Method to maintain towed dipole source orientation

A steerable receiver streamer system for marine surveys of subsurface regions for hydrocarbons, comprising:

• (a) a head unit and a tail unit, connected by a flexible streamer, said head unit being adapted to connect to a tow cable;
• (b) a plurality of receivers, spaced at intervals along the streamer;
• (c) a first lateral control means for changing position in a lateral (horizontal) plane when the streamer is submerged in water, located at the head unit;
• (d) a vertical control means adapted to decouple the head unit from tow cable force variations when the source is submerged in water;
• (e) at least one position-locating sensor, one sensor being located at the head unit, adapted to determine instantaneous position;
• and
• (f) control electronics and electrical connections between the sensors and at least the first lateral control means.

A method for producing hydrocarbons from an underwater subsurface region, comprising:

• (a) performing a controlled-source electromagnetic survey of the subsurface region, wherein a steerable horizontal electric dipole source system is towed underwater above the subsurface region, said steerable dipole source system comprising:
• (i) a head electrode and a tail electrode, connected by a flexible streamer to form a dipole, said head electrode being adapted to connect to a tow cable, said electrodes being made of an electrically conducting material;
• (ii) a first and second lateral control means for changing position of the head electrode and tail electrode, respectively, in a lateral (horizontal) plane when the source is submerged in water;
• (iii) a vertical control means adapted to decouple the head electrode from tow cable force variations when the source is submerged in water;
• (iv) two position-locating sensors, one located near the head electrode and the other located near the tail electrode, each adapted to determine instantaneous position of its respective electrode;
• and
• (v) control electronics and electrical connections between the position-locating sensors and the lateral control means, such that each control means are adjustable in real time based on the instantaneous position of its respective electrode;
• (b) using the lateral control means during the survey to maintain the electrodes positioned over a pre-determined source tow line;
• (c) using the vertical control means during the survey to maintain the head electrode at a pre-determined constant elevation above the water bottom;
• (d) obtaining analyses of electromagnetic field data obtained in the survey, said analyses indicating potentially hydrocarbon-bearing structures in the subsurface region below the water bottom;
• (e) drilling at least one well into such a structure;
• and
• (f) producing hydrocarbons from the well.