| dc.description.abstract | One of the main roles of drilling fluid is controlling the downhole pressure. Weighting materials are employed in drilling fluid for this aim. Barite is the most common agent, which is used for increasing density. There are some factors, such as gravitational force, damage, or degradation of polymers which cause a sluggish phenomenon called barite sag. During the barite sagging, suspended particles start to settle and separate from the liquid phase, and the fluid column gets denser at the bottom and less on top.
Barite can settle out from drilling fluid during tripping in and tripping out when circulation is stopped. Meanwhile, dynamic barite sag can occur during circulation. Particle settlement can be measured by two different methods, including direct and indirect measurements. In the direct method, measurement is based on sag and fluid density weight, while the indirect evaluates the particle settling by transit time.
Direct measurement is one of the methods, which has not been investigated experimentally while there are indirect methods using ultra-sonic employed to measure the barite settlement. In this work, barite particle settlement was inquired by direct measurement and then correlated with indirect results. In a basic system, direct measurement has been done by sedimentation rate criteria. Mechanical properties analyser was used to record the time taken to transfer the compressional wave from transducer to receiver through the vessel, which is filled by fluid sample. Several tests calibrated the systems regarding reference samples that had different xanthan gum content with constant barite. Then, the severity of barite sag was investigated by water-based and oil-based fluid after hot rolling in a modified system. Based on the measurements and results, empirical correlations for reference sample and real sample have been proposed to analyse the fluid behavior.
Results from the tests clearly demonstrated that the sedimentation rate increased dramatically in the first phase of sagging and then continued gradually. In the first test running, a large number of suspended particles started to settle in the MPro vessel. Compressional waves stroked the particles and made vibrations. This vibration took a long time to travel the wave from the transducer to the receiver. During the settlement, the waves were transferred in shorter transit time due to the less suspended particles, and then transit time decreased. | |
