model-driven product development, which significantly reduces development time and cost. It is the first time that a high-fidelity modeling methodology, in conjunction with full-scale experimental validation, is introduced for advanced rotary shouldered threaded connections in the oil and gas industry.