Real-Time Drilling Optimization Using Azimuthal Density Tool (ADT)

Bouchery, Thomas¹, Marcela Lorenzo¹, Gerco Stapel² (1) Shell, Assen, Netherlands (2) Shell UK Aberdeen, Aberdeen, Scotland

The Rotterdam oil Field is a faulted anticline situated below Rotterdam city in a NAM operated Concession. The 33-m thick reservoir is subdivided in two units separated by a 9­m waste zone and is compartmentalized by carbonate tight streaks.

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.