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Results
Fluid Substitution Analysis to Correct Borehole Geophysical Measurements Acquired in Gas-Bearing Formations Invaded by Oil-Base Mud
Xu, Chicheng (The University of Texas at Austin) | Torres-Verdín, Carlos (The University of Texas at Austin) | Ma, Jun (The University of Texas at Austin) | Li, Wei (China University of Petroleum)
Summary Borehole geophysical measurements acquired in gas-bearing formations can be significantly influenced by oil-base mud (OBM) invasion. Fluid substitution of density and sonic logs in OBM-invaded gas-bearing formations is necessary but difficult because resistivity logs cannot differentiate the saturations of OBM filtrate and gas. Numerical simulations indicate that invasion of OBM filtrate into gas-bearing formations is typically shallower than 30 cm and exhibits a sharp saturation front. The radial invasion profile is largely controlled by the rock’s petrophysical properties under relatively stable drilling conditions. On the other hand, density and neutron logs are mainly sensitive to invasion shallower than 18 cm while slowness/velocity processed from sonic waveforms is only affected by invasion deeper than 18 cm. Therefore, accurate fluid substitution in OBM invaded gas-bearing formations requires pre-assessment of the radial invasion profile which is governed by pore geometry, i.e., petrophysical rock type. We introduce a new method to address this technical challenge by integrating fast numerical simulation of well logs under mud-filtrate invasion and well-log based petrophysical rock classification. A field example from Trinidad onshore deltaic gas reservoirs is used to validate the proposed method.
- Asia (0.47)
- Europe > Norway > Norwegian Sea (0.45)
- North America > United States (0.32)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Enhanced Dispersion Analysis of Borehole Array Sonic Measurements With Amplitude and Phase Estimation Method
Li, Wei (China University of Petroleum-Beijing) | Guo, Rui (China University of Petroleum-Beijing) | Tao, Guo (China University of Petroleum-Beijing) | Wang, Hua (China University of Petroleum-Beijing) | Torres-Verdín, Carlos (The University of Texas at Austin) | Ma, Jun (The University of Texas at Austin) | Xu, Chicheng (The University of Texas at Austin)
Summary We introduce a new non-parametric matched-filterbank spectral estimator, referred as Amplitude and Phase Estimation (APES), to perform dispersion analysis of borehole array sonic measurements. This method extracts the dispersion characteristics of all wave modes by applying an APES filter to array sonic spectral data and converting the estimated wavenumber to slowness. The implemented adaptive filter in APES ensures that the output signal be sufficiently close to a sinusoid with a designated wavenumber in space domain, which constrains the interference from other wavenumber components and suppresses the noise gain. Consequently, the resolution and signal-noise-ratio of dispersion analysis is significantly enhanced. Dispersion fitness functions processed with APES indicate clearer and narrower ridges with minimum presence of alias. At each frequency, dispersions of all modes can be identified without knowledge a priori of the exact number of modes. More importantly, the new method is not computationally intensive compared to existing dispersion analysis methods. Processing examples with synthetic and field data are presented and compared with the weighted spectral semblance (WSS) method to demonstrate the applicability and advantages of this method.