Abstract: Methods for determining a distance from a drilling well to a magnetized target well include acquiring magnetic field measurements from the drilling well. The acquired magnetic field measurements are made at a plurality of spaced apart locations in the drilling well. The acquired magnetic field measurements are processed to obtain a ratio including at least one of the following: (i) a ratio of a magnetic field intensity to a first spatial derivative of a magnetic field, (ii) a ratio of a magnetic field intensity to a second spatial derivative of a magnetic field, and (iii) a ratio of a first spatial derivative of a magnetic field to a second spatial derivative of the magnetic field. The ratio (or ratios) is then processed to obtain the distance from the drilling well to the magnetized target well.

Abstract: Methods for improving wellbore survey accuracy and placement are disclosed. The Earth's magnetic field may be measured at a magnetically clean surface location and correlated with a non-magnetic reference direction to obtain a direction of the Earth's field (e.g., a magnetic declination or a magnetic inclination). The direction of the Earth's magnetic field may in turn be processed in combination with magnetic measurements made in a subterranean borehole to obtain one or more survey parameters.

Abstract: A method for magnetizing a portion of a pre-deployed casing string includes deploying an electromagnetic array in a cased wellbore and energizing the array. The array includes a plurality of axially spaced electromagnets and is configured to generate a magnetic field pattern having at least first and second pairs of magnetically opposing poles. Passive ranging measurements of the induced magnetic field may be advantageously utilized, for example, to survey and guide continued drilling of a twin well. The electromagnetic array may also be used in active ranging applications. An array of permanent magnets providing a similar magnetic field pattern may also be used in active ranging applications.

Abstract: A bottom hole assembly configured for a subterranean drilling operation having a drill bit; a downhole tool deployed above the drill bit, at least a portion of the downhole tool free to rotate with respect to the drill bit about a longitudinal axis of the bottom hole assembly a sensor sub deployed axially between the drill bit and the downhole tool, the sensor sub configured to rotate with the drill bit about the longitudinal axis of the bottom hole assembly and free to rotate with respect to the downhole tool about the longitudinal axis and a tri-axial magnetic field sensor deployed in the sensor sub.

Abstract: An acoustic surveying method includes computing at least one of a distance and direction between first and second subterranean boreholes. An acoustic pulsed is transmitted into a subterranean formation from the first borehole and received at three or more spaced receivers deployed in the second borehole. A distance between the two boreholes may be determined using longitudinally spaced receivers while a toolface to target direction (angle) may be determined using circumferentially spaced receivers.

Abstract: A bottom hole assembly configured for a subterranean drilling operation having a drill bit; a downhole tool deployed above the drill bit, at least a portion of the downhole tool free to rotate with respect to the drill bit about a longitudinal axis of the bottom hole assembly a sensor sub deployed axially between the drill bit and the downhole tool, the sensor sub configured to rotate with the drill bit about the longitudinal axis of the bottom hole assembly and free to rotate with respect to the downhole tool about the longitudinal axis and a tri-axial magnetic field sensor deployed in the sensor sub.

Abstract: Methods for improving wellbore survey accuracy and placement are disclosed. The Earth's magnetic field may be measured at a magnetically clean surface location and correlated with a non-magnetic reference direction to obtain a direction of the Earth's field (e.g., a magnetic declination or a magnetic inclination). The direction of the Earth's magnetic field may in turn be processed in combination with magnetic measurements made in a subterranean borehole to obtain one or more survey parameters.

Abstract: A method for magnetizing a portion of a pre-deployed casing string includes deploying an electromagnetic array in a cased wellbore and energizing the array. The array includes a plurality of axially spaced electromagnets and is configured to generate a magnetic field pattern having at least first and second pairs of magnetically opposing poles. Passive ranging measurements of the induced magnetic field may be advantageously utilized, for example, to survey and guide continued drilling of a twin well. The electromagnetic array may also be used in active ranging applications. An array of permanent magnets providing a similar magnetic field pattern may also be used in active ranging applications.

Abstract: An electromagnetic array includes a plurality of axially spaced electromagnets deployed in a non-magnetic housing. The array further includes an electrical module, such as a diode bridge, configured to provide an electrical current having a fixed polarity to at least the first electromagnet in the array. The array may be configured to generate a magnetic field pattern having (i) a single magnetic dipole when the array is energized with an electrical current having a first polarity and (ii) at least one pair of opposing magnetic poles when the array is energized with an electrical current having the opposite polarity. The invention provides multiple independent ranging methodologies for determining the relative position between the wellbores.

Abstract: An acoustic surveying method includes computing at least one of a distance and direction between first and second subterranean boreholes. An acoustic pulsed is transmitted into a subterranean formation from the first borehole and received at three or more spaced receivers deployed in the second borehole. A distance between the two boreholes may be determined using longitudinally spaced receivers while a toolface to target direction (angle) may be determined using circumferentially spaced receivers.

Abstract: A method for magnetizing a wellbore tubular includes magnetizing the tubular at three or more discrete locations on the tubular. In exemplary embodiments the magnetized wellbore tubular includes at least one pair of opposing magnetic poles located between longitudinally opposed ends of the tubular. Wellbore tubulars magnetized in accordance with this invention may be coupled to one another to provide a magnetic profile about a section of a casing string. Passive ranging measurements of the magnetic field about the casing string may be utilized to survey and guide drilling of a twin well. Such an approach advantageously obviates the need for simultaneous access to both wells.

Abstract: A method for magnetizing a wellbore tubular is disclosed. The method includes magnetizing a wellbore tubular at three or more discrete locations on the tubular. In exemplary embodiments the magnetized wellbore tubular includes at least one pair of opposing magnetic poles located between longitudinally opposed ends of the tubular. Wellbore tubulars magnetized in accordance with this invention may be coupled to one another to provide a magnetic profile about a section of a casing string. Passive ranging measurements of the magnetic field about the casing string may be utilized to survey and guide drilling of a twin well. Such an approach advantageously obviates the need for simultaneous access to both wells.

Abstract: A method for drilling substantially parallel twin wells includes drilling a first well and deploying a casing string in the first well. A magnetized section of the casing string includes a plurality of magnetized wellbore tubulars having at least one pair of opposing magnetic poles located between longitudinally opposed ends of the wellbore tubular. A portion of a second well is drilled within sensory range of magnetic flux from the magnetized section of the casing string. The local magnetic field is measured in the second well and processed to determine a direction for subsequent drilling. Drilling proceeds along the direction for subsequent drilling.

Abstract: A relative error model is used to compute a relative uncertainty in the position of a first well with respect to a second well. This relative uncertainty may be computed in real time during drilling and may be used in making subsequent steering decisions during drilling. Moreover, an absolute uncertainty in the position of a first well may be obtained by combining an absolute uncertainty in the position of a second well and the relative uncertainty in the position of the first well with respect to the second well.

Abstract: A method for drilling substantially parallel twin wells includes drilling a first well and deploying a casing string in the first well. A magnetized section of the casing string includes a plurality of magnetized wellbore tubulars having at least one pair of opposing magnetic poles located between longitudinally opposed ends of the wellbore tubular. A portion of a second well is drilled within sensory range of magnetic flux from the magnetized section of the casing string. The local magnetic field is measured in the second well and processed to determine a direction for subsequent drilling. Drilling proceeds along the direction for subsequent drilling.

Abstract: A method and apparatus for imparting a transverse magnetization to a wellbore tubular is disclosed. In certain exemplary embodiments, tubulars are magnetized to include at least one flux reversal (e.g., at the center of the tubular) at which the direction of the transverse field changes (i.e., from pointing radially inward to pointing radially outward). A plurality of such magnetized wellbore tubulars may be coupled together and lowered into a target well to form a magnetized section of a casing string. Exemplary embodiments of the invention may be utilized to impart a strong, highly uniform magnetic field about a string of wellbore tubulars, thereby providing for improved passive ranging and wellbore twinning.

Abstract: A stack of magnetized casing tubulars includes a plurality of magnetized wellbore tubulars each of which includes a plurality of north and south magnetic poles imparted to a corresponding plurality of longitudinal positions along the tubulars. The plurality of wellbore tubulars are arranged into a stack having at least two rows and at least two columns, the wellbore tubulars are stacked side by side and atop one another such that the magnetic poles on one tubular are radially aligned with magnetic poles of an opposite polarity on adjacent tubulars. Such a configuration advantageously substantially eliminates weakening of the imparted magnetic field due to interaction of the magnetic poles on adjacent tubulars.

Abstract: A method for magnetizing a wellbore tubular includes a positioning a wellbore tubular substantially coaxially in a plurality of longitudinally spaced magnetizing coils deployed on a frame. The coils are selectively connected and disconnected from electrical power such that a circumferential electrical current flows in each of the coils to impart a predetermined magnetic field pattern to the tubular. Exemplary embodiments of this invention provide for semi-automated control of tubular magnetization and thereby enable a repeatable magnetic pattern to be imparted to each of a large number of wellbore tubulars.

Abstract: A method for magnetizing a wellbore tubular is disclosed. The method includes magnetizing a wellbore tubular at three or more discrete locations on the tubular. In exemplary embodiments the magnetized wellbore tubular includes at least one pair of opposing magnetic poles located between longitudinally opposed ends of the tubular. Wellbore tubulars magnetized in accordance with this invention may be coupled to one another to provide a magnetic profile about a section of a casing string. Passive ranging measurements of the magnetic field about the casing string may be utilized to survey and guide drilling of a twin well. Such an approach advantageously obviates the need for simultaneous access to both wells.

Abstract: Methods for determining the distance and relative axial position between twin and target wells are disclosed. In one exemplary embodiment the magnitude and direction of the interference magnetic field vector are processed to determine the distance and the axial position. In another exemplary embodiment, a change in direction of the interference magnetic field vector between first and second longitudinally spaced magnetic field measurements may be processed to determine the distance and axial position. In still another exemplary embodiment of the invention, a component of the magnetic field vector aligned with the tool axis may be measured in substantially real time during drilling and utilized to determine the distance between the two wells. Embodiments of this invention improve the accuracy and/or the frequency of distance determination between twin and target wells.