Abstract

Lithology and physical rock properties of formations can be derived by utilizing acoustic logging systems. Compressive travel time from acoustic logs and shear travel time from full wave train logs are the two systems that are considered here. The ratio of shear travel time to compressive travel time is the relationship from which lithology is identified. Established techniques and existing commercial services we used to derive physical rock properties.

In order to establish the practicability lithology derivation, it was decided to incorporate this calculation into a computer program from which the physical rock properties program from which the physical rock properties are calculated from Acoustic, MICRO-SEISMOGRAM, and Density logs. The results of actual field tests in West Texas and Southeastern New Mexico were interesting and also uncovered a technique of gas identification from well logs.

Introduction

With the advent of large-volume frac treatments, interest has increased in obtaining in-situ rock properties for use in well treatment design. Also, studies have been made relating acoustic properties of formations to lithology. In the process of applying techniques for these purposes using well logs, it was observed that the presence of gas distorted the usual relation between compressive and shear velocity for the particular lithology. particular lithology. In the application of these techniques, compressive travel time is measured with conventional Compensated Acoustic Velocity Logs. Shear travel time can be calculated from full wave train logs. The relationship between compressive and shear travel time as a function of lithology is shown below.

delta ts = 1.9 = LIMESTONE delta tc 1.8 = DOLOMITE

1.6 - 1.7 = SANDSTONE

where delta ts = shear travel timedelta tc = compressive travel time

Physical rock properties such as Poisson's ratio are determined from the ratio of compressive to shear travel time.

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