GULF OF MEXICO
CHALLENGE:
While drilling a slim hole in the deepwater Gulf of Mexico with a synthetic-based drilling fluid, an operator encountered lost circulation and formation ballooning. The formation being drilled had a formation integrity test (FIT) of 17.54 lb/gal (2.1 g/cm3) equivalent mud weight (EMW). While increasing the mud weight according to the weight-up schedule, lost circulation occurred under dynamic conditions. Knowing the high pore pressure expected at deeper depths, the operator decided to run a contingency liner, which reduced the hole size from 8 ½” to 6 ½”, leading to higher equivalent circulating density (ECD). The operator drilled ahead with synthetic-based fluid, and encountered ballooning with fluid losses occurring in proportion to pump rates and then returning when pumps are turned off.
SOLUTION:
The operator decided to use an hole opener to reduce ECD and water-based fluid to address the ballooning challenge. Newpark recommended the DeepDrill® high-performance water-based drilling fluid (HPWBDF). As a water-based solution, the DeepDrill HPWBDF presents an advantage over non-aqueous fluids in that its brine base-fluid has minimal compressibility in comparison to non-aqueous fluids. If a drilling fluid compresses under pressure, the volume of barite increases in comparison to the volume of drilling fluid, thereby increasing the mud weight of the fluid. That can be enough to fracture the formation and induce ballooning.
RESULTS:
The DeepDrill system overcame formation issues from ballooning and lost returns while providing the operator with performance characteristics that are usually associated with synthetic-based fluids. The aqueous base fluid of the DeepDrill system allowed maintenance of true downhole densities. The low compressibility factor of water allowed the operator to reduce excess stress on the formation that is not possible when using conventional oil- or synthetic-based fluids.
