Analysis of Drilling Fluid Circulating Pressure Loss in Hole Annulus forMicrohole Drilling

摘要

The microhole drilling (MHD) technology is one of cutting-edge drilling technologies with wellbore diameterless than 88.9 mm and taking coiled tubing (CT) as drilling string to deliver the bottomhole assembly to drill ahead. Thenormal circulation of drilling fluid is affected because of huge annulus drilling fluid circulating pressure loss (ADFCPL)caused by small diameter wellbore, narrow hole annulus and deep well. For three flow regimes of power-law fluid inMHD, the computing models of ADFCPL are built by analyzing the relationships among annulus drilling fluid parametersaccording to power law fluid flow state equation. The ADFCPL with different flow rate, CT diameter, well depth, eccentricityand so on is calculated for the hole annulus of MHD. The calculation results show that: in 89mm diameter MHD,the ADFCPL is huge. It increases with the increase of outer diameter of CT and average flow rate of drilling fluid, and increaseslinearly with the increase of well depth, and decreases with the increase of eccentricity. The bigger the hole annulusis, and the lower the flow rate is, the less the impact of eccentricity acts on the ADFCPL is. Thus, the ADFCPL can bereduced by decreasing the outer diameter of CT and the average flow rate of drilling fluid in hole annulus. Only low flowrate can be used to drill deep well. The research results may be useful for MHD parameter selections related to theADFCPL.