Anyone familiar with drill site operations is aware that many active mud systems tend to increase in surface volume. The excess must be disposed of by some means after being hauled away, or jetted out, etc. Examine Figure 1 with the following:
Steam Assisted Gravity Drainage = SAGD “Steam-assisted gravity drainage (SAGD; “Sag-D”) is an enhanced oil recovery technology for producing heavy crude oil and bitumen. It is an advanced form of steam stimulation in which a pair of horizontal wells is drilled into the oil reservoir, one a few metres above the other. -wikipedia
The drilling fluid circulating system is like a close loop electric circuit through which drilling fluid (i.e. mud) can travel from surface to all the way down hole and back to its initial point (i.e. mud pit).
According to the requirements of scientific drilling, drilling fluid system should have performances of low viscosity, low gel, low solid content, low filter loss, and with good lubrication property.