Drilling into presalt formations has been a long-standing issue due to the rapid changes in the diameter of the borehole during drilling operations either because of creep or wash-out dissolution.
The quantities used can be quite large especially with multi-frac stimulations and/or use of slickwater fluids: for example, a total of about 12,000 m3 of water, 588 t of proppants, and 20 t of additives (of which 460 kg were biocides) were injected into the "Damme 3" borehole in three frac operations in 2008.
Flow mixing takes place depending on the abstraction regime, local hydrogeology, and borehole construction design and operation.
First, the almost constant temperature along the borehole heat exchanger in operation requires a boundary condition of essentially isothermal boreholes along the depth.
Theoretical and experimental studies, performed in Switzerland over several years, have established a solid scientific base of reliable long-term operation of borehole heat exchanger-coupled heat pump systems.
Drilling operations in a borehole can lead to problems when the friction between the drilling equipments and the host rock are not well identified.
"The work is very rewarding especially when you get involved in environmental protection and healthcare projects for the local community, such as building a village school, raising money to send children away for operations and digging boreholes.
And second, it is necessary to explore new types of horizontal wells so as to deal with borehole collapse and continue the operation in the later stage by using tree-like roof horizontal wells, single-lateral horizontal wells with casing or screen completion and fish-bone horizontal wells.
However, for lack of dynamic mathematical model analysis methods for reflecting the changes of annulus liquid level in the borehole during the "Hang's Mudding-off" operation, the actual operation is basically conducted blindly without reasonable engineering basis.
Boreholes were modelled in a soil volume using finite-element methods and heating and cooling fluxes were applied to the borehole walls to simulate the GSHP operation.
