Abstract: A method of isolating annular areas formed by multiple well casings can include providing fluid communication through a wall of one of the casings at a location where another one of the casings outwardly surrounds the first casing, then flowing a cement into an annulus formed radially between the first and second casings, then providing fluid communication through the wall of the first casing and a wall of the second casing, and then flowing another cement into another annulus external to the second casing. A method of abandoning a well can include perforating a casing at a location where another casing outwardly surrounds the first casing, flowing a cement into an annulus formed radially between the first and second casings, the cement including a tracer, perforating the first and second casings, and flowing another cement into another annulus external to the second casing, the second cement including a second tracer.

Abstract: A method for determining the downhole flow regime in a horizontal well borehole traversing a subterranean formation. A first gas holdup value within the borehole is measured using a fluid density tool. A second gas holdup value within the borehole is measured using a fullbore gas-holdup tool. The downhole flow regime is then determined as a function of the first gas holdup value and the second gas holdup value. A downhole flow regime comprised of dispersed bubble flow is indicated where the first gas holdup value is approximately equal to the second gas holdup value. A downhole flow regime comprised of annular flow is indicated where the first gas holdup value is substantially greater than the second gas holdup value and the velocity of the gas phase is substantially greater than the liquid phase. A downhole flow regime comprised of stratified flow is indicated where the first gas holdup value is less than or greater than the second gas holdup value.