Some embodiments of the inventive subject matter improve techniques for measuring downhole attributes. A method for determining a flow rate of a fluid includes positioning a tubular within a wellbore formed in a subsurface formation, wherein a flow of fluid is to move through the tubular. An orifice plate is positioned in the tubular. The orifice plate is movable between a first position and a second position to alter a flow area of the flow of fluid moving through the tubular. The method includes detecting a change in a downhole attribute that changes in response to the alteration of the flow area of the flow of fluid. Sensors positioned within or in communication with an interior of the tubular can detect the change in the downhole attribute. The method further includes determining a flow rate of the flow of fluid based on the detected change in the downhole attribute.

Some embodiments of the inventive subject matter improve techniques for measuring downhole attributes. A method for determining a flow rate of a fluid includes positioning a tubular within a wellbore formed in a subsurface formation, wherein a flow of fluid is to move through the tubular. An orifice plate is positioned in the tubular. The orifice plate is movable between a first position and a second position to alter a flow area of the flow of fluid moving through the tubular. The method includes detecting a change in a downhole attribute that changes in response to the alteration of the flow area of the flow of fluid. Sensors positioned within or in communication with an interior of the tubular can detect the change in the downhole attribute. The method further includes determining a flow rate of the flow of fluid based on the detected change in the downhole attribute.

An embodiment of a fluid control device includes a housing, a fluid channel defined within the housing, the fluid channel having a first surface and a second surface opposing the first surface and having an inlet, and a flow control body disposed in the fluid channel, the flow control body tapering toward the inlet. The body, in use, causing fluid flowing through the channel to diverge into at least a first path between the first surface and a first side of the body, and a second path defined by at least by the second side of the body. A geometry of the first path and the second path selected is based on a subcool of the fluid at a pressure of the fluid entering the fluid channel, and the geometry is selected to induce cavitation of the fluid to choke fluid flow through the fluid channel.

An embodiment of a fluid control device includes a housing, a fluid channel defined within the housing, the fluid channel having a first surface and a second surface opposing the first surface and having an inlet, and a flow control body disposed in the fluid channel, the flow control body tapering toward the inlet. The body, in use, causing fluid flowing through the channel to diverge into at least a first path between the first surface and a first side of the body, and a second path defined by at least by the second side of the body. A geometry of the first path and the second path selected is based on a subcool of the fluid at a pressure of the fluid entering the fluid channel, and the geometry is selected to induce cavitation of the fluid to choke fluid flow through the fluid channel.

A very light weight, noncompressible drilling fluid including a very light weight hydrocarbon base liquid, and a styrenic butadiene diblock copolymer is heated to achieve excellent rheology including thixotropicity, making an effective drilling fluid with a density of 8 pounds per gallon or less. Densities as low as 4 pounds per gallon are achieved with the addition of glass bubbles. The glass bubbles may, but normally will not, exceed 50% by volume. A method of making the drilling fluid includes passing the light weight liquid and the copolymer through a cavitation device. The invention includes drilling and with and recirculating the fluid to maintain the desired density, viscosity and rheology by adjusting the ingredients accordingly. A method of managed pressure drilling employs the novel fluid, enabling control of drill pressure and physical properties of the fluid including equivalent circulating density.

A very light weight, noncompressible drilling fluid including a very light weight hydrocarbon base liquid, and a styrenic butadiene diblock copolymer is heated to achieve excellent rheology including thixotropicity, making an effective drilling fluid with a density of 8 pounds per gallon or less. Densities as low as 4 pounds per gallon are achieved with the addition of glass bubbles. The glass bubbles may, but normally will not, exceed 50% by volume. A method of making the drilling fluid includes passing the light weight liquid and the copolymer through a cavitation device. The invention includes drilling and with and recirculating the fluid to maintain the desired density, viscosity and rheology by adjusting the ingredients accordingly. A method of managed pressure drilling employs the novel fluid, enabling control of drill pressure and physical properties of the fluid including equivalent circulating density.

Various embodiments provide methods and systems for providing fluid lighteners for use in downhole wells. The fluid lighteners may include one or more viscosifiers, one or more aphron generators, and a location-specific non-emulsifying surfactant.

Various embodiments provide methods and systems for providing fluid lighteners for use in downhole wells. The fluid lighteners may include one or more viscosifiers, one or more aphron generators, and a location-specific non-emulsifying surfactant.

A method for predicting a pressure window for drilling a borehole in a formation includes: obtaining a pore pressure related data value of the formation using a data acquisition tool; predicting pore pressure uncertainty from the pore pressure related data value of the formation using a processor; estimating uncertainty of a pressure window for drilling fluid using the predicted pore pressure uncertainty using a processor; and applying the estimated uncertainty to the pressure window to provide a modified pressure window using a processor.

A method for predicting a pressure window for drilling a borehole in a formation includes: obtaining a pore pressure related data value of the formation using a data acquisition tool; predicting pore pressure uncertainty from the pore pressure related data value of the formation using a processor; estimating uncertainty of a pressure window for drilling fluid using the predicted pore pressure uncertainty using a processor; and applying the estimated uncertainty to the pressure window to provide a modified pressure window using a processor.