Rune W. Time

Mechanistic model for upward two-phase flow in annuli

A mechanistic model is formulated to predict the mixture behavior for upward two-phase flow in concentric annulus. The model is composed of a procedure for flow pattern prediction and a set of independent mechanistic models for calculating gas fraction and pressure drop in bubble, dispersed hubble, slug and annular flow. Small-scale experimental data from the literature validate the predictions of the model. A full-scale experimental investigation is also executed to complete the evaluation. The experiments are performed in a 1278 m vertical well in the Petrobras research facility in Taquipe, Brazil, with an 88.9 mm x 159.4 mm (3.5 in, x 6.276 in.) annulus. Test matrix covered the whole range of possible combinations of liquid and gas injection rates for an underbalanced drilling operation in a similar geometry. The overall model performance is in good agreement with the experimental data.

Automatic Prediction of Downhole Pressure Surges in Tripping Operations

A simplified dynamic model of the tripping operation is used together with an ensemble Kalman filter to predict transient pressure surges when running the drillstring in or out of the hole. Dynamic downhole pressure measurements from a tripping operation with mud circulation are used as input to the Kalman filter. Such data can be achieved by mud pulse telemetry at the field just before the tripping operation starts. The model is automatically adapted to the particular situation (well, bit-depths, drilling mud, etc.). This is important since exact values of some downhole parameters, like viscosity of the drilling mud, might be unknown and/or changing with time. We show by comparison with filed measurements, that the automatically updated model is capable of reproducing the transient pressure surges in consecutive runs of the string without mud circulation.

Utilizing Instrumented Stand Pipe for Monitoring Drilling Fluid Dynamics for Improving Automated Drilling Operations

Abstract This paper introduces a method to enable automatic updates of the density, compressibility and frictional effects of the drilling fluid during a drilling operation. By placing pressure sensors along the circulation path from the mud pump to the connection to the drillstring, the fluid dynamics can be examined more thoroughly at various flow rates and pressures. This will help filling the gap of reliable data on drilling fluid properties, which is of great importance in automated drilling operations.

Numerical Characterisation Of Slug Flow In Horizontal Air/water Pipe Flow

In this work, the slug flow regime in an air-water horizontal pipe flow has been simulated using the CFD technique. The variables identified to characterise the slug regime are the slug length and slug initiation. Additionally, the pressure drop and the pressure distribution within the simulated pipe segment have been predicted. The volume of fluid method was employed assuming unsteady, immiscible airwater flow, constant fluid properties and coaxial flow. The model was developed in the STAR-CCM+ environment, and the grid was designed in the three dimensional domain using directed mesh. A grid independency study was carried out through the monitoring of the water velocity at the outlet section. 104,000 hexahedral cells for the entire geometry were decided on as the best combination of computing time and accuracy. The simulated pipe segment was 8 m long and had a 0.074 m internal diameter. Three cases of air-water volume fractions have been investigated, where the water flow rate was pre-set at 0.0028 m3/s, and the air flow rate was varied at three dissimilar values of 0.0105, 0.0120 and 0.015 m3/s. These flow rates were converted to superficial velocities and used as boundary conditions at the inlet of the pipe. The simulation was validated by bench marking with a Baker chart, and it had successfully predicted the slug parameters. The computational fluid dynamics simulation results revealed that the slug length and pressure were increasing as the air superficial velocity increased. The slug initiation position was observed to end up being shifted to a closer position to the inlet. It was believed that the strength of the slug was high at the initiation stage and reduced as the slug progressed to the end of the pipe. The pressure gradient of the flow was realised to increase as the gas flow rate was increasing, which in turn was a result of the higher mean velocity.