Well-control fluids were used during a routine overbalanced workover operation in an offshore well completed in high-permeability sandstone. A fluid-loss-control pill was used to control excessive losses; however, because of the high permeability of the reservoir and the absence of sized particles in the pumped pill, a large amount of fluid was lost to the formation. A comprehensive review, accompanied by laboratory work, was conducted to identify the damaging mechanism and formulate a remedial treatment.
Polymer-based fluids are beneficial in terms of generating viscosity to clean out the wellbore during any well intervention. Improper polymer selection has led to significant formation damage in several situations. Polymers also can invade the high-permeability zones, hampering hydrocarbon flow through the zones. Bipolymers generally are removed through acidizing, which breaks down the polymer backbone. The damage caused by polymers can be minimized with proper polymer selection.
Standard remedial treatments for removing the near-wellbore polymer include injecting solvents (e.g., xylene), acids, alcohols, glycols, surfactants, or a mixture of these liquids into the well.
In sandstone well treatments, formation composition should be considered carefully, especially minerals susceptible to acid attack. Three potential damaging mechanisms can occur during sandstone acidizing: formation deconsolidation in acid; reprecipitating during primary, secondary, and tertiary reactions; or the release of fines because of partial decomposition of minerals in acid.
In the case of damage with oil-based material or emulsions, microemulsion treatments have been recommended. The microemulsion will solubilize the oil and emulsions and fluidize the filter cake into a single mesophase while dissolving the acid-soluble particles and making the solids and formation rock water-wet. The oil-based-mud particles in a filter cake will disperse, allowing the produced fluid to displace these blocking particles from the damaged zone into the wellbore and through any screens.
Formation-Damage Diagnosis Facilitates Successful Remediation in Sandstone
05 January 2016