Study on Damage Characteristics and Formation Protective Drilling Fluids in Dongying Formation Low Permeability Reservoir of Chengbei Oilfield

On account of the poor protection of the Dongying formation low permeability reservoir of Chengbei oilfield, this paper researched the damage characteristics of Dongying formation low permeability reservoir, by reservoir sensitivity test, water locking damage test, TC model clogging test, and so on. Studies showed that the factors causing damage included water block, water sensitivity, and solid particles invasion. A kind of high quality pollution-free sea-drilling fluid was developed to deal with the potential damage, which had a better performance and protected the reservoir well

Dynamic analysis of the longitudinal vibration on bottom drilling tools

With extreme complexity, the drilling process is a dynamic process which is severely influenced by longitudinal vibration. Longitudinal vibration, as one of the most important reason, is directly generated by the fatigue failure of the bottom hole assembly. In this paper, the natural frequencies of longitudinal vibration along the drillstring are analyzed by the finite element method. The deformed plot, stress nephogram, and displacement contour map under 1 to 4 ordered the natural frequency of the longitudinal vibration are obtained. The analysis results show that the maximum deformation always appears in the central part of the string so that some technological process on these positions is required to reduce the collision between the string and wellbore wall. Additionally, a time series of longitudinal vibration of a bottom rotating drillstring is extracted from real-time field data, which is measured while drilling near the drill bit. Then the time-frequency and energy spectrum analysis of the longitudinal vibration is carried out. The results of the statistical analysis show that, when the drillstring uniformly rotates, the longitudinal vibration can be considered as a kind of random vibration. However, if the stick-slip phenomenon occurs during the drilling process, the energy concentration will appear in the time series spectrum of the longitudinal vibration, by which means the vibration could be regarded as random no longer

Effect of annulus drilling fluid on lateral vibration of drillstring

Annular drilling fluid between the drillstring and borehole wall has a great influence on lateral vibration of drillstring and the influence involves the added mass. Assuming the drilling fluid is incompressible, we derive the added mass coefficient that annular drilling fluid influences on lateral vibration of drillstring in the case of axial flow of drilling fluid. When the axial flow of drilling fluid is considered, the added mass coefficient is difficult to solve. We apply CFD method and dynamic mesh technique to establish the calculation model for the flow in the annulus caused by the vibration of drillstring in the annulus. The pressure distribution and velocity distribution of annular drilling fluid are obtained. The added mass force of the drilling fluid acting on the drillstring along the direction of the drillstring is obtained from the pressure distribution, and the added mass coefficient of the lateral vibration of the drillstring is obtained. This paper provides the basis to solve the added mass coefficient of the lateral vibration of drillstring considering axial flow of drilling fluid

A real-time borehole correction of electromagnetic wave resistivity logging while drilling

The response of electromagnetic wave logging while drilling is influenced greatly by borehole and drilling fluid resistivity when the size of borehole is relatively large and drilling fluid resistivity is low. Borehole radius and drilling fluid resistivity were introduced to obtain more accurate transformed resistivity on the basis of the commonly used resistivity transformation model. The influence of borehole was considered in the newly established three dimensional transformation model, and a new borehole correction method was proposed. The resistivity transformation database can be established by calculation according to a certain instrument, and the true resistivity is obtained by three dimensional interpolation search technology of real-time correction in practical use. The results of numerical simulation and modeling verification show that the transformed resistivity by real-time correction coincides with the resistivity corrected by charts. The method can eliminate the borehole influence, reduce calculation dimension, and improve the inversion efficiency of highly deviated and horizontal wells logging data. Key words: electromagnetic wave logging while drilling, resistivity, borehole influence correction, resistivity transformation mode