PRIORITY

The present application is a U.S. National Stage patent application of International Patent Application No. PCT/US2017/036538, filed on Jun. 8, 2017, the benefit of which is claimed and the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to downhole ranging and, more specifically, to improved downhole ranging techniques using spatially continuous constraints.

BACKGROUND

As the easy-to-access and easy-to-produce hydrocarbon resources have been depleted over the last century, more and more difficult wells remain. As the world's hydrocarbon demand is continuously growing, meeting this demand requires development of more advanced recovery procedures, one of which is the Steam Assisted Gravity Drainage (“SAGD”) application. SAGD addresses the mobility problem of heavy oil wells by injecting high pressure and temperature steam to reduce viscosity of the oil, thereby allowing easier extraction. The injection is performed from a wellbore (i.e., injector) that is drilled in parallel to the producing well (i.e., producer) at a distance in the order of a few meters from each other. The placement of the injector well needs to be achieved within a very small margin of error in distance, since drilling the wells tool closely exposes the producing well to very high pressures/temperatures, and drilling the wells too far apart reduces efficiency of the process. A variety of ranging techniques exist to drill such well configurations.

One major drawback to existing ranging techniques is measurement contamination. The ranging measurements may be contaminated by systematic and/or random errors which can vary with measured depth. As such, direct calculation of a range may result in unrealistic range estimates. In ranging, magnetic field and gradient data is measured and a corresponding range and direction calculated on a point-by-point basis. These ranges and directions, together with logging-while-drilling (“LWD”) navigation data, are then stitched together to form a spatial model of the target well and bottom hole assembly trajectory. In practice, however, the model may contain various anomalies, thereby rending the ranging calculations inaccurate.

