An apparatus includes a housing. The housing includes a concentrator and a plurality of signal acquisition devices. Each signal acquisition device is coupled to a respective sensor. Each sensor measures an environmental parameter outside the housing. Each signal acquisition device includes an acoustic transducer. Each signal acquisition device includes a controller to accept measurements from the respective sensor, process the measurements and format them into a transmittable form, and transmit the formatted measurements via the acoustic transducer. A concentrator includes an acoustic transducer to receive acoustic transmissions from the plurality of signal acquisition devices, a processor to process the received acoustic transmissions, and a telemetry device through which the processor can transmit the processed transmissions.

An apparatus includes a housing. The housing includes a concentrator and a plurality of signal acquisition devices. Each signal acquisition device is coupled to a respective sensor. Each sensor measures an environmental parameter outside the housing. Each signal acquisition device includes an acoustic transducer. Each signal acquisition device includes a controller to accept measurements from the respective sensor, process the measurements and format them into a transmittable form, and transmit the formatted measurements via the acoustic transducer. A concentrator includes an acoustic transducer to receive acoustic transmissions from the plurality of signal acquisition devices, a processor to process the received acoustic transmissions, and a telemetry device through which the processor can transmit the processed transmissions.

Methods and systems for optimizing the placement of perforation clusters in horizontal wells for completion include conveying a carrier through a borehole into a horizontal section of the borehole; obtaining acoustic data using one or more acoustic sensors; defining a first location for each of a plurality of perforation clusters based on a geometrical distribution; identifying a minimum horizontal stress (S.sub.hmin) for each first location based on the acoustic data; calculating a differential net pressure for the first locations based on the minimum horizontal stress (S.sub.hmin) for each first location; adjusting the location of each of the plurality of perforation clusters to a respective second location such that the differential net pressure of the second locations is less than the differential net pressure of the first locations; and deploying a plurality of perforation clusters to the second locations such that fracturing of a formation at the second locations is achieved.

Methods and systems for optimizing the placement of perforation clusters in horizontal wells for completion include conveying a carrier through a borehole into a horizontal section of the borehole; obtaining acoustic data using one or more acoustic sensors; defining a first location for each of a plurality of perforation clusters based on a geometrical distribution; identifying a minimum horizontal stress (S.sub.hmin) for each first location based on the acoustic data; calculating a differential net pressure for the first locations based on the minimum horizontal stress (S.sub.hmin) for each first location; adjusting the location of each of the plurality of perforation clusters to a respective second location such that the differential net pressure of the second locations is less than the differential net pressure of the first locations; and deploying a plurality of perforation clusters to the second locations such that fracturing of a formation at the second locations is achieved.

A method of imaging electrical conductivity distribution of a subsurface containing metallic structures with known locations and dimensions is disclosed. Current is injected into the subsurface to measure electrical potentials using multiple sets of electrodes, thus generating electrical resistivity tomography measurements. A numeric code is applied to simulate the measured potentials in the presence of the metallic structures. An inversion code is applied that utilizes the electrical resistivity tomography measurements and the simulated measured potentials to image the subsurface electrical conductivity distribution and remove effects of the subsurface metallic structures with known locations and dimensions.

A method including selecting a forward model based on a modeled well structure and including a single modeled acoustic source located in a modeled wellbore and a plurality of modeled acoustic sensors located in a modeled source area, simulating an acoustic signal generated by the single modeled acoustic source and received by each modeled acoustic sensor, calculating phases of the simulated acoustic signals received at each modeled acoustic sensor, obtaining with a principle of reciprocity a plurality of modeled acoustic sources in the modeled source area and a single modeled acoustic sensor in the modeled wellbore, calculating phase delays of the simulated acoustic signals between each modeled acoustic source and the single modeled acoustic sensor, detecting acoustic signals generated by a flow of fluid using acoustic sensors in a wellbore, and processing the acoustic signals using the phase delays to generate a flow likelihood map.

A method including selecting a forward model based on a modeled well structure and including a single modeled acoustic source located in a modeled wellbore and a plurality of modeled acoustic sensors located in a modeled source area, simulating an acoustic signal generated by the single modeled acoustic source and received by each modeled acoustic sensor, calculating phases of the simulated acoustic signals received at each modeled acoustic sensor, obtaining with a principle of reciprocity a plurality of modeled acoustic sources in the modeled source area and a single modeled acoustic sensor in the modeled wellbore, calculating phase delays of the simulated acoustic signals between each modeled acoustic source and the single modeled acoustic sensor, detecting acoustic signals generated by a flow of fluid using acoustic sensors in a wellbore, and processing the acoustic signals using the phase delays to generate a flow likelihood map.

The shape and size of a borehole may be characterized downhole, using measurements of the borehole shape in conjunction with a catalog of shapes against which the measured shape is matched. A unique identifier for the measured borehole shape, and optionally a size parameter, may be transmitted to a surface facility, generally saving bandwidth compared with the transmission of the raw measured borehole-shape data. Alternatively or additionally, downhole measurements may be adjusted based on the measured shape. Additional methods, apparatus, and systems are disclosed.

The shape and size of a borehole may be characterized downhole, using measurements of the borehole shape in conjunction with a catalog of shapes against which the measured shape is matched. A unique identifier for the measured borehole shape, and optionally a size parameter, may be transmitted to a surface facility, generally saving bandwidth compared with the transmission of the raw measured borehole-shape data. Alternatively or additionally, downhole measurements may be adjusted based on the measured shape. Additional methods, apparatus, and systems are disclosed.

An example apparatus includes a drill bit body and a leg extending from the drill bit body. A journal may extend from the leg, with a gamma ray detector at least partially within the journal. In certain embodiments, the gamma ray detector may be confined within a pressure protective cavity at least partially within the arm of the journal. In certain embodiments, the gamma ray detector may be a scintillator aligned with at least one of a photomultiplier, photodiodes, or phototransistors.