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feature slots and grooves to slow down the arrival of signals— known as tool arrivals— that travel purely through the tool. A way around the second problem, poor logs in bad hole, came from the Shell engineer responsible for that company’s first sonic tool.7 His borehole-compensating arrangement of receivers and transmitters not only eliminated the problem of poor signal in washed-out zones, but also removed the effects of tool tilt and eccentering on log response. Solving two of the three problems that plagued the earlier tools, Schlumberger incorporated this idea into the all-steel design of the borehole-compensated (BHC) sonic tool that was introduced in 1964. The BHC tool contained two transmitters and four receivers. Along with BHC technology came the ability to view registered waveforms on an


1. Schlum b erger C: “ Procé dé et Appareillage pour la Reconnaissance de Terrains Traversé s par un Sondage. ” Ré pub liq ue Franç aise Brevet d’ Invention num é ro 7 86, 863 ( J une 17 , 19 3 5 ) . Also Doll L: “ Method of and Apparatus for Survey ing the Form ations Traversed b y a Borehole, ” US Patent No. 2, 19 1, 119


( Feb ruary 20, 19 4 0) ( sub m itted b y the estate of Conrad Schlum b erger) .


2. The term s “ sonic” and “ acoustic” are used interchangeab ly .


3 . Pik e B and Duey R: “ Logging History Rich w ith Innovation, ” Hart’s E& P( Septem b er 2002) : 5 2– 5 5 , http: / / w w w . spw la. org/ ab out/ Logging-history . pdf ( accessed April 28, 2006) .


4 . From Hum b le Oil: Mounce WD: “ Measurem ent of Acoustical Properties of Materials, ” US Patent No. 2, 200, 4 7 6 ( May 14 , 19 4 0) .


From Magnolia Petroleum Com pany : Sum m ers GC and Broding RA: “ Continuous Velocity Logging, ” Geophy sics17 , no. 3 ( J uly


19 5 2) : 5 9 8– 614 .


From Shell: Vogel CB: “ A Seism ic Velocity Logging Method, ” Geophy sics17 , no. 3 ( J uly


Lé onardon, reference 1, m ain tex t. 5 . Breck HR, Schoellhorn SW and Baum RB: “ Velocity


Logging and Its Geological and Geophy sical Applications, ” Bulletin of the Am erican Association of Petroleum Geologists4 1, no. 8 ( August 19 5 7 ) : 1667 – 1682.


6. Wy llie MRJ , Gregory AR and Gardner LW: “ Elastic Wave Velocities in Heterogeneous and Porous Media, ” Geophy sics21, no. 1 ( J anuary 19 5 6) : 4 1– 7 0.


Tix ier MP, Alger RP and Doh CA: “ Sonic Logging, ” J ournal of Petroleum Technology 11, no. 5 ( May 19 5 9 ) : 106– 114 .


7 . Vogel CB: “ Well Logging, ” US Patent No. 2, 7 08, 4 85 ( May 17 , 19 5 5 ) .


8. Hottm an CE and J ohnson RK : “ Estim ation of Form ation Pressures from Log-Derived Shale Properties, ” J ournal of Petroleum Technology 17 , no. 6 ( J une 19 65 ) : 7 17 – 7 22.


9 . Hornb y BE: “ Im aging of Near-Borehole Structure Using Full-Waveform Sonic Data, ” Geophy sics5 4 , no. 6 ( J une 19 89 ) : 7 4 7 – 7 5 7 .


10. Pistre et al, reference 3 , m ain tex t. 19 5 2) : 5 86– 5 9 7 .


> A sonic-logging sonde w ith slots to slow dow n tool arrivals.


oscilloscope in the logging truck. Appearing on the screen were not only the primary (P-) arrivals, or compressional waves, but also secondary (S-), or shear waves and later arrivals. Recognizing the importance of shear waves made the mid-1960s a time of intense activity in expanding sonic applications. Specialists at Shell proposed using the ratio of P to S velocity as a lithology indicator, and also used sonic logs to predict overpressured zones.8 Schlumberger engineers and researchers evaluated use of P and S amplitudes to locate fractures. Although these and other shear-wave applications had been proposed, the acquisition systems of the time recorded only the arrival time of the P- wave. The waveform itself, including P, S and later arrivals, was not recorded. Another drawback of the BHC tool was its inability to accurately measure the true formation interval transit time in zones of invasion, shale alteration and drilling-induced damage. The 3- to 5 -ft [ 0.9- to 1.5 -m]


transmitter-receiver (TR) spacing captured only waves that propagated in the altered zone, leaving the unaltered zone away from the borehole unexplored. By increasing the spacing to 8 to 12 ft [ 2.4 to 3.7 m] , the LSS Long-Spaced Sonic Tool improved log response in altered shales. Sonic velocities of the unaltered formation are more representative of the reservoir in its natural state and yield synthetic seismograms that better match surface seismic traces. The long TR spacing also stretched the received wavetrain, separating the P-, S- and other waves into recognizable packets of energy. Efforts intensified to capture the full waveform, leading to the development of tools that recorded digital waveforms from an array of receivers. The first commercial Schlumberger version of this technology, introduced in the 1980s, was called the Array-Sonic full-waveform sonic velocity tool. Full-waveform logging gave rise to a host of new processing techniques. The late 1980s saw research experiments with a second-generation digital sonic tool. The DSI Dipole Shear Sonic Imager tool had eight sets of four monopole receivers that could function as orthogonal dipole receivers, and carried one monopole source and two orthogonally oriented dipole sources. The dipole sources generated flexural waves, allowing characterization of formation anisotropy and shear slowness in slow as well as fast formations.


Also in the late 1980s, Schlumberger researchers tested a variety of multireceiver acoustic tools for their ability to acquire sonic images— seismic-like images far from the borehole.9 The first commercial sonic-imaging service was run in 1996, but processing was time- and personnel-intensive. In 2005 , the Sonic Scanner acoustic scanning platform combined many innovations of the past and added radial measurements to simultaneously probe the formation for near-wellbore and far-field slownesses.10 The tool itself is fully characterized, with predictable acoustics. The wide frequency range of the monopole and dipole transmitters delivers excellent waveform quality in all formation types.


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