Well drilling and servicing fluids with magnesia bridging solids and methods of drilling, completing and working over a well therewith

Abstract From the Canadian patent

The invention provides well drilling and servicing fluids and methods of , drilling, completing, or working over a well therewith preferred fluids , comprise an aqueous liquid a water soluble polymer viscosifier (preferably xanthan gum), a polymeric fluid loss control additive (preferably a partially depolymerized partially crosslinked hydroxyalkyl ether derivative of starch or a hydroxyalkyl ether derivative of a partially crosslinked and partially depolymerized starch), and as a bridging agent a particulate magnesia that has an Activity Index greater than about 800 seconds preferably from about 800 , seconds to about 3000 seconds.