Paleoporosity and critical porosity in the accumulation period and their impacts on hydrocarbon accumulation—A case study of the middle Es3 member of the Paleogene formation in the Niuzhuang Sag, Dongying Depression, Southeastern Bohai Bay Basin, East China
Pet.Sci.
Paleoporosity and critical porosity in the accumulation period and their impacts on hydrocarbon accumulation-A case study of the middle Es member of the Paleogene formation 3 in the Niuzhuang Sag, Dongying Depression, Southeastern Bohai Bay Basin, East China
Liu Mingjie 2 3
Liu Zhen 1 2
Sun Xiaoming 1 2
Wang Biao 0 2
0 member , Niuzhuang Sag, Bohai Bay Basin
1 State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing) , Beijing 102249 , China
2 China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2014
3 School of Geoscience and Technology, Southwest Petroleum University , Chengdu, Sichuan 610500 , China
Similar reservoir sandbodies and fault conduit systems in the sandstone reservoirs in the middle Es3 member of the Niuzhuang Sag have been problematic for a long time. The following problems remain unsolved: 1) The distribution of sandstone porosity is inconsistent with the hydrocarbon accumulation. The oil sandstones have low porosity instead of high porosity. 2) Sandstones, which have the same properties, have different levels of oiliness, and the sandstones with almost the same properties show different degrees of oil-bearing capacity. This study analyzes the condition of reservoirs in the research area during the accumulation period in terms of paleoporosity estimation and discusses the critical porosity of the sandstone reservoirs during the same period. The following conclusions can be drawn from the results. 1) Although reservoir properties are low at present and some reservoirs have during the accumulation period. Similarly, high porosity during the accumulation period does not indicate that the present porosity is high. 2) The present reservoir location is consistent with the distribution of high paleoporosity during the accumulation period. This result indicates that high porosity belts are prone to hydrocarbon accumulation because of the dominant migration pathways generated as a result of property discrepancies under similar fault conduit conditions. Consequently, the hydrocarbon mainly accumulates in high porosity belts. Paleoporosity during the accumulation period is found to be a vital controlling factor. Therefore, high paleoporosity sandstones in the middle Es3 member of the Niuzhuang Sag have great potential for future exploration.
Paleoporosity; critical porosity; dominant migration pathways; hydrocarbon accumulation
-
Hydrocarbon mainly migrates during the accumulation
period. Both primary and secondary migration is closely
related to the properties of reservoirs. The capacity of the
hydrocarbon to migrate to sandstone reservoirs depends on
the pressure difference between the source rocks and the
reservoir rocks and indicates the lower limit of sandstone
reservoirs in the accumulation period. The indicated lower
limit is a critical property of sandstone
(Liu et al, 2006;
2007a; 2012)
. Hydrocarbon can accumulate only if reservoir
porosity is greater than the critical porosity.
S e v e r a l s t u d i e s f o c u s o n t h e l o w e r l i m i t o f t h e
petroliferous reservoir, and many methods have been
proposed to determine the cutoff value
(Guo, 2004; Wang et
al, 2009; Cao et al, 2009)
. In addition, quantitative analyses
have been performed on the lower porosity limit
(Pang et al,
2003; Zhu et al, 2006; Zhu, 2008; Jiao et al, 2009)
.
Although much research has been done on the cutoff value
of sandstone, these studies focus only on the accumulative
condition of the reservoir at present. The critical porosity
of the reservoir during the accumulation period is seldom
studied. By researching the main controlling factors of
lithologic reservoirs in different types of basins, Liu et al
(2006; 2007a; 2012) proposed the theory of four-factors
mainly controlling accumulation, wherein the critical porosity
during the accumulation period was determined to be one
of the factors. Pan et al (2011a) determined that the critical
porosity of tight sandstone in the Chang 8 member in the
area, the critical porosity of the Chang 8 member sandstone
2012).
Several problems have remained unsolved for a long
time in the middle Es3 member of the Niuzhuang Sag. The
oiliness of sandstones in the same reservoir is different, thus
indicating that the sandstones with low properties possess
superior oil-bearing capacity; the oil-bearing sandstones
with similar properties have different degrees of oil-bearing
capacity. Conventional accumulation theories have been
unable to provide satisfactory solutions to these problems, as
the present properties will not be the same as the properties
during the accumulation period. In this study, we attempt
to examine this by analyzing the relation between reservoir
porosity and hydrocarbon formation and enrichment.
2 Geologic setting and stratigraphy
The Bohai Bay Basin, an important
hydrocarbonproducing basin in China, is located in eastern China and
covers an area of approximately 200,00 (...truncated)