For HPHT wells it appears that the only industry practice for open hole sand control has been Stand Alone Screens (SAS), even for wells that should have been gravel packed.

For North Sea HPHT field developments, SAS has been chosen as the open hole sand control method. However, according to company best practice, these wells should have been gravel packed. General skepticism around gravel packing for these wells is primarily based on the risk of losses.

A study was initiated to look closely at potential losses during gravel pack pumping when compared to SAS in HPHT environment.

Key issues:

  • Narrow margin between pore pressure and fracturing gradient

  • Well control risks, technical risks and cost

  • Fluid selection

The basis for the study was to perform gravel packing with conditions as close as possible to the planned low well angle SAS wells solution. The screens were to be run in screened reservoir drilling fluid. This fluid contains filtercake repair particles. It became natural to evaluate this fluid also as a carrier fluid for the gravel, thus mitigating the risk of losses.

Due to small margin between pore pressure and fracture gradient, the gravel pumping operation would have to be planned to be performed at low rates.

To qualify the HPHT gravel placement, yard testing was performed in a mini-scale gravel pack model. Gravel was placed successfully at low rates with screened reservoir drilling fluid. Very little degree of settling in horizontal surface lines was observed at low pump rates, hence no practical consequences is expected for this in high angle well sections.

Furthermore, flowback testing in lab was performed on the particle containing carrier fluid.

The major findings in this study were:

  • Gravel can be placed effectively at low rates, minimizing ECD impact in a narrow pore/frac operational window.

  • Gravel can be placed using screened formate based Reservoir Drilling Fluid (RDF) maintaining the filtercake intact and with minimum risk of losses.

  • The particle containing carrier fluid has no adverse effect on gravel pack permeability.

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