Table of Content

01 June 2018, Volume 40 Issue 3

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Revisiting the Compaction Time of Chang 8 Sandstones in Southwestern Ordos Basin

ZHOU Xiaofeng, LI Jing, ZHANG Jianxin, LI Shuheng, YU Junmin

2018, 40(3):  1-10.  DOI: 10.11885/j.issn.1674-5086.2017.01.24.02

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Owing to disagreements in the understanding of calcite cement formation, the compaction time of sandstones of the Yanchang Formation in Ordos Basin has not yet been determined. Employing scanning electron microscopy (SEM) with energy spectrometry and casted rock thin sections, the origin of calcite cement in Chang 8 sandstones in southwestern Ordos Basin was investigated. The results show that water released from mudstone compaction during phase A of the early diagenetic stage induced calcite cementation, forming type I calcite cement with evenly distributed dissemination structures or type Ⅱ⁰ with patchy or scattered dissemination structures. Fluids cannot easily penetrate sandstones derived from type I calcite cementation, and thus water-rock reactions cannot take place. Type Ⅱ⁰ calcite cement is transformed into type Ⅱ via dissolution-precipitation during phase A of the mid-diagenetic stage. Carbon and oxygen isotopes and fluid inclusion data cannot be used as the main reference for studying calcite cement formation because their interpretation must follow rock microstructure characteristics. In view of the above, the compaction time of Chang 8 sandstones in southwestern Ordos Basin was determined to be phase A of the early diagenetic stage, and its relationship with reservoir formation is "compaction followed by accumulation."

Glutenite Compaction and Pore Formation in the Niubao Formation, Lunpola Basin

HAO Jingyu, MA Chengxian, LI Xuwen, PAN Lei, XIAO Jilin

2018, 40(3):  11-22.  DOI: 10.11885/j.issn.1674-5086.2017.01.23.01

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This study investigated the lithology and reservoir characteristics of the glutenite reservoir in the Niubao Formation of the Lunpola Basin using core, thin section and physical property analysis, and SEM data. In particular, several factors of rock compaction were analyzed from the viewpoint of diagenesis, and the relationship and sequential order between diagenesis and oil emplacement was investigated with reference to favorable conditions for pore formation. This study investigates for the first time the developmental process of reservoir pores. The results show that the reservoir space mainly comprises residual pores. A mixed sedimentation environment, relatively weak resistance to mechanical compaction, and intense carbonate cementation in the mid-late diagenetic phase are the three leading causes of reservoir compaction. Dissolution of soluble parties by acidic fluids is the main factor controlling the formation of secondary pores, whereas oil emplacement favors porosity preservation in that it causes dissolution and enlargement in some pores and forms oil films in the periphery to prevent carbonate cementation. Compaction causes significant damage to the reservoir during the shallow burial stage. As burial depth increases, acid dissolution and quartz overgrowth are enhanced and oil emplacement takes place. These lead to the formation of early carbonate cements. In the mid-late diagenesis, iron-containing carbonate cements replace early carbonate minerals and block most of the pores. The late-stage tectonic compression that follows leads to cracking in the reservoir. Based on the above, it can be concluded that pores are first formed among the primary grains, and then eliminated by compaction. Acid dissolution enlarges the pores, while oil emplacement preserves porosity and carbonate cementation destroys pores. The overlap between regions with sufficient oil emplacement and those with weak carbonate cementation is favorable for porosity preservation.

Factors Controlling Heterogeneity in the High-quality Shale Reservoirs of the Changning Region

QIAO Hui, JIA Ailin, JIA Chengye, WEI Yunsheng, YUAN He

2018, 40(3):  23-33.  DOI: 10.11885/j.issn.1674-5086.2017.08.28.02

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Based on statistical analyses on numerous experimental measurements, sub-layers of the high-quality shales in Changning, Southern Sichuan, were found to be strongly heterogeneous, and the factors controlling the development of highquality shale reservoirs were analyzed. There are high brittle mineral contents but relatively low clay mineral contents (mean 24.5%) in the lower reservoir of the Wufeng-Longmaxi Formation. The reservoir has various types of reservoir spaces, although organic matter pores dominate. Relatively strong vertical heterogeneity is noted. Porosity primarily varies between 0.73% and 10.25%, with an average of about 4.19%. The total gas contents in the five sub-layers in the Wufeng Formation and Long 1₁ sub-member of the Longmaxi Formation are 1.27~4.19 m³/t, with an average of 2.74 m³/t. The Long 1₁¹ sub-layer has the highest gas content, followed by the Long 1₁² and Long 1₁³ sub-layers, whereas the Long 1₁⁴ sub-layer has the lowest gas content. Sedimentation conditions are the basis for high-quality shale development. High contents of quartz and organic matter facilitate the formation of high-quality shale reservoirs. Compaction and cementation are the major mechanisms for densification in shale reservoirs, while dissolution and organic matter thermal maturity can improve the shale reservoir quality to a certain degree.

Characteristics of Analog Hydrocarbon Reservoir Formation in Continental Margin Delta Basins

JIA Huaicun, KANG Hongquan, LI Minggang, CHENG Tao, MENG Jinluo

2018, 40(3):  34-42.  DOI: 10.11885/j.issn.1674-5086.2017.01.04.04

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Continental margin delta basins tend to be rich in hydrocarbon resources and contain many hydrocarbon reservoirs; for example, the Niger Delta Basin in West Africa, the Ruvuma Basin Delta in East Africa, and the Mahakam Delta in the Kutai Basin, Indonesia. An analog study was conducted to examine the different petroleum-geological characteristics of different types of continental margin delta basin. Our results reveal that delta basins that formed during different stages of tectonic evolution exhibit very different basin structures, internal structural styles, source rock characteristics, and hydrocarbon reservoir formation patterns. For example, the Niger Delta and Ruvuma Basin Delta developed during the drift stage and their gravitational nappe structures are well developed. Conversely, the Mahakam Delta in the Kutai Basin developed during the depression phase of rifting and its gravitational nappe structures are poorly developed. The reservoirs in both the Mahakam Delta and Niger Delta Basin essentially consist of oil source rocks originating mainly from the delta system and are characterized by self-generation, self-preservation, and near-source formation. Conversely, reservoirs in the Ruvuma Basin in East Africa consist of cracked gas marine source rocks originating from the lower-Jurassic gulf environment and are characterized by stepped long-distance migration and far-source formation.

Preliminary Investigation on the Role of Sandstones in Interacting Caprocks of the Huagang Formation in the Xihu Depression

ZHAO Hong, QIN Lanzhi, WANG Hui, LI Ning, LI Xuanyue

2018, 40(3):  43-51.  DOI: 10.11885/j.issn.1674-5086.2016.11.05.01

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Interactions between sandstone and mudstone are present in the developmental characteristics of caprocks of the Huagang Formation in the Xihu Depression, but studies on the role of mudstone-associated sandstone-type caprocks in the sealing of petroleum are relatively scarce. The characteristics of sandstones within interactive sandstone-mudstone caprocks were analyzed using rock cores, microscopic observations, and mercury intrusion porosimetry. The results show that sandstones within the caprock are able to act as an effective seal (caprock). Sandstone-type caprocks are controlled by their sedimentary environment during early periods, and their high argillaceous mineral content led to strong compaction during these periods. The addition of clay mineral transformation and cement development in later periods imbued these rocks with the conditions necessary for the formation of a highly effective caprock. The sedimentary environment of caprocks should be the foundation for studies on the effectiveness of sandstone caprocks in different regions, and diagenetic studies should be performed on the various sandstones present. In addition, experimental analyses should be conducted on different types of sandstone samples to determine the effectiveness of sandstone caprocks.

Characterizing the Genesis of Composite Sandbodies in the Shallow Water Deltas of K Oilfield in the Bohai Sea

GUO Cheng

2018, 40(3):  52-62.  DOI: 10.11885/j.issn.1674-5086.2016.11.25.01

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The Neogene Lower Member of the Minghuazhen Formation in K Oilfield of the Bohai Sea is controlled by delta sedimentation in shallow waters, and the internal structures of the resulting composite sandbodies are highly complex. A Sand Body of the Lower Member of the Minghuazhen Formation was used as an example for determining the genesis, periods of sedimentation, and single-period distribution characteristics of composite sandbodies. The stratigraphic structure of composite sandbodies was constructed according to stratigraphic divisions, and the genesis of sandbodies was determined through a combination of well-logging and rock core data under the guidance of depositional models. Through well-seismic ties, the temporal periods of these causes were differentiated, and the distribution characteristics of single sandbodies in each of these periods were characterized. The results indicate that A Sand Body was formed by distributary channels, natural levees, terminal crevasse splays, and interdistributary bays, which may be further subdivided into three periods of sedimentation. The contact relationships of sandbodies in each of these periods may be categorized into four types according to their genetics as lateral splits in distributary channels, interchannel natural levee sedimentation, interchannel-interdistributary bay sedimentation and distributary channel-terminal crevasse splay contact.

Geochemical Tracers for Methane Microleakage Activity in the Qiongdongnan Basin

FENG Junxi, YANG Shengxiong, SUN Xiaoming, LIANG Jinqiang

2018, 40(3):  63-75.  DOI: 10.11885/j.issn.1674-5086.2017.12.01.01

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To understand methane microleakage activity in the Qiongdongnan Basin of the northern South China Sea, the concentrations of pore water anions and cations, δ¹³C_DIC, and other indices of the core samples HQ-6PC and HQ-38PC were measured using bottom stimulating reflectors (BSR) in the development zone to study the characteristics of methane microleakage. The results showed that sulfate consumption was dominated by organic sulfate reduction (OSR) and anaerobic oxidation of methane (AOM) in the HQ-6PC and HQ-38PC core samples above 5.2 m, whereas the effects of AOM were predominant in the HQ-38PC core sample below 5.2 m. The sulfate-methane transition zone (SMTZ) of the HQ-38PC core sample had a depth of 9.9 m and an upward methane flux of 32 mmol·m^-2·a^-1. The change in Mg/Ca and Sr/Ca depth in the pore water of the two core samples indicated that the authigenic carbonate minerals formed within were primarily high-magnesium calcites. The Cl^- concentration of HQ-6PC was significantly decreased below 3.5 m. Inclusions of low-salinity fluid released from hydrate decomposition are likely present. There is a relatively large salinity anomaly in HQ-38PC between 4.0~5.5 m, suggesting that there might be mixing with high-salinity fluid released during hydrate formation. Thus, there is significant methane microleakage activity in the shallow surface of the two stations and possible hydrate development underneath.

Application of Correlation Coefficients for Surface Modeling in the Songbei Area

PAN Jiazhi

2018, 40(3):  76-86.  DOI: 10.11885/j.issn.1674-5086.2016.10.24.03

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In order to improve the modeling accuracy of surface models in the Songbei region, various factors affecting the correlation coefficient values were systematically studied using an analysis of the interpolation principles of correlation coefficients and based on high density micro-logging data. Combined with the knowledge of the surface deposition patterns in the Songbei area, the method for determining the correlation coefficient values of the Songbei area was summarized. This improves the accuracy of surface modeling and the effects of single-shot excitation. Reasonable application of correlation coefficients improves the accuracy of surface modeling in the Songbei area. The accuracy of the calculation is greatly affected by surface fluctuations. It is necessary to clearly understand the surface sedimentary characteristics of the area, adopt different calculation methods according to the degree of topographic relief, and leverage human-computer interaction in order to ensure the accuracy of surface modeling.

Detection of Hydraulic Fractures in Horizontal Wells Based on Shear Wave Splitting of DSI Logging

XIA Hongquan, GUO Qiannan

2018, 40(3):  87-96.  DOI: 10.11885/j.issn.1674-5086.2016.12.20.03

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Many theoretical and technical challenges remain with the detection of hydraulic fractures in horizontal wells using dipole shear image (DSI) logging, which differs from the detection of hydraulic fractures in straight wells. Formulas for computing the phase velocity and coefficient of anisotropy of SH-waves and SV-waves in three-dimensional TTI media were derived for straight, inclined, and horizontal wells. The theoretical relationship between the coefficient of anisotropy of shear waves and the slope of fracture, azimuth of fracture, azimuth of borehole inclination, and angle of borehole inclination was then examined by performing a DSI experimental simulation of horizontal hydraulic fractures in horizontal wells. This was then applied to the field detection of hydraulic fractures in horizontal well QP52. The study found that DSI is capable of detecting vertical and diagonal fractures in horizontal wells, but not horizontal orthogonal fractures in horizontal wells. The coefficient of anisotropy of a shear wave decreases with increasing slope of the fracture and with increasing difference between the azimuth of the fracture and the azimuth of the borehole inclination. In addition, changes in borehole inclination have no impact on the detection and computation of splitting speed or the coefficient of anisotropy of shear waves. This study revealed that hydraulic fractures can be detected and fractured layers and sections can be identified by comparing the anisotropy of shear waves in areas adjacent to boreholes before and after fracturing. This provides important theoretical guidance and criteria for DSI logging projects involving the field detection of hydraulic fractures in horizontal wells.

Method for All-scale Pore-throat Measurements in Tight Reservoir Cores and Its Application

YANG Zhengming, MA Zhuangzhi, XIAO Qianhua, GUO Hekun, LUO Yutian

2018, 40(3):  97-104.  DOI: 10.11885/j.issn.1674-5086.2017.04.09.01

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A method for all-scale pore-throat measurements in tight reservoir cores was established by combining high-pressure mercury injection porosimetry, low-temperature nitrogen adsorption measurements, nuclear magnetic resonance, and centrifugation. On this basis, we compared the characteristics of pore-throat distributions at all scales in tight reservoir cores acquired from Changqing, the periphery of Daqing, and Sichuan. Compared with conventional single-measurement methods for microscopic pore-throat structure, our method for all-scale pore-throat measurements is significantly more accurate in measuring the distribution of micron-, submicron-, and nanometer-grade pore-throats. In very tight cores, our all-scale method measures the distribution of nanometer-grade pore-throats more accurately than high-pressure mercury injection porosimetry measurements. In tight reservoir cores, a lower proportion of fluids is controlled by micron-grade pore-throats, whereas a larger proportion of fluids is controlled by submicronand nanometer-grade pore-throats, as compared to cores with moderate to high levels of permeability. In a comparison between tight sandstone cores and tight limestone cores, the spectral peaks of the latter's pore-throat distribution are biased to the left and exhibit large interpeak spans, thus indicating high levels of heterogeneity. At the same level of permeability, tight cores from Changqing have a larger number of micron-grade pore-throats and a smaller number of nanometer-grade pore-throats, as compared to tight cores from Daqing. It is thus shown that the development efficiency of tight reservoirs in Changqing is likely to be better than that of tight reservoirs in Daqing.

An Experimental Study on the Porous-flow Characteristics of Heterogeneous Low-permeability Reservoirs

YU Qiannan, LIU Yikun, LIU Xue, YAO Di, YU Yang

2018, 40(3):  105-114.  DOI: 10.11885/j.issn.1674-5086.2017.05.31.01

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A plate model for heterogeneous low-permeability reservoirs was designed, and subsequently evaluated based on the similarity theory on the plate model simulation of heterogeneous low-permeability reservoirs. A physical simulation experiment was then performed to examine the porous-flow characteristics, by graphically representing the pressure gradient field and porous-flow area using the pressure data obtained via pressure sensors installed symmetrically inside the plate model. The experimental results showed that the pressure consumption in heterogeneous low-permeability reservoirs was very big in the areas adjacent to injection-production wells; pressure gradient reaches the lowest level at the midpoint of the central line of two wells of the same size; pressure gradient distribution within a flooding unit changes with variations in the rate of porous flow and degree of in-plane heterogeneity; increased porous flow results in increased pressure transmission distance, while increase in heterogeneity relates negatively to pressure transmission; when the overall porous flow of a reservoir was low, the positive effect of increased porous flow on pressure transmission outweighs the negative effect of increased heterogeneity; as the porous flow at the production terminal increased, the none-flowing area became smaller and correspondingly, the flowing area became larger, thereby leading to an increased ratio of quasi-linear porous-flow area that facilitated a better fluid flow.

Analysis and Application of Two-dimensional Steady-state Porous-flow Fields of Horizontal Wells

XUAN Jian

2018, 40(3):  115-120.  DOI: 10.11885/j.issn.1674-5086.2017.11.04.01

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Two-dimensional porous-flow fields of horizontal wells were transformed to two-dimensional porous-flow fields of straight wells by performing conformal transformation, to analyze two-dimensional steady-state porous-flow fields of horizontal wells. A parametric equation for porous-flow velocity in two-dimensional steady-state porous-flow fields of horizontal wells was derived and was used together with an equation for computing the capacity of horizontal wells to optimize the length and direction of horizontal sections of horizontal wells. The relative positioning of horizontal wells and straight water-injection wells was optimized by graphically rendering the streamline distribution of one-injection-one-production well patterns of different combinations of positioning of horizontal wells and straight water-injection wells. The results show that the length of production sections of horizontal wells for normal thin-layer oil reservoirs should be less than 100 m. When horizontal wells are used to recover oil reservoirs with gas caps or edge water, the horizontal sections should be parallel to the structural line of the reservoir to keep the direction of the main streamlines of the two-dimensional porous-flow fields of horizontal wells away from the direction of gas channeling and edge water coning. For one-injection-one-production well patterns consisting of horizontal wells and straight water-injection wells, a comparison against the graphical flow field distribution reveals that the optimum position of straight water-injection wells is on the perpendicular bisector of horizontal wells.

Law of CO₂ Immiscible Front Movement in Low-permeability Oil Reservoir

MENG Fankun, LEI Qun, SU Yuliang, HE Dongbo

2018, 40(3):  121-128.  DOI: 10.11885/j.issn.1674-5086.2017.02.28.06

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The interaction of different fluids in carbon dioxide (CO₂) immiscible flooding in a low-permeability oil reservoir is complex, and the description of the front is difficult. Therefore, the fractional flow model for the CO₂ immiscible flooding in a low-permeability oil reservoir was derived herein based on an improved relative permeability model for CO₂ flooding, considering the CO₂ dissolution in crude oil and the influence of the pressure gradient of the oil phase. The computing method of the front movement speed of CO₂ flooding and the saturation profile was established by introducing the seepage retardation factor to correct the B-L equation. The veracity of this computing method was verified by comparing with the gas saturation profile obtained from the CO₂ flooding empirical data. The CO₂ dissolution, viscosity of different crude oils, and influence of the injection pressure on the front movement speed of CO₂ flooding were analyzed. The results indicated that the front movement speed was reduced by more than 50% considering the CO₂ dissolution in crude oil. Moreover, the higher the crudeoil viscosity, the greater the front movement speed. The front movement speed decreased with the increase in the injection pressure and inflected at the point of minimum miscible pressure. The adaptability of the CO₂ flooding of three typical test sites in the Jilin, Shengli, and Yanchang oil fields was evaluated by comparing the distributions of their gas saturation profile.

An Experimental Study on Improving Recovery Rate Using Low-salinity Water Drive

SU Wenbo, LIU Yuetian, PI Jian, WANG Yunpeng, LI Changyong

2018, 40(3):  129-135.  DOI: 10.11885/j.issn.1674-5086.2017.09.13.04

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The effects of water-injection speed on the recovery rate using low-salinity water drive were studied through an indoor rock core displacement experiment. This experimental study was performed to investigate the effects of water-injection speed on recovery using water drive of different degrees of salinity. The research results showed that, with the same volume of water injected at a speed below 0.4 mL/min, low-salinity water drive resulted in a higher recovery rate but longer time to reach the maximum recovery rate compared to high-salinity water drive; and with the same volume of water injected at a speed above 0.4 mL/min, low-salinity water drive resulted in a lower recovery rate but shorter time to reach the maximum recovery rate, compared to high-salinity water drive. In other words, the maximum recovery rate corresponded to an optimum water-injection speed, irrespective of whether low-salinity or high-salinity water drive was used. Thus, the results also showed that the optimum water-injection speed for low-salinity water drive was lower than that for the high-salinity water drive.

Technologies for Fine Adjustment in the Middle-later Development Stage of Low Permeability Tight Sandstone Gas Reservoirs

FU Ninghai, TANG Haifa, LIU Qunming

2018, 40(3):  136-145.  DOI: 10.11885/j.issn.1674-5086.2017.09.15.01

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The low permeability tight sandstone gas reservoirs face the problems of how to further increase the producing degree of reserves and improve the recovery efficiency in the middle-later stage of development. Fine adjustment is an important technical means to improve the development effect. The critical technical challenges in the middle-later stage of development of this type of gas reservoir, such as the remaining reserves description, improving reserves producing degree, and well pattern adaptability evaluation, were analyzed in light of the difference between the middle-later and early stages of development in geology, production performance, and development scheme. Technical solutions were then proposed for the challenges, focusing on potential tapping and improving the recovery of the gas fields. Technical ideas and processes for fine adjustment in the middle-later stage of gas reservoir development were also proposed, based on fine gas reservoir description in the middlelater stage of development, reserves producing degree evaluation, and well spacing optimization. By taking C Gas Field as an example, this technique successfully applied in its middle-later stage of development adjustment, increased the remaining reserves producing degree and overall improved the gas field's development effect and economic benefits.

Study on the Acid Fracturing Technology for High-inclination Wells and Horizontal Wells of the Sinian System Gas Reservoir in the Sichuan Basin

LI Song, MA Huiyun, ZHANG Hua, YE Jiexiao, HAN Huifen

2018, 40(3):  146-155.  DOI: 10.11885/j.issn.1674-5086.2017.07.03.01

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The carbonate rock reservoir of the Dengying subgroup of the Sinian System in the Sichuan Basin is characterized by complex types of reservoir spaces as a result of its well-developed dissolution pores, fractures, and holes, and it is characterized by high buried depth, high temperature, high pressure, high heterogeneity, and high contents of such acid gases as H₂S and CO₂. These features and characteristics present challenges to the current reservoir reform processes. The key to reservoir reform for high-inclination and horizontal wells is the deployment of acid liquid and in-depth permeation of acid dissolution fractures in long well sections to link the natural fractures and pores in the reservoir into a connected system. The current reservoir reform processes with mechanical stratification and segmentation for high-inclination/horizontal wells were improved in light of the geological characteristics and geostress distribution patterns as follows. open-hole sections with a big difference between vertical layers or horizontal segments in physical properties were reformed with packers in a segment-by-segment manner, while perforation segments with a big intralayer or intrasegmental difference in physical properties were reformed with degradable filling materials in a layer-by-layer manner. Fracture-hole-type reservoirs with well-developed natural fractures and holes were reformed with retarded-acid based acid fracturing technology to link the fractures and holes into a connected system, while fracture-pore-type and pore-type reservoirs were reformed with pad-fluid-based acid fracturing technology to form deep acid dissolution fractures to link isolated fractures and pores into a connected system. As demonstrated by on-site tests, the two types of acid fracturing technology developed for high-inclination and horizontal wells can improve reservoir reform efficiency. An exploratory study was also conducted on self-generating acid and slick water-based acid fracturing technology for complex networks of fractures, with some degree of success in improving reservoir reform efficiency.

Analysis on Dynamics and Configurations of Deepwater Drilling Riser Systems

WANG Guorong, ZENG Cheng, MAO Liangjie, LI Yang

2018, 40(3):  156-163.  DOI: 10.11885/j.issn.1674-5086.2016.03.01.01

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Aim at the problem of drilling riser systems, this paper summarizes the basic configurational characteristics of marine drilling risers and uses the variational principle to derive mathematical dynamics equations for drilling risers. A model was constructed for the dynamic responses of drilling risers subjected to wave loads by determining the boundary conditions for the rotational stiffnesses of the upper and lower ends of a drilling riser. A cubic Hermite spline was used to discretize this model. The effects of different operating conditions on the deformation characteristics of the drilling riser were analyzed. The results showed that the displacement of the drilling riser decreases as the top tension increases. The type of oceanic current also significantly influences the deformation characteristics of drilling risers. The surface velocity of the oceanic currents has a highly significant impact on the drilling riser deformations, that is, the drilling riser displacements greatly increase with the increasing surface velocity. Under ordinary marine conditions with low wind speeds, the effects of the wind speed on the dynamic responses of a drilling riser are very small. However, the drilling riser displacement will increase significantly if extreme weather conditions (e.g., typhoons) are encountered by the system.

Reflection on Domestic and Foreign Research Status of Subsurface Safety Valves and Their Domestication

LIU Wei, YANG Song, MAI Yu, WANG Yimin, JIANG Shikai

2018, 40(3):  164-174.  DOI: 10.11885/j.issn.1674-5086.2016.08.02.02

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Motivated by the insufficient research and development of subsurface safety valves in China, the structure and classification methods of subsurface safety valves are introduced, and oil tube recovery products from four global oil-service companies and domestic enterprises are analyzed. The comparison shows that foreign companies have characteristic structures and functions of subsurface safety valves but share similar core technologies. The products can adapt to different well depths, temperatures, and pressures; however, domestic products are only applicable for shallow wells and low-pressure environments. The latest research conditions of subsurface safety valves in both China and foreign countries are studied, and the comparative analysis shows that foreign research mainly focuses on the safe reliability and functional diversity, while domestic research only focuses on the preliminary design and either indoor or outdoor detection. Eventually, key technologies of the urgent settlement of the domestication of subsurface safety valves, as well as solutions and thoughts are proposed by considering the present technical state of subsurface safety valves in China.

Performance of Polymer/Surfactant Binary Flooding in Enlarging Swept Volumes

WEI Yunyun, LIU Jianjun, LUO Litao, LIU Xiangui, YANG Zhengming

2018, 40(3):  175-184.  DOI: 10.11885/j.issn.1674-5086.2017.04.29.01

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Oil displacement experiments were carried out using microetching and slabs with interlayer and intralayer heterogeneities, in order to investigate the performance of polymer/surfactant binary floods in enlarging the swept volumes. The results indicate that the residual oils exist in the form of films, islands, throats, dead ends, columns, and clusters. On the microscopic scale, the binary flooding was found to displace residual oils from oil-containing pores that could not be swept by water flooding. On the macroscopic scale, the binary flooding generated blockages in high-permeability zones, causing the floods to enter low-permeability zones with lower levels of resistance to seepage, thus displacing residual oils in these zones. Binary flooding increased recovery rates by 13.4%~14.3% as compared to water flooding, and thus had a significant effect on enlarging the swept volumes. In binary flooding, the polymer increased the viscosity of the displacing fluid, causing the latter to become adsorbed and retained in the pores. This effectively decreased the permeability and flow rate of the displacement phase. Meanwhile, binary flooding had a very small impact on oil viscosity, and therefore the oils aggregated along the leading edge of the displacing fluid, which increased the permeability and flow rate of the oil phase. Therefore, such binary flooding reduces the mobility ratio, prevents viscous fingering, and increases water intake thickness and conformance factor, thus improving oil recovery rates.