Bohaiwan Basin Research Articles

Fluid phase behavior during multi-cycle injection and production of underground gas storage based on gas-condensate reservoirs with oil rim

Underground gas storage (UGS) plays an important role in energy supply and peak shaving of urban natural gas. Fluid phase behavior and mass transfer are complicated during multi-cycle injection and production of UGS especially based on gas-condensate reservoirs with oil rim, which will impact the fluid properties, gas-oil recovery factor and stability of UGS. This work innovatively develops an experimental approach to investigate the phase behavior during multi-cycle gas injection and production in a UGS based on gas-condensate reservoir with oil rim in Bohaiwan basin, China. The produced fluid composition, residual fluid properties and oil recovery factor are analyzed. Results indicated that the condensate oil recovery factor is only 24.12% and the oil rim influences condensate oil recovery factor during primary depletion. The oil recovery factors of individual cycles are 8.33%, 5.79%, 3.83%, 1.92% and 0.88%, respectively. The total condensate oil recovery is 20.75% after five cycles, indicating multi-cycle gas injection and production can effectively extract and evaporate oil phase especially in the first and second cycles. As the cycles increase, the composition difference between injected gas and oil rim becomes larger and the evaporation of oil rim by gas injection is weakened. The GOR of oil rim under the 24 MPa decrease from 190.5 to 162.5 m3/m3, indicating gas dissolving ability of oil rim decrease. The remaining oil saturation is 1.7% after five cycles, lower than the primary depletion (3.8%), indicating part of oil rim is also produced and the gas storage capacity is enhanced after multi-cycle injection and production. This work provides an approach to understand the phase behavior of UGS in condensate gas reservoirs with oil rim and is beneficial for the efficient operation of UGS.

Estimation of the Ambient Temperatures during the Crystallization of Halite in the Oligocene Salt Deposit in the Shulu Sag, Bohaiwan Basin, China

The centimeter-scale halite rhythmites in the first member of the Shahejie Formation in the Shulu Sag of the Bohai Bay Basin are investigated, and the Eocene to early Oligocene paleoenvironmental characteristics of a typical saline lake basin are restored by reconstructing the temperature and compositional information of ancient brines. The obtained homogenization temperatures (Th) of fluid inclusions range from 6.5 to 49.2 °C, with a relative lower Th from transparent halite samples than from gray halite samples. This suggests different temperature conditions and a probable association with seasonal changes. The ion contents of halite fluid inclusions reveal the lake brine is a Na-Mg-K-Ca-Cl type and reached the initial stage of halite deposition. The transparent halite samples plotted within different phase regions than the gray halite samples on plots of ion contents and showed significant change within phase regions. Combined with the observed cm-scale rhythm in the evaporite sequences of the Shulu Sag, these results suggest a shallow water environment and frequent dilution by inflows of fresher water caused by seasonal climate change. The gray halite formed under higher temperatures and increased inflow conditions, and the transparent halite formed under lower temperatures and decreased inflow conditions. Compared with the Jiangling Sag in Hubei Province in southern China, the Shulu Sag may have been less affected by igneous rocks in the Es1 Formation due to the material source, and the concentration of trace elements such as lithium, strontium and boron in the ancient salt lake brine was lower.

Reservoir Sedimentary Characteristics and Model of Delta and Gravity Flow System in the Dongying Sag, Bohaiwan Basin, China

Reservoir Sedimentary Characteristics and Model of Delta and Gravity Flow System in the Dongying Sag, Bohaiwan Basin, China

Seismic recognition and quantitative characterization of siliciclastic–carbonate mixed sedimentary rocks in the Bohaiwan Basin, Northeast of China

Mixed sediments often occur in continental lake basins due to the coupling effects of the climate, hydrodynamic conditions, tectonic processes, and material abundances of provenances, and the mixed sedimentary rock formed in this process has dual characteristics. The response of mixed sedimentary rock to seismic waves is different from that of conventional sandstones or carbonate rocks and easily causes errors in identification and characterization by conventional research methods. In this paper, taking the mixed sedimentary rock in the southern part of the Laizhouwan Sag in the Bohaiwan Basin as an example, the petrological characteristics of the mixed sedimentary rock are studied and its sedimentary model is established. On this basis, a comparative study of the seismic waveform characteristics is carried out. Compared with sandstone, the waveform continuity of mixed sedimentary rock is poor, the amplitudes are weak and the frequencies are low, but opposite results are found compared with the conglomerate formed by gravity flow at the bottom. Contrast analysis of the acoustic impedance shows that the value of the acoustic impedance of mixed sedimentary rocks is higher than that of sandstone and is generally greater than 6.2 × 106 kg/m3 m/s. Therefore, the threshold value between sandstone and mixed rock is set to 6 × 106 kg/m3 m/s in inversions to delineate the boundary between mixed sedimentary rock and sandstone. Finally, using seismic attribute analysis and inversion technology, the scales of the horizontal and vertical distributions of the mixed sedimentary rock platform are predicted. The range of the platform is 7100 m in length, 3100 m in width, and 15.6 km2 in area. Longitudinally, the mixed sedimentary rock layer spans the third layer of the third member of Shahejie Formation (ES33).

Influencing factors and application prospects of CO2 flooding in heterogeneous glutenite reservoirs

In recent years, large amounts of CO2 emissions have led to many environmental problems. Developing a reasonable approach to carbon dioxide emissions is one of the most important issues for the sustainable development of human civilization. Compared with CO2 geological storage, CO2 flooding has greater advantages and a higher utilization efficiency. CO2 flooding technology has been successfully applied to many types of reservoirs, such as conventional sandstone reservoirs, low-permeability reservoirs, and carbonates. In this paper, the feasibility of CO2 flooding in glutenite reservoirs is studied. First, the glutenite reservoir is divided into fine stages, and reasonable vertical development units are determined. On this basis, the distribution scale, genetic environment and formation mode of the glutenite reservoir are characterized in detail and their spatial distribution rules are depicted in three dimensions. Then, the influencing factors of CO2 flooding in the glutenite reservoir are analysed via reservoir numerical simulation technology. The effects of reservoir thickness, reservoir heterogeneity, macropores, dominant channels and fracturing on CO2 flooding efficiency are evaluated individually, and a set of reasonable parameters constituting an evaluation system for CO2 flooding in the glutenite reservoir is established. Finally, based on parameter optimization, the disadvantaged conditions of CO2 flooding in glutenite reservoirs are optimized, and their effects are gradually eliminated. In view of the characteristics of glutenite reservoirs, a unique three-dimensional well pattern arrangement is designed, different injection modes are optimized, and suitable injection agents are tested. These methods are conducive to improving the effect of reservoir parameters on CO2 flooding efficiency, allowing these reservoirs to be used for CO2 flooding. Based on these new methods, the displacement effect of the Yanjia-Yongan glutenite reservoir is predicted. Our results show that the reservoir has been developed efficiently and achieved a high recovery rate, the displacement front of the CO2 has become more uniform, and the sweep range has become wider. After extending the successful application of CO2 flooding in this reservoir to all of the glutenite reservoirs in the entirety of the Bohaiwan Basin, we predict that the oil recovery rate may reach 40%, with a cumulative oil recovery rate of approximately 3.04 × 108 t and a total CO2 consumption of 1.672 × 108 t. Thus, the proposed approach not only can improve the atmospheric environment but can also greatly improve the efficiency of oil displacement.

Experimental study the influences of geochemical reaction on coal structure during the CO2 geological storage in deep coal seam

Deep unminable coal seams are suitable geological bodies for carbon dioxide capture and storage (CCS). In order to discuss the geochemical reaction between the injected carbon dioxide (CO2) and deep coal seam, and study its influence on the structure of reservoir, the high-ash anthracite, high-volatile anthracite, low-volatile bituminous coal obtained from Qinshui basin, China, and high-volatile bituminous coal obtained from Bohaiwan basin, China, were processed to 4–8 mm. Then the simulation experiments for the CO2 injection were conducted for 10 days at the burial depth of 1500 m under in-situ reservoir conditions. The conclusions were obtained based on the changes of minerals, elemental concentrations and pore structure parameters of coal before and after the reaction. Different minerals underwent various geochemical reactions and mechanisms after CO2 injection. These geochemical reactions can transform the reservoir structure, which was mainly reflected in the connection of pores and fissures, and the blockage on the pore throat. The reactions between carbonate minerals and the CO2 acid fluid were violent and quick, which can increase the volume of macropores and fractures. While the weak reactions of silicate minerals may affects the micropores in coal. The chlorite and feldspar could continuously react with the CO2 acid fluid, with the slow dissolution of potassium, sodium and silicon, which makes it possible to use these characteristics to monitor the geochemical reaction. Besides, the volumes of the micropores (1–2 nm) in the anthracite were significantly increased, making it a potential geological body for CCS.

Carboniferous–Permian marine transgressions in the Jiyang Depression

In recent years, great attention has been paid to oil and gas exploration in the Carboniferous–Permian strata of the Bohaiwan basin, especially the Carboniferous–Permian marine transgression, using data from drilling, outcrops and carbonate acid-insoluble residue experiments together with the tectonic evolutionary history of the peripheral orogenic zones of the North China plate and the Tan-Lu fault zones. The study concludes that marine transgressions took place on six occasions during Carboniferous–Permian time in the Jiyang Depression. The marine transgressions were concentrated in the Late Carboniferous: two marine transgressions occurred in the early Late Carboniferous, and the scale of the first was smaller and the time was shorter than those of the second. The other four marine transgressions happened in the late Late Carboniferous, the first and the fourth of which were larger in scale and longer in time than the second and the third. The seawater came from the Jiaobei area, the eastward part of the Qinling–Dabie residual sea basin, and invaded progressively as a planar flow from south to north and from east to west. These findings have great significance for thorough analysis of the sedimentary characteristics and evolution of the Carboniferous–Permian strata in the Jiyang Depression.

A new texture-based operator for edge enhancement of potential-field data

Abstract Edges of potential-field anomalies are assumed to result from sharp discontinuities or interfaces between contrasting materials, such as faults, unconformities, or intrusive contacts. The superposition effects of potential fields make edge-enhancement techniques necessary to reduce edge mislocation. Distinguishable amplitude difference is the edge feature most widely utilized in common enhancement methods. But edges differ from other anomalies not only in amplitude but also in texture, and in some cases they reveal as weak difference in amplitude but of meaningful contrast in texture. Accordingly, we propose a new texture-based operator for edge enhancement. The operator is a modified version of dissimilarity extracted from modified calculation of the gray-level co-occurrence matrix. The matrix is tailored to fit in with the characteristics of potential-field data and it differs from the common co-occurrence matrix mainly in three aspects: (1) for the modified matrix only the pairs between the central point of a computing window and other points are counted; (2) except from commonly-used eight directions, other directions are added for the windows with direction number depending on the window size; (3) co-occurring pairs are given weight to differ the contribution of joint occurrence in different distance. Moreover, we set standard-deviation-based weight to the common dissimilarity in each window in order to locally enhance edges. We evaluate the utility of the operator based on synthetic models and real data examples of the Huanghua Depression in the Bohaiwan Basin, Northern China, and of the Haijiao area in the East China Sea Basin, Eastern China. The modified dissimilarity is proved advantageous to the total horizontal derivative and common dissimilarity in capturing more detailed features, and provides more straightforward and accurate illustration of edges than the tilt angle does. The edges enhanced in the gravity data of the Huanghua Depression accord well with the faults deduced from an integrated geophysical interpretation. The edges detected in the magnetic data of the Haijiao area illustrate the distribution of rocks. The results show the potential of the texture-based operator to facilitate the interpretation of potential-field data in locating faults, rocks, or contacts, and thus to promote the application efficiency of the data in exploration and engineering.

Changes to depositional palaeoenvironments within the Qikou depression (Bohaiwan Basin, China): carbon and oxygen isotopes in lacustrine carbonates of the Palaeogene Shahejie Formation

This paper reports the carbon and oxygen isotope compositions of lacustrine carbonate sediments from the Palaeogene Shahejie Formation, Qikou depression, Bohaiwan Basin, with the aim of determining the palaeoenvironmental conditions in the region. Results from Es2, the second member of the Shahejie Formation, showed values of δ13C and δ18O from –1.2‰ to +2.4‰ (average +0.6‰) and from –6.8‰ to –4.7‰ (average –5.7‰), respectively, suggesting a relatively hot climate attending deposition. The slightly closed nature of the lake, which contains brackish water, resulted in higher carbonate δ13C and δ18O values than in a meteoric environment. The values of δ13C and δ18O preserved within the carbonates of the overlying lower Shahejie I (Es1) varied between +1.3‰ and +4.9‰ (average +3.2‰) and from −4.4‰ to −1.8‰ (average −3.1‰), respectively, indicating that the climate became colder at that time. Subsequently, a marine transgression caused the salinity of the lake water to increase. The values of δ13C and δ18O were controlled by salinity. The high δ13C values were also influenced by the rapid burial of the lake organisms and by algal photosynthesis. Values of δ13C and δ18O from carbonates in upper Es1 ranged from −8.0‰ to +11.0‰ (average +10.1‰) and from −5.0‰ to −1.5‰ (average −3.4‰), respectively, indicating a slight increase in the temperature over time. In the closed and reducing environment, extremes in δ13C values resulted from biochemical fermentation. The positive δ13C excursion recorded in the carbonates of the Shahejie Formation in the Qikou depression indicates that the palaeoclimate underwent a significant transformation during the Eocene and the Oligocene.

Cenozoic structural deformation and expression of the “Tan-Lu Fault Zone” in the West Sag of Liaohe Depression, Bohaiwan basin province, China

Based on the interpretation of 3D seismic data and structural mapping we analyzed the geometry and kinematics of the fault system and validated the expression of the “Tan-Lu Fracture Zone” in the West Sag of Liaohe Depression, Bohaiwan basin province. The Cenozoic structural deformation within the West Sag of Liaohe Depression can be divided into extensional structure system and dextral structure system. The extensional system is constituted by numerous NNE-NE trending Paleogene normal faults, where the Taian-Dawa fault (F1) is the master boundary fault (MBF) dominating the deposition during Paleogene so that the sag shows a complex half-graben with “boundary fault in the east and overlap in the west”. The dextral system is constituted by 2–3 dextral basement faults in NNE-NE trending (F2, F3, F4) and associated structure, and the time of structural action started in Oligocene and continued to Quarternary so that some associated secondary faults of the dextral system cut off the Neogene and Quaternary. Under the influence of the position and attitude of NNE-NE trending basement strike-slip faults, the central north part and the south part of the West Sag show obviously different structural features. The former appears to be a complex “graben” structure limited by the reversed strike-slip fault in the west and bounded by the inverted normal fault in the east, the latter remains the complex half-graben structure with “boundary fault in the east and overlap in the west”, and the graben was mildly reconstructed by one or two normal strike-slip faults. The dextral system within the West Sag is the element of the west branch fault of the Tan-Lu Fracture Zone, which is a deep fracture zone extending along the east of the Liaodongwan Gulf. The deep fracture zone branches off into two separate faults within the Liaohe Depression. The east branch goes through from northern part of the Liaodongwan Gulf to the East Sag of Liaohe Depression and links with the Denghua-Mishan Fault near Shenyang, and the west branch passes from northern part of the Liaodongwan Gulf to the West Sag and Damintun Sag of Liaohe Depression and links with the Yilan-Yitong Fault. The principal displacement zone of the west branch of the Tan-Lu Fracture Zone cuts off the master extensional fault (F1) within the West Sag of Liaohe Depression and induces many cover faults in EW trending within the Neogene and Quaternary.

Sequence Thickness and its Response to Episodic Tectonic Evolution in Paleogene Qikou Sag, Bohaiwan Basin

AbstractThe sequence stratigraphy framework of Paleogene of Qikou Sag has been built in this paper. The evolution law of episodic subsidence in Qikou Sag has been expounded, with the analysis of the characteristic of sequence thickness, as well as the study of consedimental tectonic activity, subsidence history, paleogeomorphology and the coupling relationship among them. The faults controlling action was the dominant mechanism during rifting stage I, as the depression was the dominant mechanism during rifting stage III, which embodies a process from intense disparity fault depression to integral subsidence. Meanwhile, under the control of regional faulting and later stage depression, subsidence rate centers and paleogeomorphic concave centers are always corresponding to the sequence thickness centers, and the changes of subsidence centers and paleogeomorphology concave centers are consistent with the migration of thickness centers, which presents the restriction, coupling and response among them and clarifies the law that tectonic activity controls the basin fill by means of controlling the subsidence rate and paleogeomorphology from contributing factor angle. On this basis, the dynamic evolution of the composite pattern of structure‐subsidence‐deposition in the fault controlling actic region during the three rifting stages and their petroleum geological significance has been discussed.

A geological storage option for CO2 in the Bohaiwan Basin, East China?

Geological assessment of the Bohaiwan Basin in eastern China for the COACH (Cooperation Action within CCS China-EU) project indicated that storing carbon dioxide (CO2) in this region will be technically challenging and require a flexible storage solution. It is suggested that a pilot scheme within the Dagang oil field complex could prove the concept of Carbon Capture and Storage (CCS) and CO2-Enhanced Oil Recovery (CO2-EOR) in the challenging conditions of oil fields in this region of China. This could be followed by simultaneous injection of CO2 into a nearby larger oil field and adjacent aquifers that would offer a potential storage option by combining the larger storage space anticipated for aquifers with the possible future financial incentives of CO2-EOR.

Seismic sedimentology and its application in shallow sea area, gentle slope belt of Chengning uplift

Seismic sedimentology is a new frontier inter-discipline subject, and shows good prospect and potentiality in reservoir deposition research with seismic data and geophysics technologies. We made seismic sedimentology research of shallow sea area, gentle slope belt of Chengning (埕宁) uplift, Bohaiwan (渤海湾) basin. In shallow sea area with sparse well coverage, it was difficult to characterize the reservoir architecture with the traditional method based on wells. A new method to resolve the above problems is built: (1) information on plane and in section is inter-calibrated with each other; (2) recognize the isochronic surfaces by frequency decomposition and interpret the depositional character with technology of stratal slicing; (3) make a comprehensive research with the stratal slice interpretation and the dissection of well group. The depositional model of this area is built and used in the architecture analysis of area without wells. The architecture description reveals that the sedimentary character of pan-connection sand bodies in braided rivers is the reason for high water cut of the new horizontal wells.

Crude oil He and Ar isotopic characteristics and their geochemical significance: an example from the Gangxi oil field in the Huanghua depression

Sampled from the Gangxi oil field in the Huanghua depression, Bohaiwan Basin, the crude oil He and Ar isotopic compositions and their geochemical significance were investigated. The result shows that i) the 3He/4He values of the six oil samples free from air contamination indicate a mantle helium contribution ranging between 13.9% and 32.8% and averaging 24.1%, which means that the Gangxi oil field once had a tectonic background of the mantle-derived helium input and higher geothermal flow with an average of 75.0 mWm-2; ii) deduced from the 40Ar/36Ar aging effect the Gangxi oil should be derived from the Tertiary; iii) water injection is the main reason for the air contamination for the Gangxi oil noble gases and the relations between 3He/4He and 4He/20Ne as well as 40Ar/36Ar and 4He/20Ne are of an applicative potential in estimating the water injection effect and the connectivity of producing formations. The search for the crude oil He and Ar isotopes provides a new approach to inferring natural gas and oil sources, tectonic backgrounds, geothermal flow and water injection effect.

Features of buried hill reservoirs in Hexiwu structural belt, Langgu Sag, Jizhong Depression

Abstract The buried hill reservoirs of Hexiwu structural belt in Langgu Sag, Bohaiwan Basin are comprehensively studied by core and outcrop observation. The reservoir lithology is dominantly carbonate rock, and the reservoir spaces include dissolved pores, dissolved cavities, cracks and bedrock micropores, forming pore-cavity type, crack type, crack-cavity type and combination pore-cavity-crack type reservoirs. Multiple-phase fossil karstification is an important factor during reservoir formation. The fossil karsts are developed in the weathering and leaching belt, submerged current belt, fracture belt and bedding direction along buried hill unconformities. The cracks formed by tectonic movement increase porosity, improve connection of pores and cavities and permeability. The reservoirs developed in different lithologies and tectonic positions have different physical properties: dolomite reservoir is better than carbonate reservoir, and reservoir not overlapped by Permo-Carboniferous stratum is better than that overlapped by Permo-Carboniferous stratum, and reservoir in the fault-developed area is better than that in the non-fault-developed area. The reservoirs are favorable areas for oil and gas exploration.

A fracture network model and open fracture analysis of a tight sandstone gas reservoir in Dongpu Depression, Bohaiwan Basin, eastern China

ABSTRACTFracture systems can significantly influence productivity in tight sandstone reservoirs. Understanding the in situ fracture network is of importance in exploration and development of such reservoirs. This paper illustrates that stress‐strain analysis, based on geological processes, is a credible prediction method for fracture networks and enables an estimation of which fractures are likely to contribute most to flow based on fracture orientation. This study shows the workflow for fracture modelling and its application in a sandstone reservoir using structural validation tools and interactive fracture simulations constrained with lithology, well log and core data. The fracture network model can help us understand not only what a fractured reservoir looks like but also how the existing fracture network behaves. An important consideration is that we need to understand and constrain the geological history to assess the fracture network properly.

Hydrogeochemistry of formation water in relation to overpressures and fluid flow in the Qikou Depression of the Bohaiwan basin, China

Hydrogeochemistry of formation water in relation to overpressures and fluid flow in the Qikou Depression of the Bohaiwan basin, China

The paleoclimatic records and the relevance with the formation of hydrocarbon source rocks: A case study of Huanghekou depression, Bohaiwan basin

Bohaiwan basin, covering an area of 200 000 km2, is one of the most important oil-bearing basins in Eastern China. Rifting processes formed the basin, and two evolution phases can be recognized. The rifting phase developed in Paleogene, and post-rifting phase occurred in Neogene. More than 200 oil fields have been found in the onshore and offshore area in Bohaiwan basin in recent years. The distribution of the oil fields is closely related to the rich hydrocarbon depressions, and the Huanghekou depression is one of these rich hydrocarbon depressions. A number of large and medium-sized oil and gas fields have been found in this area, such as BZ25-1, BZ34 etc., and the hydrocarbon was mainly from the Huanghekou depression. The formation of rich hydrocarbon source rocks depended on the tectonic setting of rapid subsidence, favorable paleoclimatic conditions and paleolimnology environments. The effects of paleoclimatic condition on hydrocarbon source rocks are the focus of this paper.

Subsidence history and forming mechanism of anomalous tectonic subsidence in the Bozhong depression, Bohaiwan basin

The Bozhong depression of the Bohaiwan basin belongs to a family of extensional basins in East China, but is quite different from other parts of the basin. The Cenozoic subsidence of the depression is controlled by a combination of lithospheric thinning and polycyclic strike-slip movements. Three episodic rifts have been identified, i.e. Paleocence-early Eocene, middle-late Eocene and Oligocene age. The depression underwent syn-rift and post-rift stages, but two episodic dextral movement events of the strike-slip faults modify the subsidence of the Bozhong depression since the Oligocene. The early dextral movement of the Tan-Lu fault associated with crustal extension resulted in accelerated subsidence during the time of deposition of the Dongying Formation with a maximum thickness of 4000 m. A late reactivation of dextral movement of the Tan-Lu fault began in late Miocene (about 12 Ma), which resulted in the intense subsidence of Minghuazhen Formation and Quaternary. In addition, dynamic mantle convection-driven topography also accelerated the post-rift anomalous subsidence since the Miocene (24.6 Ma). Our results indicate that the primary control on rapid subsidence both during the rift and post-rift stages in the Bozhong depression originates from a combination of multiple episodic crustal extension and polycyclic dextral movements of strike-slip faults, and dynamic topography.

Geochemistry of formation water and its implication on overpressured fluid flow in the Dongying Depression of the Bohaiwan Basin, China

This study of the geochemistry of formation waters in the Dongying Depression of the Bohaiwan basin, East China, unravels a close relationship between vertical zonality and overpressured fluid flow. The zones have distinctive original pore waters because the sediments formed under different climate conditions. The highest value of the total dissolved solid in the formation water occurs in the ES4 member of Shahejie Formation due to the dissolution of halite and gypsum beds. In the overlying ES3 and ES2 members, low salinity water occurs, except for near syndepositional fault zones where a significant increase in salinity of formation water and a reduction in overpressure were observed. This fact indicates strong overpressured fluid flow where thermal anomalies have been observed, as evidenced from thermal gradient and fluid inclusion homogenization temperatures. The results indicate that the geochemistry of pore water may be used to help identify the main migration pathways for overpressured fluid flow with hydrocarbons.