Acoustic Scope Pictures
Authors: Fons Lloyd 
Published: December 2007

Fons, Lloyd, Member AIME, Pan Geo Atlas Corp., Tulsa, Okla.

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Within the short span of six months, acoustic scope pictures have become an integral part of well logging in Oklahoma. Scope pictures are now obtained on almost 80 per cent of all logging operations performed in the Oklahoma District by the author's company.

Acoustic scope pictures, in cased and uncased wells, supply the engineer with much additional information about lithology, fluid content and productivity of formations exposed to the borehole. In cased wells they indicate the quality of cement bonding to both casing and formation.

In conventional acoustic-type logging all signals observed by the borehole tool are amplified and sent to the surface, where they may be observed on an oscilloscope. However, conventional log curves utilize only a very small portion of the information presented to the scope, the remainder being wasted. Acoustic scope pictures provide a complete and permanent record of all measurable acoustic energy arriving at each of two subsurface receivers. They are a record of received signal frequency, amplitude and velocity and include all variations of these parameters with time at any depth.

The pictures are easily obtained and provide a means for precision monitoring of all acoustical logs. Continuous direct measurement and plot-out of scope picture data permit the construction of any conceivable acoustic type log with complete elimination of noise and cycle-skip problems.

The uses and method of photographically recording oscilloscope signals are herein described. Examples of improved fracture location technique, detection of lost circulation zones, direct location of hydrocarbons, construction of noise-free and cycle-skip-free logs, formation evaluation in cased wells, methods for editing formation response from cement bond logs, and a basic description of the scope picture process are also presented.

Introduction

All types of acoustic logging involve the periodic generation of uniform pulses of acoustic energy from a subsurface transmitter. Various measurements are taken from the resulting series of pressure waves arriving at one or more receivers a fixed distance below the transmitter, conventional recordings requiring one curve for each parameter. However, all measurable acoustic energy arriving at each of the two subsurface receivers will appear as vertical deflections vs time on a two-trace surface scope. Continuous and synchronous photographing of the scope provides a permanent record of all information presented to the scope.

The obtained pictures are a complete record of all "in situ" acoustic information obtainable. They may be used to construct accurate logs and to check the calibration and functioning of all present acoustical logging equipment.