Innovative Use of Wireline Tools Enables Successful Re-Entry on Subsea Wells

Re-entry of subsea wells can always hide unforeseen difficulties. Contingency mobilization of coiled tubing (CT) usually gives a wide spread of solutions to overcome most of the possible events. However, when operating on a winterized semisubmersible rig in the remote fields of the Barents Sea, rig-up of CT spread can be costly and complicated. Furthermore, lighter and easily deployable wireline powered mechanical tools have proven to be effective in tackling most of the possible challenges. Possible tubing obstruction issues can be resolved via clean-out/suction, pumping, or milling methods. In this instance, all three were used with different tools to clear the obstruction from the tubing and to clean with precision inside an internal fishing profile of a well head barrier plug to allow for well access. The first challenge encountered when re-entering the tubing in Well-1 was the presence of a 151m long hydrate plug. It was easily removed by an e-line tool capable of applying 10 bar of dynamic underbalance, while maintaining a continuous flow circulation. Such an application is a novel development in the use of existing tools. After removing the hydrate plug, it was discovered that the tubing was plugged by 246m of wax deposits, which were preventing communication with the reservoir. To overcome this problem, a jetting tool was utilized to continuously pump fresh wax solvent inside the landing string. Pumping continuously fresh wax dissolvent provided a unique and effective means to mechanically and chemically remove a significant obstruction. Once the communication with the reservoir was re-established, an additional obstruction of almost 129m (resistant to the wax dissolvent) was encountered. To overcome this challenge an e-line milling tool was utilized, and the resulting debris was bullheaded down into the reservoir. Similarly, when re-entering Well-2 a challenge was encountered to pull a barrier plug due to debris deposits inside the internal fishing profile. Both e-line milling and suction tools were sequentially used to resolve the problem and prepare the plug for retrieval. The tools used were already available on the market for different applications. In this case the tools were used in an alternative way, using their features to solve issues beyond conventional expectations. The result fosters confidence to plan future re-entry without the need for mobilizing a CT spread.

African lakes Nios and Mone — indicators of unique carbon element-deep respiration of the Earth

As a result of the analysis of space, geological and tectonic information, it was established that the true causes of natural ecolymnological disasters in Cameroon in 1984 and 1986 were modern fault-block tectonic movements, which are closely associated with seismic and geodynamics in one of the sections of the “living” Adamawa Mountains. The main cause of catastrophes must be considered the activation of endogenous processes occurring in the mantle and the tectonosphere of the Earth. Cosmo- and rotogenesis of the planet Earth, in the near-surface parts of the Earth’s crust of the Adamava mountain segment, led to intensive mountain-building and heat exchange processes, the causes and mechanism of which are closely associated with the rise of abnormally hot magmatic material and gas-liquid fluids containing CO2 from the mantle. Favorable transport routes for heat and mass transfer in the Earth’s lithosphere are volcanic channels, as well as the orthogonal and diagonal network of deep faults. At the same time, volcanic channels should be considered as unique drain pipes of our planet. The lethal carbon dioxide ejected from the depths of Lakes Nyos and Monun is mainly a differentiate of igneous melts, and the latter, in turn, have mantle “roots” extending to a depth of 200–300 km. The volcano-crater lakes Nios and Monun are confined to the nodes of the intersection of “living” deep faults, revealing the deep horizons of the planet, where in magmatic foci CO2 is predominant as products of differentiation. The author proposed a mechanism for the formation of a solid gas hydrate shell, a relatively tightly sealed volcanic crater. This giant gas hydrate plug prevented the gradual-passive circulation, i. e. outflow of CO2 into the hydrosphere and atmosphere coming from deep and intermediate magmatic foci. So, under the gas hydrate shell of the lakes Nios and Monun, a large amount of CO2 accumulated. Explosive emissions of significant amounts of lethal gas could appear only with the geodynamic activation of the earth’s crust, where these unique volcano-crater lakes are located. Seismotectonic processes contributed to the destruction of the gas hydrate shell and the breakthrough of CO2 through fractures, cracks and through the water membrane to the surface. Emissions of gases on the volcano-crater lakes Nyos and Monun are the brightest example (indicator) of the Earth’s carbon dioxide-deep degassing.

Hydrate Remediation Philosophy for a New Flowline Intervention System Based on Active Heating

The Electrically Trace Heated Blanket (ETH-Blanket) is a new offshore intervention system currently in development by TechnipFMC for the efficient remediation of plugs due to hydrates or wax deposit in subsea production and injection flowlines. The ETH-Blanket consists of a network of heating cables placed underneath an insulation layer which is laid onto the seabed above the plugged flowline. By applying electrical power to the cables, heat is generated by Joule effect which warms up the flowline content until hydrate dissociation or wax plug remediation through softening or complete melting. The ETH-Blanket is currently developed within a Joint Industry project (JIP) between TechnipFMC and Total. The dissociation of hydrate plugs using active heating incurs a number of risks for the integrity of the flowline and for the restoration of production to nominal conditions. As the flowline content is warmed up from ambient to hydrate dissociation temperature and during the dissociation of the hydrate plug, the pressure inside the flowline may potentially increase above design limits due to hydrate degassing and fluid volume expansion. Also, plug run-away scenarios may occur if a large pressure difference exists between both sides of the plug. The remediation operation may fail because of insufficient power or misplacement of the ETH-Blanket. Lastly, even following successful operation of the ETH Blanket, new flowline blockage may occur during subsequent operations such as cold re-start. To mitigate those risks, a hydrate remediation philosophy has been developed specifically for the ETH-Blanket Service. It is based on the development of in-house tools and procedures and builds upon experimental and modelling work performed as part of a previous JIP focusing on the dissociation of hydrate plugs using an ETH-Pipe-in-Pipe [1]. This paper introduces the different elements of the hydrate remediation philosophy, including the development and experimental validation of the dedicated tools used to define the appropriate heating sequence for the safe and efficient dissociation of hydrate plugs.

Analytical and Experimental Analysis of Static Friction Forces of Moving Cables Inside Curved Pipes

In-pipe robots are a powerful tool for hydrate plug removal inside ultradeepwater pipes. Most of these robots operate with the energy supplied by umbilical cables. The present work focuses on the development of a general strategy for computing the required forces for pulling such cables confined in ducts of generic length and geometry. Based on classical mathematical models applied in cable friction evaluation, a new equation set was developed and implemented in a computational algorithm designed to evaluate the static friction force related to the cumulative effects along the arbitrary set of curves present in a generic pipe. Therefore, the proposed computational routine can calculate the static friction forces associated with a cable inside a given pipe, whose coordinates are fed by the user. To evaluate the simulation performance, the achieved results were compared with the data obtained through experimental tests performed using a cable with polymeric coating positioned inside ducts. Different geometries, loads, and lubricating conditions were tested, and the analytical model could suitably estimate the required force to move an umbilical cable inside pipes.

To the theory of determining the location of hydrate deposits in gas pipelines by acoustic sounding

Evolution of pressure perturbations propagating in pipeline filled with gas-and-drop medium representing “wet” methane at temperature below dew point and having damaged section, in form of extended narrowing of channel due to hydrate plug, is investigated. Hydrate formation is due to the presence of water (or its vapours) and gas, the components of which dissolve in water under certain conditions form a solid phase. Hydrate deposits help to reduce the cross-country capacity of gas pipelines and therefore their detection is a pressing task. It is proposed to solve the problem using acoustic methods. For this purpose mathematical model of propagation of acoustic waves in long-wave range in gas-and-droplet medium is considered. The horizontal pipeline appears semi-pointed, the solution is sought in the form of a harmonic wave. Wave is one-dimensional, having small amplitude of oscillations. Based on dispersion equations, dependence of phase velocity and attenuation coefficient on frequency of acoustic wave disturbance and on volume content of suspended phase (water droplets) are built. In the high frequency region, the attenuation coefficient increases with the volume content. The formulas for reflection and passage coefficients are derived taking into account pipeline narrowing due to hydrate deposits. The results of numerical calculations illustrating the dynamics of pulse signals depending on the thickness of the gas hydrate on the inner wall of the pipeline are presented. Calculations are based on forward and backward Fourier transformations and the use of software. It is established that the greater the hydrate deposit on the wall in thickness, the greater the amplitude of the returned reflected signal.

Investigation into THF hydrate slurry flow behaviour and inhibition by an anti-agglomerant

In a newly built-up loop, pilot-scale experiments were carried out to study typical hydrate plug phenomena and to explore the specific reasons behind these.