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Paper Number: 22
Petroleum
System: from Conventional to Unconventional
Zhao,
J1,2, Cao, Q.,1,2, Bai, Y. 1,2, Er,
C. 1,2, Li, J. 1,2 and Wu, W. 1,2
1School
of Earth Sciences and Engineering, Xi’an Shiyou University, Xi’an,
Shaanxi 710065, China.
Email: jzzhao@xsyu.edu.cn
2Shaanxi
Key Laboratory of Petroleum Accumulation Geology, Xi’an Shiyou
University, Xi’an, Shaanxi 710065, China
___________________________________________________________________________
The work of the traditional petroleum system (PS) study is largely
concerned with the process of petroleum from source to trap and its
focus is primarily on conventional accumulation. However, as more and
more unconventional accumulations have been discovered, reconsideration
of the connotation, study guidelines and exploration strategy of
petroleum system becomes necessary. The objective of this article is to
demonstrate that both conventional and unconventional accumulations can
result from a same source kitchen and frequently three significant types
of petroleum systems are formed therein. (1) Conventional PS. In such a
petroleum system, hydrocarbon accumulation occurs in conventional
reservoirs and all of the elements and processes such as source kitchen,
reservoir, seal, trap, migration and preservation are indispensable to
hydrocarbon accumulation; migration includes primary and secondary ones,
and secondary migration can be in long distance and is mainly driven by
buoyant force; the accumulations are geographically discrete and thus
can be termed as discontinuous accumulation; hydrocarbon distribution is
complex and controlled by multiple factors. (2) Tight PS. For this type,
source kitchen, reservoir and seal are key factors affecting hydrocarbon
accumulation, while migration is predominated by primary migration and
short distance secondary migration driven principally by non-buoyant
forces; the accumulation is quasi-continuous characterized by that
hydrocarbon distribution is extensive with no defined boundaries and an
accumulation is composed of numerous small-medium reservoirs not
connected to each other [1-3]; accumulation is not restrained by
structural traps but by subtle traps such as lithologic traps;
hydrocarbon distribution is highly controlled by effective source rocks,
“sweet spot” of reservoirs and seals as well. (3) Source rock PS. Two
typical representatives of such a petroleum system are shale oil/gas
system and coalbed methane system; as source rocks also act as
reservoirs, this kind of petroleum system is self-sourced and
self-reservoired; accumulation is continuous distinguished by that
hydrocarbon distribution is extensive and consecutive with no defined
boundaries within the scope of source kitchen; traps have no effect on
the accumulation and migration is also unnecessary or inconsequential;
oil/gas accumulation and occurrence is governed by the quality of source
rocks, “sweet spots”, sealing conditions, and hydrogeological
dynamics.
It has been revealed that among the above 3 petroleum systems
resulted from a common source kitchen, close relationship and unique
laws governing hydrocarbon distribution must exist, and their richness
of hydrocarbon resources is assumed to be negatively proportional to
each other. As a result, they ought to be taken into consideration as a
closely related entirety in the study and exploration of petroleum
systems to enhance the successful rate.
References:
[1] Zhao J (2012) Natural Gas Geos 23(3): 393-406
[2] Zhao J et al. (2012) Acta Petrolei Sinica 32(s1): 37-52
[3] Zhao J et al. (2013) Oil &Gas Geol 34(5): 573-583
