Method for determining wellbore position using seismic sources and seismic receivers

A method for determining a geodetic position of a location of a first at least partially horizontal wellbore in the Earth's subsurface, comprising:

• using a sensor located on a downhole apparatus disposed in the first at least partially horizontal wellbore to ascertain data indicative of a true vertical depth at a location along the wellbore;
• actuating a seismic energy source located on the downhole apparatus disposed in the first at least partially horizontal wellbore to emit seismic energy from the source at the selected location along the wellbore;
• detecting the seismic energy from the seismic energy source using a plurality of seismic energy sensors, the plurality of seismic energy sensors comprising a first seismic sensor disposed at a first geodetic position and a second seismic sensor disposed at a second geodetic position different from the first geodetic position, wherein the first and second seismic sensors are disposed beneath the surface of the Earth;
• and
• determining the geodetic position of the selected location of the first at least partially horizontal wellbore from the detected seismic energy and the true vertical depth by treating the geological formation as having acoustically homogeneous properties, wherein the geological formation actually has acoustically heterogeneous properties;
• wherein the first seismic sensor is disposed in a second wellbore drilled substantially vertically through a weathered layer of rock formations and the second seismic sensor is disposed in a third wellbore drilled substantially vertically through the weathered layer of rock formations, and wherein the second and third wellbores each have a lower end that is shallower with respect to the first at least partially horizontal wellbore in which the downhole apparatus is disposed, and wherein the first and second geodetic positions are disposed substantially along an expected horizontal trajectory of the first at least partially horizontal wellbore in which the downhole apparatus is disposed and substantially transversely to the expected trajectory.

A method comprising:

• identifying a first geodetic location at a first surface location;
• drilling a first wellbore substantially vertically into a geological formation from the first surface location and placing a first seismic source at a lowermost end of the first wellbore;
• identifying a second geodetic location at a second surface location;
• drilling a second wellbore substantially vertically into a geological formation from the second surface location and placing a second seismic source at a lowermost end of the second wellbore;
• drilling a third, at least partially horizontal, wellbore having an expected horizontal trajectory substantially aligned along the first and second geodetic locations;
• and
• using seismic energy emitted from the first and second seismic sources to determine a third geodetic location within the third, at least partially horizontal, wellbore where a seismic sensor is located, by determining in a plane substantially parallel to the surface of the Earth a lateral distance between the first seismic source and the second seismic source and a substantially vertical line representing a true vertical depth of the third geodetic location using a ratio of seismic energy travel time from the first seismic source to the seismic sensor and seismic energy travel time from the second seismic source to the seismic source as if the geological formation were acoustically homogeneous despite actually being acoustically heterogeneous.