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.

Systems and methods for measuring the viscosity of a fluid may comprise a rotor cup having an inner chamber; a first bob rotatably disposed within a first region of the inner chamber; and a second bob rotatably disposed within a second region of the inner chamber, wherein the second bob rotates relative to the first bob based on a difference in viscosity of fluid in the first region and the second region.

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 system for use in the drilling of oil or gas wells in conjunction with a mud injection device, said mud injection device adapted to maintain fluid pressure control within the borehole of a well bore when operating a drillstring therethrough, the system comprising: a gas reservoir containing gas; adapted for injection to control borehole pressure; compression system fluidly connected to the gas reservoir and the borehole; a pressure regulation system operatively connected to the gas reservoir and the borehole and adapted to measure the pressure within the annulus and relay such to a computer; wherein, when a drilling operation is halted to add a new stand to the drillstring and the mud injection device is stopped, the gas is injected to maintain the borehole pressure within the annulus of the borehole at a near constant value.

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.

An effective amount of at least one anionic surfactant may be present within a high salinity foamed fluid composition in an effective amount to generate an IFT as low as 10.sup.−3 mN/m. The anionic surfactant may be a sulfonate surfactant and/or a sulfate surfactant. The foamed fluid composition may be used to perform an operation, including but not limited to, a gas lift operation, a drilling operation, a completion operation, a stimulation operation, a fracturing operation, an injection operation, an enhanced oil recovery operation, and combinations thereof.

An effective amount of at least one anionic surfactant may be present within a high salinity foamed fluid composition in an effective amount to generate an IFT as low as 10.sup.−3 mN/m. The anionic surfactant may be a sulfonate surfactant and/or a sulfate surfactant. The foamed fluid composition may be used to perform an operation, including but not limited to, a gas lift operation, a drilling operation, a completion operation, a stimulation operation, a fracturing operation, an injection operation, an enhanced oil recovery operation, and combinations thereof.

Methods and systems for automatically performing a sweep operation in a borehole penetrating an earth formation including conveying a drillstring through a borehole, the drillstring having one or more sensors located thereon, determining that a sweep operation should be performed based on information obtained from the one or more sensors, determining characteristics of a pill to be used for a sweep operation based on information obtained from the one or more sensors, preparing a pill in accordance with the determined characteristics, deploying the pill into the drillstring and conveying the pill through the drillstring, and monitoring the sweep operation while the pill is within the drillstring and verifying the sweep operation. At least one of the determination that a sweep operation should be performed, the determination of the pill characteristics, or the preparation of the pill is performed automatically.

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.