Technical Paper: Deepwater Improvements Using Real-Time Formation Evaluation

Society: SPE
Paper Number: 74397
Presentation Date: 2002
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In contrast to many parts of the United States that have significant production declines, the total Gulf of Mexico (GOM) production is on the increase thanks to technology advances that have allowed the industry to move into deeper water.Deepwater drilling has many challenges to overcome, such as narrow pore-pressure/fracture-gradient relationships that require multiple casing runs. Wellbore instability, kicks, lost circulation and shallow-water flows are common during the drilling process. The depths of wells often reach 30,000 ft, resulting in high bottomhole pressures and temperatures that limit the options of measurements and mud-pulse telemetry. The drilling rigs required in this difficult environment are very expensive, and nondrilling times have a large impact on well or projects economics. Thus new technology was required to drill cost effectively in deep water.

Logging while drilling (LWD) tools have already presented great opportunities, yet we continue to push this new technology to its limits. In fact, a suite of nuclear (with retrievable source), acoustic, and electromagnetic tools have been simultaneously deployed in the drillstring to acquire real-time formation-evaluation data and pore pressure prediction information to help reach the desired depth. Quick-answer products delivered on site, such as full borehole images and real-time Internet data transmission to the shore office, empowered a dispersed group of geologists, geophysicists, petrophysicists and drilling engineers to function as a team to promote efficiency.

This paper discusses the methods of using the data from azimuthal density, neutron, array compensated resistivity, and sonic tools that have enabled an operator to conduct a full formation-evaluation program. The field drilling program was based on the latest LWD technology enhancements such as dual-frequency resistivity measurements, blended-resistivity processing, 16-sector density, full-borehole imaging, and compressional transit time.

This paper also provides insight into the measurement while drilling (MWD) and LWD technology that has enabled data transmission from far-reaching depths. For example, fast telemetry settings, attaining 6 bps, allowed highly reliable data (2 samples per foot) to be recorded and sent uphole at an ROP of 100 ft/hr, synchronizing the frequency to further accommodate mud-attenuated signals in deeper wells. High flow-rate capability (up to 2,500 gpm) in large boreholes combined with high pressure (up to 25,000 psi) gamma-ray, resistivity, density, and neutron (quad-combo) tools in deep, slim holes played an important role in keeping the flow of the information from downhole without interruption until the final drilling depth was reached.