Flow Pattern and Pressure Fluctuation of Severe Slugging in Pipeline-riser System

During the exploitation of offshore oil and gas,it is easy to form severe slugging which can cause great harm in the riser connecting wellheads and offshore platform preprocessing system.The flow pattern and pressure fluctuation of severe slugging were studied in an experimental simulation system with inner diameter of 0.051 m.It is found that severe slugging can be divided into three severe slugging regimes：regime I at low gas and liquid flow rates with large pressure fluctuation,intermittent flow of liquid and gas in the riser,and apparent cutoff of liquid phase,regime II at high gas flow rate with non-periodic fluctuation and discontinuous liquid outflow and no gas cutoff,regime III at high liquid flow rate with degenerative pressure fluctuation in form of relatively stable bubbly or plug flow.The results indicate that severe slugging still occurs when the declination angle of pipeline is 0,and there are mainly two kinds of regimes：regime I and regime II.As the angle increases,the formation ranges of regime I and regime III increase slightly while that of regime II is not affected.With the increase of gas superficial velocity and liquid superficial velocity,the pressure fluctuation at the bottom of riser increases initially and then decreases.The maximum value of pressure fluctuation occurs at the transition boundary of regimes I and II.

Pressure leaching of bismuth sulfide concentrate containing molybdenum and tungsten in alkaline solution

The leaching results of bismuth sulfide concentrate containing molybdenum and tungsten in air-H2O2-NaOH system, pressure-O2-Na2CO3 system and pressure-O2-NaOH system were investigated. The results show that the extraction of molybdenum, tungsten and sulfur goes up with the increase of NaOH concentration, oxygen partial pressure and reaction time. The extraction of molybdenum and tungsten also rises up with temperature, but the leaching ratio of sulfur increases initially to a peak of 98% at 150℃ and then decreases with the increase of temperature. Under the optimal conditions, the extraction of molybdenum, tungsten and sulfur is more than 95.6%, 93.8% and 96.0%, respectively, and the main phases of residue are Bi2O3 and Fe2O3. Therefore, the method of pressure leaching in alkaline solution is provided as an effective separation of molybdenum, tungsten and sulfur from bismuth and a beneficial pretreatment for consequent process.

In-situ stress measurements and stress change monitoring to monitor overburden caving behaviour and hydraulic fracture pre-conditioning

A coal mine in New South Wales is longwall mining 300 m wide panels at a depth of 160–180 m directly below a 16–20 m thick conglomerate strata. As part of a strategy to use hydraulic fracturing to manage potential windblast and periodic caving hazards associated with these conglomerate strata,the in-situ stresses in the conglomerate were measured using ANZI strain cells and the overcoring method of stress relief. Changes in stress associated with abutment loading and placement of hydraulic fractures were also measured using ANZI strain cells installed from the surface and from underground. Overcore stress measurements have indicated that the vertical stress is the lowest principal stress so that hydraulic fractures placed ahead of mining form horizontally and so provide effective pre-conditioning to promote caving of the conglomerate strata. Monitoring of stress changes in the overburden strata during longwall retreat was undertaken at two different locations at the mine. The monitoring indicated stress changes were evident 150 m ahead of the longwall face and abutment loading reached a maximum increase of about7.5 MPa. The stresses ahead of mining change gradually with distance to the approaching longwall and in a direction consistent with the horizontal in-situ stresses. There was no evidence in the stress change monitoring results to indicate significant cyclical forward abutment loading ahead of the face. The forward abutment load determined from the stress change monitoring is consistent with the weight of overburden strata overhanging the goaf indicated by subsidence monitoring.