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In China, sandstone geothermal reservoirs are large in scale and widely distributed, but their exploitation is hindered by low recharge efficiency. In this paper, an unblocking and permeability enhancement technology using a rotary water jet for low recharge efficiency wells in sandstone geothermal reservoirs is proposed to solve this problem. This paper presents a series of studies about the proposed technology, including experiments, simulation and field application. Firstly, an experiment was carried out to verify the scale removal effect of a high-pressure water jet on the inner wall of the screen tube and its impact on sandstone. Secondly, the numerical models of the rotary jet flow field in the wellbore were established by ANSYS Fluent to study the influence of parameters. Finally, based on the simulation and experiment results, a rotary jet tool applicable to unblocking and descaling low-efficiency wells was designed, and a field application for low-efficiency wells in sandstone thermal reservoirs was conducted. The study results show that the unblocking and permeability enhancement technology using a rotary water jet is effective in removing the blockages and improving the permeability near the well. In conclusion, the presented technology can solve the problem of low efficiency during the reinjection of cooled thermal waters back into sandstone geothermal reservoirs and has great effectiveness in field application. [ABSTRACT FROM AUTHOR]

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This paper proposes a novel method of screen pipe completion and jet flow washing of horizontal well double tubular strings to enhance coalbed methane (CBM) recovery. The specially designed double tubular strings structure achieved the critical functions, including maintaining wellbore stability and providing an efficient channel for CBM transport by the outer string screen pipe system, and the continuous well flushing operation by the inner string jet flow washing system to remove coal fine blockage, reduce reservoir damage from drilling and fracturing fluids and improve the permeability. The field application achieved the average daily gas production was increased from less than 1000 m3/d to 11,500 m3/d in coal seam No. 15 of Panhe block in the southeast of Qinshui Basin in China, which is a breakthrough for enhancing the CBM recovery of coal seam No. 15 as typical TDCs reservoir with the permeability ranged from 0.08 mD to 0.15 mD that is far below 1.0 mD as the critical value for CBM commercial development. In summary, it can be suggested as an adaptive approach for enhancing the CBM recovery and is significant for releasing the gas productivity of tremendous CBM resources of the strong deformation TDCs. • Proposed screen pipe completion and jet flow washing of horizontal well double tubular strings. • The principle, special apparatus and detailed technological procedures were presented. • The field applications of this technique achieved a good coalbed methane production. [ABSTRACT FROM AUTHOR]

This study uses eddy kinetic energy analysis and a targeting method to investigate how an extratropical transition (ET) event induced downstream development (the modification of the midlatitude flow downstream of the ET system) in the midlatitude jet environment. The downstream development showed distinct characteristics of 'coupling development' and being 'boundary-trapped'. Eddies (potential disturbances) first developed at the upper levels, and these triggered lower-level eddy development, with all eddies decaying away from the tropopause and the surface. Thereafter, a lower-level eddy caught up with the upper-level eddy ahead of it, and they coupled to form a cyclone extending through the whole troposphere. Vertical ageostrophic geopotential flux may be a crucial dynamic factor throughout the eddy's lower-level growth, boundary-trapping, and coupling development. Together with barotropic conversion, the ageostrophic geopotential fluxes that were transported from Hurricane Fabian (2003) to the midlatitudes by the outflow led to downstream ridge development in the upper-level jet. The strong downstream advection of eddy kinetic energy in the exit region of the jet streak triggered downstream trough development. The well-known ridge-trough couplet thus formed. The vertical ageostrophic fluxes that were transported downward from the developed upper-level systems converged near the surface and resulted in lower-level eddy growth. Baroclinic conversion was negligible near the boundaries, while it was the main source of eddy kinetic energy at mid-levels. In the upper-level jet, potential energy was converted to the mean kinetic energy of the jet, which in turn was converted to eddy kinetic energy through barotropic conversion. [ABSTRACT FROM AUTHOR]

Upwellings are observed on the northern shelf of Taiwan during northeasterly winds. Analytical and realistic numerical models are used to explain how vertical motions are created by divergence and convergence produced by wind acting on the vorticity field of two strong jets: the Kuroshio and the Taiwan Warm Current. The seaward increase in cyclonic vorticity near the Kuroshio’s western edge favors a stronger Ekman transport away from the jet, producing upwelling at the shelfbreak under a northeasterly wind. A similar mechanism for generating vertical motions is found across the Taiwan Warm Current. The numerical model results indicate that the vorticity effects can account for up to 30%–50% of the total variation in the surface Ekman transport. Except during summer’s weak southwesterlies, northeasterly wind is dominant over the East China Sea, suggesting that the vorticity effects may be prominent in the observed shelfbreak upwelling in nonsummer months. [ABSTRACT FROM AUTHOR]