The present invention relates generally to well drilling operations and, more particularly, to well drilling operations using magnetic field measurements from an electric dipole to ascertain the relative location of a new well to an existing well.
Heavy oil may be too viscous in its natural state to be produced from a conventional well. To produce heavy oil, a variety of techniques may be employed, including, for example, Steam Assisted Gravity Drainage (SAGD), Cross Well Steam Assisted Gravity Drainage (X-SAGD), or Toe to Heel Air Injection (THAI). While SAGD wells generally involve two parallel horizontal wells, X-SAGD and THAI wells generally involve two or more wells located perpendicular to one another.
X-SAGD and THAI techniques function by employing one or more wells for steam injection or air injection, respectively, known as “injector wells.” The injector wells pump steam or air into precise locations in a heavy oil formation to heat heavy oil. One or more lower horizontal wells, known as “producer wells,” collect the heated heavy oil. For an X-SAGD well pair including an injector well and a producer well, the injector well is a horizontal well located above and oriented perpendicular to the producer well. In contrast, for a THAI well pair including an injector well and a producer well, the injector well is a vertical well located near and oriented perpendicular to the producer well.
Steam or air from an injector well in an X-SAGD or THAI well pair should be injected at a precise point in the heavy oil formation to maximize recovery. Particularly, if steam is injected too near to a point of closest approach between the injector well and the producer well, steam may be shunted out of the formation and into the producer well. Using many conventional techniques, the point of closest approach between the two wells may be difficult to locate or the location of the point of closest approach may be imprecise.
Moreover, the relative distance between the injector and producer wells of an X-SAGD or THAI well pair may affect potential recovery. The wells should be located sufficiently near to one another such that heavy oil heated at the injector well may drain into the producer well. However, if the wells are located too near to one another, steam or air from the injector well may shunt into the producer well, and if the wells are located too far from one another, the heated heavy oil may not extend to the producer well. Using conventional techniques, it may be difficult to accurately drill one well perpendicular to another well.