One of the most innovative recent advances in downhole drilling tool activation has been the introduction of mechanical extrusion technology, incorporating the use of rigid metal darts to improve the cycling and control of a variety of processes and devices. Increasingly, operators are recognizing mechanical extrusion by means of dart activation as a time-, cost-, and labor-saving alternative to traditional ball activation methods.
For example, conventional cycling of drilling bypass valves has used a polymer extrusion process that relies on balls as the activation device. However, Churchill Drilling Tools has developed an effective and accurate mechanical extrusion method that uses a dart-based valve. The system can perform activations up to five times faster than polymer methods.
The company’s MX (mechanical extrusion) system allows the use of rigid Smart Darts for multicycle control and exploits their robustness and resilience at high pressures and temperatures (up to 660°F) to deliver greater operating speed, reliability, and performance. The system’s unique feature is its two configurable shearing modes, which solves reliability and power delivery problems. It requires a radius as small as 0.0075 in. for power transmission, thereby making implementation extremely compact.
With the ability to control and power three or more tools independently, users eliminate the conventional inner diameter (ID) and obstruction conflicts between different tools in a string. This has implications for mono-cycling ball and shear systems, which commonly obstruct the bore after use. These can be turned into multicycling, nonobstructive, and multitool systems. The system can also enhance multicycling ball-activated tools that are based on polymer extrusion by improving performance and delivering greater multitool compatibility and interoperability.
The system allows the mechanical extrusion to be delivered in a range of settings to suit the specific cycle application. With a variety of latching, sealing, and flow path geometries, as well as the adjustable shear mode ratings, this element of the system provides a tangible change in string design and program implementation. For example, in bypass valve implementation, users can cover multiple flow path contingencies with a single valve in hole and choose from the range of darts to establish the optimal setting for the situation encountered.
The system advances the capability of simple hydromechanical control and its power and reliability benefits into areas that previously needed more complex electronic systems. Being mechanical, it is not subject to the same high pressure and high temperature limits that affect electronics and electrical components.
Smart Darts enable a multicycle circulating sub (circ sub) tool to deliver a reliable and versatile bypass on demand. Whatever the drilling application, whether planned or a contingency, the system enables a rapid and reliable switching to the optimal flow path configuration.
The correct flow path mode is vital for a given application. There is no need to set up a Dart Activated Valve MX configuration in advance, as one tool in hole will do everything. Each bypass application has its own dart to “quick set” the valve into the right mode. Functions such as spotting lost circulation material (LCM), split-flow hole cleaning, and dry tripping can operate on a “plug and play” basis.
The closing cycle is likewise easy by using a rapidly deployed universal closing dart to allow drilling to resume quickly without loss of hydraulic performance. Multiple dart cycles can be performed in any sequence.
System Benefits
When curing losses, boosting hole cleaning, or performing other circulation applications, conventional bottomhole assembly (BHA) bypass relies on balls landing on seats. Landing seats are sized to withstand a pressure-up activation cycle and then succumb to a blowthrough shear-out sequence to regain circulation to the bit. The emergence of the mechanically extruding dart technology, as an alternative to polymer extrusion, has presented tool designers with an opportunity to push some of the performance boundaries of conventional valves.
Circulating Objectives
The goal for any tool is to maximize performance and value while being as simple, reliable, and flexible to use as possible. For drilling bypass valves, a specific analysis to assess the current conventional limits follows.
Activation Speed and Ball Displacement Algorithms: With heavy losses, fast activation is critical to stem mud loss to the formation. Overzealous activator displacement, which fails to take into account the depth, angle, and mud density parameters, creates a risk of blowthrough misfire. Conservative displacement can increase delays and may make activation pressure more difficult to detect from the surface. Therefore, polymer extrusion systems can lead to comparatively slow activation sequences, as time is taken for displacement calculations and detection of the activation point before curing can begin. In contrast, darts eliminate the calculation element and activate at high pump rates. And with a positive opening stroke clearly indicated by a pressure drop, losses can be treated more quickly.
Cycling Reliability: The properties of the extrusion determine the performance window of the cycle. Using polymer extrusion, the designer has to create interference between the ball and the seat that can withstand the landing shock and allow the ball to overcome the inertia of the piston/mandrel in the valve before it reaches its extrusion threshold. In single-cycle circ subs, this interference can be overengineered to guarantee opening. But for multicycling, the shear-out point needs to be in pump range so that circulation can be regained by extruding the ball. For valve closing by polymer extrusion to be possible, it must also remain possible for the ball to misfire by definition. By creating a dual shear point characteristic (Fig. 1), mechanical extrusion simultaneously addresses reliability and the activation speed.
Multimodal/Application Flexibility: When selecting a valve, it is prudent to perform a weighted risk assessment to identify the circulating contingencies that are most likely for a given well. For example, while hole cleaning might be a major issue, contingency for heavy losses might be prioritized on the basis of well control. The operator then selects a tool based on these priorities.
In polymer extrusion systems, tool choice is an important consideration because of the multiple configuration permutations during bypass. The introduction of an activation ball sets the polymer extrusion tool in primary bypass mode. However, this may not be the optimal setting, meaning that performance is either limited or delayed while smaller secondary setting balls are pumped to secondary seats to create application specific flow paths. By contrast, dart-based mechanical extrusion can optimize bypass for almost any application in a single step, thereby simplifying the tool selection and application.
Genuine BHA Isolation: Using polymer extrusion, contamination of the BHA during pill spotting can occur even when 100% bypass has been configured. A ball on a seat seals in just one direction. Once the pumps are switched off, U-tubing and buoyancy forces will determine whether the ball stays on its seat or floats or rolls away to allow curing fluids to make their way into the BHA. Dart latching through mechanical extrusion ensures isolation.
Simplicity of Operation and Design: Complexity downhole invariably adds risk and decreases reliability. While the permutations of polymer extrusion methods allow the skilled user to activate and configure for almost any application, the need for skill and expertise adds risk for the operator. Multisized operating balls and complicated displacement procedures for activation can increase the risk of error and nonproductive time. Furthermore, caution about trying unfamiliar or complex procedures could lead to suboptimal use and diminished return on investment in the tool.
For the mechanical extrusion system, a simple port and piston assembly housing a low-profile ceramic “socket” to catch the darts is all that is required. The darts themselves determine performance. Individually sealed, the dart is kept isolated from the downhole environment until the last minute and is used once. The dart’s robustness allows deployment and landing at speeds up to 2,000 ft/min, five times faster than polymer extrusion methods. This can save more than an hour of waiting time and provides positive opening indications to reduce uncertainty.
Case Histories
In more than 120 applications through 2012, the system has achieved a 100% reliability record. For example, a European land operator used a single dart cycle to set hole cleaning and tripping dry modes simultaneously, saving time and improving rig floor safety to a level previously unattainable.
In another instance, a North Sea operator planned for hole cleaning and jetting, but when unexpected losses occurred, it was able to switch strategies in a timely manner and select a dart that would deliver LCM into the formation and protect the BHA from contamination.
The system has been used successfully in bypass valves for more than 80 wells since January 2011, including in the Gulf of Mexico.
Handling Pressure
In December 2011, mechanical extrusion was applied to a fourth dart in a new tool for string integrity testing. The Pressure Testing Sub MX system provides a simple, accurate way to test a drillstring up to a specific preset pressure with the capability to regain circulation between each test. This allows users to perform multiple tests at various pressures in a single run. The system can be run in any length of pipe, at any angle or temperature, and with any type of circulation fluid.
The subs have fully tapered internals, provide unrestricted circulation and have a full through-bore before the first cycle. The dart is dropped and pumped into place with the load transmitted through pins in the dart into the sub. The pins determine the shear-out pressure. Pressure can be held at the required test level for as long as necessary. When testing is complete, a small increase in pressure is used to shear out the dart into the catcher below (Fig. 2). The benefits of the system are that multiple test cycles can be performed, full circulation can be regained between each test, and that the shear-out point can be accurately modified by altering the dart’s pins before it is dropped.
The system was first successfully used in Norway by a major pipe manufacturer in 2011 with shearing accuracy results of 99.6%. Subsequently, a full program of further drillstring development applications with the system has been scheduled. The system is also being used in the United Kingdom Continental Shelf for leak detection in operational drillstrings in pre-emptive integrity tests before ultracritical high-pressure phases.
Choosing the Right Tool for the Job
The Smart Dart can easily be integrated into existing tool designs by replacement of the landing seat and does not require a redesign of their ball activated systems. The dart is available in a range of sizes with easily adjustable shearing points. Whereas a typical ball system requires about 13.4% of the bore ID for use in power delivery, the MX system requires less than 1% of the bore ID for that purpose. This compactness aids tool implementation and flexibility for multitool compatibility and interoperability.
The system enables the improvement of BHA design through the reduction of ID restrictions and an increase in operational performance windows. To achieve this, ball seats within a series of conflicting tools can be replaced with dart seats that catch only the darts intended for that tool. This simplifies the process for the user, as more options are available for operating the BHA.
Smart Darts can provide an unlimited combination of geometries, latches, seals, and chokes that can be rapidly deployed to set the tool into its optimal configuration.
Conclusion
Mechanical extrusion by means of dart use is helping to make existing processes faster, simpler, and more cost-effective. This merits an evaluation of mechanical extrusion for its potential to become the conventional system for a range of downhole deployments.