ABSTRACT

1. INTRODUCTION

ABSTRACT:

This paper focuses on the geomechanical evaluation of an unconventional tight gas sand reservoir of the Neuquén basin, Argentina, consisting mainly of a thick sequence of deltaic and fluvial sandstones and siltstones. A comprehensive core analysis and rock mechanical test program was done with the intent to map geomechanical properties of interest across the target units, in order to optimize the design of future hydraulic fracturing treatments. The reconciliation of several types of core measurements established their respective importance in capturing the contrasts between soft units and more competent formations, which could not detected by the suit of standard wireline sonic tools. We venture an explanation for the discrepancy between wireline and core data based on the difference of sensitivity of acoustic wave velocity to stress between hard and soft rocks. Velocity differences between soft and hard rocks exist under low confinement but are much less pronounced under reservoir in-situ stresses. This has important implications in the context of reservoir stimulation by hydraulic fracturing. In particular, the problem of proppant embedment and early fracture closure requires a mapping of static elastic properties of the rock under stresses that are significantly less than the in situ stress state. The careful integration of core analysis results with standard wireline logs prompted some fundamental questions on the capability of wireline sonic tools to reliably image the complexity of the tight sand formation, and therefore to provide a suitable basis for a detailed geomechanical studies of its reservoirs

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