A downhole electromagnetic logging tool comprises a transmitting system, a magnetic field sensor array and a control module. The transmitting system and the magnetic field sensor array are both connected to the control module. The transmitting system comprises an upper emission coil and a lower emission coil, which are respectively arranged above and below the magnetic field sensor array, for generating magnetic fields of opposite polarities, allowing the magnetic fields to be concentrated at the magnetic field sensor array. A casing generates a secondary magnetic field, which is received by the magnetic field sensor array to complete detection of the casing.

The present disclosure describes methods and systems for downhole well integrity reconstruction in a hydrocarbon reservoir. One method for downhole well integrity reconstruction in a hydrocarbon reservoir includes: positioning, a laser head at a first subterranean location, wherein the laser head is attached to a tubular inside of a wellbore; directing, by the laser head, a laser beam towards a leak on the wellbore; and sealing the leak using the laser beam.

The present disclosure describes methods and systems for downhole well integrity reconstruction in a hydrocarbon reservoir. One method for downhole well integrity reconstruction in a hydrocarbon reservoir includes: positioning, a laser head at a first subterranean location, wherein the laser head is attached to a tubular inside of a wellbore; directing, by the laser head, a laser beam towards a leak on the wellbore; and sealing the leak using the laser beam.

In some implementations, optical analysis systems use an integrated computational element (ICE) that includes a planar waveguide configured as an ICE core. In other implementations, the ICE used by the disclosed optical analysis systems includes a planar waveguide configured as a spectrograph, the spectrograph to be integrated with a conventional ICE.

Various embodiments include apparatus and methods structured to interrogate a plurality of sensor assemblies, where each sensor assembly may have one or more transmissive optical sensors. The plurality of sensor assemblies can be arranged to couple between two optical fibers. The interrogation can include generating optical signals to each sensor assembly such that each sensor assembly can be selectively and individually interrogated using semiconductor optical amplifiers. Additional apparatus, systems, and methods are disclosed.

A method of determining the presence and/or extent of an event comprises determining a plurality of temperature features from a temperature sensing signal, determining one or more frequency domain features from an acoustic signal, and using at least one temperature feature of the plurality of temperature features and at least one frequency domain feature of the one or more frequency domain features to determine the presence and/or extent of the event at one or more locations.

A method of determining the presence and/or extent of an event comprises determining a plurality of temperature features from a temperature sensing signal, determining one or more frequency domain features from an acoustic signal, and using at least one temperature feature of the plurality of temperature features and at least one frequency domain feature of the one or more frequency domain features to determine the presence and/or extent of the event at one or more locations.

Optical fiber connections and their applications in downhole assemblies are described herein. The downhole assembly includes a well completion element with an end that couples with a corresponding well completion element. An optical fiber extends along at least a portion of the well completion element and transmits an optical signal using a first mode. The well completion element includes an optical fiber connector that is coupled to the optical fiber. The connector also includes a mode converter that receives the optical signal from the optical fiber and converts the optical signal from the first mode to a second larger mode. This second larger mode may be more robustly communicated to a corresponding optical fiber connector affixed to the corresponding well completion element.

Among the methods provided is a method comprising: providing a fracturing fluid that comprises a base fluid and an additive having a high dielectric constant; and introducing the fracturing fluid into least a portion of a subterranean formation.

Some implementations provide a tool assembly for monitoring reservoir water salinity and reservoir production performance at a borehole, the tool assembly comprising: a water salinity measuring probe that includes a pair of electrodes, wherein the water salinity measuring probe is mounted at a tip of the tool assembly and configured to measure a water conductivity between the pair of electrodes when the tool assembly is immersed inside the borehole; a spinner tool configured to measure a total flow rate at where the tool assembly is immersed inside the borehole, wherein the spinner tool is located above the water salinity measuring probe when the tool assembly is immersed inside the borehole; and a temperature probe configured to measure a temperature at where the tool assembly is immersed inside the borehole, wherein the temperature probe is located above the spinner tool when the tool assembly is immersed inside the borehole.