Table of Content

01 October 2015, Volume 37 Issue 5

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Characteristics of Interstitial Material in Tight Standstone and Its Effects on Reservoir

Yang Yong1，2*, Huang Yougen2, Feng Yansong2, Liu Bin3, Lei Bianjun4

2015, 37(5):  1-8.  DOI: 10.11885/j.issn.1674-5086.2013.12.09.31

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The Shan1 He8 Member is tight sandstone with many consedimental volcanics in the middle-north of Ordos Basin.
Compared with common clastic rocks，the fillings of tight sandstone are of many types，complicated components，and intensive
diagenetic evolution. The fillings consist of consedimental volcanic ash，clay mineral，carbonate cement and metasome，
siliceous cement，slender glimmer，muddy debris and carbon dust. Based on the research of reservoirs，the relativity of the
fillings and pore evolution was studied by using slices，scanning electron microscopy，cathode luminescence and so on. The
analysis is mainly focused on genesis，character，diagenetic evolution of fillings. Research shows that consedimental volcanic
ash is mother material of secondary dissolved pores；calcite cement strongly damage pore in late-diagenetic period，and certain
amount of kaolinite is favorable for pore growing.

Depositional System and Gas Potential of Shanxi Formation and Member 8#br# of Xiashihezi Formation in Southwest Ordos Basin

Guo Xiaojun1*, Chen Shiyue2, Wang Lianguo1, Li Desheng3, Liu Lang3

2015, 37(5):  9-15.  DOI: 10.11885/j.issn.1674-5086.2013.10.23.03

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The main provenances of the Shanxi Formation and Member 8 of Xiashihezi Formation in southwest Ordos Basin
are analyzed on the basis of field geological profile，the core wells，logging data single factor graphs such as stratigraphic
thickness，sand thickness and sand ratio are plotted. Combined with sedimentary facies of single well facies profile and well
comparing to profile，we find the sedimentary period of Shanxi formation mainly include meandering river，meandering river
delta and shallow lake facies. During the deposition of Member 8 of Xiashihezi Formation，braided river，braided river delta
and shallow lake facies developed. Shibangou-Huanxian，Pingliang-Zhenyuan-Qingyang，Kouzhen-Xunyi-Zhengning delta
succession develop in the Shanxi Formation and Member 8 of Xiashihezi Formation. Study area has good hydrocarbon source
rock and reservoir and cap conditions. According to the source rock，reservoir，cap characteristics and well logging，gas test
results，we select“Zhenyuan-Qingcheng-Huanxian”as favorable exploration area and“Xunyi-Chunhua”exploration target
area. Althoughnatural gas exploration degree is not adequate，the exploration potential is tremendous in southwest Ordos
Basin.

Natural Gas Accumulation Sequence Research：A Case Study on#br# Jurassic Petroleum System in Taibei Sag

Zhang Yu1*, Zhang Jinchuan1, Yang Shengyu2, Huang Weidong3

2015, 37(5):  16-22.  DOI: 10.11885/j.issn.1674-5086.2013.12.30.03

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Conventional gas，tight gas and shale gas are very rich in Jurassic petroleum system in Taibei Sag. Geological
analysis pointed out that the distribution rules and reservoir features of the shale gas，tight gas and conventional gas are of
sequential characteristics. Based on exploration and development practices，we concluded that shale gas，tight gas and conventional
gas always exist together in a petroleum system. They have experienced source rock retaining，primary migration，
secondary migration and accumulation，and formed different types of gas reservoirs in shale，tight sand and conventional reservoirs
respectively. Sequential characteristics including migration periods，accumulation times，distributions，gas contents，
development techniques，reserve characteristics and E & P periods were summarized. In one petroleum system with suitable
geological environments，different types of gas reservoirs can be found after any types of reservoirs in the sequence which was
discovered first. This rule could be a new approach in gas exploration.

Recognition of High Yield and Stable Yield Factors of Daanzhai Tight#br# Oil，Guihua Oilfield

Huang Dong1*, Yang Guang1, Wei Tengqiang1, Deng Yan1, Tan Yaqian2

2015, 37(5):  23-32.  DOI: 10.11885/j.issn.1674-5086.2013.12.17.05

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Based on study of Guihua Oilfield，the most productive Da′anzhai Oilfield in Sichuan，we recognize that there are
several pay beds of Da′anzhai reservoir and the Da2 sub-member is the most productive one. Shelly-beach limestone near the
sedimentary facies transformation zone are preferentially filled by the hydrocarbon laterally migrated from source rock on the
other side of this zone. Pressure difference caused by the hydrocarbon-generating pressurization is the migration force and low
angle fractures contributes to the oil & gas migration. According to analysis of the latest drilled horizontal well，GQ1H，we
come to the conclusion that low velocity abnormal bodies in shelly-beach limestone near the sedimentary facies transformation
zone are going to be the favorable targets of next horizontal oil well.

The Continental Incised Valley Filling Architecture in#br# Qinhuangdao H Oilfield，Bohai Bay

Chen Fei1*, Hu Guangyi1, Fan Ting′en1, Sun Lichun1, Zhao Chunming2

2015, 37(5):  33-39.  DOI: 10.11885/j.issn.1674-5086.2013.10.16.07

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The continental incised valley is a kind of U topography with strong erosion，and filling sandbody is good reservoir.
According to the analysis of cores，seismic interpretation and well-logging，the authors have thoroughly studied the sedimentary
facies characters of the Neogene Minghuazhen Formation of Qinhuangdao H oilfield in the Bohai Bay Basin with grain size
analysis and a great deal of laboratory testing data. The authors propose that the sedimentary facies type of NmII and NmIV of
Minghuazhen Formation lies incised valley. Detailed studies have been made on the rock types and sedimentary structures of
incised valley，and relevant sedimentary models have been established. Incised valley water power suddenly increased，which
is dominated by medium and fine sandstone，grain size is relatively big. The sandbody transports on certain direction，cutting
and stacking each other，which presents the imbricated structure. The study demonstrates that the falling of relative lacustrine
level and the strong hydrodynamic conditions are the major causes of incised valley.

Hydrocarbon Accumulation and Distribution in the Periphery of#br# Guangrao Buried Hill in the Dongying Sag

Gao Xia1*, Wang Jianwei2

2015, 37(5):  40-46.  DOI: 10.11885/j.issn.1674-5086.2013.12.13.01

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Aiming at the research difficulty of hydrocarbon accumulation period and enrichment process in the periphery of
Guangrao buried hill in the Dongying Sag，critical moments and process of reservoir forming are analyzed in this paper. Genetic
relationship among oil-bearing blocks is determined through the methods of multi-layer oil-water interface statistical analysis
and paleohydrocarbon-water contact reconstruction. Late Guantao depositional period and late Minghuazhen depositional period
are the two critical moments of reservoir forming. Due to the limited blocking capability of the unconformities with high
sand/shale ratio，with the continuous hydrocarbon supply from the northern hydrocarbon generation sag，multi-layered hydrocarbon
reservoirs constantly adjust around the large scale unconformity surface，and a dynamic accumulation model is formed
which is characterized by gradual adjustment from north to south in multiple layers. Petroleum accumulation in the study area
should be universal and it will be of good guiding significance for petroleum exploration in the similar areas.

Research and Targets Prediction of Mesozoic Volcanic Reservoir in#br# Central Bohai Sea Area

Zhang Hongguo*, Wang Xin, Lu Fengting, Guan Dayong, Gao Kunshun

2015, 37(5):  47-54.  DOI: 10.11885/j.issn.1674-5086.2014.02.24.03

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Buried hill of Mesozoic volcanic rocks are of excellent reservoir forming conditions，but exploration degree was
not adequate which was confined by study of reservoir. Focusing on factors which affect reservoir development，combined
analysis of geophysics and petroleum geology materials，we began with lithology，lithofacies and types of reservoir spaces，
and concluded that acid lava reservoir was better developed while reservoir of basic lava and tuff was closely related with
the intensity of secondary transformation on the same condition. Furthermore，lithology，lithofacies and structural movements
controlled the devolvement of reservoirs. Based on the results of the above analysis，combined with the lithology and exploration
stage of Mesozoic volcanic in study area，favorable exploration targets could be determined with analysis focused on recognition
of characteristic lithology and lithofacies in single well，and analysis on intensity of regional structural moments.

Late Fault Adjustment and Late Accumulation Pool-forming#br# Model in Qionghai Uplift，Pearl River Mouth Basin

Zhang Yingzhao1, Zhu Weilin2*, Gao Yangdong2

2015, 37(5):  55-63.  DOI: 10.11885/j.issn.1674-5086.2013.11.24.01

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To figure out hydrocarbon distribution pattern，the adjustment of hydrocarbon reservoirs of Miocene Zhujiang
formation under Miocene tectonic background and secondary pool-forming pattern were analyzed in Qionghai uplift，Pearl
River Mouth basin of South China Sea. The upper pools and lower pools which were divided by T41 subsurface boundary were
characterized by late accumulation and late fault adjustment respectively. The lower pools with great reservoir storage property
had relatively heavy and high viscosity oil. The upper pools had light and low viscosity oil. Hydrocarbon of both upper pools and
lower pools had derived from same source rock. Mid-Miocene NWW SEE trend echelon fault system had adjusted lower pools
and migrated hydrocarbon upwards to form upper pools. The hydrocarbon pool-forming model with characteristics of late fault
adjustment and late accumulation was proposed reasonedly，that is，part hydrocarbon from lower pools of Zhujiang Formation
had migrated upwards along late fault system and accumulated in the upper reservoirs. The lower pools after adjustment and
upper pools superimposed vertically，form relatively heavy lower pools and light upper pools.

Acoustic Properties of Low Permeability Cores and its Application to#br# Reservoir Gas Predication

Fan Yiren1，2*, Xing Donghui1，2, Deng Shaogui1，2, Li Runze3, Ge Xinmin1，2

2015, 37(5):  64-70.  DOI: 10.11885/j.issn.1674-5086.2013.08.11.07

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To solve the problem in qualitative identification and quantitative prediction of gas content in low permeability
reservoir，an acoustic rock physics experiment was carried out which simulates the reservoir conditions and a quantitative
research of the influence of confining pressure，pore pressure，effective stress and pore fluid on compression and shear wave
velocity was done. Then the relationship between compression and shear wave velocity，elastic parameters and the gas saturation
was systematically analyzed. And the experimental result was checked with Krief elastic parameters prediction method. The
experimental results and numerical simulations show that the acoustical properties are affected by combination of factors such
as porosity，pressure，fluid property etc.，and shear wave velocity ratio-wave impedance intersection and compression and shear
wave square intercept can be used to identify gas. The ability of using acoustic logging data to identify reservoir fluid can be
improved with the two methods.

A Study on the Method of Keeping SNR in the Phase#br# Decomposition Deconvolution

Zhang Hua1，2，3*, Zhang Jinfeng4, Yang Bo5, Yuan Xiaohua5, Chen Aiping2，3

2015, 37(5):  71-78.  DOI: 10.11885/j.issn.1674-5086.2013.09.03.02

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The deconvolution technology is the major method to improve the resolution of seismic data. The traditional deconvolution
is based on minimum phase wavelet assumption，but in fact，this is inconsistent with the actual situation of mixed
phase seismic wavelet. Due to the formation′s absorption effect and the weak high frequency signal in the real seismic data，
the high frequency signal is susceptible to high frequency noise pollution. The traditional deconvolution reduces the SNR of
seismic record at the same time when improving the resolution，so the conflicts of the SNR and resolution of in practical seismic
exploration work is serious. This paper puts forward a kind of mixed phase wavelet deconvolution method，which can keep the
SNR of seismic data and at the same time finish phase decomposition. This method when improving seismic record resolution，
can automatically control the high-frequency noise of seismic data to achieve harmony between the resolution and SNR，and
improve the ability of seismic record characterization of subsurface structure.

Influence of Mercury Injection Pressure on Lower Limits Analysis of Tight#br# Sandstone Reservoirs

Li Ye*, Sima Liqiang, Wu Feng, Huang Dan, Li Qing

2015, 37(5):  79-84.  DOI: 10.11885/j.issn.1674-5086.2013.08.29.06

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The minimum flow pore throat radius method is often used to determine the lower limits of porosity and permeability
of tight sandstone gas reservoirs. This method is based on mercury intrusion method. It can determine the lower limits
by quantitative analysis of relationship between micro pore structure and permeability. Researches indicate that high mercury
injection pressure may affect rock pore structure，which triggers the pondering over whether mercury injection pressures influences
lower limits and how to choose appropriate mercury injection data to acquire lower limits suitable for practical geological
situation. These problems have not been deeply discussed by far. So this paper focuses on these problems，taking the tight
sandstone reservoirs in P area of the central part of Sichuan Basin as an example. The research results show the lower limit of
porosity determined by minimum flow pore throat method falls when the selected mercury injection pressure rises from 30 MPa
to 200 MPa. The calculated results and production testing results are in good agreement when the mercury injection pressure is
close to the formation pressure.

Experimental Investigation on the Flow Characteristics of the Local#br# Oil-water Two Phases Flow System in Hilly-terrain Tube

Xu Guangli1，2*, Zhang Xin3, Cai Liangxue1, Zhang Jing3, Wang Gaozhuang4

2015, 37(5):  85-90.  DOI: 10.11885/j.issn.1674-5086.2013.07.09.12

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The study is motivated by the problem of pipeline corrosion due to water accumulation at low spots. Lab-scale
experiments were conducted to identify the flow patterns of the hilly-terrain transparent organic glass tube. Test loop with
pipe diameter of 50 mm I.D. with diesel and tap water was used. The oil-water flow patterns were found to develop from the
smooth stratified flow to wavy stratified flow and even to emulsive stratified flow when residual water sheared by the faster
flowing oil. With the increasing oil superficial velocity，the average water velocity increases linearly while the average water
holdup decreases linearly once all the water entered the upwards inclined tube. The oil superficial velocity corresponding to the
minimum Uos carrying all the water entering the upwards inclined tube was found to increase with the increasing inclination
angle，but change a little with increasing water volume. These results show that water can be carried out by flowing oil.

Research on Phase Behavior of High CO2 Fluid of Songnan#br# Volcanic Reservoir

Jia Ying1*, Yan Jin1, Sun Lei2, Shi Zhiliang1, Zhen Rongchen1

2015, 37(5):  91-98.  DOI: 10.11885/j.issn.1674-5086.2013.04.24.01

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Songnan volcanic gas reservoir has high concentration of CO2 and the phase behavior is very complex. In the
near critical region，the phase change trend，such as density and viscosity over temperature，is different from that of common
hydrocarbon gas. The abnormal phase change may influence the development of gas field，and even create the production
accidents. Thus，it is necessary to carry out research on high CO2 fluid of Songnan gas reservoir. Firstly，a series of PVT
experiments of high CO2 fluid were conducted. PVT parameters of fluid with different CO2concentration were detected and
calculated. Then，in order to analyze the near-critical character of CO2 fluid，the EOS for fluid with high concentration of CO2
was modified. Finally，p − T phase graph of fluid with CO2 concentration was drawn，which provided the foundation for the
judgment of the phase behavior of Songnan gas field.

Experimental Studies on Oil and Gas Coordinated Development#br# Mechanism of Oil Rim Reservoirs

Liu Jia1，2*, Cheng Linsong2, Fan Zifei3, Huang Shijun2, Zhang Jian4

2015, 37(5):  99-105.  DOI: 10.11885/j.issn.1674-5086.2013.08.11.02

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In order to study the mechanism of oil and gas coordinated development in oil rim reservoirs，three-dimensional
visualized gas-cap reservoir physical simulation device was established to simulate the processes of oil and gas development
at different gas production rates. Monitoring and records of the interface migration law and well performance can be realized
through visualization window. According to experimental results，migration speed of oil-gas interface was reduced with increasing
gas production rates while migration speeds of internal and external oil-gas interfaces gradually became close，which
effectively slows down occurrence of gas channeling，reduces production gas oil ratio and increases the swept volume of gas
drive，so as to improve its development effect. And by means of the material balance principle，engineering methods for gas-cap
oil-rim reservoir by collaborative development are worked out to deduce the migration law of oil gas interface under different
development methods. When the gas production rate is small while the gas production rate is big，the oil gas interface tends to
intrude oil rim in a much slower way，and proper oil production rate and gas production rate can maintain the balance of oil gas
interface.

Researches on Fluid Flow Features and Water Flooding Suitability in#br# Network Fractured Well

Su Yuliang1*, Wang Wendong1, Zhao Guangyuan2, Yuan Bin3, Ren Long1

2015, 37(5):  106-110.  DOI: 10.11885/j.issn.1674-5086.2013.06.23.30

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The single well productivity of network fractured well can increase tremendously than that of conventional fractured
well in tight oil reservoirs in Ordos Basin. However，due to the low pressure coefficient，the development efficiency depending
on natural energy is not very good. Therefore，exploration on water flooding network fractured well is of significance. Based
on the characteristics of complex fracture network，the fracture network numerical simulation model is established to analyze
the fluid flow features in vertical network fractured well. Taking rectangular well pattern as example，stimulation mechanism
for vertical network fractured well is studied on the condition of water flooding well pattern，and the water flooding suitability
is explored. Results demonstrate that fracture network increases the degree of producing reserves，enlarges the sweep volume
on the side of vertical wall of fractures and improves the sweep efficiency between injection and production well. Due to
the “shortest flowing distance”，production well′s water cut increasing rate in fracture network increases fast after water
breakthrough. Case analysis is made on the vertical network fractured well in typical tight oil reservoir of Changqing oilfield.
Furthermore，the optimized well pattern for network fractured water flooding is designed and discussed.

The Research on Fracture Initiation Mechanism for Sand Jetting#br# Perforation Technology

Qu Hai1*, Liu Ying2, Xu Ying1

2015, 37(5):  111-116.  DOI: 10.11885/j.issn.1674-5086.2013.03.11.04

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Compared with the shaped charge perforation，sand jetting perforations are characterized by bigger diameter，longer
length and smaller perforation number. Because the fracture morphology will be affected by perforated tunnel，the stress distribution
around tunnels and fracture initiation mechanism were studied for sand jetting perforation. Based on the 3D finite element
computation method and the research results of indoor experiments，hole distribution，perforation azimuths and azimuths of
horizontal well are evaluated to reveal three fracture shapes around wellbore. The results show that the fracture easily initiate
from the root of perforation tunnels；when the degree of included angle θ between horizontal section and minimium horizontal
stress is less than 30°，double layer perforation method can create one fracture，and multiple fractures are generated by helical
perforation and symmetric perforation. Because longitudinal fracture is more easily created than transverse ones，hydraulic
fracture process will lead to a contortion fissure. In the condition of θ more than 80°，there is only a longitudinal fracture in
horizontal wellbore，which is not affected by perforation parameters. The result was also a theoretical basis for reasonable use
of jetting perforation and hydraulic fracturing in horizontal well.

An Experimental Study on Anti-channeling Technology with Foam in#br# CO2 Flooding

Liu Zupeng1*, Li Zhaomin2

2015, 37(5):  117-122.  DOI: 10.11885/j.issn.1674-5086.2013.11.04.04

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In the pilot test of CO2 flooding in Yaoyingtai Oilfield，early CO2 channeling decreased its sweeping volume and
production capacity. Low permeability fractured core models were generated by core cutting technique. The foam blocking
ability and flooding performance were measured by core flooding experimental apparatus and the effects of different foam
injection schemes on foam plugging and EOR results of foam displacement following water and gas flooding were conducted.
The experiment results show that CO2 foam can increase fluid flow resistance in the fracture，reduce liquid motility effectively
with resistance factors between 46∼80；there is a foam apparent viscosity in the fracture that has an impact on the initial flow of
foam；for the oil saturated fractured cores flooded by water and gas，oil recovery was increased by 26% and 35% respectively
and the mechanism of CO2 foam EOR in low permeability fractured reservoirs are revealed.

Research on the Model of Separate Layer CO2 Injection Well System

Liu Yonghui1*, Luo Chengcheng1, Zhang Liehui1, Wang Feng2, Xin Taoyun2

2015, 37(5):  123-127.  DOI: 10.11885/j.issn.1674-5086.2013.05.29.01

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Separate layer CO2 injection is an important method to settle the contradictions among layers in the process of
gas injection EOR and it can，ensure effective injection of CO2 into layers with different permeabilities，maintain formation
pressure and improve producing reserves of gas drive and recovery. Based on the idea of separate layer CO2 injection，this paper
establishes a temperature-pressure coupling mathematical model considering the temperature of wellbore and the phase change
of CO2，a gas-injection of reservoir model depending on the period of gas-injection and an injection well model coupling choke
loss and taking multilayers into consideration，then proposes a corresponding numerical method. Simulation and calculation
results show that wellhead injection pressure should reach a critical value in order to improve the injection rate of reservoir with
poor gas-injection capacity. Choosing the wellhead injection pressure and the choke diameter reasonably is the key to fulfilling
separate layer CO2 injection. The research results provide a theoretical support for separate layer CO2 injection.

Kick Detection and Simulation in Accurate Managed Pressure Drilling

Zhang Xingquan1，2*, Zhou Yingcao1, Zhai Xiaoqiang1, Liu Wei1, Tang Geng3

2015, 37(5):  128-132.  DOI: 10.11885/j.issn.1674-5086.2013.12.27.03

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The current gas kick detection method cannot detect the trace of overflow，and thus we propose the overflow detection
methods for managed pressure drilling（MPD）and establish the wellbore overflow calculation model based on the gas-liquid
two-phase theory. A comparison of the simulation results with the measured date of MPD，reveals that it is difficult to detect
the overflow quickly and accurately；overflow can be detected by comparing the in flow and out flow to determine the type
of bottomhole complex trouble. If the out flow greater than the in flow，there may have overflow in the wellbore. When the
gas flows out from reservoir over 1 000 m of wellbore，there may be expansion in the wellbore，and the gas void and out flow
increase and the mud pit increases at the same time. But if the wellbore back pressure increase，the parameters increment may
decline. The flow out results simulated by the computer coincide with the results measured by the MPD. The overflow detection
by MPD can accurately find the kick，and the results of computer simulation is reliable in finding and controlling the overflow.

An Analysis on Performance Characteristics of the Tight Oil Reservoir

Peng Hui1*, Liu Yuzhang1, Ran Qiquan1, Wang Xin2, Tong Min1

2015, 37(5):  133-138.  DOI: 10.11885/j.issn.1674-5086.2013.06.08.12

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Generally，there are natural fractures of varied sizes distributed in the tight oil reservoir. According to the size and
density of fractures and the porosity and permeability of matrix，the tight oil reservoirs could be classified into 4 types：the
Porous Type，the Fracture-porous type，the Porous-fracture type and the Fracture-type. This paper is mainly focused on the
performance characteristics analysis of the different types. The performance curves of different types exhibit different decline
trends. Applying Eclipse software into the tight oil reservoir simulation，we built 4 different models to study their performance.
Based on the results analysis，the fracture permeability and matrix porosity is proved to be very key parameters to the initial
production rate and the decline rate. Thus，fractures are the necessary conditions to get a high initial production rate and the
matrix with considerable storage capacity is the necessary conditions to get a high cumulative production.

Application and Research of Hot Self-generated CO2 Technology in#br# Steam Soaking

Guo Rixin*

2015, 37(5):  139-144.  DOI: 10.11885/j.issn.1674-5086.2013.12.04.01

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Hot self-generated CO2 technology is focused on the problems of recovery difficulty，poor effect of steam soaking
and so on for heavy oil reservoirs. This technology combines steam flooding and gas flooding and improves the effect of steam
soaking in heavy oil reservoir. Its main mechanism is the application of steam to heat blowing agent and generate a large volume
of gases（including CO2，NH3，etc）in the formation. Some of these gases react with the oil to reduce the oil viscosity，others
form miscible flooding to reduce water interfacial tension，so as to enhance oil recovery. An optimized selection of the heat
blowing agents was performed. By comparing the difference of blowing agent solution before and after the reaction，we find
that alkaline increases after the reaction（pH changes in value from 8.26 to 9.71~10.02），which is helpful to reduce oil viscosity
and lower interfacial tension，etc. Studies indicate that Heat-generating CO2 flooding technology can get a maximum viscosity
reduction rate of 76.7%；oil-water interfacial tension decreases by 54.77%，and further improve oil recovery by 4.18% in the
5th steam soaking. Single cycle input-output ratio averages 1.0：3.2，which shows a technical advantage toward conventional
EOR method and a preferable economic profit. The field experiments found that the technique can greatly improve the oil
production，which will provide a powerful technical supporting for the efficient development of heavy oil.

Mechanisms of Low Salinity Waterflooding Enhanced Oil Recovery#br# and Its Application

Wu Jian1，2*, Chang Yuwen1, Li Jia1, Liang Tao1, Guo Xiaofei1

2015, 37(5):  145-151.  DOI: 10.11885/j.issn.1674-5086.2013.11.04.06

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To explain the reasons why low salinity injection water enhance oil recovery，the low salinity waterflooding is studied
thoroughly. Literatures，laboratory and oilfield experimental data are investigated，and research results prove that the main
reasons for improved oil recovery by low salinity are clay migration and wettability alteration，its main mechanisms including
fine migration，multi-component ionic exchange，cation exchange，multication bridging，electrical diffuse double layers expansion，
pH variation，oil-water mobility ratio reduction，salting effect，rock cement dissolution and so on；all mechanisms
work collaboratively to improve oil recovery，but some mechanisms may be absent and some mechanisms are the main factors
of enhanced oil recovery because of the different oilfield conditions. If the reasonable low salinity is controlled，there are about
5%~20% improvement of oil recovery. Low salinity waterflooding has become an attractive enhanced oil recovery method
as it shows more advantages than conventional chemical EOR methods in terms of low costs，low environmental pollution
and comparatively easier procedures. This technology is also applicable to onshore and offshore oilfields，which reveals the
potential in oilfield development.

Deflection Analysis of a Tubular String with Connectors#br# Constrained in a Wellbore

Huang Wenjun*, Gao Deli

2015, 37(5):  152-158.  DOI: 10.11885/j.issn.1674-5086.2013.11.17.03

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Deflection of a tubular string with connectors constrained in a wellbore includes three cases: no contact，point contact
and wrap contact. The deflection curves of tubular strings under the three cases were obtained on the basis of the fundamental
equations of tubular strings buckling and corresponding boundary conditions. The critical parameters from no contact to point
contact and from point contact to wrap contact were calculated according to the transitional conditions between different contact
cases. The relationship between the critical parameters（φ）and the ratio of the apparent radius of the tubular string to that of
the connector（λ）was analyzed. The results show that when λ is slightly larger than 1，φ is sensitive to λ，but when λ is larger
than 2，φ is not sensitive to λ and tends to stay at a stable value. Take λ=2 for instance，the entire process of contact state
transitions was depicted in detail. The results in this paper can be applied to the analysis of the effect of connectors on tubular
strings buckling in field operation

An Analysis of the Wet Modal Vibration of Marine Riser

Jiang Feng*, Zheng Yunhu, Liang Rui, Du Chaofei

2015, 37(5):  159-166.  DOI: 10.11885/j.issn.1674-5086.2013.11.11.03

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To solve the problems of the wet modal vibration of marine riser，we studied the natural frequency of the riser and the
corresponding vibration modes. Using Acoustic Extension module of ANSYS Workbench，we analyzed the wet modal vibration
of the marine riser，described the wet modal modeling methods and techniques，and obtained 12 natural frequencies and modes.
By comparing with the 12 dry modal analysis，we found the differences between the two，which indicates that the wet modal
analysis is irreplaceable in doing underwater research in structural vibration. By calculating the vibration characteristics of the
optimized structure，we demonstrated the feasibility of optimization. Modal analysis provides a certain basis for the study of
the vibration characteristics and the optimizing of structure，and a certain reference for preventing structure resonance.

Study on Fault Diagnosis Technology for Fluid End of Drilling Pump

Zhang Zhidong1，2*, Ai Zhijiu1, Zheng Wei3, Li Ben4, Zhong Gongxiang1

2015, 37(5):  167-173.  DOI: 10.11885/j.issn.1674-5086.2013.12.31.01

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The fault diagnosis method of fluid end that combines the statistical indexes and neural network is proposed in this
paper based on the analysis of fault diagnosis methods for fluid end of mud pump and the features of structure and operating
condition of mud pump. Firstly，the following indexes of vibration signal are selected to illustrate the characteristic index：
effective value，variance，peak index，impulsion index，kurtosis value and margin index，etc. At the same time，vibration
testing signal is collected by using a dynamic data acquisition instrument and piezoelectric acceleration sensors and the average
index for vibration signal is caculated. In order to construct the BP neural network and set network parameters，the selected
characteristic indexes are normalized. As the training samples，then these indexes are put into the BP neural network for training，
after which the constructed BP neural network can entirely meet the set training precision requirement. The corresponding
diagnostic errors of different plungers in field are 0.007 7，0.017 9，0.017 7 and 0.021 6，which shows that the constructed BP
network can reach the demands of plunger fault diagnosis. Therefore，this method may accurately diagnose fault of fluid end
of mud pump，which can be applied to engineering practice.

Simulation of Damage Zone Due to Lost Circulation of Drill-in Fluid in#br# Fractured Tight Reservoirs

Kang Yili1*, Huang Fansheng1, You Lijun1, Xu Chengyuan1, Mi Guangyong2

2015, 37(5):  174-182.  DOI: 10.11885/j.issn.1674-5086.2013.08.11.01

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The invasion of drill-in fluid into reservoir formation can lead to a damage zone around the wellbore during the process
of over balanced drilling and completion in fractured tight reservoirs，which will strongly affect the production performance
of a well. Taking the tight conglomerate reservoir of Jiulongshan structure as the research object，the mathematical model of
solute transport in fractured network was established by double continuous medium method；the dimensionless concentration at
any time in different position from wellbore was determined by using finite difference method to solve the developed model；the
extent of formation damage caused by drill-in fluid loss was quantitatively evaluated，and the numerical results were validated
by pressure built-up test analysis and dynamic damage assessment of drill-in fluid. The numerical results show that the depth
of drill-in fluid invasion increases over time，and pollutions induced by the drilling fluid loss continuously push and cumulate
in depth of the formation with the kill fluid loss；respectively，the radius and equivalent skin factor of damage zone due to lost
circulation of drill-in fluid is about 17.0 m and 7.5，the relative errors between the numerical results and the results of pressure
built-up test analysis and dynamic damage assessment are less than 10%，which proves the reliability of the model.