The most common problem during the sand control operation is fluid loss. It is an inherent problem encountered worldwide, due to the high permeability of sandstone reservoirs which allows easy fluid flow into the formation matrix. Many wells which are candidates for sand control produce from marginal reservoirs and have insufficient bottomhole pressures to support a column of fluid in the wellbore. Still other wells with high pressure zones require high density completion fluids in order to balance the reservoir pressure during the gravel pack operation. In either case the positive pressure leads to fluid being lost to the pressure leads to fluid being lost to the reservoir. The result presents several potential problems: (1) formation damage potential problems:
formation damage caused by swelling of clay minerals within the formation,
formation damage due to particle invasion into the formation
particle invasion into the formation
formation damage due to dissolution of matrix cementation promoting migration of fines within the formation
flow channel blockage by precipitates caused by ionic interactions between well servicing fluids and formation fluids
interactions between well servicing fluids and formation fluids causing emulsion blocks, water block,, or changes in wettability of a producing sand and
flow channel producing sand and
flow channel blockage due to viscous fluids creating a barrier in the near wellbore region.
The need for mechanical fluid loss control systems in these situations is, therefore, obvious.
During many sand control operations the standard procedure is to acidize the formation prior to gravel packing, thus increasing the near wellbore permeability. Then it is recommended that the acid treatment be followed immediately with the gravel pack treatment until a sandout occurs. After gravel packing, the wellbore is frequently in a lost circulation condition. This requires either keeping the hole full, resulting in large volumes of fluid lost to the formation, or unknowingly spotting an inappropriate fluid loss pill. Both options can result in formation damage and excessive costs.