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Sensitivity analysis in geosteering horizontal wells allows the estimation of parameter uncertainty

IP.com Disclosure Number: IPCOM000188450D
Publication Date: 2009-Oct-08
Document File: 1 page(s) / 12K

Publishing Venue

The IP.com Prior Art Database

Abstract

Sensitivity analysis in geosteering horizontal wells allows the estimation of parameter uncertainty facilitating decisions while drilling a horizontal well. The main concern is to keep the drain hole in the targeted reservoir, avoiding premature exit into the adjacent formations. Information is sent to surface regarding the down-hole environment, among these a crucial one is the distance to an approaching boundary, commonly known as "Distance to Bed". This parameter, calculated through inversion of resistivity measurements, is subject to some uncertainty due to noise in the data. The amount of noise influences the level of uncertainty in the measurements. The method to calculate this uncertainty is called sensitivity analysis. While "Distance to Bed" is the most important for real-time geo-steering decision making, other parameters (resistivities and anisotropy ratios for bed and shoulder, relative tool inclination, tool rotation) recovered from resistivity or other measurements could affect overall confidence in the inversion results. The method proposed allows the uncertainty investigation for different subsets of the mentioned above parameters depending on the amount of data transmitted to the surface in real-time. The sensitivity analysis that we propose to use to estimate the uncertainties in the parameters of interest assumes that we know the a priori model and the noise in the data (measurement noise, geological errors, etc). The level of noise can be fixed at a standard threshold value (tool error), calculated using the misfit between the simulated response and the actual acquired measurements (model error), or combine both errors. Since the earth models do not consider the noise when synthetic resistivity responses are calculated, a near-to-perfect match (low misfit) will indicate a very low level of noise. On the contrary, higher misfit values imply higher noise in the data. The sensitivity analysis provides a quantitative estimate of the parameters uncertainty with respect to the total noise level of data.

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Title of Invention:

Sensitivity analysis in geosteering horizontal wells allows the estimation of parameter uncertainty

Abstract of the Invention:

Sensitivity analysis in geosteering horizontal wells allows the estimation of parameter uncertainty facilitating decisions while drilling a horizontal well. The main concern is to keep the drain hole in the targeted reservoir, avoiding premature exit into the adjacent formations. Information is sent to surface regarding the down-hole environment, among these a crucial one is the distance to an approaching boundary, commonly known as "Distance to Bed". This parameter, calculated through inversion of resistivity measurements, is subject to some uncertainty due to noise in the data. The amount of noise influences the level of uncertainty in the measurements. The method to calculate this uncertainty is called sensitivity analysis. While "Distance to Bed" is the most important for real-time geo-steering decision making, other parameters (resistivities and anisotropy ratios for bed and shoulder, relative tool inclination, tool rotation) recovered from resistivity or other measurements could affect overall confidence in the inversion results. The method proposed allows the uncertainty investigation for different subsets of the mentioned above parameters depending on the amount of data transmitted to the surface in real-time. The sensitivity analysis that we propose to use to estimate t...