Huanghekou Sag Research Articles

Risk assessment of fault reactivation considering the heterogeneity of friction strength in the BZ34-2 Oilfield, Huanghekou Sag, Bohai Bay Basin, China

The hazards of fault reactivation caused by fluid injection are a growing concern. However, traditional evaluation methods of fault stability are likely to underestimate the risk in fault segments with a high clay content. Therefore, an extended evaluation method of fault stability (ECPP) incorporating the heterogeneity in friction strength caused by variation in the clay content within the fault zone is established in this study. After characterizing the current stress field of the BZ34-2 Oilfield in the Huanghekou Sag, Bohai Bay Basin, the reactivation potential of faults is evaluated using both traditional and ECPP methods. Traditional evaluation of fault stability shows that all faults are stable in the present stress field. Faults oriented ENE have a relatively high risk. The maximum sustainable fluid pressure Δp is approximately 8.8–8.9 MPa and 9.3–9.9 MPa. When considering the heterogeneity in fault friction strength, the fault stability is clearly controlled by the clay content of the faults. The high-risk fault segments assessed using traditional methods are no longer obvious, which reflects the importance of incorporating friction strength heterogeneity in the process of fault evaluation. Moreover, the results also show that most fault segments are activated when the fault zone is dominated by montmorillonite, reflecting the strong influence of clay mineral types on fault stability. The factors influencing the heterogeneity of fault friction strength are very complicated in actual situations. Therefore, future work should focus on establishing a database through a large number of experiments and investigating the relationship between the friction coefficient and the main controlling factors.

Correlation of Neogene Oil and Paleogene Source Rocks in the Middle Huanghekou Sag, Bohai Bay Basin

Several billion-ton Neogene oil fields have been successfully discovered in the middle Huanghekou sag over the past few years. However, the source of the crude oil needs to be clarified, and the relevant oil-source correlation was less carried out. Six source rocks of the third member of the Paleocene Shahejie Formation (Es3) from five wells and sixteen Neogene crude oil samples from nine wells in the middle Huanghekou sag were investigated for the oil-source correlation with the biomarkers and carbon and hydrogen isotopes of saturated hydrocarbon monomers. The distribution characteristics of n-alkanes, C19/C23 ratio of tricyclic terpanes, long-chain tricyclic terpene ratios (ETR), C24 tetracyclic terpane to C26 tricyclic terpene, and distribution characteristics of conventional steranes suggest that the Es3 parent material is of a mixed-source input from terrestrial higher plants and aquatic phytoplankton. The gammacerane to C30 hopane ratio is low, ranging from 0.094 to 0.134, with a mean value of 0.118; the Pr/Ph ratio is less than 1.5. The Neogene oils show the characteristics of a saturated hydrocarbon biomarker similar to Es3. The carbon and hydrogen isotopes of saturated hydrocarbon monomers also corroborate the oil-source correlation from the depositional environment and parent material source, which characterize the low salinity of the water during the Es3 sedimentary period, which was a brackish or a freshwater delta deposition under weak oxidation–weak reduction conditions. The parity dominance of CPI and OEP values (both greater than 1), higher ratios of Ts/Tm (1.174 to 1.383, mean 1.278) and the C29Ts/C29 norhopane, high values of diahopane and diasterane contents (C30diaH/C30H, C27diaS/C27S), and hopane and sterane isomerization parameters (%22S, %20S, %ββ) confirm that the Es3 source rock samples are mature enough to provide crude oil for the middle Huanghekou sag. The biomarker characteristics of regional Neogene crude oil are significantly different from those of Es4 source rocks in the surrounding depressions (sags), indicating the Es4 strata’s absence in the middle Huanghekou sag. Suitable traps need to be discovered around the hydrocarbon-generating center of the Es3 source rock for oil and gas exploration in the future.

Sediment supply mechanism and its influence on hydrocarbon accumulation in the Paleogene of the northern Huanghekou Sag, Bohai Bay Basin, China

Tectonic activity and sediment supply have significantly affected the rifted basin fillings and hydrocarbon accumulations. The Huanghekou Sag in the southeastern Bohai Bay Basin is a hydrocarbon rich sag and was bounded by the Bonan Uplift to the north in the Paleogene, which strongly affected sediment disribution and hydrocarbon accumulation in this region. The sediment supply mechanism of the Paleogene parent rocks in this area has not been revealed yet. Therefore, the Huanghekou Sag is a natural laboratory to reveal the relationship between the tectonic activties and hydrcoarbon accumulations in a rifted basin. In this study, the tectonic evolution characteristics of the Bonan Uplift in different geological periods are revealed during the main fault depression periods. Then, the direction of the provenance and distribution of the depositional system of the Bonan Uplift are analyzed based on the sedimentary system and mineralogy analysis. Finally, the sediment supply in the Bonan Uplift in different geological periods has been systematically studied. The results indicated that sediment supply is the dominant factor of hydrocarbon accumulation in the Paleogene in the Huanghekou Sag. During the Paleocene-Middle Eocene, extensive denudation occurred in the Bonan Uplift, sediments were mainly sourced from the Bonan Uplift in the northern margin of the Huanghekou Sag. During the Late Eocene to Early Oligocene, the Bonan Uplift had a large angle rotation and subsidence due to the strong rifting of the Bozhong Sag in the north, and the sand supply capacity was seriously reduced. Due to the different sediment supply in different geological periods, high quality reservoir and cap conditions were formed in the Paleogene in the central and northern parts of the Huanghekou Sag, which is conducive to the accumulation and preservation of oil and gas.

The origin of two distinct diagenetic depth zones in hydrocarbon-bearing sediments of Huanghekou Sag, offshore Bohai Bay Basin, China

Formation waters from the Huanghekou Sag, offshore Bohai Bay Basin, exhibited two depth zones with elevated total dissolved solid (TDS) composition. The shallow diagenetic zone at a depth of ∼1200–2000 m (∼45–70 °C) and the deep diagenetic zone at a depth of ∼3000–4000 m (∼100–130 °C) have TDS concentrations exceeding 70,000 mg/L, while the depth interval in between the two zones has TDS concentrations lower than 35,000 mg/L. Isometric log-ratio interpretations of the reconstructed formation water compositions, crude oil compositions, stable hydrogen and oxygen isotopes, light microscopy and clay mineral analysis were used to interpret the origins of the two diagenetic depth zones. Formation waters within each stratigraphic unit were dominantly composed of Na–K–Cl type. Processes affecting the deep diagenetic zone were attributed to (1) the dissolution of halite, albite and albitization, which predominantly caused the TDS enrichment, and (2) the dilution of TDS caused by the inter-layer H2O released from the transformation of smectite to illite (salinity reversal at depths > ∼3500 m). In comparison, the enrichment in TDS in the shallow diagenetic zone was attributed to hydrocarbon biodegradation, which consumed free water. The crude oil composition indicates severe hydrocarbon biodegradation. Biodegradation of low-molecular-weight organic carbons such as hexadecane (through methanogenesis) and benzene (through microbial sulfate reduction) could consume sufficient H2O to enrich TDS to the observed levels. At the same time, relatively constant Na/Cl and Ca/Cl ratios versus TDS can be explained by water consumption as well. This work could serve as a reference for the interpretation of two diagenetic zones characterised by distinct TDS enrichments in other hydrocarbon-bearing sedimentary basins.

Seismic Attribute Gradient Analysis and Reservoir Configuration Study of Shallow Water Delta Reservoir in Huanghekou Sag

Seismic Attribute Gradient Analysis and Reservoir Configuration Study of Shallow Water Delta Reservoir in Huanghekou Sag

Study on Fault Lateral Sealing Based on SGR Method

Bozhong A Oilfield is located in the northeast of Huanghekou Sag in the Bohai Bay Basin, and is a complex fault block oilfield. The main oil bearing horizon is the lower Minghuazhen Member, belonging to shallow water delta sedimentation. For the rolling exploration and evaluation of adjacent fault blocks, this paper uses the mudstone smear method to analyze and accurately characterize the lithological contact relationship between the two walls of the fault. Based on the establishment of different reservoir docking modes on the two walls of the fault, the sealing parameters are calculated to evaluate the sealing ability of the fault, thereby evaluating its reservoir formation characteristics, and predicting the height of the oil column. The above methods provide geological basis for further rolling expansion and potential tapping in the study area and surrounding areas, and have guiding significance for exploration and rolling potential tapping in similar blocks in the Bohai Sea.

Mapping the facies and geomorphology of igneous bodies by integrating multiple disciplines data: A case study of the BZ-A oilfield, Bohai Bay Basin, China

The BZ-A oilfield is one of the significant discoveries within the Huanghekou Sag, the southern Bohai Sea Basin, China, and the reservoirs of the BZ-A oilfield were deposited in the Paleogene period. Unfortunately, the spatial continuity of the Paleogene clastic reservoirs of the BZ-A oilfield was destroyed by the widely distributed igneous rocks. Characterizing those “isolated” clastic geobodies is the main task in the exploration and production phases. The exploration wells within the BZ-A oilfield demonstrate that the size of the clastic geobodies is one of the main factors that determine if a new drilled well is a commercial oil-producing well. The spatial distribution and the size of igneous rocks are other important factors affecting whether a drilled well is an oil-producing well. Thus, the analysis of 3D geomorphology of igneous rocks is among the most important tasks in well and development planning. We integrate 3D seismic data, well logs, and core data to characterize the Paleogene igneous bodies within the BZ-A oilfield. The analyzing procedure begins with determining the igneous rock types by analyzing the texture of cores and corresponding thin sections. Then, the volcanic/volcaniclastic facies are defined by integrating the well logs and igneous rock. Finally, the volcanic edifices are interpreted by integrating the seismic data, well logs, and core data. The analysis demonstrates that the volcanic edifice usually consists of five facies (volcanic conduit, effusive, explosive, extrusive, volcanic sedimentary, and subvolcanic facies). The overall shape of the edifice and the distribution of each facies are controlled by the volcanic eruption styles. In our study area, the seismic variance attribute can be used to locate the volcanic conduit facies, and the seismic root-mean-square amplitude can characterize the volcanic effusive facies.

Stratigraphic Constraints on Sandy Conglomerates in Huanghekou Sag, Bohai Bay Basin, via In Situ U-Pb Dating of Vein Calcite and Detrital Zircons, and XRD Analysis

The discovery of the BZ19-6 large-scale condensate gas field illustrates the great potential of the sandy conglomerate reservoirs in the Bohai Bay Basin. However, the stratigraphic correlation of the sandy conglomerate sequence in northern Huanghekou Sag remains a challenge due to the lack of syn-depositional volcanic layers and biostratigraphic constraints. The challenge limits understanding the regional strata distribution and further exploration deployment. In this study, we conducted in situ U-Pb dating of vein calcite and detrital zircons of the sandy conglomerate samples from borehole BZ26-A. The vein calcite age and the youngest age of detrital zircons provide the upper and lower bounds of the depositional age, respectively. We also correlated the samples with those from well-understood strata through a comparison of XRD mineral components. The absolute age of 47.0 Ma of the vein calcite and the youngest detrital zircon age of 103.5 Ma suggest the sedimentary sequence is supposed to be referred to as the Kongdian Formation (65–50.5 Ma). The XRD data and petrological analysis suggest that the lithostratigraphy of the Kongdian Formation in Huanghekou Sag could be divided into at least three members, with Member 3 consisting of red sediment deposited in a hot and dry climate; Member 2 and Member 1 deposited as fan delta with major parent rock of Mesozoic volcanic rocks and Precambrian meta-granitoid, respectively. Member 1 shows significant potential for energy exploration due to high brittle mineral components and fracture development.

The geochemical characteristics of the Paleogene lacustrine source rock and Cenozoic oil in the eastern Huanghekou Sag, Bohai Bay Basin, China: An oil–source rock correlation

Oil source correlations were conducted through bulk carbon isotope composition, source-related biomarkers, and maturity-related parameters to characterize the differences between two Paleogene lacustrine source rocks the Shahejie third (Es3) and fourth (Es4) members, utilizing seven Cenozoic crude oils. Es3 is dominated by type II1 sapropel kerogen, and Es4 is dominated by type II2 humic kerogen. The Es4 source rock has high gammacerane content, low Pr/Ph, high C30 steranes, high dinosteranes, and low β-/γ- and α-/γ-methyltrimethyltridecylchroman (MTTC), indicating a transgression in a saline lake during sedimentation. The low abundance of short-chain n-alkanes, high carbon peak number, abundant perylene, cadalene, and retene indicate that the Es4 input included significant amounts of ferns and gymnosperms. In contrast, the Es3 source rock was deposited in a moderately deep freshwater lake and had relatively more angiosperm and algal input with high oleanane to C30 hopane and high 1,2,7-/1,2,6- trimethylnaphthalene (TMN) ratios. The oils have relatively high sulfur content except oil O1. The larger population of oils were derived from the Es4 system, and were mixed with the low sulfur oil produced by Es3. The oil maturity parameters are generally higher than those seen in the two source where sampled, indicating that the oils were generated from source kitchens of higher thermal maturity in the east and south. The results of this study will contribute to the understanding of the evolution of Paleogene sedimentary environments and regional oil and gas exploration.

Mixed siliciclastic-carbonate deposition and cyclical evolution of the Upper Shahejie Formation and its impact on reservoir development in the Eocene Huanghekou Sag, Bohai Bay Basin, East China

We have systematically investigated a typical lacustrine mixed siliciclastic-carbonate sedimentary system in this study, which primarily deposited in the Eocene Upper Shahejie Formation (Es1 formation) of the Huanghekou Sag, Bohai Bay Basin. Using synthetic lithologic data sets, we summarized eight lithofacies from mixed siliciclastic-carbonate rocks and classified them into siliciclastic- and carbonate-dominated groups, indicating the variation of relative intensity between fluvial/deltaic process and carbonate productivity. Combining petrological and mineral component analysis, most lithofacies are compositionally replaced by micrite dolomite and show vertically different scales of cyclicity. The high-level cyclicity suggests the alternation between siliciclastic- and carbonate-dominated mixed rocks, whereas the lower level indicates interbedding of different dolomite-dominated lithofacies. The controlling factors on both levels are different. The higher level is probably controlled by climate changes, which finally resulted in the relative variations of siliciclastic supply, although the lower level of cyclicity changes more frequently and is considered to have been controlled by fluctuating hydrodynamic conditions. Typical mixed rock depositing patterns are summarized as the “sandwich type,” which are mainly distributed at siliciclastic-dominated sections and the “interbedded type” at carbonate-dominated sections. Besides, reservoir physical properties among lithofacies display significant differences as well, and the grain-supported framework of carbonate-dominated lithofacies suggests most constructive in keeping intergranular pores. The investigated lacustrine cyclical sedimentation in mixed siliciclastic-carbonate rocks has been less concerned in previous studies and may serve as a useful reference for lacustrine mixed rocks analysis in other rifted basins.

Anastomosed Shallow-water Delta of the Lower Member of Minghuazhen Formation in Huanghekou Sag

Anastomosed Shallow-water Delta of the Lower Member of Minghuazhen Formation in Huanghekou Sag

A model for faults to link the Neogene reservoirs to the Paleogene organic-rich sediments in low-relief regions of the south Bohai Sea, China

Fault acts as an important vertical migration conduit for hydrocarbons in rift basins and can transport hydrocarbons from deep-buried organic-rich sediments to shallow-buried coarse-grained sequences. Such migration process is expected, but generally needs to pass through thick mudstone intervals and its controlling factors are not well understood. The low-relief regions of the south Bohai Sea in the Bohai Bay rift basin, comprising both Paleogene and Neogene hydrocarbon traps, can act as a good case study for the factors controlling the hydrocarbon transporting capacity of faults. By comparing the hydrocarbon generation potential of source rocks in different formations, we confirm that the hydrocarbons trapped in the Neogene traps mainly originate from the Eocene Shahejie Formation, and need to pass through a thick Oligocene regional caprock. Hydrocarbon fluid inclusions within the Neogene reservoir sandstones indicate two major hydrocarbon charging events in the middle Pliocene to Quaternary, based on which we chose the T02 seismic marker bed to calculate fault displacement. Seismic profiles show that Neogene hydrocarbon-charged traps are commonly linked to faults with large-amount displacement, where the regional caprock has a limited thickness. Using statistics of the Neogene charged traps in a regional 3D seismic grid, we draw the minimum fault displacement for hydrocarbon migration in the Laizhouwan Sag at 53.6 m and in the Huanghekou Sag at 56 m, and the biggest caprock thickness for hydrocarbon migration in the Laizhouwan Sag at 240.7 m and in the Huanghekou Sag at 320.2 m. These observations emphasize the coupling of fault displacement and regional caprock thickness controlling the hydrocarbon transporting capacity of faults in a rift basin.

A prediction model of specific productivity index using least square support vector machine method

In the design of oilfield development plans, specific productivity index plays a vital role. Especially for offshore oilfields, affected by development costs and time limits, there are shortcomings of shorter test time and fewer test sampling points. Therefore, it is very necessary to predict specific productivity index. In this study, a prediction model of the specific productivity index is established by combining the principle of least squares support vector machine (LS-SVM) with the calculation method of the specific productivity index. The model uses logging parameters, crude oil experimental parameters and the specific productivity index of a large number of test well samples as input and output items respectively, and finally predicts the specific productivity index of non-test wells. It reduces the errors caused by short training time, randomness of training results and insufficient learning. A large number of sample data from the Huanghekou Sag in Bohai Oilfield were used to verify the prediction model. Comparing the specific productivity index prediction results of LS-SVM and artificial neural networks (ANNs) with actual well data respectively, the LS-SVM model has a better fitting effect, with an error of only 3.2%, which is 12.1% lower than ANNs. This study can better reflect the impact of different factors on specific productivity index, and it has important guiding significance for the evaluation of offshore oilfield productivity. Cited as : Wu, C., Wang, S., Yuan, J., Li, C., Zhang, Q. A prediction model of specific productivity index using least square support vector machine method. Advances in Geo-Energy Research, 2020, 4(4): 460-467, doi: 10.46690/ager.2020.04.10

Geochemically Distinct Oil Families in the Gudong Oilfield, Zhanhua Depression, Bohai Bay Basin, China.

Twenty crude oil samples were obtained from the Gudong Oilfield and their organic geochemical characteristics were analyzed. The oil samples were classified into three families by hierarchical cluster analysis and principal component analysis based on 13 source-related and depositional environment-related biomarker parameters. Oils in family I have low ratios of C19/C23 tricyclic terpanes and C24 tetracyclic terpane/C26 tricyclic terpanes, and relatively high ratios of steranes/hopanes and C30 4-methylsteranes/ααα20R C29 sterane, thus indicating that microalgae were the dominant organic matter input for the source rocks of family I. The gammacerane/C30 hopane ratios are higher than that of family II and family III, whereas the C35/C34 homohopane ratios are lower, thus indicating a suboxic, brackish water environment for the source rocks. The inferred source rock is the first member of the Shahejie Formation in the Huanghekou Sag. Family II is characterized by high ratios of C19/C23 tricyclic terpanes and C24 tetracyclic terpane/C26 tricyclic terpanes but relatively low ratios of steranes/hopanes and C27/C29 αααR steranes. These findings suggest that the original organic matter of the source rocks had a greater contribution from terrigenous higher plants than from microalgal. The relatively low ratios of gammacerane/C30 hopane and C35/C34 homohopane suggest that the source rocks were deposited in an oxic environment with a low salinity, thus corresponding to the Dongying Formation in the Huanghekou Sag. Family III oils have high C27/C29 ααααR steranes ratios and low C30 4-methylsteranes/ααα20R C29 ratios, which indicate the contribution of microalgae (especially zooplankton algae) to the source rocks. The relatively high abundance of C35 homohopane and low gammacerane/C30 hopane ratios suggest a weakly reducing condition with low salinity, which is in accordance with the third member of the Shahejie Formation in the Gunan Sag. The C31S/(S + R) homohopane ratios imply that oil samples in this study are in the mature stage, although the ratios of C2920S/(20S + 20R) and C29ββ/(αα + ββ) steranes suggest that the maturity of family II is higher than that of family I and family III.

Characteristics and sedimentary model of a reticular shallow-water delta with distributary channels: lower member of the Neogene Minghuazhen Formation in the Bozhong area of the Huanghekou Sag, China

The Bohai Bay Basin entered a late stage of structural depression during the sedimentary depositional period of the lower member of the Minghuazhen Formation in the Bozhong area of the Huanghekou Sag, China. Numerous analyses of geological and geophysical data have shown that the climate was relatively humid in the Bozhong area. Additionally, the basin basement subsided at a stable rate, creating a broad basin with gentle slopes. The research area in this study was close to the sediment source, which supplied it with a sufficient amount of sediment. The lake shoreline changed relatively frequently, and the lake was deep, which allowed shallow-water deltas to develop widely. The reticular shallow-water delta in the research area has the following sedimentary characteristics: (1) the fine-grained lithology, low component and textural maturities, and the cumulative probability particle size curve suggest tractive flow deposition. (2) Deltas with low sandstone contents and widely distributed red mudstone are widespread. (3) Chaetosphaeridium and biological disturbances are common. (4) The lake level fluctuates frequently. (5) Delta-front subfacies are mainly developed in the Bozhong area; they show a reticular planar distribution, comprise composite sandbodies, and are superposed by multi-stage underwater distributary channels. (6) The river channel is narrow and developed a large number of main river channels in different directions. (7) The underwater distributary channel microfacies are distributed within multibranched and bifurcated channels and generally show a discontinuous positive rhythm; however, the estuary dam sandbody is not well developed. This work suggests that a reticular shallow-water delta sedimentary system formed under humid climate conditions in the Bozhong area and is characterized by its near-source type, fine granularity, wide distribution, and vertically and horizontally overlapping of underwater distributary channel sandbodies. During the exploration process, this sedimentary system can provide a reasonable guide with which to predict the sandbody distribution in a lithologic reservoir.

The geochemical evidences of sulphur oil sources in the BZ35/36 structures of the Huanghekou Sag, Bohai Bay Basin, China

Crude oils in the BZ35/BZ36 fields found within the Paleogene Dongying and Shahejie formations in the Huanghekou Sag of the Bohai Bay Basin, China have generally high density, viscosity, and sulfur content. Their physical properties and geochemical features have obvious differences when compared with crude oils from other structures within the Huanghekou Sag. The comparison and analysis of biomarkers(e.g., pristine/phytane, gammacerane, C24Te/C26TT, C2920S/(20S + 20R), C29ββ/(ββ+αα), etc.) show that sour crude oil from the BZ35/BZ36 fields is similar to the sour oil in the Miaoxi Sag adjacent to the eastern of Huanghekou Sag. Sour, low maturity oils in the Miaoxi Sag have likely migrated southwest, while the sweet, higher maturity oils in the Huanghekou Sag have migrated northeast. Crude oils generated from these two sags have focused in the BZ35/BZ36 structures. The source rock of the sour crude oil was most likely formed in a dry climate and strong reducing saline lake.

Sedimentary features and their controls in a mixed siliciclastic–carbonate system in a shallow lake area: An example from the BZ‐X block in the Huanghekou Sag, Bohai Bay Basin, Eastern China

Mixed siliciclastic–carbonate sediments were well developed in the BZ‐X block as a subunit in the Huanghekou Sag in the southeastern part of the Bohai Bay Basin (China) during the Member 1 of the Shahejie Formation. An integrated approach based on detailed microscopic observation and core descriptions was applied to characterize the lithofacies types, facies associations, and depositional environment of the mixed sediments system. A detailed sedimentary facies analysis suggests that various lithofacies types can be grouped into four facies associations: mixed bioclastic sandy beaches (FA1), mixed clastic bioclastic shoal (FA2), mixed sandy oolitic shoals (FA3), and mixed distal bioclastic sandy beaches (FA4). These facies associations are interpreted to be deposited in varying depositional environments ranging from foreshore to shoreface setting in a shallow lake setting. An interplay of the climate regime, nearshore carbonate productivity, and current activity was proved to control the lithofacies types, dispersion and depositional environment change of mixed sediments in different depositional phases. Meter‐scale mixed cycles were found in this shallow lake setting and their features seem to differ from the classical mixed sediment models. It is suggested that these particular cycles in the stratigraphic record might indicate a typical mark of mixed sediment system in shallow areas of the lacustrine basin.

Geologic-seismic models, prediction of shallow-water lacustrine delta sandbody and hydrocarbon potential in the Late Miocene, Huanghekou Sag, Bohai Bay Basin, northern China

The Huanghekou Sag is located at the southeast part of the Bohai Bay Basin, northern China. Large-scale shallow lake delta developed in the Neogene provided suitable geological conditions for the formation of a subtle oil-gas reservoir in this area. The key for analyzing sandstone reservoir and sedimentary facies is by using seismic attributes (amplitude) to establish the relationship between lithology combination and seismic attributes. The lower unit of Late Miocene Minghuazhen Formation at the BZ34 block in the Huanghekou Sag was subdivided into 10 parasequence sets (PSS). Thicker sandstones mainly occurred in PSS1 and PSS10, whereas thin sandstones are mostly observed within other parasequence sets. This study presents statistics and analyses of lithology, i.e., statistics of root-mean-square (RMS) amplitude and lithology of well locations in different parasequence sets of the study area, as well as 1-D forward seismic models of 7 types of lithology combinations, the establishment of a spatial distribution of 2-D sandbody, forward seismic models etc. Our study indicates that high amplitude peaks correspond to thicker sandbodies, while low amplitude indicates non-development of sandbodies (generally less than 2 m), and medium amplitude agrees well with large sets of mudstones interbedded with medium and thinner sandstones. Different sand–mudstone combinations genetically reflect a combination of multiple micro-facies, therefore, amplitude features can predict sandbodies as well as facies characteristics.

黄河口凹陷复杂断块油气田水平井着陆技术

黄河口凹陷复杂断块油气田水平井着陆技术

Pore Fluid Evolution Influenced by Volcanic Activities and Related Diagenetic Processes in a Rift Basin: Evidence from the Paleogene Medium-Deep Reservoirs of Huanghekou Sag, Bohai Bay Basin, China

Volcanic activities exert a significant influence on pore fluid property and related diagenetic processes that substantially controlled reservoirs quality. Analysis of Paleogene medium-deep sandstones on the Huanghekou Sag provides insight into relating the diagenetic processes to pore fluid property evolution influenced by volcanic activities. Three distinct types of pore fluids were identified on the basis of an integrated and systematic analysis including core and thin section observation, XRD, SEM, CL, and trace element. Alkaline aqueous medium environment occurred in E2s1+2 where volcanic activities have insignificant influence on pore fluids, evidenced by typical alkaline diagenetic events such as K-feldspar albitization, quartz dissolution, feldspar dissolution, and carbonate cementation. During the deposition of E3d3, influx of terrestrial freshwater and alteration of ferromagnesian-rich pore water result in the formation of mixing aqueous medium environment through volcanic eruption dormancy causing zeolite dissolution, clay mineral transformation, and K-feldspar albitization. Ferromagnesian-rich aqueous medium environment developed resulting from the intensive hydrolysis of the unstable ferromagnesian minerals formed due to intense volcanic activities during E3d1+2 and corresponding predominant diagenetic processes were characterized by the precipitation and dissolution of low-silica zeolites. Therefore, the differential properties of pore fluids caused various diagenetic processes controlling reservoir quality.