758:
conflict means these logs are not accurate. That is actually not true. Quite often there is drilling induced damage or chemical alteration around the borehole that causes the near-borehole formation to be up to 15% slower than the deeper formation. This "gradient" in slowness can be as large as 2–3 feet. The long-spaced measurements (7.5–13.5 ft) always measures the deeper, unaltered formation velocity and should always be used instead of the shorter offset logs. Discrepancies between
22:
346:
535:
If it is necessary to compensate for tool tilt and variations in the borehole width then both up-down and down-up arrays can be used and an average can be calculated. Overall this gives a sonic log that can be made up of 1 or 2 pulse generators and 2 or 4 detectors, all located in single unit called
757:
The accuracy of modern compressional and shear sonic logs obtained with wireline logging tools is well known now to be within 2% for boreholes that are less than 14 inches in diameter and within 5% for larger boreholes. Some suggest that the fact that regular- and long-spaced log measurements often
548:
The returning signal is a wavetrain and not a sharp pulse, so the detectors are only activated at a certain signal threshold. Sometimes, both detectors won’t be activated by the same peak (or trough) and the next peak (or trough) wave will activate one of them instead. This type of error is called
777:
To improve the tie between well data and seismic data a "check-shot" survey is often used to generate a calibrated sonic log. A geophone, or array of geophones is lowered down the borehole, with a seismic source located at the surface. The seismic source is fired with the geophone(s) at a series of
558:
called the rock matrix and the time spent travelling through the fluids in the pores. This equation is empirical and makes no allowance for the structure of the rock matrix or the connectivity of the pore spaces so extra corrections can often be added to it. The Wyllie time-average equation is:
557:
Many relationships between travel time and porosity have been proposed, the most commonly accepted is the Wyllie time-average equation. The equation basically holds that the total travel time recorded on the log is the sum of the time the sonic wave spends travelling the solid part of the rock,
539:
An additional way in which the sonic log tool can be altered is increasing or decreasing the separation between the source and receivers. This gives deeper penetration and overcomes the problem of low velocity zones posed by borehole wall damage.
642:
272:
and increasing with an increasing effective confining stress. This means that a sonic log can be used to calculate the porosity, confining stress, or pore pressure of a formation if the seismic velocity of the rock matrix,
769:. However, this is usually prone to leading one to the wrong conclusions because the more compliant formations that are prone to washouts or diameter enlargements also inherently have "slower" velocities.
365:
thickness, there are actually two receivers, one near and one far. This is because the travel time within the drilling mud will be common for both, so the travel time within the formation is given by:
453:
842:
Wyllie, M. R. J., Gregory, A. R. & Gardner, G. H. F. 1958. An experimental investigation of factors affecting elastic wave velocities in porous media. Geophysics, 23: 459–93.
264:, which is a measure of a how fast elastic seismic compressional and shear waves travel through the formations. Geologically, this capacity varies with many things including
394:
530:
262:
492:
747:
725:
304:
692:
331:
665:
564:
215:
765:
Some suggest that to investigate how the varying size of a borehole has affected a sonic log, the results can be plotted against those of a
762:
and sonic log data are due to upscaling and anisotropy considerations, which can be handled by using Backus
Averaging on sonic log data.
185:
105:
549:
cycle skipping and is easily identified because the time difference is equal to the time interval between successive pulse cycles.
43:
39:
86:
164:
58:
65:
889:
208:
177:
778:
different depths, with the interval transit times being recorded. This is often done during the acquisition of a
779:
72:
334:
32:
399:
169:
54:
852:
884:
833:
Sheriff, R. E., Geldart, L. P., (1995), 2nd
Edition. Exploration Seismology. Cambridge University Press.
358:
201:
791:
154:
372:
759:
269:
236:
497:
242:
462:
142:
730:
697:
276:
670:
309:
79:
137:
357:
transmitter to the receiver, normally with the units microsecond per foot (a measure of
650:
878:
354:
811:
362:
232:
121:
637:{\displaystyle {\frac {1}{V}}={\frac {\phi }{V_{f}}}+{\frac {1-{\phi }}{V_{mat}}}}
766:
149:
132:
21:
799:
265:
345:
344:
353:
The velocity is calculated by measuring the travel time from the
795:
268:
and rock textures, most notably decreasing with an increasing
15:
733:
700:
673:
653:
567:
500:
465:
402:
375:
312:
279:
245:
46:. Unsourced material may be challenged and removed.
741:
719:
686:
659:
636:
524:
486:
447:
388:
325:
298:
256:
349:Source and receiver relationships for a sonic log
829:
827:
536:a “sonde”, which is lowered down the well.
209:
8:
361:). To compensate for the variations in the
216:
202:
117:
734:
732:
705:
699:
678:
672:
652:
620:
610:
601:
590:
581:
568:
566:
506:
501:
499:
471:
466:
464:
429:
424:
408:
403:
401:
377:
376:
374:
317:
311:
284:
278:
246:
244:
106:Learn how and when to remove this message
823:
727:= seismic velocity of the rock matrix;
120:
694:= seismic velocity of the pore fluid;
333:, are known, which is very useful for
667:= seismic velocity of the formation;
239:interval transit time, designated as
7:
448:{\displaystyle {t_{far}}-{t_{near}}}
44:adding citations to reliable sources
378:
247:
14:
532:= travel time to near receiver.
20:
494:= travel time to far receiver;
31:needs additional citations for
1:
794:, especially exploration for
790:Sonic logs are also used in
389:{\displaystyle {{\Delta }t}}
186:Nuclear magnetic resonance
178:Measurement while drilling
906:
786:Use in mineral exploration
525:{\displaystyle {t_{near}}}
257:{\displaystyle {\Delta }t}
487:{\displaystyle {t_{far}}}
780:vertical seismic profile
341:Process of sonic logging
742:{\displaystyle {\phi }}
720:{\displaystyle V_{mat}}
335:hydrocarbon exploration
299:{\displaystyle V_{mat}}
170:Logging while drilling
743:
721:
688:
661:
638:
526:
488:
449:
390:
350:
327:
300:
258:
744:
722:
689:
687:{\displaystyle V_{f}}
662:
639:
527:
489:
450:
391:
348:
328:
326:{\displaystyle V_{l}}
301:
259:
235:tool that provides a
165:Spontaneous potential
773:Calibrated sonic log
731:
698:
671:
651:
565:
553:Calculating porosity
498:
463:
400:
373:
310:
277:
243:
40:improve this article
853:"Check-shot survey"
792:mineral exploration
739:
717:
684:
657:
634:
522:
484:
445:
386:
351:
323:
306:, and pore fluid,
296:
270:effective porosity
254:
890:Petroleum geology
857:Oilfield Glossary
660:{\displaystyle V}
632:
596:
576:
226:
225:
116:
115:
108:
90:
897:
869:
868:
866:
864:
849:
843:
840:
834:
831:
748:
746:
745:
740:
738:
726:
724:
723:
718:
716:
715:
693:
691:
690:
685:
683:
682:
666:
664:
663:
658:
643:
641:
640:
635:
633:
631:
630:
615:
614:
602:
597:
595:
594:
582:
577:
569:
531:
529:
528:
523:
521:
520:
519:
493:
491:
490:
485:
483:
482:
481:
454:
452:
451:
446:
444:
443:
442:
420:
419:
418:
395:
393:
392:
387:
385:
381:
332:
330:
329:
324:
322:
321:
305:
303:
302:
297:
295:
294:
263:
261:
260:
255:
250:
218:
211:
204:
189:
181:
173:
145:
118:
111:
104:
100:
97:
91:
89:
48:
24:
16:
905:
904:
900:
899:
898:
896:
895:
894:
875:
874:
873:
872:
862:
860:
851:
850:
846:
841:
837:
832:
825:
820:
808:
788:
775:
755:
729:
728:
701:
696:
695:
674:
669:
668:
649:
648:
616:
603:
586:
563:
562:
555:
546:
502:
496:
495:
467:
461:
460:
425:
404:
398:
397:
371:
370:
343:
313:
308:
307:
280:
275:
274:
241:
240:
222:
193:
187:
179:
171:
143:
112:
101:
95:
92:
55:"Sonic logging"
49:
47:
37:
25:
12:
11:
5:
903:
901:
893:
892:
887:
877:
876:
871:
870:
859:. Schlumberger
844:
835:
822:
821:
819:
816:
815:
814:
807:
804:
787:
784:
774:
771:
754:
751:
737:
714:
711:
708:
704:
681:
677:
656:
645:
644:
629:
626:
623:
619:
613:
609:
606:
600:
593:
589:
585:
580:
575:
572:
554:
551:
545:
544:Cycle skipping
542:
518:
515:
512:
509:
505:
480:
477:
474:
470:
457:
456:
441:
438:
435:
432:
428:
423:
417:
414:
411:
407:
384:
380:
342:
339:
320:
316:
293:
290:
287:
283:
253:
249:
224:
223:
221:
220:
213:
206:
198:
195:
194:
192:
191:
183:
175:
167:
162:
157:
152:
147:
140:
135:
129:
126:
125:
114:
113:
28:
26:
19:
13:
10:
9:
6:
4:
3:
2:
902:
891:
888:
886:
883:
882:
880:
858:
854:
848:
845:
839:
836:
830:
828:
824:
817:
813:
810:
809:
805:
803:
801:
797:
793:
785:
783:
781:
772:
770:
768:
763:
761:
752:
750:
735:
712:
709:
706:
702:
679:
675:
654:
627:
624:
621:
617:
611:
607:
604:
598:
591:
587:
583:
578:
573:
570:
561:
560:
559:
552:
550:
543:
541:
537:
533:
516:
513:
510:
507:
503:
478:
475:
472:
468:
439:
436:
433:
430:
426:
421:
415:
412:
409:
405:
382:
369:
368:
367:
364:
360:
356:
355:piezoelectric
347:
340:
338:
336:
318:
314:
291:
288:
285:
281:
271:
267:
251:
238:
234:
230:
229:Sonic logging
219:
214:
212:
207:
205:
200:
199:
197:
196:
190:
184:
182:
176:
174:
168:
166:
163:
161:
158:
156:
153:
151:
148:
146:
141:
139:
136:
134:
131:
130:
128:
127:
123:
119:
110:
107:
99:
88:
85:
81:
78:
74:
71:
67:
64:
60:
57: –
56:
52:
51:Find sources:
45:
41:
35:
34:
29:This article
27:
23:
18:
17:
885:Well logging
861:. Retrieved
856:
847:
838:
812:Well logging
789:
776:
764:
760:seismic data
756:
749:= porosity.
646:
556:
547:
538:
534:
458:
363:drilling mud
352:
233:well logging
228:
227:
159:
122:Well logging
102:
93:
83:
76:
69:
62:
50:
38:Please help
33:verification
30:
863:11 December
767:caliper log
237:formation’s
155:Resistivity
879:Categories
818:References
66:newspapers
800:potassium
736:ϕ
612:ϕ
608:−
584:ϕ
422:−
379:Δ
266:lithology
248:Δ
144:Gamma ray
96:July 2022
806:See also
753:Accuracy
359:slowness
138:Density
133:Caliper
124:methods
80:scholar
647:where
459:where
82:
75:
68:
61:
53:
231:is a
188:(NMR)
180:(MWD)
172:(LWD)
160:Sonic
87:JSTOR
73:books
865:2015
798:and
796:iron
59:news
150:Mud
42:by
881::
855:.
826:^
802:.
782:.
396:=
337:.
867:.
713:t
710:a
707:m
703:V
680:f
676:V
655:V
628:t
625:a
622:m
618:V
605:1
599:+
592:f
588:V
579:=
574:V
571:1
517:r
514:a
511:e
508:n
504:t
479:r
476:a
473:f
469:t
455:;
440:r
437:a
434:e
431:n
427:t
416:r
413:a
410:f
406:t
383:t
319:l
315:V
292:t
289:a
286:m
282:V
252:t
217:e
210:t
203:v
109:)
103:(
98:)
94:(
84:·
77:·
70:·
63:·
36:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
