wAbstract
@Hydrocarbon source rocks contain significant volumes of organic
matter, are capable of expelling petroleum when heated, and have
produced most of the world's known oil volumes. Recently, source
rocks have also become recognized as unconventional economic reservoirs.
Here we present a new way of identifying, characterizing, and
mapping spatial distributions and variations of thick source rocks
(20 m) that is based on seismic data only. This has a significant
impact on the prospect risk assessment of petroleum plays. Rock
property studies of organic-rich claystones show that the acoustic
impedance (AI), which is the product of compressional velocity
and density, decreases nonlinearly with increasing total organic
carbon (TOC) percent. Claystones mixed with low-density organic
matter (TOC3-4) have significant lower AI and higher intrinsic
anisotropy than otherwise similar nonorganic claystones. This
gives the top and base source rock reflections characteristic
negative and positive high amplitudes, respectively, which dim
with increasing reflection angle. In addition, the TOC profile,
which is a smoothed TOC percent curve, influences the top and
base amplitude responses. An upward-increasing TOC profile has
the highest amplitude at the top, while the opposite asymmetry
is observed for downward-increasing TOC profiles. By using seismic
data, we therefore can map lateral distribution, thickness, variation
in TOC profiles, and, with local well calibration, convert AI
data to TOC percent. This approach to mapping source rocks may
change the way petroleum systems are evaluated.x
Introduction
Influence of organic matter on rock properties
Seismic data quality
Seismic expression of source rock
@TOC profiles
@Interpreting the source rock interval
Conclusions
Acknowledgments
References cited