Combined thermochemical and chelating agents useful for well cleanup
View Patent ↗A well cleanup process involves removing an impermeable filter cake from a formation face with thermochemical and chelating agents to allow formation fluids to flow from a reservoir to a wellbore. The method may be used with oil and water-based drilling fluids with varied weighting agents, e.g., bentonite, calcium carbonate, or barite. Such thermochemical agents may involve two salts, e.g., NO 2 − and NH 4 + , which, when mixed together, can generate pressure and heat, in addition to hot H 2 O and/or N 2 . For example, the thermochemical agents may comprise Na + , K + , Li + , Cs + , Mg 2+ , Ca 2+ , and/or Ba 2+ with NO 2 − and NH 4 + with F − , Cl − , Br − , I − , CO 3 2− , NO 3 − , ClO 4 − , and/or − OH. The thermochemical agents in combination with a chelator such as EDTA can removed the filter cake after 6 hours with a removal efficiency of 89 wt % for the barite filter cake in water based drilling fluid, exploiting the generation of a pressure pulse and heat which may disturb the filter cake and/or enhance barite dissolution and polymer degradation.
1. A method of removing a filter cake mass from a wellbore wall in a subterranean formation, the method comprising:
introducing into a wellbore an aqueous composition and contacting the aqueous composition with a wellbore face coated with the filter cake mass; and
allowing the aqueous composition to reach a temperature in the wellbore sufficient to initiate an exothermic chemical reaction of at least two components present in the aqueous composition and sufficient to raise a temperature, cause a pressure surge, or both raise a temperature and cause a pressure surge at the wellbore face to disrupt the filter cake mass from the wellbore face,
wherein the aqueous composition comprises, at a pH of no less than 10:
a first combination comprising a hydrated sulfate salt and a polyacrylamide, wherein the hydrated sulfate salt is an alkaline metal sulfate salt or an alkaline earth metal sulfate with saturated hydration; and
at least 20 wt. % ethylenediamine tetraacetic acid, based on total aqueous composition weight.
2. The method of claim 1 , wherein the hydrated sulfate salt comprises at least one selected from the group consisting of Na + and Mg 2+ .
3. The method of claim 1 , wherein the hydrated sulfate salt comprises at least 95 wt. % Na 2 SO 4 .10H 2 O, relative to total sulfate salt weight.
4. The method of claim 1 , wherein the hydrated sulfate salt comprises at least 95 wt. % MgSO 4 .7H 2 O, relative to total sulfate salt weight.
5. The method of claim 1 , wherein the aqueous composition comprises the ethylenediamine tetraacetic acid in a range of from 22.5 to 30 wt. % of the total aqueous composition weight.
6. The method of claim 1 , wherein the temperature in the wellbore is in a range of from 50 to 150° C., prior to the introducing.
7. The method of claim 1 , wherein the aqueous composition comprises at least 65 wt. % of barite.
8. The method of claim 1 , which achieves the removal of at least 85 wt. % of the filter cake mass within 6 hours.
9. The method of claim 1 , wherein at least 95% of the removal of the filter cake mass achievable by the method is within 6 hours after the introducing starts.
10. The method of claim 1 , wherein the ethylenediamine tetraacetic acid has a potassium counterion.