Acoustic And Biaxial Measurement Of Rock Mechanical Properties For Interpretation Of Logs For Design Of Well-Completion Operations
Authors: Nielsen Ramona M. , Kohlhaas Charles A. 
Published: December 2007

Mechanical properties of rock formations Poisson's Ratio and Young's Modulus, are Poisson's Ratio and Young's Modulus, are critical for the design of fracture treatment casing programs, drilling programs, perforations, analysis of subsidence, description perforations, analysis of subsidence, description of sand stability, and design of sand control techniques. various logging techniques, all based on acoustic logs, have been used to describe these properties in situ. Accuracy of these techniques has been variable and questionable; primarily because of a lack of understanding of relationships between acoustically measured dynamic properties and static properties as measured in standard triaxial tests and their efficiency for describing rock failure downhole.

Equipment has been designed which approximates downhole stress conditions and with which both dynamic (acoustic) and static measurements of rock characteristics may be measured simultaneously under downhole condition. These results show that the dynamic and static properties may be correlated and used for analysis of rock behavior during various wellbore operations of drilling, completion, and production.

These results are of considerable value for interpretation of log data for analysis of the completion operations listed above.

Gassman's correlations for acoustic losses in aggregates are modified with the experimental results to provide a better correlation. Variations of acoustic and modulus results are presented as a function of stress so logmeasurements of Poisson's Ratio and Young's Modulus may he corrected for surfacewave interference, stress variations, refraction near the wellbore, and depth. These corrections are particularly useful for predicting whether a particular formation predicting whether a particular formation requires sand control in unconsolidated formations and vertical fracture growth inconsolidated formation from borehole acoustic log measurements.

Introduction

Acoustic Measurements have been used for determination of the elastic properties of materials. With the advent of acoustic-logging borehole devices in the late 1950's considerable research attention was devoted to the interpretation and analysis of measurements from these tools. This research centered on the many characteristics of acoustic measurements which result from borehole geometry and the peculiar nature of sedimentary rocks. Many papers were published presenting results of fundamental research regarding relationships between properties of sedimentary rocks and acoustic borehole measurements. In addition, there was, and is, an extensive body of research with regard to earthquake seismology and exploration geophysics which concerns similar phenomena.

None of this work attracted much attention from petroleum engineers, however, who, at that time, considered acoustic logs primarily asporosity-measuring tools. With increased use of density logs for porosity determination in the 1960's, interest in acoustic measurement waned.

In 1971, Stein and Hilchie pointed out the benefits of using acoustic measurements for determination of rock mechanical properties which could be used for correlation with certain aspects of rock mechanical behavior associated with sand production. The Mechanical Properties Log, described by Tixier, Loveless, and Anderson was an attempt to use combined density and acoustic log measurements for determination of elastic moduli. The log was based on correlations which limited its applicability to local areas of the Gulf Coast, however, and attempts to use it in other areas were generally unsuccessful. Stein later described his technique in more detail.