Formation-Evaluation Challenges and Opportunities in Deepwater
- Roland Chemali (Halliburton) | Wade Semac (Halliburton) | Ron Balliet (Halliburton) | Paul Cooper (Halliburton) | David Torres (Halliburton) | Chris Jones (Halliburton)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- April 2014
- Document Type
- Journal Paper
- 124 - 135
- 2014. Society of Petrophysicists & Well Log Analysts
- 2 in the last 30 days
- 417 since 2007
- Show more detail
Formation evaluation plays multiple critical roles in deepwater exploration and development. From the point of view of safety, real-time formation evaluation helps mitigate drilling-associated risks and optimize drilling parameters. The practices of pore-pressure prediction and wellbore stability estimates are based on real-time logs, including acoustic and gamma measurements and formation-pressure tests, as well as surface-data logs. By continually monitoring and interpreting the measurements, formation-evaluation specialists help the drillers stay within safe limits, while optimizing the rate of penetration. In more recent applications, real-time borehole-geometry logs help recognize potentially unstable zones. From the point of view of well positioning, real-time information helps the geophysicist and the geologist recognize the strata and locate the well more accurately on the structure. Some of the same sensors used for drilling safety and for drilling optimization are also instrumental in locating the well on the geological section.
Because the economics for deepwater require significantly more rigor and better risk assessment and reduction than for land or for near-shore prospects, formation evaluation is generally comprehensive and thorough. Operators will deploy the most advanced technology in order to obtain a more complete view of the reservoir. In addition to the traditional triple-combo logging sensors, advanced 3D resistivity sensors and magnetic-resonance logs are routinely utilized in deepwater. There are striking examples of fluid typing with the latter, while the former helps evaluate turbidite reservoirs, and in some cases determine the structural dip. Fluid-sampling analyzers continue to improve in sensitivity and accuracy. A new integrated optical spectrometer provides direct compositional fluid analysis based on analog optical computation methods.
Formation evaluation in deepwater is performed with either wireline or LWD or a combination of both. Wireline has been traditionally considered as more accurate and with a more complete offering. The quality gap however is narrowing with the introduction of the latest technology in LWD. Formation fluid sampling and high-resolution borehole imaging are now possible in LWD, although with less flexibility, at this writing. Logs acquired while drilling encounter significantly less invasion and fewer borehole irregularities than with wireline. They are often as accurate as their wireline counterparts, but remain limited in accommodating the large range of borehole sizes seen in deepwater. LWD logs are sent via telemetry to the surface as “insurance logging”, should the well be lost. LWD logs do provide actionable information for real-time decisions, including geopressure information, identification of geological events and their characteristics, and the precise location of oil-water contact, gas-oil contact, formation tops, fractures and faults.
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