A New Characterization of Bulk-Volume Irreducible Using Magnetic Resonance
G.R. Coates, D. Marschall, D. Mardon: NUMAR, Houston, TexasJ. Galford: NUMAR Australia, Perth, Western Australia

Abstract: Irreducible water volume from the new magnetic resonance (MR) logging tools provides the log analyst with insight into a formation's permeability and its water-cut potential. However, the traditional T2 cutoff method to determine the bulk volume of irreducible water (BVI), currently in wide use, has been found to be inadequate for some formations and fluid conditions. A new method to characterize bulk volume irreducible that addresses these issues is presented in this paper. The method is based on the premise that each pore size has its own inherent irreducible water saturation. Given that relaxation time is related to pore size, this method utilizes core MR measurements to relate each relaxation time to a specific fraction of capillary bound water. Thus, the bulk volume irreducible becomes a direct output of the inversion of the echo data, and it utilizes the entire T2 distribution. Core data are presented that demonstrate the spectral bulk volume irreducible (SBVI) petrophysical model and the method used for its characterization. Log examples of the SBVI implementation are presented to demonstrate the improvements brought by this development.

Theory and Numerical Simulation of Induction and MWD Resistivity Tools in Anisotropic Dipping Beds
Stéphane Graciet and Liang C. Shen: Department of Electrical and Computer Engineering, University of Houston

Abstract: Shale formations as well as thinly laminated sequences of shale and sand are anisotropic formations often encountered in electromagnetic logging. Also, many wells are deviated from the direction perpendicular to the formation beds. The combined effect of dip and anisotropy on the readings of induction and measurement-while-drilling (MWD) resistivity tools is studied. Solutions of Maxwell's equations in anisotropic media are obtained, and computer codes are developed to model responses of induction and MWD resistivity tools. Numerical results show that 1) the induction and MWD tool responses in thin sand-shale sequence and in anisotropic beds show different characteristics; 2) in the case of an MWD tool, the anisotropy can be identified by the difference between the phase-based and the amplitude-based apparent resistivities and the difference increases with the dip angle; 3) although a simple equation can be used to account for anisotropy in thick beds, it becomes inaccurate in thin anisotropic beds. A typical correction chart is presented to demonstrate that the apparent resistivity at the center of a thin anisotropic bed is very different from the apparent resistivity predicted by that equation.

Wyllie Revisited with Respect to Carbonate Permeability
William R. Hoyle: Retired Log Analyst, Shawnee, OklahomaJack Bowler: Bowler Petrophysics, Inc., Denver, Colorado

No abstract

Geosteering Methods: Predicting the Geology Ahead of the Bit
Tom Schroeder and Bryan C. Dugas: Baker Hughes INTEQ, Houston, Texas

Abstract: Geosteering involves predicting the geology ahead of the bit to optimize the drilling of a horizontal well. This paper shows how MWD real-time logs can be used to predict bed dip, avoid bed boundaries, and estimate the distance of a horizontal well from the top of a target while drilling. Applications are run at the rigsite on a laptop computer. The geosteering team using the results to modify or confirm the geologic interpretation makes necessary adjustments to the well path. Adjustments are communicated quickly so that the directional driller can maintain a smooth well path while optimizing the location of the horizontal well in the target zone.