A rotary drill bit may include a bit body rotatable about a central axis. The rotary drill bit may also include at least one cutting element coupled to the bit body. The at least one cutting element may have a cutting face, a cutting edge adjacent the cutting face, and a back surface opposite the cutting face. The at least one cutting element may be oriented so that a substantial portion of the cutting edge has a positive clearance angle, which may be defined by a first vector that is normal to the cutting face and a second vector that is tangential to a helical path traveled by the cutting edge during drilling.

Methods of treating a subterranean formation are described. The methods include introducing a treatment fluid that includes a friction reducing polymer (e.g., a cationic friction reducing polymer) into the subterranean formation. The cationic friction reducing polymer is allowed to degrade and release choline chloride or polyDADMAC, which can each act as a clay stabilizer.

An apparatus for continuously generating and controlling the density of foam has a fluid in-flow manifold in communication with a source of liquid and comprising a pressure sensor. A plurality of branch lines are in fluid communication with the in-flow manifold a foam out-flow manifold. Each branch line has a flow control valve, a Venturi tube and in fluid communication with a throat of each Venturi tube an air induction control valve. The foam out-flow manifold has a pressure sensor. At least one in-flow control valve is disposed between the source and the in-flow manifold and at least one out-flow control valve is in communication with the out-flow manifold. The branch valves, air valves, the in-flow control valve and the out-flow control valve are operable to provide a chosen flow rate of the liquid and a selected foam product flow rate at a selected density of the foam product.

An apparatus for continuously generating and controlling the density of foam has a fluid in-flow manifold in communication with a source of liquid and comprising a pressure sensor. A plurality of branch lines are in fluid communication with the in-flow manifold a foam out-flow manifold. Each branch line has a flow control valve, a Venturi tube and in fluid communication with a throat of each Venturi tube an air induction control valve. The foam out-flow manifold has a pressure sensor. At least one in-flow control valve is disposed between the source and the in-flow manifold and at least one out-flow control valve is in communication with the out-flow manifold. The branch valves, air valves, the in-flow control valve and the out-flow control valve are operable to provide a chosen flow rate of the liquid and a selected foam product flow rate at a selected density of the foam product.

A drilling assembly includes a drill bit connected to a gas injector sub-assembly, which is connected to the bottom of a drill rod. The top of the drill rod is connected above ground to an entry sub-assembly, which has connected atop a drill rig rotary head, which drives the connected drill rod. As drilling proceeds, further drill rods may be joined between the drill rod in the hole being drilled and the entry sub-assembly. The drilling assembly has a central cuttings conduit in fluid connection with the drill bit to evacuate cuttings upward, a gas injection passage arranged concentrically around the cuttings conduit to inject gas into the central cuttings conduit in the gas injector sub-assembly to provide lift to the cuttings therein. A drilling liquid passage is arranged concentrically around the cuttings conduit and the gas injection passage to deliver drilling liquid down to the drill bit.

A drilling assembly includes a drill bit connected to a gas injector sub-assembly, which is connected to the bottom of a drill rod. The top of the drill rod is connected above ground to an entry sub-assembly, which has connected atop a drill rig rotary head, which drives the connected drill rod. As drilling proceeds, further drill rods may be joined between the drill rod in the hole being drilled and the entry sub-assembly. The drilling assembly has a central cuttings conduit in fluid connection with the drill bit to evacuate cuttings upward, a gas injection passage arranged concentrically around the cuttings conduit to inject gas into the central cuttings conduit in the gas injector sub-assembly to provide lift to the cuttings therein. A drilling liquid passage is arranged concentrically around the cuttings conduit and the gas injection passage to deliver drilling liquid down to the drill bit.

A method for pumping a liquid-gas mixture into a subsurface well includes introducing gas into a liquid at a first pressure to generate a mixture. The mixture is pumped through a first positive displacement pump to a second pressure greater than the first pressure. The mixture at the second pressure is pumped through at least a second positive displacement pump to a third pressure greater than the second pressure. The mixture is moved into the subsurface well at at least the third pressure.

A method for pumping a liquid-gas mixture into a subsurface well includes introducing gas into a liquid at a first pressure to generate a mixture. The mixture is pumped through a first positive displacement pump to a second pressure greater than the first pressure. The mixture at the second pressure is pumped through at least a second positive displacement pump to a third pressure greater than the second pressure. The mixture is moved into the subsurface well at at least the third pressure.

A double-channel fluid injection apparatus includes a main shaft, a bearing box, and a sealing box. The main shaft includes an outer tube and an inner tube. An internal channel of the inner tube and a vertical through channel constitute a first fluid passageway. The inner tube and the outer tube form an annular gap, and a channel D is radially formed at a lower part of the outer tube and is in communication with the annular gap, thus constituting a second fluid passageway. The bearing box is mounted on a boss of the outer tube. The sealing box includes a sealing cylinder fixedly connected to a lower end of a lower end cap of the bearing box. A channel E in communication with the second fluid passageway is radially formed at a position of the sealing cylinder corresponding to the channel of the outer tube.

A double-channel fluid injection apparatus includes a main shaft, a bearing box, and a sealing box. The main shaft includes an outer tube and an inner tube. An internal channel of the inner tube and a vertical through channel constitute a first fluid passageway. The inner tube and the outer tube form an annular gap, and a channel D is radially formed at a lower part of the outer tube and is in communication with the annular gap, thus constituting a second fluid passageway. The bearing box is mounted on a boss of the outer tube. The sealing box includes a sealing cylinder fixedly connected to a lower end of a lower end cap of the bearing box. A channel E in communication with the second fluid passageway is radially formed at a position of the sealing cylinder corresponding to the channel of the outer tube.