Chapter 11: AVO Anomalies From Clean, Wet Sands
In this chapter, we describe two cose histories in which AVO anomalies were drilled and found to correspond to thick, porous, clean, wet sands. Modeling confirms that a porous, clean, wet sand can produce an increase in amplitude with offset resembling that produced by gas sands.
It is important to know the Vp/Vs ratio of the target and surrounding rocks to a reasonable degree of accuracy, as Vp/Vs ratios are a major determiner of AVO response.
Clean, porous, wet sands can cause AVO anomalies similar to those caused by gas sands in less porous rocks.
Figures & Tables
A cursory look at the contents of the book might lead the reader to belive that AVO is not a successful hydrocarbon indicator, as we show many examples of AVO predictions gone awry, and dry holes drilled based on AVO anomalies. However, a closer look at the pages will give the reader the message we are trying to convey: used properly and cautiously, AVO can be a valuable tool for direct detection. The preponderance of unhappy endings in the book is unavoidable, as the goal of this book is to provide information that may prevent other dry holes being drilled. Inevitably, the best lessons are learned from mistakes, a statement that applies to life in general as well as to seismic interpretation.