Microwave-based downhole activation method for wellbore consolidation applications
Wellbore strengthening during drilling may be achieved by including chemicals in the drilling fluid that can be polymerised when exposed to microwave energy. Selected chemicals are mixed with the drilling fluid but do not react with it. The chemicals concentrate in a filter cake on the borehole wall during drilling-fluid circulation. A tool, which comprises a microwave source, is used to trigger polymerisation or crosslinking reactions within the filter cake. The polymerisation or crosslinking reactions cause the formation of a film or gel that strengthens the wellbore.
1. A method of constructing a borehole, the method comprising:
drilling the borehole using a drilling fluid comprising a chemical system capable of being polymerised;
allowing the drilling fluid to circulate and form a filter cake on at least part of the borehole wall in which the chemical system accumulates; and
during circulation, irradiating at least part of the filter cake with microwave radiation so as to cause the chemical system to polymerise or cross-link and so strengthen the filter cake.
2. The method as claimed in claim 1 , wherein the chemical system comprises methacrylate based systems, dimethyldiallylammonium chloride monomer, methylenebis acrylamide, polyethylene glycol and/or polydimethylallylammonium chloride.
3. The method as claimed in claim 1 , wherein a tool comprising a microwave radiation source is provided in the borehole for irradiation of the filter cake, the method comprising positioning the tool near to the part of the filter cake to be irradiated, and operating the microwave source to irradiate the filter cake.
4. The method as claimed in claim 3 , wherein the tool comprises at least one microwave antenna, the method comprising positioning the antenna near to the filter cake and using the antenna to irradiate the filter cake.
5. The method as claimed in claim 3 , comprising operating the microwave source to vary the level of microwave radiation used to irradiate the filter cake.
6. The method as claimed in claim 1 , comprising adjusting the level of the chemical system in the drilling fluid so as to obtain a concentration in the filter cake that can be cross-linked or polymerised by microwave radiation.
7. An apparatus for use in construction of an open borehole, comprising:
a tool body;
a source of microwave radiation located in the tool body; and
means for irradiating borehole wall with microwave radiation from the source;
wherein the means for irradiating the borehole wall comprises an antenna that can be positioned near to the borehole wall, and the source is operable to initiate polymerisation or cross-linking in a chemical system in a filter cake on the borehole wall.
8. The apparatus as claimed in claim 7 , further comprising at least one arm mounted on the tool body, the microwave antenna being mounted at the end of the arm.
9. The apparatus as claimed in claim 8 , wherein the arm is extendable.
10. The apparatus as claimed in claim 8 , comprising multiple arms spaced axially, azimuthally, or both, on the tool body.
11. The apparatus as claimed in claim 10 , wherein each arm carries an antenna that is connected to the microwave source.