SYSTEMS AND METHODOLOGY FOR DETECTING A CONDUCTIVE STRUCTURE Technical Field The invention relates generally to apparatus for making measurements related to oil and gas exploration. Background In drilling wells for oil and gas exploration, understanding the structure and properties of the associated geological formation provides information to aid such exploration. In addition, drilling can be enhanced with systems and methods to detect conductive structures below the earth's surface. The conductive structures can include metal piping used in various drilling techniques, where the positioning of the metal piping can be important to the drilling operation. Brief Description of the Drawings Figure 1 illustrates an example system operable to determine a position of a conductive structure, in accordance with various embodiments. Figure 2 shows features of an example method of determining a position of a conductive structure relative to a tool structure on which receiver sensors are mounted, in accordance with various embodiments. Figure 3 shows an example of a current on a casing that induces a magnetic field that is detected by a receiver on a drilling pipe, in accordance with various embodiments. Figure 4 shows an example tool to detect a conductive structure in a formation, in accordance with various embodiments. Figure 5 shows a relationship between a conductive structure and receivers of a tool disposed on a structure parallel to the conductive structure, in accordance with various embodiments. Figure 6 shows tangential and normal magnetic fields on the surface of the structure on which the tool of Figure 5 is disposed, in accordance with various embodiments. Figures 7A and 7B show simulated tangential measurements of a receiver of Figure 4, in accordance with various embodiments. Figure 8 shows measurements of a normal component of a magnetic field with respect to bin number, in accordance with various embodiments. Figure 9 shows a relationship between distance and the ratio of maximum magnetic field and minimum magnetic field, in accordance with various embodiments. Figure 10 shows a relationship between the real distance and computed distance, in accordance with various embodiments. Figure 11 shows two bins at which a curve of a tangential magnetic field and a curve of a normal magnetic field intersect, in accordance with various embodiments. Figure 2 depicts a block diagram of features of an example system having a tool configured with receiver sensors, in accordance with various embodiments. Figure 13 depicts an example system at a drilling site, where the system includes a tool configured with receiver sensors, in accordance with various embodiments. Detailed Description The following detailed description refers to the accompanying drawings that show, by way of illustration and not limitation, various embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice these and other embodiments. Other embodiments may be utilized, and structural, logical, and electrical changes may be made to these embodiments. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The following detailed description is, therefore, not to be taken in a limiting sense. Figure 1 shows a block diagram of an embodiment of a system 100 having a tool 105 to determine a position of a conductive structure. System 100 includes a tool structure 103 having an arrangement of sensors 111-1, 111-2 . . . 111-(N-1), 111-N along a longitudinal axis 117 of tool structure 103. Each sensor 11-1, 111-2 . . . 11l-(N-l), 1 1 -N can be utilized as a transmitting sensor or a receiving sensor under the control of control unit 1 operating in region 102. Tool 105 and the methods of using tool 105 can be applied in deepwater exploration to obtain structure dip angle, azimuth, and resistivities, R and . Two sensors 111-J and 1- of the sensors 1 1 1-1, 1 1 1-2 . . . 111-(N-1), 1-N can be structured to determine the position of a conductive structure relative to tool structure 103. The two sensors 111-J and 111-K can be arranged as receiver sensors with the two sensors 111-J and 1 1 1-K oriented orthogonal to each other. Tool 105 may be realized as a tool dedicated to determine a position of a conductive structure, where the tool consists of one or more pairs of receiver sensors with receiver sensor of each pair oriented orthogonal to each other. Tool 05 can include a control unit 11 operable to manage collection of received signals at the receiver sensors 111-J and 11-K with respect to current flowing on a conductive structure below the earth's surface to determine the relative position of the conductive structure. Such a determination can be realized in a data processing unit 120 of tool 105, where data processing unit 120 can be structured to process the received signals to determine a position of the conductive structure. System 1 0 can include a cunent transmitter to flow current on the conductive structure. The current transmitter can be managed by control unit 11 . Data processing unit 120 and control unit 115 can be structured to be operable to generate magnetic-related values from the received signals at receiver sensors 1 1-J and 111-K; and to process the magnetic-related values to determine, relative to the tool structure 103, the position of the conductive structure from the magnetic-related values and a bin angle associated with the receiver sensors 111-J and 111-K attached to the tool structure 103. Tool structure 103 may be part of a drilling pipe and the conductive structure, whose position is under determination, may be a casing in formation layers below a surface of a drilling region of a well. The conductive structure may be a casing in formation layers below the bottom of a water region, for example, associated with offshore drilling. The conductive structure may include other piping and conductive structures associated with drilling operations. Figure 2 shows features of an example method of determining a position of a conductive structure relative to a tool structure on which receiver sensors are mounted. At 210, signals corresponding to received signals in two receiver sensors of a tool disposed below the earth's surface are acquired. The two receiver sensors can be arranged oriented orthogonal to each other. The signals received at the two receiver sensors can be measured voltages that correspond to a magnetic field at the receiver sensors. Attaining the received signals can include using two receiver coils on the tool oriented orthogonal to each other to collect the signals generated from the conductive structure. The tool structure may be oriented parallel with the conductive structure. The conductive structure can include a casing associated with a well and the tool structure can be structured as part of a drilling pipe. At 220, magnetic-related values from the acquired signals are generated. The magnetic-related values may be ratios of the maximum measured magnetic field and the minimum measured magnetic field. The magnetic-related values may be ratios of x and y components of a measured magnetic field. The magnetic-related values may be ratios of tangential and normal components of a measured magnetic field. At 230, the magnetic-related values are processed to determine, relative to a structure to which the two receiver sensors are coupled, a position of a conductive structure from which the received signals were generated in response to current flowing on the conductive structure, The current flowing on the conductive structure can include directly generating the current on the conductive structure. Processing the magnetic-related values can include calculating distance to the conductive structure based on the generated magneticrelated values. Processing the magnetic-related values can include calculating an azimuthal angle of the tool relative to the conductive structure based on the generated magnetic-related values. Determining a position of a conductive structure relative to a structure on which a tool, having two receiver sensors, is mounted can include collecting received signals at the two receiver sensors with the tool rotating; associating the received signals with a bin of the tool, the bin corresponding to an angle of the tool when the signals are collected; collecting additional received signals and assigning the additional received signals to different bins, each bin corresponding to an azimuthal direction of the rotating tool; and determining angular position of the conductive structure, relative to the relative to the structure to which the two receiver sensors are coupled, from determining which bin includes a largest absolute value of a difference between a maximum magnetic-related value derived from the received signal in the respective bin and an average magnetic-related value. Determining the position of the conductive structure can include determining, with no current on the tool structure and with value of the current on the conductive structure unknown, distance (Dis) with respect to a ratio related to minimum magnetic field measured, i imu and maximum magnetic field measured, M im m Determining the position of the conductive structure can include determining, with current on the tool structure, distance (Dis) with respect to a ratio related to minimum magnetic field measured, HMinimum maximum magnetic field measured, H jmu . Determining a position of a conductive structure relative to a structure on which a tool, having two receiver sensors, is mounted can include collecting received signals at the two receiver sensors with the tool in a non-rotating mode; generating magnetic-related values based on the received signals as orthogonal magnetic-related component values; and calculating the angular position of the conductive structure relative to the tool using the orthogonal magnetic-related component values and a bin angle of the tool in the non-rotating mode. Determining a position of a conductive structure relative to a structure on which a tool, having two receiver sensors, is mounted can include associating the received signals at the receiver sensors with a bin angle of the tool, the bin angle corresponding to an angle of the tool when the received signals are collected; and performing an inversion process using a measured parameter of the received signal and the bin angle to generate an azimuthal angle of the tool with respect to the conductive structure. Performing the inversion process can include using curve-fitting functions. In various embodiments, a tool is operated to determine the relative position of a conductive structure in a formation with respect to a structure on which the tool is mounted. The tool can operate according to various embodiments of a methodology that operates on signals received by the tool from the conductive structure. The position can be determined by computing the relative azimuthal angle of the conductive structure with respect to the tool based on the receive signals and by computing the distance between the structure on which the tool is mounted and the conductive structure based on the received signals. Different methodologies can be applied based on the settings of receivers on the tool, for example operating as a rotating tool or as a non-rotating tool. The tool and methodologies can be applied to a casing of a drilling operation with respect to a drilling/logging tool. A tool can be operated based on signals received from the conductive structure that the tool is being used to detect. The source of the signals, which can be used to detect the conductive structure such as a casing, can be a current flowing on the conductive structure. This current can be induced by another source or can be applied to the conductive structure directly. The current on the conductive structure can induce magnetic fields around the conductive structure, which can be measured by receivers mounted on the tool. The measured signal from the receivers can be used to determine the position of the conductive structure. The receivers can be mounted on a drilling pipe to determine the position of a casing relative to the drilling pipe. Figure 3 shows an example of a current on a casing 301 that induces a magnetic field that is detected by a receiver 311 on a drilling pipe 303. Figure 4 shows an example embodiment of a tool 405 to detect a conductive structure in a formation. Tool 405 can include receivers 410, 415 selected as orthogonal coils. Receivers 410, 4 5 of tool 405 can be arranged as intersecting coils, where D is the distance between the center of the receiving coils 410, 15 and the center 7 of the drilling pipe 403 on which tool 405 is disposed. One coil 410, referred to herein as R , can be positioned parallel with the surface of a drilling pipe 403 and the other coil 415, referred to herein as R , can be positioned perpendicular to the surface of drilling pipe 403. The measurements on RN and R can be realized as voltages induced by normal and tangential magnetic fields, respectively. The measurements can be transferred to X and Y directional measurements with a tool rotation operation. Figure 5 shows a relationship between a conductive structure 501 and receivers of a tool 505 disposed on a structure parallel to the conductive structure 501. The relationship is shown as a relative azimuthal angle of conductive structure 501 with respect to tool 505. X-direction and Y-direction components of a magnetic field are generated at tool 505 by the current on conductive structure 501 . The structure can be realized as a drilling pipe parallel to a casing, where the casing is conductive structure501, whose position is to be determined. Figure 6 shows tangential and normal magnetic fields on the surface of the structure on which tool 505 of Figure 5 is disposed. The tangential and the normal magnetic fields can be computed by the following formula from Xdirection and Y-direction components: where , , H n , H x , and H represent tangential, normal, X-direction, and Ydirection magnetic fields. The angle fBΐ is the bin angle. For a tool that can be rotated, such as being arranged on a drilling pipe that rotates, the rotation can be divided into a number of equal partitions of 360 degrees of rotation, where the partitions are referred to as bins. For example, measurements over 360 degrees can be divided into 32 bins, where each bin covers 1 .25 degrees. The number of bins can be less than or more than 32 bins. The tool can be operated without rotation, while making measurements relative to a bin. Corresponding tangential and normal voltage measurements, Vt and Vn can be expressed as coils, respectively. Since measured voltages and magnetic fields can be transferred between each other, the following discussion can be based on measured magnetic fields, but are applicable for the measured voltages. Figures 7A and 7B show simulated tangential measurements of receiver RT of Figure 4 . Figure 7A displays the simulated results of tangential measurements with respect to bin number for a drilling pipe without current flowing. Figure 7B displays the simulated results of tangential measurements with respect to bin number for the drilling pipe with current flowing. The simulated magnetic field in Figure 7B should be a shift from Figure 7A, since the measurement of includes the magnetic field induced by the current on the drilling pipe, directly, which is independent to the rotation angle. The curves, shown in Figures 7A and 7B, look like a sinusoidal curves, but actually are not, e |H „,. m . The difference between these two differences can be used to compute the distance from a structure, on which a tool is located, to a conductive structure, such as the distance from a drilling pipe to a casing. Figure 8 shows measurements of a normal component of a magnetic field with respect to bin number. The measurements of R display 90° bin shift from RTmeasurements. Since the Tmeasurements are not sensitive to the magnetic field induced by the current on drilling pipe, the measurements only reflect the conductive structure such as a casing. If measurements of the tangential component are taken, the and ence, the direction of the conductive structure can be extracted from real-time bin curves. In addition, the conductive structure is located at the plane, which is perpendicular to the direction from the bin with minimum value to the bin with maximum value of R measurements. If the structure on which the tool is disposed does not rotate, for example when the tool slides down a borehole, the shape of curve with respect to bin number, shown in Figure 8, cannot be obtained. Nevertheless, equation (2a) and equation (2b) can be used to compute the azimuthal angle of the conductive structure with respect to the X direction, shown in Figures 5 and 6, if the current on the structure is DC. i , o H > 0. (2a) H =— + tan (^), for H > 0. (2b) 2 H where H =-H, sin(^. ) + H cos(^,,) , (2c) Hy =H , cos(^,,) + H sin(^,.J, (2d) If there is no current on the structure containing the tool and the current on the conductive structure is unknown, the following formula can be used to compute the distance from the drilling tool to the casing: ( + ) £ Dis = k . (3a) 1- . (a + ) · Dis = k , (3b) where a , = and is a constant which can be determined by calibration. Figure 9 shows a relationship between the distance and the ratio a for D = 4 inch, where the distance D is shown in Figure 4 and is the one of ( - i) or (e¾-l) that is greater than zero. Figure 10 shows a relationship between the real distance and computed distance. If the current on a conductive structure, such as a casing, is known, the average of absolute maximum measurement value and the absolute minimum measurement value can be used to compute the distance with the following formula: Dis = k (4) H . \H xi u where H Minimum , / is the current on the conductive structure, k, is a constant, which can be determined by calibration. If equation (3) is used to compute the distance and this distance is substituted into equation (4), an equivalent current on the conductive structure can be computed: A, ( 1 + ) · H (5a) k ] - a ( + ) D (5b) Once the equivalent current is known, it can be used to compute the distance to the conductive structure with the following formula when the tool slides down and does not rotate, since the current on a conductive structure such as a casing drops very slowly: Dis = k , (6) where H = H +H or H = H . + H N and is a constant, which can be determined by calibration. If the structure on which the tool is disposed has current flowing, the following formula can be used to compute the distance from the structure to the conductive structure: ( + « , ) Dis = k , (7a) (1 Dis = k , (7b) - 1 where a , = constant which can be determined by calibration. In various embodiments, received signals at receiver sensors of the tool can be associated with a bin angle of the tool, where the bin angle corresponds to an angle of the tool when the signal is collected. An inversion process using a measured parameter of the received signals and the bin angle can be performed to generate an azimuthal angle of the tool with respect to the conductive structure. Inversion is a process of searching for optimum match between simulated data and measurements. Performing the inversion process can include usin curve-fitting functions, Examples of curve fitting functions include direction + B N , for normal direction measurements, where is an average tangential magnetic field, B is an average normal magnetic field, A and A are curve-fitting coefficients, dis is the distance from the tool to the conductive structure, fBί is bin angle, D is distance between center of the receiver sensors and center of a tool structure on which the receiver sensors are mounted, and f is azimuthal angle of the tool structure with respect to the conductive structure. Four parameters, with respect to the conductive structure in Figure 5, that can be inverted include A, B, dis, and azimuthal angle f . For tangential direction measurements, 0 or f = — + tan - (- ) , for Hx > 0 where Ey 1 H 2 and ¾ are y and x magnetic field components and are functions of the bin angle. 13. The method of claim 11, wherein determining the position includes determining distance (Dis) given by Dis - k — , where H and is a calibration constant, where H and ¾ are y and x magnetic field components. 14. The method of claim , wherein the method includes: associating the received signals at the two receiver sensors with a bin angle of the tool, the bin angle corresponding to an angle of the tool when the signal is collected; and performing an inversion process using a measured parameter of the received signals and the bin angle to generate an azimuthal angle of the tool with respect to the conductive structure. . The method of claim 1 , wherein performing the inversion process includes using curve fitting functions H T =A C0S + Y ) + t for tan ge t a i direction - dis 2 +D - 2 dis D cos(^ +f ) measurements, , for normal direction measurements, where B is an average tangential magnetic field, B is an average tangential magnetic field, A and A are curve fitting coefficients, dis is the distance from the tool to the conductive structure, f ! is bin angle, D is distance between center of the two receiver sensors and center of the structure to which the two receiver sensors are coupled, and f is azimuthal angle of the tool structure with respect to the conductive structure. 6. The method of claim 1, wherein the conductive structure includes a casing associated with a well and the tool structure is part of a drilling pipe. 17. The method of claim 1, wherein the method includes determining, relative to the structure to which the two receiver sensors are coupled, the position of the conductive structure with the structure, to which the two receiver sensors are coupled, oriented parallel with the conductive structure. 18. A machine-readable storage device having instructions stored thereon, which, when performed by a machine, cause the machine to perform operations, the operations comprising the method of any of claims 1 to 17. 1 . A system comprising: two receiver sensors of a tool structured to couple to a structure operable to be disposed below the earth's surface to receive signals in the two receiver sensors disposed below the earth's surface, the two receiver sensors arranged orthogonal to each other relative to the structure to which the two receiver sensors are coupled; and a control unit operable to manage collection of received signals at the receiver sensors with respect to cunent flowing on a conductive structure below the earth's surface; and a data processing unit to process the received signals to determine a position of the conductive structure. 20. The system of claim , wherein the system includes a current transmitter to flow current on the conductive structure. 1. The system of claim 1 , wherein the data processing unit and the control unit are operable to generate magnetic-related values from the received signals; and to process the magnetic-related values to determine, relative to the structure to which the two receiver sensors are coupled, the position of the conductive structure from the magnetic-related values and a bin angle associated with the two receiver sensors. 22. The system of claim 1 , wherein the receiver sensors includes two coils arranged orthogonal to each other. 23. The system of claim 19, wherein the system includes a machine-readable storage device having instructions stored thereon, which, when performed by the system, cause the system to perform operations, the operations comprising the method of any of claims 1 to 17. 24. The system of claim 1 , wherein the two receiver sensors, the control unit, and the data processing unit are configured to operate according to any of claims 1 to 17.