Diagenesis and reservoir quality of the Lower Cretaceous Quantou Formation tight sandstones in the southern Songliao Basin, China

Sedimentary Geology 330 (2015) 90–107
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Sedimentary Geology
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Diagenesis and reservoir quality of the Lower Cretaceous Quantou
Formation tight sandstones in the southern Songliao Basin, China
Kelai Xi a,b,⁎, Yingchang Cao a,⁎⁎, Jens Jahren b, Rukai Zhu c, Knut Bjørlykke b, Beyene Girma Haile b,
Lijing Zheng d, Helge Hellevang b
a School of Geosciences, China University of Petroleum, Qingdao, Shandong 266580, China
b Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern 0316, Oslo, Norway
c Research Institute of Petroleum Exploration & Development, Beijing 100083, China
d College of Energy, China University of Geosciences, Beijing 100083, China
⁎ Corresponding author at: School of Geosciences, C
Qingdao, Shandong 266580, China.
⁎⁎ Corresponding author.
E-mail addresses: kelai06016202@163.com, xi.kelai@g
cyc8391680@163.com (Y. Cao).
http://dx.doi.org/10.1016/j.sedgeo.2015.10.007
0037-0738/© 2015 Elsevier B.V. All rights reserved.
a b s t r a c t
a r t i c l e i n f o
Article history:
Received 16 August 2015
Received in revised form 20 October 2015
Accepted 23 October 2015
Available online 30 October 2015
Editor: Dr. B. Jones
Keywords:
Tight sandstone diagenesis
Reservoir quality
Quartz cement
Carbonate cements
Oil emplacement
Songliao Basin
The Lower Cretaceous Quantou Formation in the southern Songliao Basin is the typical tight oil sandstone in
China. For effective exploration, appraisal and production from such a tight oil sandstone, the diagenesis and
reservoir quality must be thoroughly studied first. The tight oil sandstone has been examined by a variety of
methods, including core and thin section observation, XRD, SEM, CL, fluorescence, electron probing analysis,
fluid inclusion and isotope testing and quantitative determination of reservoir properties. The sandstones are
mostly lithic arkoses and feldspathic litharenites with fine to medium grain size and moderate to good sorting.
The sandstones are dominated by feldspar, quartz, and volcanic rock fragments showing various stages of disin-
tegration. The reservoir properties are quite poor, with low porosity (average 8.54%) and permeability (average
0.493 mD), small pore-throat radius (average 0.206 μm) and high displacement pressure (mostly higher than
1 MPa). The tight sandstone reservoirs have undergone significant diagenetic alterations such as compaction,
feldspar dissolution, quartz cementation, carbonate cementation (mainly ferrocalcite and ankerite) and claymin-
eral alteration. As to the onset time, the oil emplacementwas prior to the carbonate cementation but posterior to
the quartz cementation and feldspar dissolution. The smectite to illite reaction and pressure solution at stylolites
provide a most important silica sources for quartz cementation. Carbonate cements increase towards interbed-
ded mudstones. Mechanical compaction has played a more important role than cementation in destroying the
reservoir quality of the K1q4 sandstone reservoirs. Mixed-layer illite/smectite and illite reduced the porosity
and permeability significantly, while chlorite preserved the porosity and permeability since it tends to be oil
wet so that later carbonate cementation can be inhibited to some extent. It is likely that the oil emplacement oc-
curred later than the tight rock formation (with the porosity close to 10%). However, thicker sandstone bodies
(more than 2 m) constitute potential hydrocarbon reservoirs.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
As one of themost important unconventional hydrocarbon resources,
tight sandstone oil is widely distributed inmajor petroliferous basins, po-
tentially forming large-scale petroleum reserves in China (Zou et al.,
2013; Zou et al., 2014; Wang et al., 2015). Tight sandstone is defined as
reservoirs with a porosity less than 10%, in situ formation permeability
less than 0.1 mD or air permeability less than 1 mD in Chinese basins
(Zou et al., 2012). Reservoir quality is considered as the primary factor
in tight sandstone oil exploration (Fic and Pedersen, 2013; Storker et al.,
hina University of Petroleum,
eo.uio.no (K. Xi),
2013; Zou et al., 2013). In general, tight sandstone reservoirs are deeply
buried and have gone through complicated diagenetic alterations, pro-
gressively changing the reservoir quality (Vinchon et al., 1996; Karim
et al., 2010; Yang et al., 2012; Zhang et al., 2015). Therefore, it is important
to have a detailed understanding of the diagenesis (Rahman andMcCann,
2012). However, there are still uncertainties related to quantification of
mineral dissolution and precipitation processes that have significant ef-
fects on reservoir quality (Schmid et al., 2004; Gier et al., 2008; Taylor
et al., 2010; Bjørlykke, 2014). Diagenetic evolution (time and tempera-
ture), cement sources andmass transfer (open vs closed system) in sedi-
ments as well as their impacts on reservoir quality are still debated
(Schmid et al., 2004; Taylor et al., 2010; Bjørlykke and Jahren, 2012;
Yuan et al., 2015). In addition, the role of hydrocarbon emplacement on
mineral reactions is also still debated (Cao et al., 2012; Liu et al., 2014).
The Lower CretaceousQuantou Formation tight sandstone is a prolific
oil-producing unit in the southern Songliao Basin (Li et al., 2013).
91K. Xi et al. / Sedimentary Geology 330 (2015) 90–107
Although there are many publications dealing with stratigraphy, sedi-
mentology and hydrocarbon accumulation in the southern Songliao
Basin, little attention has beenpaid to sandstone diagenesis and reservoir
quality evaluation (Li et al., 2007; Zhang et al., 2007; Hu et al., 2008;
Xiong et al., 2008; Feng et al., 2013; Dong et al., 2014). Authigenic quartz,
carbonate cements, dissolved feldspars and clay minerals are commonly
observed in the reservoirs determining the reservoir quality (Li et al.,
2013; this study). Former studies on diagenesis in this area only focused
on quartz cement and its origin, but did not investigate in detail any
other diagenesis reactions linked to reservoir quality (Xi et al., 2015). Fur-
thermore, the origin of the carbonate cements and timing of diagenesis,
especially the diagenetic history and the processes controlling reservoir
quality, have not been studied thoroughly. Understanding quantitative
diagenetic processes (including oil emplacement) and cement sources
in sandstones and their impact on reservoir quality are essential to further
exploration, appraisal and production of tight sandstone oil within this
area.
The objectives of this paper were mainly focused on the different
aspects of diagenesis compared to the former studies focusing only on
quartz cementation and its origin: (1) perform a detailed diagenetic
analysis and identify the sources of the carbonate cements in these
tight sandstones; (2) reconstruct the diagenetic history of the tight
sandstones and evaluate if oil emplacement affected the inorganic dia-
genesis; and (3) assess the effects of the different diagenetic processes
in time and space on the reservoir quality.
Fig. 1. (A) Locationmap of the study area and sub-tectonic units of the Songliao Basin (I)Weste
Uplift Zone, (V) Southeastern Uplift Zone, (VI) Southwestern Uplift Zone, (VII) Kailu Depression
2. Geological background
The Songliao Basin is a Jurassic–Neogene lacustrine basin with a
dual-structure fault-depression in northeastern China (Fig. 1). The
basin is located between 42°25′ to 49°23′ N and 119°40′ to 128°24′ E
with an area about 26× 104 km2 (Zhang and Zhang, 2013). It can be fur-
ther subdivided into seven first class tectonic zones (Zhou et al., 2012),
namely the Western Slope Zone, Northern Pitching Zone, Central
Depression Zone, Northeastern Uplift Zone, Southeastern Uplift Zone,
Southwestern Uplift Zone and Kailu Depression Zone (Xi et al., 2015)
(Fig. 1). The study area, as one of the most oil-rich areas, belongs to
the Central Depression Zone and consists of three