Design and Application of Removable Plugging Slurry for Fractured Carbonate Reservoir
To meet the requirements of leakage stopping and reservoir protection at the same time in fractured formation, the removable plugging slurries with high temperature tolerance were designed, evaluated and applied in the field successfully. Analysis shows that the fibre materials can deposit onto crack surface, bridge and seal fractures quickly and the selected particles can bridge in throat near wellbore. The comprehensive grading of filling particles was determined from the point of view of gradient filling. The designed plugging slurries KJD155 and KJD200 with higher total dissolution rates sealed 1 mm, 2 mm, 3 mm, and 4 mm crack blocks effectively at room temperature and high temperature (KJD155 at 155 °C; KJD200 at 200 °C) respectively. Their pressure bearing ability of them was up to 5 MPa under bottom hole conditions, which was beneficial to the next operation. Field application of the designed plugging slurries was carried out successfully and showed that they were removable and did smaller damage to reservoir.
Characteristics of high temperature cementitious lost-circulation control materials for geotherman wells
Materials systems have been formulated for thein situ conversion of water-based bentonite drilling fluids into cementitious lost-circulation control materials (CLCM) for use in geothermal wells at temperatures up to 300° C. The formulations consist of a cement hardener, a borax admixture, and a fibre glass bridging material which are added to the bentonite fluids. Evaluations of the properties of the slurry and the cured CLCMs revealed that the ions supplied by dissociation of the borax in the CLCM slurry awed to suppress the bentonite hydra tion and retarded the hardening ran of the cement et elevated temperatures. The CaO-SiO2-H2O (C-S-H) phases formed during curing of the CLCM play essential roles in improving the quality of the hardened CLCMS. It was observed that xonotlite-truscottite transformations resulted in strength reductions and increased water permeability. The plugging ability of fibre glass depends on the concentration and fibre size. The silicate ions dissolved by hot alkaline disintegration of the fibreglass were chemisorbed with Ca2+ ions from the cement and led to the precipitation of C-S-H compounds on the fibre surfaces, which improved bond strength at the matrix-fibre interfaces.
Magnetic properties of Lu2Fe17 crystals
Abstract We present the results of crystal structure and magnetization studies of three single crystals grown from melts of different nominal compositions in the vicinity of the Lu2Fe17 stoichiometry. The ferromagnetic state of the crystals is strongly dependent on the real sample composition and the local atomic ordering. A drastic difference is observed in the behaviour of the ferro–antiferromagnetic transition, even in crystals for which almost identical composition and crystal parameters were determined by microprobe and X-ray analysis.