Experimental Determination of the Variation of Torsional Resistance of Mudcakes with the Variation of Mud and Mudcake Composition

摘要

Torque and drag problems are major operational problems inrndeviated, horizontal and extended reach wells. Hence,rnmanagement of torque and drag resistance of mudcakes as lowrnas possible is an important design consideration for a superiorrnmud design for horizontal and extended reach wells.rnSeveral mudcakes of variable compositions were testedrnusing a newly developed test facility. The results indicate thatrnthe torsional resistance of mudcakes is strongly influenced byrnthe physics and chemistry of the mud additives. Fresh waterbasedrnbentonite mudcake gave the lowest torsional resistancernand starch containing salt water based NaCl-bentoniternmudcake gave the highest torsional resistance. The presence ofrnsalts, especially salts containing divalent and larger hydratedrnionic diameter cations dramatically increases the torsionalrnresistance of bentonite mudcake. The drilling engineeringrnimplication of this observation is that salt contamination ofrnbentonite mud may turn the mudcake more shear resistant andrnthus expected to create higher torque and drag problems. Thernpresence of barite in a fresh water based bentonite mud alsornincreases the shear resistance of the mudcake. Hence,rnmudcake deposited by a weighted bentonite mud is expectedrnto cause increased torque and drag problems. Therncontamination of bentonite mud by cations of smaller hydratedrnionic diameter (KCl salt) causes a smaller increase in torsionalrnresistance compared to the presence of cations of largerrnhydrated ionic diameter (NaCl and CaCl_2 salts). The presencernof anionic CMC (carboxy-methyl cellulose) in NaCl-based saltrnwater mud caused negligible changes in the torsionalrnresistance of the mudcake. However, the presence ofrnpolyanionic cellulose (PAC) in the mud caused a significantrnreduction in the torsional resistance of salt water-basedrnmudcake. The drilling engineering significant of thisrnobservation is that the fluid loss additives like PAC is morernsuitable for deviated, horizontal and extended reach drilling tornminimise the torque and drag problems.