Two pass window milling system that can be deployed and operated in one trip

A milling apparatus configured for use in a wellbore formed in one or more subsurface formations, the milling apparatus comprising:

• a whipstock including an interior guide track, wherein the interior guide track is distinct from a taper face of the whipstock;
• a first tubular configured to pass through an outer milling body positioned in the wellbore;
• a milling head and guide assembly coupled to a downhole end of the first tubular, wherein the milling head and guide assembly comprises a guide configured to slot into the interior guide track of the whipstock;
• and
• a retaining section positioned at a downhole end of the interior guide track and configured to receive the milling head and guide assembly.

A method comprising:

• performing, using a milling assembly, a milling operation to mill a first window into a target tubular via a single trip into a wellbore formed in one or more subsurface formations, wherein performing the milling operation includes,
• decoupling, in the wellbore, a first tubular from a whipstock via one or more releasable retaining devices, wherein an uphole end of the first tubular is coupled to a drill string, and wherein a downhole end of the first tubular is coupled to a milling head and guide assembly,
• positioning the first tubular such that a guide of the milling head and guide assembly is positioned within an interior guide track of the whipstock, wherein the interior guide track is distinct from a taper face of the whipstock,
• moving the first tubular and the milling head and guide assembly along an exterior of the whipstock, wherein the moving of the first tubular is guided by the guide in the interior guide track, and
• applying rotation to the first tubular via the drill string, wherein one or more cutters of the milling head and guide assembly are used to mill the first window into the target tubular.