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The most important mechanical properties of casing and tubing are burst strength, collapse resistance and tensile strength. These properties are necessary to determine the strength of the pipe and to design a casing string. If casing is subjected to internal pressure higher than external, it is said that casing is exposed to burst pressure loading. Burst pressure loading conditions occur during well control operations, casing pressure integrity tests, pumping operations, and production operations. The MIYP of the pipe body is determined by the internal yield pressure formula found in API Bull. This equation, commonly known as the Barlow equation, calculates the internal pressure at which the tangential (or hoop) stress at the inner wall of the pipe reaches the yield strength (YS) of the material.
Use of several types of production logs in combination can provide important information, often quite cost effectively, for diagnosing a gas kick encountered during drilling. An example is discussed below. During the coring of a gas sand at 15,000 ft, a pressure kick occurred, gas pressure was then lost at the surface, and mud was added periodically to keep the drillpipe full. On the day after the gas kick, noise and temperature logs were recorded during the same run inside the drillpipe with the well static. These logs were run to identify the flow path of a likely underground blowout.
Although many measurements are taken while drilling, the term MWD refers to measurements taken downhole with an electromechanical device located in the bottomhole assembly (BHA). Telemetry methods had difficulty in coping with the large volumes of downhole data, so the definition of MWD was broadened to include data that were stored in tool memory and recovered when the tool was returned to the surface. Power systems in MWD generally may be classified as one of two types: battery or turbine. Both types of power systems have inherent advantages and liabilities. In many MWD systems, a combination of these two types of power systems is used to provide power to the MWD tool so power will not be interrupted during intermittent drilling-fluid flow conditions.
The one-circulation method is a well-control procedure. To implement this method certain guidelines must be followed to ensure a safe kick-killing exercise. Although the procedure is relatively simple, its mastery demands basic knowledge of the practical steps taken during the process. A kill sheet is normally used during conventional operations. It contains prerecorded data, formulas for the various calculations, and a graph--or other means--for determining the required pressures on the drillpipe as the kill mud is pumped.
A kick is a well control problem in which the pressure found within the drilled rock is higher than the mud hydrostatic pressure acting on the borehole or rock face. When this occurs, the greater formation pressure has a tendency to force formation fluids into the wellbore. This forced fluid flow is called a kick. If the flow is successfully controlled, the kick is considered to have been killed. An uncontrolled kick that increases in severity may result in what is known as a "blowout." Several factors affect the severity of a kick.
Underbalanced drilling (UBD) can create special challenges for well completion. The majority of wells previously drilled underbalanced could not be completed underbalanced - the wells were displaced to an overbalanced condition with kill fluid prior to running the liner or completion. Depending on the completion fluid type, some formation damage would take place. The damage is not as severe for completion brine as with drilling mud because there are no drilled cuttings and fines in the brine. However, reductions in productivity of 20 to 50% have been encountered in underbalanced drilled wells that were killed for the installation of the completion.
Akita, Emmanuel (University of Oklahoma) | Dyer, Forrest (University of Oklahoma) | Drummond, Savanna (University of Oklahoma) | Elkins, Monica (University of Oklahoma) | Duggan, Payton (University of Oklahoma) | Ahmed, Ramadan (University of Oklahoma) | Florence, Fred (Rig Operations, LLC)
Summary The use of drilling automation is accelerating, mostly in the area of rate of penetration (ROP) enhancement. Autonomous directional drilling is now a high focus area for automating drilling operations. The potential impact is immense because 93% of the active rigs in the US are drilling directional or horizontal wells. The 2018–2019 Drilling Systems Automation Technical Section (DSATS)‐led international Drillbotics® Student Competition includes automated directional drilling. In this paper, we discuss the detailed design of the winning team. We present the surface equipment, downhole tools, data and control systems, and lessons learned. SPE DSATS organizes the annual Drillbotics competition for university teams to design and develop laboratory‐scale drilling rigs. The competition requires each team to create unique downhole sensors to allow automated navigation to drill a directional hole. Student teams have developed new rig configurations to enable several steering methods that include a rotary steering system and small‐scale downhole motors with a bent‐sub. The most significant challenge was creating a functional downhole motor to fit within a 1.25‐in. (3.18 cm) diameter wellbore. Besides technical issues, teams must demonstrate what they have learned about bit‐rock interaction and the physics of steering. In addition, they must deal with budgets and funding, procurement and delivery delays, and overall project management. This required an integrated multidisciplinary approach and a major redesign of the rig components. The University of Oklahoma (OU) team made significant changes to its existing rig to drill directional holes. The design change was introduced to optimize the performance of the bottomhole assembly (BHA) and allow directional drilling. The criteria for selecting the BHA was hole size, BHA dynamics, a favorable condition for downhole sensors, precise control of drilling parameters, rig mobility, safety, time constraints, and economic practicality. The result is an autonomous drilling rig that drills a deviated hole toward a defined target through a 2 × 2 × 1‐ft (60.96 × 60.96 × 30.48 cm) sandstone block (i.e., rock sample) without human intervention. The rig currently uses a combination of discrete and dynamic modeling from experimentally determined control parameters and closed‐loop feedback for well‐trajectory control. The novelty of our winning design is in the use of a small‐scale cable‐driven downhole motor with a bent‐sub and quick‐connect‐type swivel system. This is intended to replicate the action of a mud motor within the limits of the borehole diameter. In this paper, we present details of the rig components, their specifications, and the problems faced during the design, development, and testing. We demonstrate how a laboratory‐scale rig can be used to study drilling dysfunctions and challenges. Building a downhole tool to withstand vibrations, water intrusion, magnetic interference, and electromagnetic noise are common difficulties faced by major equipment manufacturers.
Abstract Emerging technologies, stringent permanent well abandonment regulations, and increasing well complexity affect the way we execute well intervention operations. One of the major operators in the Netherlands had an objective to set underbalanced cement plugs in brine across a deviated section using managed-pressure equipment to overcome high reservoir bottomhole pressure. The project involved several challenges: large-diameter production casing with a requirement to maintain high shut-in wellhead pressure, complex wellbore geometry, operations from a workover rig with zero discharge allowance, corrosive salt environment, and small cement slurry volume. These challenges had to be addressed to complete well abandonment to minimize safety risks, maximize efficiency, and achieve compliance with industry standards and regulatory requirements. This paper discusses two case studies involving underbalanced pump-and-pull and conventional balanced plug placement techniques. Thorough analysis and risk assessment, engineering design approach, comprehensive laboratory testing, and fit-for-purpose surface equipment and downhole tools enabled flawless job execution and placement and achievement of long-term zonal isolation. The first well-barrier elements were successfully verified by tagging and pressure testing in both cases. Results of this study include the following observations and conclusions: Managed-pressure cementing was proven to be an ideal solution for a well abandonment in a reservoir environment of high bottomhole pressure. Highly magnesium-resistant cement slurry design should be considered when setting cement plugs across an extremely corrosive salt environment. Successful verification of the first well-barrier element simplifies operations for subsequent cement plugs. Cost-effective solutions for permanent well abandonment under challenging downhole conditions attracts increasing interest from petroleum engineers due to increasing well complexity and low oil prices that challenge the economics of wells, leading to abandonment. The current paper describes the challenging conditions under which the wells had to be abandoned, thorough analysis of the risks involved, and an effective solution. The design strategy, execution, evaluation, and results for these two wells are discussed in detail and will help to guide success and solve problems related to permanent well abandonment under similar challenging conditions.
Numerous continuous-length tubular service concept trials and inventions paved the way for the creation of present day coiled tubing (CT) technology. The following discussion outlines some of the inventions and major milestones that directly contributed to the evolution of the continuous-length tubular products used in modern CT services. The origins of continuous-length, steel-tubing technology can be traced to engineering and fabrication work pioneered by Allied engineering teams during the Second World War. Project 99, code named "PLUTO" (an acronym for Pipe Lines Under The Ocean), was a top-secret Allied invasion enterprise involving the deployment of pipelines from the coast of England to several points along the coast of France. The reported dimensions of the conundrums were 60 ft in width (flange-to-flange), a core diameter of 40 ft, and a flange diameter of 80 ft.
Summary Variable ram blowout prevention (VRBOP) valves are elastomeric material-based flow control devices used in offshore oil drilling applications as the primary safety mechanism to respond to high wellbore pressure emergency situations. During their operation, the elastomer deforms and distorts extensively to form a tight seal around the drillpipe. Because of the large deformation and distortion of the elastomer, developing a Lagrangian-based finite element analysis model to simulate the operation of a VRBOP valve is quite challenging. The finite elements of the Lagrangian finite element mesh degrade in quality because they deform with the material when the deformation becomes excessive. This leads to poor convergence of the numerical solution. In this study, we first demonstrate that the numerical convergence issues can be resolved by using a suite of modeling techniques: explicit integration scheme, Ogden second-order hyperelastic constitutive model for the elastomer, and the selection of appropriate values for element sizes and other modeling parameters. After resolving the convergence issues, we used the model to study the sealing efficiency and material failure of a VRBOP valve for two different operating temperatures and drillpipe diameters. The sealing efficiency is studied using two performance criteria: the uniformity of the sealing pressure around the drillpipe and the magnitude of the overall deformation of the elastomer. For the material failure analysis of the elastomer, we used multiple failure criteria. The results of this study provide many new insights that have the potential to improve VRBOP valve design. For instance, results show that elevated temperature improves the sealing efficiency of a VRBOP valve because of the higher flexibility of the elastomer at elevated temperatures. Likewise, the wellbore pressure also improves the sealing efficiency. However, all these improvements in sealing pressure come with the risk of a higher probability of material failure.