Well path control is one of the most complex, sensitive and critical phases while drilling a highly deviated, extended reach or a horizontal well. The development of new directional drilling programs and the design of high technology tools offer a significant help in the effective guiding and placement of the well in the subsurface area. The main problem however, is the integrated exploitation of the advantages of all the available technologies, to create an environment for a real-time well path evaluation and control.

This paper presents a computerized method for well path monitoring, placement and guiding to and through the selected target area. The method can be used, while drilling, in combination with conventional or advanced MWD/LWD tools. The proposed approach provides the capability to evaluate and to adjust the actual well profile in an interactive, real-time mode, according to the subsurface environment characteristics and to the 3-d target shape, boundaries or areal tolerances, each time a new data set is collected at the bit.


Horizontal and extended-reach drilling are now well established techniques with growing popularity and application in almost any type of reservoir. Their recent "booming" success is significantly related to the development and application of specialized technology permitting now the feasible drilling and completion of lateral sections in distances longer than 5 km.

The increased complexity involved in drilling any horizontal or extended-reach well imposed the use of well established and more sophisticated methods for the planning approach accounting all the information and the demands from geologists, reservoir and production engineers. The development of advanced computational tools for 3-dimensional design of highly deviated wells ensures a more precise well path design directly in space and subsequently the best possible representation of the expected placement of the well in the subsurface environment.

Although much effort has been put in the design methods, well control remains one of the most crucial problem in drilling operations. Various conventional techniques (rotary BHA tools with stabilizers) have been used in the past to add directional control in drilling process, but only the use of the recently developed steerable drilling systems and geosteering offers results with significant technological improvements.

Surface 3-D seismic data ensures improved subsurface definition prior to drilling. Integration of MWD systems and directional drilling services provide measurements for well bore orientation and drilling parameters while drilling, permitting the real-time guidance of the actual well trajectory. The most recent expand of MWD technology through the use of Logging-While-Drilling (LWD) sensors allows the real-time formation identification and characterization. Steerable motor drilling technology and the use of long-life PDC bits make now possible the drilling of entire hole sections in only a single bit run, improving drilling efficiency, drilling time and cost saving. Therefore, the integrated use of all the existing technologies and the correlation of their operation results is the main factor for an effective planning and a successful execution of a drilling program.

It is the purpose of this work to present a mathematical method for the real-time control of the actual well path orientation where information provided by MWD and MWD/LWD tools is utilized. The method involves corrective procedures that cover the problem of well control up to the target entry point as well as the problem of the well placement inside the target zone according to the reservoir boundaries or tolerances, parameters that continually change in space as new information come to the surface.

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