Schlumberger

Technical Paper: Applications of a New Magnetic Resonance Logging-While-Drilling Tool in a GOM Deepwater Development Project

Society: SPWLA
Paper Number: 2002eee
Presentation Date: 2002
 

Abstract

This paper describes the collaborative field testing of a new nuclear magnetic resonance (NMR) logging-while-drilling (LWD) tool on a series of seven deepwater Gulf of Mexico development wells, comprising both oil- and gas-bearing formations. The bottomhole assembly (BHA) included an unprecedentedly large combination of measurement-while-drilling (MWD) tools, all transmitting their measurements to the surface in real time. Although wireline data were acquired on some of the wells, the primary decisions as to when to sidetrack versus when to complete were made based on LWD data. 

The NMR tool primarily acquired data while drilling ahead in a mixture of rotary and sliding modes, requiring neither special measures nor additional rig time. The data were generally high quality, although in a few intervals the longer formation T2 values were somewhat reduced because of the lateral tool motion while drilling. These motion effects could be predicted from accelerometry-derived quality control measurements made by the NMR tool itself. In addition, some data were acquired while sliding the tool after drilling (while circulating bottoms-up after reaching total depth in the well). As expected, these data sets showed an improved measurement quality, enabling the detection of longer formation T2 values. 

The real-time NMR data included porosity and bound-fluid volume (BFV), which were computed downhole in the tool and sent uphole via mud-pulse telemetry. As field testing proceeded, several modifications to the downhole processing were implemented, resulting in increased precision of the real-time data. Also, porosities computed from two different polarization times (acquired in an interwoven antenna firing mode) were transmitted, enabling a T~-based hydrocarbon quicklook to be shown in real time while drilling for pay detection and reservoir delineation. 

All tool configuration and data-acquisition activities were conducted by a dedicated field-test engineer on the offshore rig. Close communication was maintained between the operator's office and the service company's engineering staff, with the field-test engineer acting as point person. With this type of teamwork, improvements to the LWD-NMR acquisition modes and software were implemented quickly during the course of the project, and produced noticeably improved log results. This type of collaborative approach enabled both parties to achieve the maximum benefit from the field test of this new technology.

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