There are described downhole devices, methods and other apparatus, which may be used to generate energy, monitor fluids and/or provide control signals or otherwise trigger for actuation. The devices, methods, etc. may provide improved autonomy and/or accuracy, while at the same time minimise any effect on the operation of a well. Such devices and methods may be particularly useful downhole and in remote locations. An example of a device comprises a generating material having a fluid contact surface, that contact surface being configured to be in contact with a fluid downhole. The generating material may be configured to generate an electric charge at the material in response a fluid at the contact surface. In some examples, the device further comprises a signal source configured to provide a signal in response to a generated electric charge at the generating material.

A temperature-controllable microfluidic device includes: a microfluidic channel generally extending in a first direction for passing a specimen fluid; a microheater disposed along the microfluidic channel, the microheater being made of a resistive wire having a pair of serpentine-shaped portions generally extending in the first direction along respective sides of the microfluidic channel; and a temperature sensor disposed along the microfluidic channel, the temperature sensor being made of a resistive wire having a pair of serpentine-shaped portions generally extending in the first direction along the respective sides of the microfluidic channel.

The present disclosure relates to a system and program for predicting shearing by fluid pressure, the system and program capable of predicting shearing information such as the minimum pressure P.sub.cm required for hydraulic shearing, the sufficient pressure P.sub.co for hydraulic shearing, and the optimal shearing direction using input information including the vertical stress .sub.v, the maximum horizontal stress and the minimum horizontal stress of a rock to which fluid is to be injected, a joint friction angle , a reservoir rock density .sub.r, an injected fluid density, and a coefficient of the sufficient pressure for hydraulic shearing .

The invention provides a method which predicts a ratio of the increase in frictional resistance of a rough surface in a simple manner, quickly and without variations in predicted results among individuals. The method for predicting the frictional resistance of a rough surface having a variation in roughness wavelength, and being in contact with a fluid flowing at varied velocities includes evaluating the total projected area of all prominent peaks standing out above the viscous sublayer thickness per unit area, and calculating the friction increase ratio FIR (%) or the frictional resistance increase .

There are described downhole devices, methods and other apparatus, which may be used to generate energy, monitor fluids and/or provide control signals or otherwise trigger for actuation. The devices, methods, etc. may provide improved autonomy and/or accuracy, while at the same time minimise any effect on the operation of a well. Such devices and methods may be particularly useful downhole and in remote locations. An example of a device comprises a generating material having a fluid contact surface, that contact surface being configured to be in contact with a fluid downhole. The generating material may be configured to generate an electric charge at the material in response a fluid at the contact surface. In some examples, the device further comprises a signal source configured to provide a signal in response to a generated electric charge at the generating material.

A temperature-controllable microfluidic device includes: a microfluidic channel generally extending in a first direction for passing a specimen fluid; a microheater disposed along the microfluidic channel, the microheater being made of a resistive wire having a pair of serpentine-shaped portions generally extending in the first direction along respective sides of the microfluidic channel; and a temperature sensor disposed along the microfluidic channel, the temperature sensor being made of a resistive wire having a pair of serpentine-shaped portions generally extending in the first direction along the respective sides of the microfluidic channel.

A low-profile shear-sensing unit includes a floating plate surrounded by a frame and a displacement sensor that measures in-plane movement of the floating plate. Covered with a surface sample, the floating plate is displaced by the friction drag (i.e., shear) on the surface caused by the flow of fluid and the in-plane displacement is measured by the displacement sensor. The shear force on the sample surface is then obtained by multiplying the measured displacement and the spring constant of the flexure beams, which suspend the floating plate. The floating plate and the flexure beams are formed out of one plate or substrate to achieve monolithic construction with a beam geometry that leads to a high-resolution measurement.

The present disclosure relates to a system and program for predicting shearing by fluid pressure, the system and program capable of predicting shearing information such as the minimum pressure P.sub.cm required for hydraulic shearing, the sufficient pressure P.sub.co for hydraulic shearing, and the optimal shearing direction using input information including the vertical stress .sub.v, the maximum horizontal stress and the minimum horizontal stress of a rock to which fluid is to be injected, a joint friction angle , a reservoir rock density .sub.r, an injected fluid density, and a coefficient of the sufficient pressure for hydraulic shearing .

The invention provides a method which predicts a ratio of the increase in frictional resistance of a rough surface in a simple manner, quickly and without variations in predicted results among individuals. The method for predicting the frictional resistance of a rough surface having a variation in roughness wavelength, and being in contact with a fluid flowing at varied velocities includes evaluating the total projected area of all prominent peaks standing out above the viscous sublayer thickness per unit area, and calculating the friction increase ratio FIR (%) or the frictional resistance increase .

A low-profile shear-sensing unit includes a floating plate surrounded by a frame and a displacement sensor that measures in-plane movement of the floating plate. Covered with a surface sample, the floating plate is displaced by the friction drag (i.e., shear) on the surface caused by the flow of fluid and the in-plane displacement is measured by the displacement sensor. The shear force on the sample surface is then obtained by multiplying the measured displacement and the spring constant of the flexure beams, which suspend the floating plate. The floating plate and the flexure beams are formed out of one plate or substrate to achieve monolithic construction with a beam geometry that leads to a high-resolution measurement.