Schlumberger

Technical Paper: Integrating Diverse Measurements to Predict Pore Pressure With Uncertainties While Drilling

Society: SPE
Paper Number: 90001
Presentation Date: 2004
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Abstract

An accurate estimate of the formation pore pressure is a key element for safe and cost-effective drilling. We describe here a methodology that integrates information from diverse measurements to predict pore pressure in a well before and during drilling. The data we can incorporate include surface seismics, sonic and density well logs, checkshots, mud weights, and measured pore pressures. The distinctive feature of our method is that uncertainties in the predicted velocities and pore pressures are quantified and updated while drilling. Quantifying uncertainties allows us to properly integrate all data and to show how measurements acquired while drilling reduce the uncertainty in the predicted pore pressures.

In practice, we use a Monte Carlo method to sample the posterior probability distribution (given all the data) of the compressional-wave velocity profile and of coefficients in the relationships that relate velocity to pore pressures. For each sampled value of velocities and other coefficients, we compute the corresponding pore-pressure profile along the well trajectory; the range of all sampled pore pressures describes the pore-pressure uncertainty. We demonstrate the methodology in two examples where the uncertainty in pore pressure predicted before drilling (from seismic velocities obtained by reflection tomography) is reduced by additional data acquired while drilling (checkshot, sonic log, mud weights, and pore-pressure data).

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