Lithologic Reservoirs

Seven lithofaciese including thick sand, middle-thick sand, thin sand, sandstripe, massive mudstone, thin mudstone and middle-thick mudstone developed on the outcrop of deep water deposits at Lucheng of Tianlin county in Guangxi. Every two of these lithofaciese combined into a lithofacies assemblage, thus there are 7 lithofacies assemblages can be recognized, including thick sand and massive mudstone, thick sand and thin mudstone, middle-thick sand and thin mudstone, middle-thick sand and middle-thick mudstone, thin sand and thin mudstone, thin sand and middle-thick mudstone, as well as middle-thick mudstone with striped sand. The assemblages then superimposed one by another to form 7 patters of the layer cake typed stratigraphic configuration, including stacked thick sand, stacked thick sand and middle-thick sand, stacked middle sand, stacked middle sand and thin sand, stacked thin sand, stacked thin sand and mudstone, mudstone with striped sand. Although the configuration of deep water deposits is simple, it has complex reservoir heterogeneity, and it can forms both conventional and unconventional reservoirs. These cognitions have great significance for hydrocarbon exploration and development of deep water deposits.

Influencing factors of shale gas-bearing property of Lower Cambrian Niutitang Formation in northwestern Hunan

Huang Yanran， Yang Rongfen， Xiao Zhenghui， Yu Ye， Yang Xian

2015, Vol.27(4): 11–16 Abstract ( 631 ) PDF (915 KB) ( 497 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.002

The Lower Cambrian Niutitang Formation in northwestern Hunan developed a set of organic-rich shale which is characterized by stable distribution and large size, with great burial depth and relatively complete conservation in synclinorium of Sangzhi-Shimen area. The gas content of the enriched shale gas area of Niutitang Formation is between 1.48 m3/t and 8.75 m3/t, so these areas have a good potential of industrial development. Organic carbon content determines the resources potential of shale gas, and meanwhile affects the adsorption and storing capacity. There are five genetic types reservoir space, including primary intercrystalline or intergranular micropores, organic material micropores, dissolved micropores of unstable mineral, structural fractures and cleavage fissures. The adsorption and resolution of shale gas is easy to happen. The storage state of shale gas is under the combined influence of organic material content and the type of reservoir space. The natural gas generated by high and over-matured organic-rich shale can accumulate and form reservoir under good preservation conditions. Temperature, pressure, burial depth and mineral composition have little effects on the gas-bearing property of Niutitang Formation.

Reservoir characteristics of shale gas of Upper Permian Dalong Formation in Lianyuan-Shaoyang depression, central Hunan

Xiao Zhenghui， Niu Xianqiang， Yang Rongfeng， Yu Ye， Huang Yanran， Chen Xinyue

2015, Vol.27(4): 17–24 Abstract ( 1058 ) PDF (2852 KB) ( 449 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.003

To evaluate shale gas exploration potential in Upper Permian Dalong Formation in Lianyuan-Shaoyang depression, central Hunan, the reservoir characteristics of shale gas were investigated by the analysis of total organic carbon （TOC） content, mineral composition, microscopic characteristics of pores and fractures, porosity and permeability of shale. The results show that the TOC content has close relationship with lithology, the TOC content of siliceous mudstones were the highest, with an average value over 3%, which shows that it is obviously controlled by sedimentary environment. The brittle mineral contents in the siliceous mudstones were 67.7% on average, which is essentially the same as the brittle mineral contents in Barnett siliceous shale of America. The tectonic fractures developed well, and they are related to the brittle mineral contents and geological structure. The organic micropore is the main composition of pore-fracture system in the siliceous mudstones with higher TOC content. The porosity and permeability of siliceous mudstones were both low, being lower than 5% and 0.01 mD respectively. Fracture development degree is the dominant factor for influencing porosity and permeability of siliceous mudstones.

Sedimentary characteristics of sandstone in Chang 10₁ stage of Yanchang Formation in Ordos Basin

Ding Xiong， Tian Jingchun， Yao Jingli， Yu Hanghang， Li Yinghong

2015, Vol.27(4): 25–31 Abstract ( 664 ) PDF (2099 KB) ( 442 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.004

The fluvial-delta-lacustrine depositional system develops for long in Chang 101 stage of Triassic Yanchang Formation in Ordos Basin. The sedimentary microfacies as braided channel and meandering channel of fluvial facies, braided subaqueous distributary channel, land distributary channel, subaqueous distributary channel and mouth bar of delta facies all develop sandstones. Based on the sedimentary facies study, the sedimentary characteristics of each sedimentary microfacies sandstone are deeply studied. The result shows that scour surface, trough cross-bedding, tabular cross-bedding and parallel bedding mainly developed in sandstone of braided channel, braided distributary channel and braided subaqueous distributary channel distributed in the west of the basin with fining-upwards normal cycle as the dominate feature. The grain-size probability curve of sandstone mostly has two steps or three steps. In the east of the basin, scour surface, trough cross-bedding, tabular cross-bedding, parallel bedding and sand bedding mainly developed in sandstone of meander channel, land distributary channel, subaqueous distributary channel and mouth bar with finingupwards normal cycle as the dominate feature while coarsening-upward inverse cycles can be recognized as well. The grain-size probability curve of sandstone mostly has two steps or three steps, moreover, four steps. Further comparative analysis indicates that sand bodies are mostly developed in braided channel, braided distributary channel, meandering channel and land distributary channel, followed by braided subaqueous distributary channel, subaqueous distributary channel and mouth bar in Chang 101stage.

Fractal characteristics of shale pores of Longmaxi Formation in southeast Sichuan Basin

Xu Yong， Lu Chengfu， Chen Guojun， Zhong Jiaai， Yang Wei， Xue Lianhua

2015, Vol.27(4): 32–39 Abstract ( 705 ) PDF (1333 KB) ( 629 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.005

Based on fractal theory and methods and the nitrogen adsorption results of shale samples from the Lower Silurian Longmaxi Formation in southeast Sichuan Basin, the fractal characteristics of pores were studied, the fractal dimension was calculated by using the fractal Frenkel-Halsey-Hill（FHH） model, and the relations of fractal dimension with pore structure, organic carbon content and shale composition were discussed. The results show that mesopores are the main pores in shale, and mainly consist of ink-bottle-like and slit-shaped pore. The fractal dimension of shale samples is between 2.629 2 and 2.898 0, which reflects the complexity and heterogeneity of the shale porosity. The smaller the average pore diameter is, the more the micropores are, the more complex the pore structure is, the more irregular the specific shale face is, the larger the specific surface face is, and the higher the fractal dimension is. Organic carbon content and the degree of micropore development impact a lot on the fractal dimension.

Dolomite genesis of Carboniferous Huanglong Formation ineastern Sichuan Basin

Liu Shiyu， Hu Mingyi， Hu Zhonggui， Dai Weiyan

2015, Vol.27(4): 40–46 Abstract ( 588 ) PDF (1426 KB) ( 295 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.006

The Carboniferous Huanglong Formation in eastern Sichuan Basin is an important producing formation for natural gas. Dolomitization is a requirement for the development of high quality reservoir, and the research of genetic types for dolomite has important meaning for oil and gas exploration. Based on core observation and outcrop description, combined with thin section analysis data, it is considered that Huanglong Formation mainly developed the following types of dolomite: mud-microcrystalline dolomite, powder to fine-grained dolomite and residual particles powder to fine-grained dolomite as well as dolomite cement filling in pores, holes and cracks. On the basis of the data of X ray diffraction analysis and geochemical characteristics of stable isotope δ13C and δ18Ο, it is found that formation conditions and physical characteristics of different types of dolomite in the study area exhibit different characteristics, and it’s more reasonable to use different origin types for the explanation. Four kinds of genetic model of dolomite of Huanglong Formation were summarized, including: diagenetic dolomitization evaporation pump model for mud-microcrystalline dolomite, burial diagenetic dolomitization compaction model for （residual particles） powder to fine-grained dolomite, diagenetic adjustment dolomitization model for freshwater dolomite and construction hydrothermal dolomitization diagenetic model for abnormal morphology dolomite.

Pore characteristics of shale of Lower Paleozoic in southern Sichuan-northern Guizhou

Yang Wei，Chen Guojun， Hu Shijun， Lu Chengfu， Xu Yong， Yang Shuang

2015, Vol.27(4): 47–52 Abstract ( 656 ) PDF (1038 KB) ( 300 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.007

Pore types, size, morphology, distribution and fracture feat ures by field emission scanning electron microscope imaging were studied on shale samples of the Lower Paleozoic Niutitang Formation, Wufeng FormationLongmaxi Formation in the southern Sichuan-northern Guizhou. The results show that there are four main pore types developed in shale, including: intergranular pores, organic-matter pores, dissolved pores and microfracture. Organicmatter pores developed well in shale, which is favor of storing adsorbing-gas. Dissolved pores distributed sporadically, but the cumulative pore volume is much larger with wider pore diameters which are almost macropores and even reach to micrometer-scale. Intergranular pores developed relatively less, with little contribution to pore volume. Microfractures developed in shale can connect other types of pores, which is beneficial to shale gas store and flow. Additionally, the major components of shale are composed of quartz, feldspar, carbonate and clay minerals. The brittle minerals content with an average of 54.9% is conducive to the formation fracturing and exploration.

Reservoir characteristics and evaluation of the Permian Xiazijie Formation in Wuerhe area, Junggar Basin

Chen Bo， Liu Yunli， Liu Haishang， Chen Zhen， Wen Ge， Shi Ji’an

2015, Vol.27(4): 53–60 Abstract ( 669 ) PDF (2171 KB) ( 464 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.008

Base on core observation and casting thin section, combination with mercury injection property, this paper studied the reservoir characteristics of the Permian Xiazijie Formation in Wuerhe area, Junggar Basin. The results show that the reservoir rock types are mainly conglomerate and sandstone, conglomerate is dominated by glutenite and the sandstone types are mainly composed of lithic sandstone, occasional lithic feldspar sandstone. Pore types are mainly primary pores, with some primary pores and small amounts of micro cracks. The pore structure is poor, and the porosity and permeability are low. The reservoir properties are mainly affected by the sedimentation and diagenesis, sedimentation determines the original porosity of sand body and the late diagenesis types and intensity of the reservoir, and diagenesis is the key to decide whether sand body eventually become effective reservoir or not. Strong compaction and cementation and relative weakness dissolution experienced in the study area are the main causes of poor reservoir properties. Accorded to the reservoir properties and pore parameters, the reservoir in the study area can be divided into five types, mostly concentrated in type Ⅳ and Ⅴ, and most belong to low porosity and low permeability reservoir. The reservoir properties of the second member of Xiazijie Formation are better than that of the first member, of which the reservoir is of relatively high quality in background of low porosity and low permeability.

Research on heterogeneity of Chang 2 reservoir in Taiyangwan area, Ordos Basin

Xie Qing， Wang Jianmin， Shi Shengbiao

2015, Vol.27(4): 61–67 Abstract ( 656 ) PDF (1809 KB) ( 491 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.009

Reservoir heterogeneity is one of the important factors that affect remaining oil distribution. In recent years, retention phenomenon of remaining oil in Taiyangwan area is serious. In view of this phenomenon, accorded to the practical geological situation, geological data of lithologies, physical properties, electric properties and oiliness were adopted to conduct qualitative evaluation of Chang 2 reservoir heterogeneity and its cause, and to analyze the influences of heterogeneity on remaining oil distribution of the reservoir. By using experiment，logging and standard contrast methods, this paper divided heterogeneity into the intra-layer, inter-layer, plane and microscopic heterogeneities for respective discussion. The result shows that the intra-layer heterogeneity is strong in the study area, which is mainly controlled by sedimentary structure, rhythm, permeability and interlayers; inter-layer heterogeneity is generally strong with uneven development in each layer, the heterogeneity of the Chang 23 is the strongest, followed by Chang 21 and Chang 22; the plane heterogeneity is mainly affected by the distribution of sand body and sedimentary microfacies; pore structure at micro level is complex, and various diagenesis heightened reservoir heterogeneity degree. The research of the reservoir heterogeneity provides important theory basis for grasping the distribution of remaining oil and later exploitation in the study area.

Research advances of microseismic monitoring

Gui Zhixian， Zhu Guangsheng

2015, Vol.27(4): 68–76 Abstract ( 723 ) PDF (698 KB) ( 598 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.010

In recent decades, microseismic monitoring technology in oil and gas operation has got rapid and comprehensive developments. These progresses are mainly manifested as the further affirmation and high appraisal of the microseismic hydraulic fracture monitoring, gradual commercialization of the microseismic monitoring software and hardware, the thorough and specialized researches about the methods of data acquisition, data processing and interpretation in microseismic monitoring. The work of microseismic monitoring technology and services increase rapidly. Only in the basins in North America, hydraulic fracturing microseismic imaging is conducted in thousands of wells every year. With the rise of shale gas exploration and development in China, fast promotion appears in microseismic monitoring technology as well.

Microseismic information extraction in low signal-to-noise ratio microseismic signal based on S-transform

Wang Peng， Chang Xu， Gui Zhixian， Wang Yibo

2015, Vol.27(4): 77–83 Abstract ( 622 ) PDF (2367 KB) ( 289 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.011

Low porosity and permeability reservoirs, especially shale gas reservoirs, have been the focus of current oil and gas exploration and development. Fracturing is the main stimulation method for this kind of reservoirs. Moreover, microseismic monitoring is an effective tool of the fracturing processing monitoring and evaluation, and it is based on the microseismic detection and information extraction. However, it is difficult to record satisfied microseismic signal under complex geological conditions. This paper analyzed the characteristics of low signal-to-noise ratio microseismic signal using timefrequency analysis based S-transform. According to the time-frequency analysis of contaminated signals, S-wave component of microseismic events has a robust feature of anti-noise. Using the characteristics above, a satisfied result is achieved in the real microseismic monitoring processing with low signal-to-noise ratio.

Abstraction of frequency-dependent AVO attributes based on generalized S transform

Gao Gang， Li Yuhai， Gui Zhixian， Wang Wentao

2015, Vol.27(4): 84–88 Abstract ( 687 ) PDF (1287 KB) ( 516 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.012

In recent years, laboratory and theoretical studies showed that fluid-media often leads to varying degrees of dispersion and attenuation of seismic waves, which provides a basis for identifying the reservoir fluid. In order to identify reservoir fluid more effectively, it is necessary to study to improve the accuracy and reliability of the seismic wave dispersion attributes. Firstly, the theory of the seismic wave dispersion attributes was summarized, the advantages and disadvantages of a variety of time-frequency analysis method were analyzed and compared, generalized S transform was optimized to process and analyze seismic data because it’s time window is flexibly adjusted according to the frequency distribution characteristics of seismic signals. Secondly, the corresponding calculation process was conducted. Finally, this method was applied in actual data calculation of K71 fault block, and the result is in good correspondence with actual drilling results.

Identification method of shale reservoir based on well logging and log information

Yan Jianping， Wen Danni， Sima Liqiang， Yan Yu， Geng Bin

2015, Vol.27(4): 89–95 Abstract ( 466 ) PDF (1 KB) ( 347 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.013

Shale oil and gas reservoir becomes a concerned target in unconventional oil and gas exploration. Taking shale strata of Funing Formation in Gaoyou Sag of Subei Basin as a research subject, this paper used core and testing oil data to demarcate well logging and log information, and further to research the recognition method of unconventional shale oil reservoir. Through the analysis of shale reservoir types and its well logging and log response characteristics, it was found that most shale reservoirs developed calcite lithofacies （crack） with high content of brittleness mineral, and a few developed mudstone facies with low content of brittleness mineral and containing or not containing calcareous. In view of these two kinds of shale reservoir types, the corresponding two kinds of interpretation model were put forward. The bubble chart and radar map can be used to show the differences between two models. The identification method of shale reservoir based on the combination between well logging and log infor mation were established, which can provide a basis for shale oil and gas reservoir recognition and effective development in Subei Basin.

Well logging evaluation methods of shale gas reservoir: A case study from Shunan area, Sichuan Basin

Zhong Guanghai， Xie Bing， Zhou Xiao

2015, Vol.27(4): 96–102 Abstract ( 708 ) PDF (1199 KB) ( 735 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.014

Shale gas is an important unconventional natural gas resource, and research on well logging evaluation methods of shale gas reservoir is still at the starting stage in China. Based on well logging evaluation methods of shale gas reservoir at home and abroad, a petrophysical model of shale gas reservoir was established by some core data. Meanwhile, methods to calculate total organic carbon content, adsorbed gas content and free gas content were studied, a method to calculate the main reservoir parameter for shale gas reservoir was initially formed, and the corresponding well logging interpretation module was also developed. So, a set of shale gas reservoir logging evaluation techniques was establishment, which can provide guidance and technical support for the shale gas exploration and development in Sichuan Basin.

AVO response characteristics of coalbed methane stratum in Qinshui Basin

Feng Xiaoying， Qin Fengqi， Tang Yutong， Liu Hui， Wang Ya

2015, Vol.27(4): 103–108 Abstract ( 473 ) PDF (2235 KB) ( 559 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.015

With the deepening of exploration and development of coalbed methane in Qinshui Basin, It was found that the enrichment rule of coalbed methane is one of the key factors influencing the development efficiency, and AVO technique is important to predict the enrichment rule of coalbed methane. What are the AVO response characteristics of coalbed and coalbed methane? Are they as the same as sand bed gas? For these questions, this paper studied the fluid substitution of different lithologies and its AVO response characteristics under different gas saturation in Qinshui Basin. The result shows that the AVO response characteristic of coalbed is different from coalbed methane, the AVO characteristic of coalbed is “dim spot”, and the AVO characteristic of coalbed methane is “relatively bright spot”. This study can provide reliable technical support for the exploration and development of coalbed methane.

Apparent permeability model of shale gas considering stress sensitivity and adsorption

Guo Xiao， Ren Ying， Wu Hongqin

2015, Vol.27(4): 109–112 Abstract ( 580 ) PDF (541 KB) ( 620 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.016

Multi-scale flow is observed obviously in the shale gas reservoir, and stress sensitivity and adsorption also make the flow mechanism of shale gas more complex. A corrected apparent permeability model considering the two factors is derived based on the Beskok-Karniandakis model. The effects of stress sensitivity and adsorption on shale gas apparent permeability were analyzed by using the new model. The following results were achieved in the calculation and analyses of the model: when the pore radius is over 5 nm, the apparent permeability declines and then goes up with the pressure drops down under the influence of the stress sensitivity together with the adsorption; when the pore radius is less than 5 nm, the permeability loss caused by the stress sensitivity is less than the permeability increase created by adsorption and slippage, thus the apparent permeability presents an upward trend with the pressure drops down.

Effect of water invasion on production of horizontal well in low permeability water drive gas reservoir

Yuan Lin， Li Xiaoping， Wang Changqing

2015, Vol.27(4): 113–118 Abstract ( 608 ) PDF (688 KB) ( 506 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.017

During the developing of low permeability water drive gas reservoir, even if water did not breakthrough at the bottom of the horizontal well, local water invasion was still an important factor for affecting the production of horizontal well. Based on the Joshi method, this paper simplified the three-dimensional seepage field of horizontal well into two two-dimensional seepage fields, namely the zone far from well and near wellbore, considering the local water invasion in the zone far from well and flow characteristic in low permeability gas reservoir, used the method of conformal transformation to build a new model for studying the production change law of horizontal well during the water invasion in low permeability water drive gas reservoir. Sensitivity analysis indicates that as the increasing of gas-water volume ratio, distance of water advance and stress sensitivity index, the production of horizontal well decreases, while as the increasing of primary formation permeability and slip factor, the production of horizontal well also increases, unless in the high pressure gas reservoir, water-bearing gas reservoir and gas wells with lower producing pressure drop, the effect of slippage effect and stress sensitivity on production can be neglected. This study can provide a new solution to study production change law of horizontal well during water invasion in low permeability water drive gas reservoir.

Exploration status, main geologic characteristics and their differences of tight oil between America and China

Qiu Zhen， Li Jianzhong， Wu Xiaozhi， Wang Shejiao， Zheng Min， Guo Qiulin

2015, Vol.27(4): 119–126 Abstract ( 966 ) PDF (1180 KB) ( 715 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.018

In recent ten years, great progress has been made in the tight oil exploration around the world, suggesting that tight oil resources have great potential, which has became the most realized target for exploration of the unconventional oil. Based on pervious studies referring to tight oil, this paper summed up the exploration status of tight oil between America and China, and discussed the main geologic characteristics of them and their differences. The main geologic characteristics of tight oil are as follows: （1）it was commonly developed in the sediment-tectonic setting with well preservation; （2）organic-rich source rocks associated with it extend over large areas with high hydrocarbon-generating intensity; （3）tight oil reservoirs are distributed in a large area continuously with giant reservoir space; （4）tight oil reservoirs were effectively coexisted with source rocks with highly active accumulation. The differences of geologic characteristics of tight oil between America and China mainly exit in three aspects of source rocks, tight reservoirs and oil deposits. These above conclusions are hoped to provide some beneficial suggestions for next tight oil exploration in China.

Progress of reservoir uncertainty modeling

Dai Weiyan， Li Shaohua， Qiao Jiayi， Liu Shiyu

2015, Vol.27(4): 127–133 Abstract ( 521 ) PDF (558 KB) ( 598 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.04.019

Due to the incomplete information and reservoir heterogeneity, it is unable to accurately determine the distribution of reservoir and its properties. Stochastic modeling technique can characterize the uncertainty of geologic model by generate multiple realizations through changing the stochastic simulation path. Reservoir uncertainty modeling is a new technology developed on the basis of the stochastic modeling, and it paid more emphasis on the characterization and evaluation of uncertainty that resulted from data acquisition, modeling parameter and response of models. Based on a large number of relevant references, this paper classified the sources of uncertainty in the process of reservoir modeling, expounded the local uncertainty, spatial uncertainty and response uncertainty in reservoir modeling, and put forward some methods to reduce the uncertainty. The research of the reservoir uncertainty mainly focused on the aspects of uncertainty evaluation and uncertainty reduction at present, and the research of uncertainty modeling methods should be strengthen.