High-Definition Lateral Log - Resistivity Device: Basic Physics And Resolution

The High-Definition Lateral Log (HDLL) system is a new logging resistivity array developed by Western Atlas Logging Services (WALS) in cooperation with Shell International Exploration and Production, Research and Technical Services (SIEP-RTS). The logging instrument has been designed to provide high-resolution resistivity distributions in both the radial and vertical direction. The HDLL tool has a single-current electrode and acquires a multitude of measurements, including electrode potentials and electric fields (represented by first-potential differences) at several distances from an injection electrode. The high accuracy under which the electric fields are measured allows for an accurate calculation of the potential second differences that are used to detect formation boundaries. High-resolution estimates of formation resistivities are obtained by inverting the HDLL acquired data. Based on a subset of the acquired data, a number of synthetic-focused measurements can be generated that provide a first indication of the formation resistivity distribution in the formation surrounding the borehole. A separate paper at this conference presents techniques for generating synthetic curves, HDLL inversion, and results of a field study. Here, we mainly focus on the basic physical principles and HDLL array resolution. We evaluate three zones of a current flow, which have different links to formation parameters and also consider an asymptotic theory leading to the concept of current leakage. The resolution of the HDLL array is also discussed and we analyze how noise affects the interpretation. The resolution analysis comprises, in a single scheme, the simulated data, their associated sensitivity to formation parameters, and a statistical noise model. Synthetic and field examples are presented that illustrate the high-information content and resolution power of the HDLL instrument.