Thin bed responses and correction methods for cased hole density logging

The study of the thin bed responses and correction methods in cased hole density logging can provide a theoretical basis for research to improve data processing methods. By using the Monte Carlo program MCNP, the change of detector count from thin beds with the vertical depth was calculated at different casing thicknesses. The calculation showed that with the low density thin bed moving upward, detector count first increased to a maximum then decreased. The responses of a thin bed with a high density were opposite to those of a thin bed with a low density. The change curve was symmetrical, and the maximums or minimums appeared at the midpoint between the detector and source. Besides, detector count increased with increasing thin bed thickness. At a specific thin bed thickness, further increase of thin bed thickness resulted in a slow increase of detector count then the count rate leveled off. In actual logging, the influence of adjacent formations on density log measurements can be ignored. Finally, based on numerical simulation correction methods for the dual influence of casing and thin beds are discussed.

Ultrasonic tomography and its applications in oilfield

UTT （Ultrasonic Tomography Tool） is widely used in the oil industry and can be used to inspect corrosion, casing wall damage, casing breakoff, and casing distortion in the well borehole with the maximum environment temperature being 125 ℃, and the pressure being 60 MPa. UTT consists of tool head, upper centralization, electronic section, lower centralization, transmitters, and receivers. Its outer diameter is 4.6 cm and length is 320 cm. The measured casing diameter ranges from 60 mm to 254 mm. The tomography resolution is 512×512. The borehole measurement accuracy is 2 mm. It can supply 3D pipe tomography, including horizontal and vertical profile. This paper introduces its specification, measurement principle, and applications in oilfield.

Performance of a centrifugal compressor with holed casing treatment in the large flowrate condition

As demonstrated by former work,the holed casing treatment can be used to expand the stall margin of a centrifugal compressor with unshrouded impeller.In addition,the choked margin can also be expanded as experimental results indicated.Moreover,the compressor performance,especially the efficiency,on the whole working range is improved.As shown by experiments,the stall margin and choked margin of the compressor are extended,and the maximum efficiency improvement is 14%at the large flowrate of 1.386.Numerical simulations were carried out to analyze the flow in the impeller and in the holes in the case of large flowrate.The results indicate that in large flowrate conditions,there is a low-pressure region on the throat part of the impeller passage,leading to the bypass flows appearing in the holes,which means the flow area at the inlet of the impeller is increased.The bypass flow can also contribute to the decrease of the Mach number at the throat part near the shroud end-wall which implies that the choked margin is expanded.Besides,as the bypass flow would inhibit the development of the vertexes in the tip clearance and suppress the flow recirculation in the shroud end-wall region,both the pressure ratio and efficiency of the compressor are improved,which agrees well with the experiments.