Alberto Mezzatesta

A Pore-Level Approach to Petrophysical Interpretation of Well Logging Measurements

An accurate description of water- or oil-bearing reservoirs and the assessment of reserves strongly depend on a robust determination of their petrophysical parameters, e.g., porosity, permeability and fluid distribution, reflecting fluid type, content, and mobility. Downhole measurements provide means to formation evaluation; however, they do not directly provide the petrophysical properties of interest. To interpret well logging data, a range of empirical models are usually employed. These empirical relationships, however, lack scientific basis and usually represent generalizations of the observed trends. To provide a link between a detailed description of the physical processes occurring at the pore scale and the macroscopic properties of sedimentary rocks, a new pore-level approach to petrophysical interpretation of logging measurements is suggested in this work. A powerful means to create such a link is to develop quantitative relationships between the petrophysical properties and the geologic processes involved in forming the rocks. Here we describe the use of simple but physically representative models of the results of several rock-forming processes, e.g., sedimentation, cementation, and the formation of authigenic clay minerals. The key feature of these models is that they are geometrically determinate or precisely defined based on knowing the location of every grain comprising the model rock and hence the morphology of the pore space at the grain scale. We outline a method for computing macroscopic petrophysical properties using the proposed rock models. Unlike many approaches to pore-level modeling, our approach introduces no adjustable parameters and thus can be used to produce quantitative, a priori predictions of the rock macroscopic behavior. These a priori predictions, in turn, allow for successfully inverting and interpreting logging data to obtain petrophysical parameters of sedimentary rocks, such as absolute and relative permeabilities as well as capillary pressure curves. For example, NMR (Nuclear Magnetic Resonance) logs contain information about grain size, allowing for an accurate petrophysical interpretation by means of the pore- level approach presented in this work. The proposed methodology is also applied to real field data and the corresponding interpretation results are included in this paper.

3D modeling of electromagnetic field in subsurface and borehole environments.

* SUMMARY We report development of a code for modeling electromagnetic In this publication we report development of a full 3-D code fields in complicated 3-D environments. The efficiency of the based on a similar technology. code is demonstrated on typical models used in subsurface and borehole electromagnetics. The code is based on an integral equation for the scattered electromagnetic field in the form used by the Modified Iterative Dissipative Method (MIDM). Due to contraction properties of the scattering operator, the iterative- The electric current j(r,z) induced in the medium with perturbation method applied to such equation always results in a convergent sequence of approximations. On a finite numerical grid, the integral equation is replaced by a system of linear equations. For a numerical algorithm to be robust, the system should preserve contraction properties of the continuous equation. This requirement is satisfied if the numerical formulation of the algorithm is derived using projection onto a subspace of piece-wise constant functions associated with the numerical grid. For such system of linear equations, the iterative-perturbation approximations converge to the solution at the rate which is independent of the numerical grid.

Joint Inversion of MWD And Wireline Measurements

Summary Traditionally, measurement-while-drilling (MWD) data are used primarily for geosteering purposes and drilling decisions such as monitoring of hole direction, deviation, and delineation of abnormally pressured zones. Wireline resistivity measurements, galvanic and induction, play a fundamental role in identifying and delineating oil- and gas-bearing formations. The availability of both MWD and wireline data not only provides the interpreter with abundant information about subsurface formations but also poses a new challenge to generate a unique model(s) that better explains both data sets. Generally, MWD and wireline data are interpreted independently to estimate formation resistivities that may result in inconsistent earth models. In this study, we performed a joint inversion of MWD Multiple propagation resistivity (MPR), and wireline High Definition Induction log (HDIL) data to come up with an earth model that best explains bot the data sets. An inversion strategy using a dual earth model, that describes the appropriate logging conditions of both wireline and MWD was also used in theinversion. Finally, the proposed algorithm was implemented on synthetic and the Gulf of Mexico data examples, and the results were compared with conventional MPR and HDIL processing results.