Prediction of thin shoal-facies reservoirs in the carbonate platform

PETROLEUM EXPLORATION AND DEVELOPMENT Volume 40, Issue 3, June 2013 Online English edition of the Chinese language journal Cite this article as: PETROL. EXPLOR. DEVELOP., 2013, 40(3): 359–366.

RESEARCH PAPER

Prediction of thin shoal-facies reservoirs in the carbonate platform interior: A case from the Cambrian Xixiangchi Group of the Weiyuan area, Sichuan Basin LI Ling1,*, TAN Xiucheng1,2, ZHAO Luzi3, LIU Hong1, XIA Jiwen4, LUO Bing5 1. School of Resource and Environment, Southwest Petroleum University, Chengdu 610500, China; 2. State Key Laboratory of Oil and Gas Reservoir Geology and Exploration, Southwest Petroleum University, Chengdu 610500, China; 3. Exploration Department of PetroChina Southwest Oil and Gasfield Company, Chengdu 610051, China; 4. Shu’nan Gas Field, PetroChina Southwest Oil-gas Field Company, Chengdu 646001, China; 5. Exploration and Development Research Institution, PetroChina Southwest Oil-gas Field Company, Chengdu 629000, China

Abstract: This paper presents a geological prediction method of thin shoal facies reservoir through the analysis of shoal facies reservoir’s genetic mechanism of the Middle-Upper Cambrian Xixiangchi Group in the Weiyuan area, Sichuan Basin. The development of shoal facies reservoirs is controlled by shoal thickness. Both sedimentary rates and scales of the shoal are closely related to microtopographic highs, which can develop inheritably for a long time under a stable tectonic background. So we present a prediction method that depositional microtopographic highs and shoal reservoirs’ development probability can be portrayed by the thickness variation of isochronal geological bodies, which mainly composed of grain stone formed in a short time. Based on it, a prediction model was built for thin shoal facies reservoirs of the Middle-Upper Cambrian Xixiangchi Group, where useful geological data are extremely poor. The method was used to predict the distribution of shoal facies reservoirs within the research area. Later drilling showed that the prediction is consistent with the drilling result. This study can provide reference to the exploration of shoal facies reservoirs. Key words: carbonate platform; shoal; thin reservoir; prediction method; Cambrian Xixiangchi Group

1

Overview

In recent years, with the continuity of oil and gas exploration, more and more attention has been paid to structural-lithologic and lithologic reservoirs [1−3], which exhibit extremely strong heterogeneity in distribution. Therefore, predicting the distribution of the reservoir accurately is a key issue in exploration [4−6]. Marine carbonates are very important for oil and gas exploration in China, especially in some smallscale grain shoal reservoirs. The current commonly used seismic technology for reservoir identification can only recognize reservoirs whose thickness are over 10 m [7−8], however the shoal reservoirs in the platform are small in scale, with meter-scale thin reservoirs being very common [9−14]. Hence it is of great significance to discuss how to predict the distribution of this type of thin reservoirs. The Weiyuan structure in the Sichuan Basin is located in the upper slope zone in the southwest of the Leshan– Longnüshi paleouplift, and is currently the largest anticlinal

structure in the Sichuan Basin (Fig. 1). In this structure, the Sinian gas reservoir was discovered in 1964, and the Lower Permian Maokou gas reservoir was discovered in 1965. However, the reserve-to-production ratio has decreased rapidly after 40 years development, so it is strategically necessary to look for new succeeding strata. In 2005, the old wells in the Middle and Upper Cambrian Xixiangchi Group recorded a well-head tested productivity of 129.19×104 m3/d, which indicated a good exploration prospect in the Cambrian strata of this structure. However, no commercial gas flow was obtained in the six new completed exploratory wells. The actual coring observation (Fig. 2) showed that the heterogeneous reservoir distribution is the key to the problem. In the Weiyuan structure, there are 121 wells in total encountering the Cambrian, out of which 115 wells were mainly drilled in the 1960s– 1970s with the Sinian reservoir as the target bed. The logging suite is incomplete in these old wells and only more than ten wells meet the requirements for reservoir logging interpreting. Hence it is hard to predict the planar distribution of the reser-

Received date: 28 Mar. 2012; Revised date: 27 Mar. 2013. * Corresponding author. E-mail: [email protected] Foundation item: Supported by National Science and Technology Major Project (2011ZX05004-005-03); PetroChina Science and Technology Innovation Fund Project (2011D-5006-0105). Copyright © 2013, Research Institute of Petroleum Exploration and Development, PetroChina. Published by Elsevier BV. All rights reserved.

LI Ling et al. / Petroleum Exploration and Development, 2013, 40(3): 359–366

Fig. 1

Location and regional structural units of the study area, and the Cambrian lithological histogram

GR – Natural gamma ray; Δt – Acoustic travel time; φCore – Core porosity; Rt – Resistivity; RXO – Flushed-zone resistivity

Fig. 2

Relationship between the intra-platform shoal and the development of the reservoir of the Xixiangchi Group in Well Weihan 103

voir. This article discusses a geological prediction method for thin shoal facies reservoir distribution with the Cambrian

Xixiangchi Group in the Weiyuan area as an example, and tests its practical application effect.

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2

The Xixiangchi Group grain shoal

The middle-upper Cambrian Xixiangchi Group in the Weiyuan gas field is mainly composed by dolomite, and the lithology mainly includes gray, dark gray micritic–crystal powder dolomite intercalated with light gray oolitic dolomite, arenitic dolomite and gritty dolomite, etc. It was found from comprehensive analysis of the data from drilling, mud logging, logging and the sedimentary facies markers that the Xixiangchi Group is characterized by a restricted platform facies, with the subfacies of the intra-platform shoal being the main reservoir lithofacies (Fig. 2). With high-energy water from tides and waves in the intra-platform shoal, different types of grainstone developed, mainly including light gray oolitic dolomite, gritty dolomite, or bioclastic dolomite, etc. Corresponding to the change in secondary sea-level, there developed deepening-upward vertical and shallowing-upward sedimentary sequences [15-16]. The reservoir development was closely related to the grain shoal and mostly happened in the middle or upper parts of a single deposited grain shoal (Fig. 2). The reservoir is composed of “pinhole” oolitic dolomite, arenitic dolomite and gritty dolomite (Fig. 2). Microscopic observation revealed that the “pinholes” are dominated by residual intergranular pores and dissolved-enlargement residual intergranular pores (Fig. 3). The reservoir is low in porosity and permeability. In addition, the reservoir is small in scale, with single layer logging interpreted less than 4 m in thickness. Therefore, the reservoir presents the characteristics of thin layer, poor horizontal correlation, and multiple sets of thin reservoirs vertically superposed (Fig. 4).

3

Origin of shoal reservoir

Research has found that shoal reservoirs with primary intergranular pores as the main reservoir space have characteristics of being grain-supported, with cement being undeveloped at initial compaction and early shallow burial stages, with intergranular cement being undissolved[9]. Comparative analysis revealed the characteristics of the reservoir with primary intergranular pores in this area. It is controlled by the grain shoal. The reservoir space types are dominated by residual

Fig. 3 han 1

intergranular pores and dissolved-enlargement residual intergranular pores. The pores have fabric selectivity and only seabed cement developed at the places where grains contacted. Linear-convex-concave-contact framework support was seen among the grains under the initial compaction (Fig. 3). With respect to the reservoir space type, moldic pores or intragranular dissolved pores, formed as a result of early selective dissolution, were rarely seen, which indicates that the grain shoal did not undergo early exposure after deposition (Fig. 3) and the development of the grain shoal reservoir of the Xixiangchi Group in the area was closely related to the preserved intergranular pores. As for the intergranular pore preservation mechanism, Tan Xiucheng et al. [17−18] suggested that, after seabed cementation, the grains with early rimmed cement became frameworksupported and with a narrowed throat under initial compaction; the pressure-released fluid cementation resulted in the tight shoal margin, and the limited shallow-buried cement in the intergranular pores clogged the throat, while the cementation terminated after the diagenetic fluid reached the dissolution-cementation balance. After the shallow burial stage, the grain shoal reservoir formed an isolated diagenetic lens, and this isolated state continued to exist until the large-scale reconstruction period of the reservoir. The above analysis shows that the preservation status of the primary pores in an unexposed shallow shoal is related to the overlying static pressure, and is closely related to the sedimentary rates in different micro-environments. The microtopographic highs are often located above the wave base where the sedimentary rate is relatively high. They are characterized by a developed shoal core micro-environment, and the single thickness and cumulative thickness of grain shoals is quite high, which is favorable to the preservation of primary pores to form a reservoir. In contrast, at places with relatively low topography, where the sedimentary rate is low, the grain shoals are finger-like and the sedimentary grains mainly contact at the points under the static pressure of overlying strata. The pressure-released saturated fluid can be effectively discharged to complete the cementation of intergranular pores, thus unfa-

Photographs of residual intergranular pores in spar arenitic dolomite from the Xixiangchi grain shoal at 2217.74 m in Well Wei-

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Fig. 4 Vertical and horizontal distribution of the Xixiangchi reservoir in Well Wei 89 – Well Wei 88 – Well Weihan 102 – Well Wei 26 – Well Wei 37

vorable to the preservation of intergranular pores. Therefore, the thickness of grain shoals forming in the same period not only represents the microtopographic fluctuation but also predicts the approximate reservoir development probability.

4 Relationships between grainstone thickness, microtopography and reservoir development Microtopographic highs in a carbonate platform are usually located above the wave base and grain shoals develop there. The sedimentary rate of the grain shoals is faster than other microfacies, and for an unexposed shallow shoal zone, the sedimentary rate of grain shoal in a microtopographic high is always higher than that in other zones [18], so the topographic difference is enhanced. Moreover, after the deposition of grain shoal, a framework-supported structure would form within the grain sediments under the physical compaction from the accretion of the overlying sediments. Therefore, the compaction ratio is far lower than that of fine-grained sediments. As a result, difference in sedimentary thickness due to the topographic difference between different microfacies is further enhanced [19]. It indicates that compaction correction is not necessary considering that the microtopography of the sedimentary period within the platform is almost recovered. The mi-

croscopic observation also showed that the arenite was composed of micritic dolomite; the spar arenitic dolomite with such characteristic came into being when the micritic dolomite, which formed at the early stage during the evaporating concentration process of sea water, was broken by the strengthened water power. And the dolomitization could be considered as isometric displacement, so contributed little to the newly added reservoir spaces. The greater contribution of the dolomitization to the grain shoal reservoir lied in the fact that it provided a framework resistant to pressure solution, so little influence was exerted on the cement filling of intergranular pores due to the small number of pressure solution product, which was favorable to the preservation of intergranular pores [20]. It was found from the core observation that pressolution suture lines did not develop in the grain stones, so it is also possible for compaction correction not to be considered for the recovery of microtopography of unexposed grain shoal during early dolomitization. In summary, for a sedimentary body mainly composed by grain shoal, the thickness of its approximately isochronal geological bodies can be used to approximately recover the microtopographic relief at the time when it was formed, and to further characterize the development probability of the reservoir.

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In the platform interior, microtopography also changes during the geological historical period, especially the syndepositional tectonic activity period, when the tectonic activities would lead to changes in sedimentation and subsidence centers [18]. In a larger area, sedimentary and subsiding rates of different facies may differ greatly [21]; in the early and middle sedimentary periods of the middle-upper Cambrian Xixiangchi Group, the tectonic environment in the Sichuan Basin was relatively calm and stable subsidence was the main activity [22]. In a relatively small area of the same facies in the platform, sedimentary rates did not vary much, but because the disturbance of the wave base did not go very deep, a relatively larger sedimentary difference was still seen between the local high and low places. With such a large difference and the effect of high-frequency change in sea level, the single-cycle isochronal geological bodies formed are often small in scale and vertically exhibit multicycle superposition, which leads to difficulty in the identification and comparison of isochronal geological bodies. If long lasting stability were seen in the synsubsidence and syndeposition environment, regionally traceable and comparable isochronal geological bodies with high thickness would form. Given the minor difference in the microtopography of the platform, thickness mostly differed on the meter-scale among the isochronal geological bodies, which formed over a short period. However, it is just the tiny variation in sediment thickness that can predict the approximate microtopographic changes that happened during the sedimentary period. In summary, for the platform’s interior environment, formed as a result of stable syndepositional subsidence in the

Fig. 5

period with relatively calm tectonism, the thickness variation of approximately isochronal geological bodies (mainly composed by grainstone sediments that are traceable and mostly in the same layer) can be used to approximately characterize the approximate microtopographic relief of unexposed shallow shoals and the development probability of the reservoir. 4.1 Selection of approximately isochronal geological bodies and the topographic relief The middle-upper Cambrian Xixiangchi reservoirs are mainly grain-shoal controlled reservoirs whose development distribution is closely related to the sedimentary face distribution. Based on this principle, it is possible to predict the distribution of favorable reservoir zones through the thickness distribution of the Xixiangchi grain shoals. Analysis of the sedimentary evolution of the Xixiangchi Group in the study area showed that in the sedimentary period of the Xixiangchi Group, the structure subsided stably; the basin saw a resurgence in energy caused by the initial transgression, so that the basin was in the phase when transgressive shallow shoal based on the restricted platform flat of the Gaotai Formation developed. There was a large area of stable dolomite distribution which had been deposited in the area in the early sedimentary period of the Xixiangchi Group and was mainly composed of high-energy grainstone [22]. The response of the natural gamma-ray logging curve showed two peaks with a trough; this set of grainstones at the bottom lied on the same horizontal level, so it could be regarded as one entity of the approximately isochronal geological body (Fig. 5). Such set of isochronal geological bodies with grainstone as the main

Microtopographic interpretation profile of the Xixiangchi Group in the Weiyuan area

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component was horizontally traceable and comparable, and its thickness only differed on meter-scale, which reflected the topographic difference in the sedimentary period. In Well Wei 26 and Well Wei 42, the isochronal geological body at the bottom of the Xixiangchi Group is relatively thicker, suggesting high topography in the sedimentary period. 4.2 Correlation between approximately isochronal geological body and reservoir development Tan Xiucheng and others believed that under stable tectonic environment, the microtopography in a carbonate platform formed during the sedimentary period continued to exist over a relatively long period, controlling the distribution of grainstone and shoal reservoir [18]. The tectonic setting of the middle-upper Cambrian Xixiangchi Group in the Sichuan Basin was relatively calm during the sedimentary period, which controlled the subsequent grain shoal thickness variation and reservoir distribution to a certain extent. From the correlation between the thickness variation of the approximately isochronal geological body at the bottom of the Xixiangchi Group and the cumulative reservoir thickness interpreted by the logging data, it can be seen that they are highly positively correlated (Fig. 6). It indicates that the development of the Xixiangchi reservoir in the area can be roughly represented by the thickness of the bottom approximately isochronal geological body, mainly composed by grainstones, and a geological model can thus be established. The re-tested productivity of old wells in the area showed that the thickness of the approximately isochronal geological body in the Weiyuan structure had a significant positive correlation with the re-tested productivity of old wells. For example, the tested productivity exceeded 10×104 m3/d in Well Wei 26 and Well Wei 42 which are both located in microtopographic highs, or where the approximately isochronal geological body is thick, whereas at microtopographic lows or where the approximately isochronal geological body is thin, the single-well productivity tested were mostly less than 1×104 m3/d. This indicates that the thickness of the isochronal geological body is closely related to the microtopography reservoir scale and tested productivity (Figs. 7 and 8). The

Fig. 6 Relationship between the thickness of grainstone at the bottom of the Xixiangchi Group and the reservoir thickness interpreted by logging data

Fig. 7 Relationship between the thickness of grainstone at the bottom of the Xixiangchi Group and the tested productivity

Fig. 8 Relationship between the microtopographic relief of the Xixiangchi Group in the Weiyuan area and the result of productivity test

above exploration results also show that the idea and method of predicting the distribution of the middle-upper Cambrian Xixiangchi thin shoal reservoir in the Weiyuan area, where the approximately isochronal geological bodies are mainly composed of the grainstone at the bottom of the Xixiangchi Group, meets the objective geological situations. 4.3 Prediction model for the distribution of Xixiangchi reservoir and detection of favorable reservoir zones Using data about the thickness of the approximately isochronal geological body of the Xixiangchi Group in the study area, a thickness isoline map was plotted (Fig. 9), which shows that the grain shoals in the area is distributed from the northeast to the southwest; the outer belt of the grain shoals is larger in scale while the inner belt of the grain shoals is smaller in scale, because the outer belt is blocking the inner belt. Considering the tested productivity and reservoir thickness, the criteria for the prediction of the distribution of reservoir development were set: (1) the most favorable reservoir zone, where the bottom grain dolomite thickness is more than 18 m; (2) the favorable reservoir zone, where the bottom grain dolomite is 17–18 m; (3) the relatively favorable reservoir zone, where the bottom grain dolomite is 16–17 m; (4) the average reservoir zone, where the bottom grain dolomite thickness is less than 16 m. The most favorable reservoir zones include the Wei 55–Wei 5 well area, Wei 42–Weishui 2–Wei 78–Wei 21 well area, Wei 26–Wei 37 well area, Wei 54 well area and Wei 13–Wei 89 well area. In these most favorable reservoir zones, high-output industrial tested gas has been detected in multiple wells; the

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Fig. 9 Thickness of grain dolomite of the approximately isochronal geological bodies on the bottom of the Xixiangchi Group and distribution of favorable reservoir zones

When the geological model was first established, the well data for the Cambrian Xixiangchi Group in the Weiyuan area was limited to that from the wells drilled specifically into the Sinian strata and six wells drilled only into the Cambrian strata, i.e., Well Weihan 1, and Well Weihan 101–Weihan 105. After the geological model was established, Well Wei 001-H1 and Well Wei 001-H2 were drilled for the re-development of the Sinian strata in 2007, which are respectively located in the favorable reservoir zone and the average reservoir zone. The logging interpretation showed significant differences in the reservoir development of these two wells whose cumulative reservoir thicknesses are 13.4 m and 8.0 m respectively. This fact fully demonstrated the correctness of the above prediction idea and method. The results show that it is reliable to use the thickness of approximately isochronal geological bodies mainly composed by grainstone to represent the topography in the sedimentary period and predicting the development probability of reservoir.

micro-environment develops, the single grain shoal and cumulative grain shoals are relatively high in thickness. This is favorable to the preservation of primary pores and to the formation of reservoirs. In contrast, at places where topography is relatively low, the sedimentary rate is low and the grain shoals are finger-like. Single grain shoal and cumulative grain shoals there are low in thickness, which is unfavorable to the preservation of intergranular pores. Therefore, the thickness of the grain shoals formed in the same period not only indicates the microtopographic fluctuation, but is also able to approximately represent the probability of reservoir development. The microtopography in carbonate platform of the sedimentary period could continue to exist over a relatively long period, controlling the sedimentation of the adjacent sequence and the distribution pattern of the reservoir. So the thickness of the approximately isochronal geological body composed grainstone can be used to vicariously indicate the probability of reservoir development. This method has a good application effect for the Xixiangchi Group in the Weiyuan area, indicating that this method can be used for reservoir prediction in old areas with enough drilling wells, old data and lacking tri-porosity logging suite, and for the potential tapping of new reservoirs.

5

References

favorable reservoir zones are distributed from the northeast to the southwest, mainly seen in the Wei 112–Wei 101 well area, where low-output gas wells are common (Fig. 9). 4.4

Analysis of method effectiveness

Conclusions

Most of the Xixiangchi reservoirs in the Weiyuan area are multiple sets of thin, unexposed, superposed, shallow shoal reservoirs. In microtopographic highs where the shoal core − 365 −

[1]

Zhao Zongju, Li Yuping, Wu Xingning, et al. Conditions for migration and accumulation of Ordovician giant lithologic oil


and gas reservoirs in Tazhong region and exploration poten[2]

[3]

[4]

Ma Yongsheng, Cai Xunyu, Guo Xusheng, et al. The discov-

[13] Tan Xiucheng, Mou Xiaohui, Luo Bing, et al. Main control-

ery of Puguang Gas Field. Engineering Science, 2010, 12(10):

ling factors for intraplatform oolitic bank of the Member 1 of

14–21.

Lower Triassic Feixianguan Formation in southern Sichuan

Kang Baoping, Zhang Fan, Zhang Jian, et al. Control factors

Basin. Journal of Palaeogeography, 2010, 12(1): 49–55.

of Carboniferous stratum-structure composite traps in the east

[14] Liu Hong, Tan Xiucheng, Li Ling, et al. Characteristics and

of Sichuan. Journal of Oil and Gas Technology, 2008, 30(1):

main controlling factors of porous carbonate reservoirs: A

184–187.

case from the Jia 5 Member of the Jialingjiang Formation,

Xie Zhan’an, Zhou Jinming. New ideas improving capability

southwest Sichuan Basin. Petroleum Exploration and Devel-

of subtle oil/gas reservoir exploration. Oil Geophysical ProsHao Fang, Zou Huayao, Fang Yong. The difficulties and fron-

model for deep high-porosity and high-permeability carbonate

tiers of subtle oil/gas reservoir research. Earth Science Fron-

reservoir and its applications: Examples in Puguang Gas Field. Oil Geophysical Prospecting, 2011, 46(2): 275–280.

tiers, 2005, 12(4): 481–486. [6]

Bao Shihai, Zhang Xiuping, Yang Yufeng, et al. Gas potential

[16] Liu Hong, Tan Xiucheng, Zhou Yan, et al. Prediction of plat-

identification of the oolitic beach reservoirs in Feixianguan

form-edge bank carbonate reservoir in Feixianguan Formation

Formation in the north part of east Sichuan. Natural Gas In-

of Huanglongchang Gas Field in the northeastern Sichuan Basin. Acta Petrolei Sinica, 2009, 30(2): 219–224.

dustry, 2003, 23(Supp.): 35–37. [7]

Ma Yongsheng, Guo Xusheng, Guo Tonglou, et al. Discovery

[17] Zhao Zongju, Zhou Xinyuan, Wang Zhaoming, et al. Distribu-

of the large-scale Puguang gas field in the Sichuan Basin and

tion of marginal facies and main controlling factors of reservoirs

its enlightenment for hydrocarbon prospecting. Geological

in the Ordovician, the Tarim Basin. Oil & Gas Geology, 2007, 28(6): 738–744.

Review, 2005, 51(4): 477–480. [8]

[9]

opment, 2011, 38(3): 275–281. [15] Huang Handong, Luo Qun, Zhao Di. Lithofacies identification

pecting, 2005, 40(5): 609–615. [5]

Basin. Petroleum Exploration and Development, 2011, 38(3): 268–274.

tial. China Petroleum Exploration, 2004, 9(5): 12–20.

Ran Longhui, Xie Yaoxiang, Dai Tanshen. New knowledge of

[18] Tan Xiucheng, Nie Yong, Liu Hong, et al. Research on the

gas-bearing potential in Cambrian system of southeast Si-

method of recoverying microtopography of epeiric carbonate

chuan Basin. Natural Gas Industry, 2008, 28(5): 5–9.

platform in depositional stage: A case study from the layer A

Li Ling, Tan Xiucheng, Ding Xiong, et al. Difference in depo-

of Jia 2~2 Member in Moxi Gas Field, Sichuan Basin. Acta

sitional characteristics between intra-platform and mar-

Sedimentologica Sinica, 2011, 29(3): 486–494.

ginal-platform shoals in Leikoupo Formation, Sichuan Basin

[19] Xia Jiwen, Li Ling, Luo Bing, et al. Cambrian depositional

and its impact on reservoirs. Acta Petrolei Sinica, 2011, 32(1):

system in southwest Sichuan. Journal of Southwest Petroleum University, 2007, 29(4): 21–25.

70–75. [10] Ding Xiong, Chen Jingshan, Tan Xiucheng, et al. Structural

[20] Moore C H, Druckman Y. Burial diagenesis and porosity evo-

characteristics of intra-platform shoal in the Leikoupo Forma-

lution, Upper Jurassic Smackover, Arkansas and Louisiana.

tion (T2) in the transitional zone of the central and southern Sichuan Basin. Petroleum Exploration and Development,

AAPG Bulletin, 1981, 65(4): 597–628. [21] Li Ling, Tan Xiucheng, Zhou Suyan, et al. Sequence lithofacies paleography of Leikoupo Formation, Sichuan Basin. Journal of

2012, 39(4): 444–451. [11] He Yunlan, Fu Xiaoyue, Liu Bo, et al. Control of oolitic beaches sedimentation and diagenesis on reservoirs in Feixianguan Formation, northeastern Sichuan Basin. Petro-

Southwest Petroleum University: Natural Science Edition, 2012, 34(3): 13–22. [22] Li Ling, Tan Xiucheng, Xia Jiwen, et al. Influences of eustatic movement on the Cambrian reservoirs of bank facies in Wei-

leum Exploration and Development, 2012, 39(4): 434–443. [12] Tan Xiucheng, Luo Bing, Li Zhuopei, et al. Jia 2 Member doloarenite reservoir in the Moxi gas field, middle Sichuan

− 366 −

yuan gas field, the Sichuan Basin. Natural Gas Industry, 2008, 28(4): 19–21.