GUILDFORD, UK – Cleansorb is helping an unnamed major operator enhance recovery from a maturing UK offshore field.
Achieving drilling damage removal in new water injector wells is critical to reaching target injection rates without fracturing the reservoir, Cleansorb said.
The company is applying its ORCA system for water-based mud (WBM) to open-hole injector wells with sand screens to remove drilling damage. ORCA for WBM dissolves drilling fluid filter cakes and other acid-soluble damage caused by water-based drilling fluids.
In this case, the operator is seeking to extend the life of field, which started production 20 years ago, by a further two decades or more with the existing injection and associated production wells.
To date, six injector wells have been treated with ORCA for WBM to remove carbonate/polymer DIF filter cake from the reservoir wellbore face before starting water injection.
Without this intervention, residual drilling damage would likely have prevented water injection under matrix conditions, resulting in pressure build-up and unwanted fracturing of the formation.
Cleansorb claims that each of the treated wells, upon starting water injection, have attained their target injection rates at well below formation fracture pressure, and without back flowing wells prior to injection.
Two more injector wells on the field are due to undergo similar treatment this year, and the operator is now assessing possible use of ORCA for other future field developments.
According to Cleansorb, the conventional approach is to spot acids in the wellbore to break down mud filter cake.
HCl acid-based treatments dissolve any carbonate component that may be present as drilling cuttings fines from the formation or added at surface as a weighting agent. However, it can be very difficult to achieve this uniformly across long intervals.
Also, water-based reservoir drill-in fluids typically include biopolymers such as starch, cellulose and xanthan, and often these polymeric components cannot be tackled effectively by acid alone, the company claims.
After reviewing the chemical composition of a drill-in fluid and the downhole conditions where it will be applied, the company’s technicians select an ORCA treatment fluid formulation for the application, with lab tests at reservoir temperature to confirm that they will effectively disrupt mud cakes prepared from corresponding drill-in fluid samples.