Real-Time Drilling Optimization Using Azimuthal Density Tool (ADT)
Bouchery, Thomas1, Marcela Lorenzo1,
Gerco Stapel2 (1) Shell,
In 2003, a well was planned to drain the eastern flank of the structure. An 800-m subhorizontal section through the reservoir was designed to maximize recovery. Subtle structural variations were not properly imaged by the 3D seismic. Unexpected reservoir dip changes could have resulted in a sub-optimal positioning of the well in the flank.
An LWD azimuthal density tool (ADT) was used to acquire real time data to update the structural cross section while drilling. The objectives were to penetrate the entire stratigraphy and maximize the length in both payzones.
The reservoir presents density contrasts, which can be used to obtain structural information. The offset measurement between the bottom and top quadrants of the ADT relates to the well inclination and the formation dip. The apparent formation dip was calculated using a simple trigonometric formula.
Two geologists updated a cross section after each deviation survey (every 27 meters) to monitor progress of the well. The data showed that the bit was skidding on siderite streaks and inclination built up to 92°. An aggressive BHA configuration was selected which led to an 82º inclination; the bottom payzone had a shorter penetration but its connection to the wellbore was ensured.
This simple and cheap methodology proved invaluable for making critical real time operational decisions, including bit selection and trajectory modifications.