Whilst drilling the 5 7/8” section, the bit became completely plugged and circulation was not possible. Reverse circulation was attempted but this did not clear the blockage.
With the bit at 15,602ft MD and at a 55 degrees inclination, the decision was made to open the 5” OD NC38 Coretrax DAV MX circulation sub. Due to the bit being plugged, the Coretrax EOB (Emergency Opening Ball) was dropped into the 4” 14# XT39 work string and allowed to gravitate to seat inside the DAV MX, whilst at the same time the string was rotated and reciprocated.
After 55 mins, the ball had reached the DAV MX ball seat and the string was pressured up to open the annular ports of the tool. At 3,000 psi, the DAV functioned to the open position allowing conventional return circulation to surface. Note: The DAV will normally function at 2,000psi but due to the lower BHA being blocked, a further 1,000psi was required to compress the fluid below.
With the DAV now fully open, one and a half bottoms ups were pumped and then the open hole was displaced from 97PCF OBM to 103PCF OBM for the trip out of the hole which would not have been possible without having the DAV MX in the string.
The onsite Drilling Superintendent stated that he was very happy how efficiently the DAV had functioned.
Summary
The DAV MX allowed open hole circulation that in turn allowed the BHA to be lubricated thus possibly avoiding a stuck pipe incident and also allowed the well to be displaced to a heavier mud which was needed for the trip out of the hole, as the well was being drilled slightly under balanced.
