ABSTRACT

Cost-effective deviated drilling requires accurate determination of the drill bit in four-dimensional space, including its stratigraphic and structural position, as well as its trajectory orientation and rate. Failure to maintain the desired trajectory, for example by drilling out of the target horizon or below the oil/water contact, can cost millions. I introduce an analytical method for forward-modeling and actual drilling of deviated wells, that allows for rapid spatial locating of the bit, integrating data from measurement-while-drilling instruments. The method, based on a single parent equation with appropriate derivative formulas, predicts the bit's location and trajectory relative to stratigraphy, to fluid contacts, and to structure, including relations to fractures and fault displacements, thus providing feed-back information towards well-bore corrections and adjustments. Analysis of an offshore Gulf of Mexico deviated test well illustrates the effectiveness of the method, in which entry into the target zone, an undesirable exit into overlying nonproductive strata, and subsequent reentry into the target zone well accurately predicted tens to hundreds of feet in advance--real-time analysis, that is during actual drilling rather than my subsequent analysis, might have prevented the costly target exiting. As measurement-while-drilling technology advances, decreasing the spacing between the bit and measurement-while-drilling instruments, equating to decreasing the time lag between when the bit is at a specific position and when geologic data about that position is obtained, the locating, predictive and wellbore corrective capabilities of this method can only increase.

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