Abstract

Sandstone reservoirs in the Gulf of Mexico typically do not form horizontal planes, and a predetermined course for a horizontal well cannot ensure that the well path will remain within the producing interval throughout the horizontal section. Detecting approaching bed boundaries and fluid contacts early enough to make the changes necessary to keep the well path in the producing interval is an important technical issue that must be addressed when planning and drilling horizontal wells. In the first two horizontal wells drilled in the Gulf of Mexico, this objective was achieved using Measurement-While-Drilling (MWD) resistivity measurements and supporting computer modeling for bed boundary detection.

MWD propagation resistivity measurements can effectively detect approaching bed boundaries several feet from the borehole if there is a significant resistivity contrast between the two beds. In the well planning stage, the MWD log response can be modeled from the horizontal well plan and data from offset wells. While drilling, the modeled log response can be compared to real-time directional and log data in order to monitor and correct the well path as necessary. Finally, the MWD log and directional data can be used in post-drilling evaluation to (a) perform a petrophysical evaluation of the well, (b) determine actual reservoir geometry, and (c) plan completion and production strategies.

Actual case histories illustrate how a combination of MWD measurements can be used to plan horizontal well paths, to maintain real-time stratigraphic control of the horizontal well path, and to evaluate the reservoir without requiring the deployment of open hole wireline logs in the horizontal section.