The Principles and Procedures of Geosteering

Abstract

The management of directionally drilled wells has recently progressed to the stage where targets have been reduced in size to a point in the earth with no tolerances. These targets can and are changed during the drilling process. The management of these point moving targets, usually in high angle or horizontal wells, is a predse form of directional drilling now called geosteering. It is this predse placement of the wellbore that creates the value in drilling these wells.Sever~ technolo~es have made this advancement possible. These mclude rehable steerable systems, improved and new physical formation measurements, log data modeling, sensors near the bit and instrumented motors, and detailed reserYoir mapping with the help of 3D seismic processing. ~lost papers on geosteering have concentrated on one of these advances. This paper addresses how these technologies are merged to execute the successful geosteering project.New systems, sensors, and computations have created a m~s. of data and control parameters that require real-time deCisions by operator persom1el based on technical recommendations from service companies. These decisions have ~ critical impact on the net worth of a project. The team mvolved must rely on each other's expertise and under~tan~ t~e overall objective of a geosteering project. To do this, lt 1s paramount that data from these different technological areas be merged into a 3D visualization encompassing geological stn1ctures and drilling trajectories.Patterns in procedures have developed from these projects over the past three years which demonstrate the difference b~tween a ~uccessful project and a failure. 1he examples in this paper Illustrate the techniques that will enable a change 133 in the outlook towards precision directional drilling and completion projects.

A Decision Analytic Framework for Autonomous Geosteering

“…In order to gather more information about the sand location, suppose that the team at a cost could perform an azimuthal test whose reliability depends on the depth measurements, tool-face settings, and survey data sampling rates (Lesso and Kashikar, 1996). Thus, the well-placement decision situation now also includes a data-gathering option (performing an azimuthal test), and the driller should decide whether to perform this test.…”

Bayesian Decision Networks for Optimal Placement of Horizontal Wells

“…Consider the following case, which is based on the example in Lesso and Kashikar (1996). Figure 3 shows a part of the 2D subsurface structure of the target section in the reservoir.…”

“…The inconsistency between distance to the borders of the formation in the structural plot and the logs' data prompted the question of what to do next. Because it was not clear whether the drill-bit has exited the top or base of the designed window (zone A), they had to choose one of the following alternatives: (1) sidetrack to the planned well-path from an optimal place, (2) drill up with an appropriate recovery, or (3) drill down with an appropriate recovery (Toby, 2005;Lesso and Kashikar, 1996) to get back in the planned path.…”

“…In order to gather more information about sand location, suppose that the team at a cost could perform an azimuthal test whose reliability depends on the depth measurements, tool-face settings, and survey data sampling rates (Lesso and Kashikar, 1996). This could be improved by an optimal design of the test.…”

Geosteering Horizontal Wells using Resistivity Anisotropy obtained in an Offset Vertical Well

“…These parameters are then used as the principal criteria for chosing the target bed in the planning the trajectory of the horizontal producer well, and in developing a layered earth model, to be used for geosteering the section. 1 From a location slightly offset laterally from the vertical well, the high angle producer well is then drilled towards the location of the vertical well, and landed in the the target zone identified from the anisotropy processing, and cased.…”