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The micro-sonde well logging system is a concept for obtaining along-well measurements of temperature, changes in fluid velocity and pressure while drilling. The micro-sondes are encapsulated, self-contained measurement devices designed to follow the flow from the bottom hole assembly to surface. Once retrieved at surface, the measurements can provide information about well conditions such as the presence of cuttings beds, washed out zones and gain/loss zones. Post-processing of the data requires knowledge of the forces acting on the micro-sonde and the resulting trajectories from the release point at the bottom hole assembly and to surface. The main objectives of the studies presented in this work are to understand the micro-sonde motion in the mud flow and to design and construct a demonstration device. We have performed a literature study, CFD-modelling and experiments to better understand the behavior of a micro-sonde in a typical annular flow domain. The trajectory of a single micro-sonde has been investigated as it passes tool-joints under the influence of inner string rotation. Further, the experiments investigated the likelihood of transporting the micro-sonde intact to surface for a drilling application. For the experimental studies, two annular flow loops, one vertical without rotation of the drill-string and one horizontal with a rotating drill-string, including tool-joints and a model bottom hole assembly have been constructed and utilized.

A traction tool has been built and tested as a part of the development of a long reach well concept. The application of the traction tool to assist the running of liners and sand screens in challenging wellbores is studied and the results and conclusions are described.Full-scale testing of the traction unit prototype has demonstrated that it can deliver large axial forces to the string. A prototype tool for assisting during the completion phase of challenging wellbores is described, including the tool's measured performance from testing in casing.The industry partners supporting the development work identified an opportunity to utilize the device to assist the completion operation to ensure that the target depth is reached.Different scenarios where a traction device can provide a benefit include: Buckling of the running string in extended reach wellsInsufficient available string weight in shallow reservoirsAvoid rotating sand screens to reduce axial frictionThe benefit of utilizing this tool is demonstrated by simulating the completion operation. Comparative well case studies are performed to study the completion operation, with and without the traction system included. A torque and drag model is used to estimate the mechanical forces present during the running of the completion string and these are compared to the buckling and load limits. Input parameters such as wellbore geometry, friction factors and completion string specifics are taken from relevant well examples. The operational performance for different positions of the tool in the running/completion string is also investigated.

Current Extended Reach Drilling (ERD) well technology limits the well lengths to roughly 12 km with a horizontal departure of approximately 10 km. This paper presents a concept that enables simultaneous drilling and completion with an aim to substantially extend well reach and with an ultimate objective of constructing 30 km long production wells. Longer reach wells can be used to drain remote reserves using existing production facilities, as well as provide a means to access reservoirs located beneath environmentally sensitive areas. The key technology elements that enable the concept to construct long reach wells are multiple sliding packer traction units in combination with a dual casing drilling system, comprised of a casing with an inner tubing. The sliding packer traction units provide two primary functions; continuous well control along the length of the borehole and traction to overcome axial friction. In addition, the traction packers provide a stable bottom-hole drilling platform avoiding the occurrence of drilling instabilities such as stick-slip, which can damage conventional bottom-hole assemblies and the drill bit in particular. The dual casing provides the conduit for drilling fluid circulation to the bit and cuttings transport to surface. The drilling fluid is pumped through the annulus formed between the casing and inner tubing. The drill cuttings are transported to surface through the inner tubing, ensuring efficient cuttings transport with a low-pressure loss. The concept has been developed through a five-year project, kicked off in 2010. A prototype has been built and tests have shown that each sliding packer traction unit is able to push the drill bit or pull a completion string with a large axial force in excess of the estimated requirement. In the paper, elements of the system are described in detail and the results of the full-scale yard tests are presented. The concept represents a new well construction method incorporating advanced completion technology. It enables drilling and completion of long reach wells and can operate in areas with complex pressure regimes, such as can occur from pressure depletion due to production or pressurizing as a result of the injection of water or gas. Well control is provided by packers placed in pairs that seal off the annulus at predefined intervals along the drill string. Production takes place through a large inner diameter. It is a well construction method with no flat time.

Accidental electrostatic sparks in industrial plant producing/handling powders/dusts occur whenever a non-earthed electrically conducting object has been charged tribo-electrically to a high voltage and suddenly discharges its energy to earth via an air gap of appropriate length. When assessing the electrostatic spark ignition hazard in an industrial plant, the parameters of prime concern are the capacitances C of electrically conducting plant items that may become charged tribo-electrically, the voltages U to which they may become charged, and the minimum electric spark ignition energies (MIE) of the dust clouds of concern. Whenever 1 2 C U 2 > MIE , there is a possibility of accidental electrostatic spark ignition. Current standard apparatuses for determining MIE of dust clouds have a lower spark energy limit of 2–3 mJ. In an investigation by the present authors, discussed in detail elsewhere, a new spark generator capable of producing synchronized capacitive sparks of energies down to the order of 0.01 mJ was developed and used for testing a selection of ignition-sensitive powders for MIE. Several of the MIEs found were 1–2 orders of magnitude lower than the lower energy limit of current standard test apparatus. Other experiments by the present authors, also reported elsewhere, have shown that quite low MIEs can be found for some dusts even with a less optimal synchronization mechanism, which may occur accidentally in practice. The main object of the present paper is to discuss possible practical concerns arising from the finding that clouds in air of some dusts can have very low MIEs. In such cases, one may have to pay attention to even minor C values, i.e. minor plant items. Alternatively, with larger C values, even quite low voltages may give rise to hazardous spark discharges. However, some types of fine metal powders of low MIEs will quite readily form electrically conductive layers on the solid surfaces with which they make contact. Hence, electrostatic spark ignition inside process equipment containing such dusts may be less probable than in the case of process equipment containing non-conducting dusts of correspondingly low MIEs. There may be a need for a new standard test method for determination of MIEs of dust clouds in the

The lower energy limit of current standard test apparatus for determining the minimum ignition energy (MIE) of dust clouds is in the range of 1–3 mJ. This is a quite severe limitation because many dusts ignite readily at this energy level. A new spark generator, capable of producing synchronised sparks of very low energies and with an integrated system for measurement of spark energy, has therefore been developed and employed to a number of easily ignitable dusts. Before testing the MIE of dust clouds, it was considered essential to calibrate the new spark generator against a gas of known MIE. For this purpose, a mixture of propane and air was selected. However, a comprehensive literature review revealed that the reported MIEs of this gas mixture vary significantly, depending on the spark discharge characteristics, including discharge duration. When taking these factors into account, it was concluded that the new spark generator yielded reasonable results for propane/air. Applying the new spark generator to explosive dust clouds showed that a number of dusts do in fact have MIEs that are one to two orders of magnitude lower than 1 mJ. The new spark generator may therefore offer a basis for developing a standard test apparatus in the low-energy region. When using a method of triggering the spark by the explosive dust cloud itself, which probably is a more industrially relevant process than synchronisation between the dust dispersion and sparkover, somewhat higher MIEs were found compared to those determined when using synchronised sparks. However, even with this method of spark triggering, MIEs below 1 mJ were found.

Conventional tests for investigating the minimum ignition energy (MIE) of dust clouds are restricted to energies above a few mJ, due to the challenges of producing sparks of very low energies that can be synchronised with a transient dust cloud. In this paper, a new circuit for generating capacitive sparks of significantly lower energies than 1 mJ is presented. A measurement system for capturing voltage and current waveforms has been integrated in the circuit, offering the energy delivered to the spark by integration of the power-versus-time curve. When working with such low energy discharges, which are highly transient phenomena, attention must be paid to the measurement technique and methods of noise reduction in the measurement instruments. The measured spark energies range from 0.03 to 7 mJ, and they were found to constitute between 60 and 90 per cent of the energy stored on the discharge capacitors prior to breakdown. Losses to the measurement resistors are increasingly significant at higher energies and larger electrode gaps, due to the relatively large currents, and correspondingly small spark resistances. A simple circuit simulation, in which the spark conductivity is assumed proportional to the spark energy, offers voltage and current waveforms in good agreement with the measured ones, indicating that the spark is mainly resistive. In addition, the discharge channel's ability to carry current depends strongly on the supplied energy. The proportionality factor is found to depend on the breakdown voltage.

An investigation of ignition of dust clouds by the use of electric spark discharges triggered by the explosive dust cloud itself has been conducted. This method of triggering capacitive sparks probably represents a realistic mechanism for initiating accidental dust explosions in industrial practice. Unlike the conventional method for determining the minimum ignition energy (MIE) in the laboratory, the delay between dust dispersion and spark discharge is not a degree of freedom. In stead, the transient dust cloud itself is used to initiate spark breakdown between electrodes set at a high voltage lower than breakdown in pure air. In the present study, different kinds of dusts were tested as ‘spark triggers’, and they exhibited quite different abilities to trigger breakdown. Large particles were found to initiate breakdown at lower voltages than smaller ones. In general, conductive particles were not found to initiate breakdown at lower voltages than dielectric ones when using the same dust concentration. Minimum ignition energies (MIE) of three dusts (Lycopodium clavatum, sulphur and maize starch) were determined using the authors' method of study. The MIEs were somewhat higher than those obtained using conventional methods, but relatively close to the values obtained through conventional methods.