Bottom-hole pressure fluctuation and seepage pattern during well drilling in Che-66 Block

Drilling operations in the Che-66 Block are susceptible to blocking, formation collapsing, lost circulation, blowout and other complexities. Based on fluid dynamics in annulus and with consideration to formation permeability features, magnitudes of swabbing pressure and surge pressure produced during tripping and drilling operations were analyzed, together with effects of drilling fluid viscosities, densities, well depths and ROPs. In accordance with linear seepage theory, models for unidirectional fluid spherical centripetal flow and plane radial flow were deployed to determine seepage patterns and lost circulation of drilling fluids during penetration of reservoir formations under negative pressure. Research results show that higher bottom-hole differential pressure and formation permeability may lead to higher speed in seepage of formation fluids and higher volume of drilling fluids lost. The conclusions highlighted fluctuation in bottom-hole pressure during drilling, together with seepage pattern and relevant influencing factors. The research results can provide necessary foundation for optimization of borehole structural design.