Well had been drilled to T.D. but encountered a fracture in the casing along a natural fault line. Operator cemented hole and cut window to sidetrack back to target zone. An invert emulsion mud was used initially out the window until extreme problem conditions were encountered. The well was intermittently experiencing lost circulation (into fault zone) and heavy salt water flows. The decision was made to displace the oil mud with a specially designed lignosulfonate mud system. The particular conditions that the lignosulfonate mud was designed to overcome were (1) sensitive shales, (2) low pressure sands, (3) interlying high pressure stringers, (4) natural fault zone, and (5) potential salt water flows. The lignosulfonate mud system was treated with 4 lbs./bbl. of Super-Slide Glass Beads, 4 lbs./bbl. of Blen-Fyber, and 6% #2 diesel oil. These materials were used in this system to prevent excessive seepage loss and differential sticking in the low pressure zones. Oil wet filter cakes were designed to minimize borehole problems such as increased torque and drag or shale instability. The problems encountered were to a depth of 14,799 feet. Original mud weight (invert emulsions) was 16.8 lbs./gal. lignosulfonate system the problems were overcome and the mud weight was later raised to 17.0 lbs./gal. By use of the specialty materials in this system, the 4 1/8" wellbore was healed and drilled to a T.D. of 15,232 ft., where a 3 ½" liner was set. The operator was pleased by the ability of this program to overcome serious problems and allow this well to be completed in spite of adverse conditions. |