Optimizing formulations for reservoir drilling fluids

Abstract

When drilling a well, equivalent circulation density exceeding the fracture gradient can cause lost circulation. In a reservoir section, invasion of drilling fluids can potentially cause a permanent permeability reduction in the near wellbore area, which can be detrimental to well productivity. Low-permeable filter cakes that reduce fluid loss and are easily removed during drawdown are desirable to prevent damaging the formation.

The main focus of the thesis is to find formulations for low-permeable formation drilling fluids that prevents loss to the formation and simultaneously prevent formation damage. Fluid properties for fractured scenarios in a reservoir zone are also investigated.

Eleven samples of conventional drilling fluids and five samples of Lost Circulation Material (LCM) pills for severe losses were prepared with varying concentrations and additives. Calcium carbonate (CaCO3) and fibers were added as LCM, while modified and crosslinked potato starch were used as filtration control polymers. HTHP fluid loss tests of conventional drilling fluids were performed on porous discs and filter paper, while pressure tests of LCM pills were performed on tapered discs.

The results show how addition of fibers in conventional drilling fluids with CaCO3 as LCM may improve sealing capabilities and maintain low formation damage when containing effective filtration control polymers. For LCM pills, addition of CaCO3 may regulate the thickness of the filter cake and the ability to remove it.

When drilling a well, equivalent circulation density exceeding the fracture gradient can cause lost circulation. In a reservoir section, invasion of drilling fluids can potentially cause a permanent permeability reduction in the near wellbore area, which can be detrimental to well productivity. Low-permeable filter cakes that reduce fluid loss and are easily removed during drawdown are desirable to prevent damaging the formation.

The main focus of the thesis is to find formulations for low-permeable formation drilling fluids that prevents loss to the formation and simultaneously prevent formation damage. Fluid properties for fractured scenarios in a reservoir zone are also investigated.

Eleven samples of conventional drilling fluids and five samples of Lost Circulation Material (LCM) pills for severe losses were prepared with varying concentrations and additives. Calcium carbonate (CaCO3) and fibers were added as LCM, while modified and crosslinked potato starch were used as filtration control polymers. HTHP fluid loss tests of conventional drilling fluids were performed on porous discs and filter paper, while pressure tests of LCM pills were performed on tapered discs.

The results show how addition of fibers in conventional drilling fluids with CaCO3 as LCM may improve sealing capabilities and maintain low formation damage when containing effective filtration control polymers. For LCM pills, addition of CaCO3 may regulate the thickness of the filter cake and the ability to remove it.