Method and system for drilling underbalanced radial wells utilizing a dual string technique in a live well

A method of drilling multiple radial wells in the well using underbalanced drilling, comprising the following steps:

• a) drilling a principal wellbore;
• b) providing a first carrier string having a deflection member on its lowermost end to a certain depth within the principal wellbore;
• c) lowering a second drill string of coiled tubing, down the bore of the carrier string, so that the drill bit on the end of the second string is deflected by the deflection member in a direction from the principal wellbore;
• d) pumping a second fluid into an annular space between the coiled tubing and the carrier string to a position that it co-mingles with the first fluid;
• e) returning the co-mingled fluids and any hydrocarbons upward to the rig through the annular space between the borehole and the carrier string;
• f) providing a volume of liquid within the carrier string;
• g) retrieving the drill bit at the end of the coil tubing from the bore hole;
• h) reorienting the direction of the deflection member to a second depth within the borehole;
• and
• i) lowering the coil tubing and drill bit to the second depth to drill a second radial well, while the well is maintained alive.

A method of drilling radial wells using underbalanced drilling, comprising the following steps:

• a) drilling a principal wellbore;
• b) providing a first carrier string having a deflection member on its lowermost end to a certain depth within the principal wellbore;
• c) lowering a second drill string of coiled tubing, down the bore of the carrier string, so that the drill bit on the end of the second string is deflected by the deflection member in a direction from the principal wellbore;
• d) pumping a first fluid down the coil tubing to rotate the drill bit downhole;
• e) pumping a second fluid into an annular space between the coiled tubing and the carrier string to a position that it co-mingles with the first fluid downhole creating an underbalanced state;
• f) returning a third fluid, comprising the first and second fluids and any hydrocarbons upward to the rig through the annular space between the borehole and the carrier string;
• g) providing a volume of liquid within the carrier string;
• h) retrieving the drill bit at the end of the coil tubing from the bore hole;
• i) reorienting the direction of the deflection member to a second depth within the borehole;
• and
• j) lowering the coil tubing and drill bit to the second depth to drill a second radial well, which the well is maintained alive.

In a method of drilling radial wells from a principal wellbore;

• where there is provided a first carrier string having a deflection member on its lowermost end to a certain depth within the principal wellbore;
• where there is lowered a second drill string of coiled tubing, down the bore of the carrier string, so that the drill bit on the end of the second string is deflected by the deflection member in a direction from the principal wellbore;
• where there is pumped a first fluid down the coil tubing to rotate the drill bit downhole, and a second fluid into an annular space between the coiled tubing and the carrier string to a position that it co-mingles with the first fluid downhole;
• and where there is returned a third fluid, comprising the first and second fluids and any hydrocarbons upward to the rig through the annular space between the borehole and the carrier string;
• the improvement comprising the following steps:
• a) providing a volume of liquid within the carrier string;
• b) retrieving the drill bit at the end of the coil tubing from the bore hole while the volume of fluid within the carrier string maintains the well in equilibrium;
• c) reorienting the direction of the deflection member to a second depth within the borehole;
• and
• d) lowering the coil tubing and drill bit to the second depth to drill a second radial well, without killing the well.