Abstract: The invention relates to measuring and generating electrical fields downhole. In one embodiment a system is provided that includes an amplifier connected to a first electrode in electrical contact with the Earth via an operative capacitive coupling. An additional electrode and amplifier are disposed in the borehole opposite the first electrode and constitute a first pair of electrodes spaced in a direction orthogonal to the axis. A second electrode is part of a group of counter electrodes spaced from each other and disposed outside the borehole. The first pair of electrodes and the amplifiers are configured to be one of a source that generates an electrical field in a direction substantially orthogonal to the axis of the borehole and a sensor that measures an electric field substantially orthogonal to the axis of the borehole.

Abstract: An electromagnetic data acquisition system and an associated method for measuring subsurface structures with electromagnetic fields is employed for removing near surface effects from borehole to surface electromagnetic data. Preferably, the system is used to obtain information about deep, target structures located deep below the Earth, especially in oil and gas fields, while mitigating the effect of near surface geological shallow structures on collected electromagnetic (EM) data by using a series of electromagnetic measurements and data treatments that preferentially illuminate near surface geologic shallow structures so that the shallow structures may be recovered separately from deep structures of interest.

Abstract: An electromagnetic geophysical survey is performed by transmitting current from a first source into earth, the first source being located in a borehole. An electromagnetic field generated by the current transmitted from the first source is measured to create subsurface data. In addition, a background model is constructed and a leakage current distribution is calculated. A resistivity distribution of the earth is calculated using the subsurface data, the background model and the leakage current distribution, with the leakage current distribution being used as a source current distribution.

Abstract: The integrity of a well is evaluated using a non-invasive and lower cost screening system and method. The system and method identify whether well integrity has degraded and whether there is a clear break in the casing of a well, a corroded patch or faults in the casing. This is accomplished without requiring entry into the well.

Abstract: A downhole drilling tool is adapted to be placed in a borehole formed in the earth. The downhole drilling tool has mounted thereto at least one of a transmitter for generating and a receiver for sensing at least one component of an electromagnetic field within a distant earth region. The tool also has a device configured to acquire subsurface data from the at least one component of the electromagnetic field; and a device configured to calculate a resistivity distribution of the distant earth region from the subsurface data. A geophysical survey is performed with a downhole drilling tool by transmitting at least one component of an electromagnetic field through the distant earth region; acquiring subsurface data from the at least one component of the electromagnetic field; and calculating a resistivity distribution of the distant earth region from the subsurface data.

Abstract: A system measures and/or estimates the distribution of current flowing in or on a Long Conductor, such as a borehole casing. This allows greater precision in data interpretation and in calculating input to geologic models.

Abstract: A method is provided for determining whether a change in a subsurface formation, such as fractures produced within the earth during a fracturing process, has reached and/or crossed a given boundary. The method provides near real time assessment of fracture propagation that can be used to guide a fracturing, particularly a hydrofacturing process.

Abstract: A first electrode is located at a borehole and a second electrode is located at the surface of the earth. At least one transmitter is selectively connected to one or both of the first and second electrodes to cause current to flow within a subsurface of the earth. When the at least one transmitter is connected to the first electrode, a current is caused to flow at a deep depth within the subsurface and deep source data is acquired. When the at least one transmitter is connected to the second electrode, a current is caused to flow at a shallow depth within the subsurface and shallow source data is acquired. The deep and shallow source data are then combined.

Abstract: An electromagnetic sensing system operates either in land environments or in marine environments on the floor of a body of water to measure electromagnetic fields. The sensing system has electrodes that provide capacitive coupling to the local environment where measurements are being made. A new method of deployment in water provides considerable size and weight reductions. The size and weight reductions also facilitate deployment and rapid repositioning on land. The system is particularly beneficial for surveying sites adjacent to bodies of water.

Abstract: A method for efficiently calculating a subsurface distribution of electrical resistivity or conductivity generated by an electromagnetic (EM) source is provided wherein a significant fraction of the electric current produced by a source flows along a casing of a borehole. The method is comprised of two steps: calculating EM fields produced by the casing in the background lithology; and calculating EM fields caused by a resistivity anomaly in the presence of an EM field produced by the casing within a subsurface or survey model that does not include the casing.

Abstract: The invention relates to measuring and generating electrical fields downhole. In one embodiment a system is provided that includes an amplifier connected to a first electrode in electrical contact with the Earth via an operative capacitive coupling. An additional electrode and amplifier are disposed in the borehole opposite the first electrode and constitute a first pair of electrodes spaced in a direction orthogonal to the axis. A second electrode is part of a group of counter electrodes spaced from each other and disposed outside the borehole. The first pair of electrodes and the amplifiers are configured to be one of a source that generates an electrical field in a direction substantially orthogonal to the axis of the borehole and a sensor that measures an electric field substantially orthogonal to the axis of the borehole.

Abstract: A system enables a borehole casing to be used to connection with establishing electromagnetic fields within the earth at the depth of formations of interest over a significant surface area. A particular advantage is that a borehole casing can be used as an essential part of the system, without needing to open the borehole.

Abstract: An electromagnetic data acquisition system and an associated method for measuring subsurface structures with electromagnetic fields is employed for removing near surface effects from borehole to surface electromagnetic data. Preferably, the system is used to obtain information about deep, target structures located deep below the Earth, especially in oil and gas fields, while mitigating the effect of near surface geological shallow structures on collected electromagnetic (EM) data by using a series of electromagnetic measurements and data treatments that preferentially illuminate near surface geologic shallow structures so that the shallow structures may be recovered separately from deep structures of interest.

Abstract: A system and method are provided for delivering current to a lower exposed end of a well in which a source of current is connected to a middle section of a well casing or tubing inserted in the casing with the middle section being electrically isolated from a first or upper section by an insulative coupler and treated to be electrically resistive. A cable is attached to the middle section and used to deliver current along the wall of the middle section to the lower exposed end such that the lower exposed end is used to generate an electric field in nearby geological zones. Changes in the generated electric field resulting from the nature of materials in the geological zones can be detected by surface or below ground monitors or sensors.

Abstract: Resistivity in subsurface earth at locations kilometers away from wells in the reservoirs is mapped and monitored. An electromagnetic source with an electrode is deployed a borehole in the reservoir, and a group of sensors at counter electrodes is deployed at a number of other locations radially spaced at some distance from the well. The source transmits a current which flows to the counter electrodes causing an electromagnetic field which is sensed at the sensors. The source is activated at different depths in the well and ratios of the electromagnetic field sensed with the source at different depths used to obtain data to map the resistivity. The sensors are capable of sensing electromagnetic fields along two orthogonal axes, and the measurements at a sensor along these axes used to reduce undesirable effects of noise and other factors on the data measurements.

Abstract: A downhole drilling tool is adapted to be placed in a borehole formed in the earth. The downhole drilling tool has mounted thereto at least one of a transmitter for generating and a receiver for sensing at least one component of an electromagnetic field within a distant earth region. The tool also has a device configured to acquire subsurface data from the at least one component of the electromagnetic field; and a device configured to calculate a resistivity distribution of the distant earth region from the subsurface data. A geophysical survey is performed with a downhole drilling tool by transmitting at least one component of an electromagnetic field through the distant earth region; acquiring subsurface data from the at least one component of the electromagnetic field; and calculating a resistivity distribution of the distant earth region from the subsurface data.

Abstract: Errors produced in a borehole to surface electromagnetic (BSEM) survey by near surface electrical anomalies on the estimates of formation properties are reduced. The effects of variations in subsurface electrical resistivity near the surface are separated from electrical resistivity changes at locations in the formations of interest far from the measurement region. A survey system includes one or more electrodes to inject electrical current at formation depth within a borehole, one or more counter electrodes which collect such current on the surface of the earth, and one or more electrodes to inject current on the surface. A transmitter is selectively connectable to different sets of the electrodes to cause a current to flow between the selected electrode sets. The resultant fields from the current flow are sensed and processed. The effects of near surface anomalies are detectable in the data and removable from the survey data of interest regarding the formations.

Abstract: A system and method are provided for delivering current to a lower exposed end of a well in which a source of current is connected to a middle section of a well casing or tubing inserted in the casing with the middle section being electrically isolated from a first or upper section by an insulative coupler and treated to be electrically resistive. A cable is attached to the middle section and used to deliver current along the wall of the middle section to the lower exposed end such that the lower exposed end is used to generate an electric field in nearby geological zones. Changes in the generated electric field resulting from the nature of materials in the geological zones can be detected by surface or below ground monitors or sensors.

Abstract: An electromagnetic geophysical survey is performed by transmitting current from a first source into earth, the first source being located in a borehole. An electromagnetic field generated by the current transmitted from the first source is measured to create subsurface data. In addition, a background model is constructed and a leakage current distribution is calculated. A resistivity distribution of the earth is calculated using the subsurface data, the background model and the leakage current distribution, with the leakage current distribution being used as a source current distribution.

Abstract: Methods, systems, and apparatuses for measuring an electric potential in the earth, which includes a first sensor are disclosed. The first sensor includes a sensing plate for placement in an environment in close proximity to the earth. The sensing plate has an operative capacitive coupling with the earth and measures the earth's electric potential. The sensor also includes a barrier providing electrochemical segregation between the sensing plate and the earth and an amplifier having at least one stage for receiving and amplifying a first signal carrying the potential measured by the sensing plate. The sensor also includes a first connection carrying the first signal from the sensing plate to the amplifier; and a reference voltage for application to the first stage of the amplifier, the reference voltage providing a reference against which the potential measured by the sensing plate is compared. Other embodiments are described and claimed.