Minghuazhen Formation Research Articles

Relationship between fault activity and hydrocarbon accumulation in the Baxian Depression, Bohai Bay Basin, China

Based on the fluorescence microscopic features of fluid inclusions and the combined analysis of the homogenization temperature and burial history modeling, the hydrocarbon charge history was divided into two phases, among which the second phase was the main pool-forming period and took place during the deposition of the Minghuazhen Formation (12–2 Ma). Based on the calculation of the rate of fault displacement and the duration of fault activity, the fault activity characteristics are quantitatively evaluated. The result shows that the average rate of fault displacement during this interval was 6.9 m/Myr, and the duration of fault activity was about 0–6 Myr. Reservoirs formed in the non-hydrocarbon generating strata are overwhelmingly situated adjacent to the faults which have the most rapid displacement rates and longest periods of activity.

A simplified assessment method for estimating recoverable geothermal resources

As geothermal reinjection has been required in the rapid development of geothermal industry market, geothermal heating projects are in badly need of recoverable geothermal resources assessment for target areas feasibly and reasonably. This paper proposed a simplified method of assessing recoverable geothermal resources for a doublet well production pattern. The assessment method was based on the analytical investigation of computational method of influence area when water flows through and extracts heat from geothermal reservoirs. The model was validated and verified by comparison with numerical simulation results. This method has been applied to assess recoverable geothermal resources and district heating potential of lower Minghuazhen Formation in Bazhou, Hebei province, China. This resources assessment method can provide the accurate recoverable geothermal evaluation results based on the optimization extraction-reinjection strategies for efficient decision-making of geothermal projects. With the help of the simplified geothermal resources assessment method, geothermal heating enterprises will adapt to the rapid development of geothermal industry by reducing time and cost of geothermal heating projects.

Source rocks evaluation of the Paleogene Shahejie 3 Formation in the Dongpu Depression, Bohai Bay Basin

Present simulation results based on two-dimensional basin cannot obtain accurate evaluations of petroleum resources because of not combining the thermal history in the Dongpu Depression. In this paper, Shahejie 3 Formation source rocks are evaluated using the geochemical data, and based on the thermal history, the thermal maturity evolution of typical wells and the top and bottom of the Shahejie 3 Formation source rocks are modeled using BasinMod software. Results show that source rocks are mainly distributed in the Haitongji-Liutun and Qianliyuan areas, and dominated by medium to high maturity source rocks. Organic matter types are primarily types II and III kerogen with a small amount of type I. The Shahejie 3 Formation source rocks in the Menggangji area experienced two stages of hydrocarbon generation: (1) during the Dongying Formation depositional period (33–17 Ma) and (2) from the Minghuazhen Formation depositional period to present (5.1–0 Ma). The source rocks are generally underdeveloped with low potential for hydrocarbon generation due to nonpoor and thin source rocks in this area. The two stages of hydrocarbon generation are not obvious for other areas. When the bottom of the source rocks reached overmature stage, the mid-lower Shahejie 3 Formation experienced the peak of hydrocarbon generation during the Dongying Formation depositional period. The thermal maturity evolution of the Shahejie 3 Formation source rocks revealed that the main hydrocarbon generation period was during the Dongying Formation depositional period. Therefore, petroleum exploration is suggested to be performed at the Shahejie 3 Formation source rocks in the Qianliyuan and Haitongji-Liutun areas to study the lithology and discover complex petroleum reservoirs in the Dongpu Depression.

Hydrocarbon migration and accumulation in the northwestern Bozhong subbasin, Bohai Bay Basin, China

An important exploration breakthrough has been achieved in the western subsag of the Bozhong subbasin, but the hydrocarbon accumulation mechanism was not clear. The hydrocarbon migration and accumulation mechanism of the western subsag of the Bozhong subbasin is discussed based on the modeling of hydrocarbon migration pathways and the study of late-stage reactivation of neotectonic faults. Three processes for lateral petroleum migration and accumulation can be recognized in the studied area: 1) migration and accumulation along the T8 unconformity; 2) migration and accumulation within the Guantao Formaiton (N1g); and 3) interaction of migration and accumulation along the T8 unconformity and Guantao Formation (N1g). The reactivation of faults in the studied area began 5.1 Ma. Following hydrocarbon lateral migration, late-stage reactivated neotectonic faults serve as effective vertical conduits for hydrocarbon migration and accumulation into the shallow Minghuazhen Formation (N1m) reservoirs.The modeling results of preferential petroleum migration pathways (PPMPs) and favorable accumulation areas are consistent with the actual exploration results. Two kinds of potential exploration targets can be predicted in the northwestern Bozhong subbasin: the first kind is hydrocarbon accumulation areas near or within generative kitchens (e.g. Target 1); the other kind is hydrocarbon accumulation areas removed from the generative kitchens, but with hydrocarbon sourcing from multiple generative kitchen and numerous PPMPs (e.g. Target 2). Studying preferential petroleum migration pathways will help reduce exploration risk.

Fused spectral-decomposition seismic attributes and forward seismic modelling to predict sand bodies in meandering fluvial reservoirs

Abstract Understanding the hierarchical architectural elements of fluvial sand bodies is important for planning their development strategy and to enhance oil recovery. Red-Green-Blue (RGB) blending of multiple seismic attributes and forwarding seismic modelling are commonly used in the analysis of compound sand bodies. However, RGB blending of multiple seismic attributes can only qualitatively describe the boundaries and thickness of sand bodies. The forward seismic modelling techniques previously documented in the literature are not effective when depicting the geometry of, and stacking relationships between, sand bodies (i.e., reservoir compartmentalisation). Hence, we propose in this work a new workflow that combines fused spectral-decomposition seismic attributes (SDSAs) and forwarding seismic modelling to quantitatively predict sand thickness, and to characterise stacking relationships between sand bodies. First, we employ a Support Vector Machine (SVM) algorithm to fuse high, middle, and low frequency components (attributes) of seismic data so as to quantitatively predict the thickness of sand bodies. Second, we define the seismic waveform response patterns corresponding to the typical conceptual stacked sand bodies. With the constraints of waveform patterns and predicted sand thickness (fused SDSAs), the geometry and stacking relationships of the sand bodies are characterised by forward seismic modelling. To illustrate the effectiveness of our proposed workflow, we apply it to the Neogene Minghuazhen Formation (Nm) of the QHD 32–6 oil field, Bohai Bay Basin, China. We define five architectural elements of a meandering fluvial reservoir by analysing the hierarchy of sand bodies using our workflow. The predicted sand bodies in this workflow were further proven by horizontal drilling and production data.

Mapping sediment-dispersal characteristics of Neogene deltas using seismic geomorphology, Liaodongdong area, Bohai Bay Basin, China​

ABSTRACTSeismic geomorphology has provided effective technical support for the study on the sediment dispersal system in poorly drilled area based on seismic data. In this paper, taking the Neogene strata of eastern Liaodong region in the Bohai Bay Basin, eastern China, as an example, strata slicing was performed in the 3D seismic data volume with phase adjustment under the constraints of a few drilling and logging data, which aims to depict the planar distribution and evolution of the sandbodies of Guantao–Minghuazhen Formation layer by layer. One hundred and seventy-five isochronous strata slices of amplitude attribute were extracted in the time domain, which had greatly improved the quality of sandbody planar distribution map and provided an effective method for analyzing the sedimentary microfacies of different periods and their evolution in the study area.

Geological Conditions of Hydrocarbon Accumulation in the South of Liaozhong Sag

The south of Liaozhong sag is a hydrocarbon-rich area but lack of detailed study. This paper aims to analyze the geological conditions of pool forming in this area. Based on the geochemical and other geological data, it is known that source rocks of the study area are suggested to the third member of Dongying Formation and the whole Shahejie Formation. Reservoirs are allocated to the Guantao Formation and Minghuazhen Formation with middle to high permeability and high porosity. As for the caprock, it is considered to be the well-developed mudstones or shale of lower Ed, Es1 and Es3 Formation. There are two kinds of source-reservoir-caprock combinations, the lower generation to upper reservoir and self-generation to self-storage. In addition, the hydrocarbon reservoirs are mostly related to faults.

Division of “layer exploration unit” and high-efficiency exploration in mature exploration area

Abstract To realize high-efficiency and sustainable exploration of the Jiyang depression at the stage of high exploration degree, a hydrocarbon accumulation-geological evaluation method is developed on the basis of current geologic knowledge and extent of fine exploration. The concept of “layer exploration unit” is proposed in the study, and it is defined as an exploration geological unit that has a relatively complete and unified tectonic system, sedimentary system and hydrocarbon migration & accumulation system in a tectonic layer or tectonic sublayer within a fault basin. Then, an approach to dividing and evaluating the “layer exploration unit” is developed. With this approach, the Jiyang depression is divided into 305 layer exploration units, thus helping realize precise and stereoscopic geological understanding and exploration deployment. Fine splitting of remaining resources and benefit evaluation of exploration targets are conducted by “layer exploration units”. As a result, 66 efficient “layer exploration units” in four major areas (i.e. Paleogene upper Es4−Dongying Formation, Neogene Minghuazhen Formation−Guantao Formation, Paleozoic buried-hill, and Paleogene Kongdian Formation−lower Es4) are determined as the targets for obtaining more reserves and breakthroughs in the short and medium term.

Identification of flow units using the joint of WT and LSSVM based on FZI in a heterogeneous carbonate reservoir

The objective of this study was to develop an accurate method for predicting hydraulic unit types in a heterogeneous carbonate reservoir. There is a significant practical potential in the use of the flow unit characterization. Identification of flow units in inhomogeneous carbonate reservoir presents a great challenge to geologists and engineers. A new method for dividing the flow units was proposed in this study based on the joint of wavelet transform (WT) and least squares support vector machine (LSSVM) within the most productive carbonate reservoir of the Minghuazhen Formation in Region A, Block X in the Petrochina Dagang oilfield. Petrophysical properties derived from core data and logging from 21 representative wells were analyzed. The flow units were classified as five types based on the flow zone index (FZI) approach. The WT and LSSVM were jointly used for learning and training each unit. The well logs were broken down into high and low frequency data using WT. Sensitivity analysis of parameters of training samples to select the largest impact was performed with C5.0 decision tree to obtain a WT-trained set. A predictive model was then established by training LSSVM model. The final trained model with the identification rule and criterion for the classification of flow units was used for identifying flow units in the cored and non-cored intervals of reservoir. The result from this study is consistent with core data and is more accurate than that from the previous investigations. It is concluded that using the combination of the WT and LSSVM improved the accuracy of classification of flow units in the Minghuazhen Formation.

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.

Hydrocarbon migration and accumulation of the Suqiao buried-hill zone in Wen'an Slope, Jizhong Subbasin, Bohai Bay Basin, China

The hydrocarbon migration and accumulation of the Suqiao deep buried-hill zone, in the Jizhong Subbasin, the Bohai Bay Basin, eastern China, was investigated from the perspective of paleo-fluid evidence by using fluid inclusions, quantitative fluorescence techniques (QGF), total scanning fluorescence method (TSF) and organic geochemical analysis. Results show that the current condensate oil-gas reservoirs in the study area once were paleo-oil reservoirs. In addition, the reservoirs have experienced at least two stages of hydrocarbon charge from different sources and/or maturities. During the deposition of the Oligocene Dongying Formation (Ed), the deep Ordovician reservoirs were first charged by mature oils sourced from the lacustrine shale source rocks in the fourth member of Shahejie and Kongdian Formations (Es4+Ek), and then adjusted at the end of Ed period subsequently by virtue of the tectonic movement. Since the deposition of the Neogene Minghuazhen Formation (Nm), the reservoirs were mainly charged by the gas that consisted of moderate to high-maturity condensate and wet gas sourced from the Es4+Ek lacustrine shale source rocks and mature coal-derived gas sourced from the Carboniferous-Permian (C-P) coal-bearing source rocks. Meanwhile, the early charged oil was subjected to gas flushing and deasphalting by the late intrusion of gas. The widely distributed hydrocarbon inclusions, the higher QGF Index, and FOI (the frequency of oil inclusions) values in both gas-oil and water zone, are indicative of early oil charge. In addition, combined with the homogenization temperatures of the fluid inclusions (<160 °C) and the existence of solid-bitumen bearing inclusions, significant loss of the n-alkanes with low carbon numbers, enrichments of heavier components in crude oils, and the precipitation of asphaltene in the residual pores suggest that gas flushing may have played an important role in the reservoir formation.

Establishment of Geological Knowledge Database for Meandering River Reservoirs in Offshore Oilfields With Large Well Spacing

Based on quantitative logging microfacies identification, seismic constraint facies map compilation and horizontal wells architecture analysis, the reservoir geologic knowledge database of different grades configuration unit was established for meandering river reservoirs of Lower Minghuazhen Formation in Q oilfield. The results show that the average point bar sand body width is 360-783 m, the average sand body thickness is 4.0-8.5 m, the ratio of width to thickness mainly distributed in 40-100. Average lateral accretion layers dip is 5.7°, lateral accretion layers horizontal interval mainly distributed in 70-200 m. On the basis of reservoir geological knowledge database, a fine geological model was established together with sequential indicator method and equivalent characterization method. Base on the reservoir geologic knowledge database and geological modeling results, 130 adjustment wells were successfully deployed and implemented at the comprehensive adjustment process of Q oilfield, these wells made an obvious oil production increase effect.

Evolution of lacustrine basin in relation to variation in palaeowater depth and delta development: Neogene Bohai Bay Basin, Huanghekou area, northern China

This paper presents revision of the Neogene chronostratigraphic framework of the Huanghekou area in the Bohai Bay Basin, northern China, on the basis of integration of palaeomagnetic data and Neogene seismic stratigraphy. The modern Lake Dongting was selected for analyses of bottom sediments, water depth and elemental composition. Four elements, namely Al, V, Ni and Ga with R 2 value larger than 0.7, were chosen to establish a quantitative relationship (F P) between elemental composition and water depth of bottom sediments. A water depth of ~2.4 m was identified as an accumulation depth of Candoniella albicans, which is used to derive environmental variable (Φ) of formula F P. Candoniella albicans is also found within the Neogene well W10 in the Huanghekou area. Considering 2.4 m as D value in formula F p and measured element values at different depths of W10, Φ values were obtained at different depths. The quantitative palaeowater depths of each drilling well were estimated for the first time in this area by considering elemental composition of chip samples of four drilling wells in the Huanghekou area, which are directly iterated to the F F. Palaeowater depth reconstruction of the Neogene in the Huanghekou area indicates an initial deepening trend and a later shallowing trend during the evolution, with average and deepest bathymetry at ~2.3 and ~4.8 m, respectively. Frequent fluctuations of palaeowater depth control the sand dispersal pattern in a shallow delta during the lower part of the Lower Member of Minghuazhen Formation.

The analytic wavelet transform with generalized Morse wavelets to detect fluvial channels in the Bohai Bay Basin, China

The Middle Miocene Minghuazhen Formation of the Bohai Bay Basin is dominated by fluvial channels and shallow-lacustrine deltaic systems. These depositional facies, along with complex postdepositional faulting, make it difficult to detect fluvial channels. As a useful seismic attribute to solve this problem in the Bohai Bay Basin, spectral decomposition of 3D seismic data can provide significant information to understand the subsurface fluvial channels. The analytic wavelet transform (AWT) is a promising approach for implementing spectral decomposition to provide a detailed time-frequency representation. In particular, by varying two parameters (beta and gamma) controlling the wavelet forms, the generalized Morse wavelets (GMWs) can be given a broad range of characteristics while remaining exactly analytic. To detect fluvial channels with thickness around and lower than the tuning thickness, we have proposed a suitable (beta = 1 and gamma = 3) pair of parameters for GMWs because such an exactly analytic Morse wavelet substantially outperforms the approximately analytic Morlet wavelet for high time localization. We have applied the AWT with a GMW (beta = 1 and gamma = 3) to 3D seismic data in the Lower Minghuazhen Formation, Bohai Bay Basin, China. The stratal slicing of spectral decomposition volumes at depositional cycle 2 of the Lower Minghuazhen Formation shows its potential for channel interpretation and the optimization of well patterns.

Comprehensive assessment of source rocks in the Bohai Sea area, eastern China

The Bohai Sea area, offshore of the Bohai Bay Basin, is one of the most petroliferous regions in China, with proven original oil in place of approximately 2.4 × 109 m3 (150.94 × 108 bbl) and proven original gas in place of over 5 × 1012 m3 (1.76 × 1013 ft3). Cumulative oil production is over 50 million tons (3.5 × 108 bbl). In this study, using the limited data on source rock thickness, core samples, and Rock-Eval pyrolysis along with sedimentary facies analysis, source rock characteristics of different depositional settings were identified, and the thickness, richness, organic matter type, and thermal evolution of four sets of source rocks in the Bohai Sea area— the second member of Dongying Formation (E3d2), the third member of Dongying Formation (E3d3), the first and second members of Shahejie Formation (E2s1-2), and the third member of Shahejie Formation (E2s3)—were predicted and evaluated. Subsequently, the intensity and history of hydrocarbon expulsion for different sags was systematically compared and analyzed. The greatest thickness of the four sets of source rocks in the Bohai Sea area is 400–800 m (1300–2600 ft). The average richness of the organic matter of these source rocks is 1.74%–2.87%. The E2s3 set has the highest organic matter abundance; E2s1-2 has the lowest. The organic matter of these source rocks is mainly type I and type II, but their evolutions differ. The vitrinite reflectance of E3d2 is 0.5%–1.0%, that of E3d3 is 0.7%–1.25%, that of E2s1-2 is 0.75%–1.75%, and that of E2s3 is 0.75%–2.0%. The cumulative hydrocarbon expulsion of the four sets of rocks is 4.14 × 1010 t (2.90 × 1011 bbl). The E2s1-2 set has the greatest expulsion amount: 1.75 × 1010 t (1.22 × 1011 bbl). The peak stages of hydrocarbon expulsion of the four sets of source rocks were during Neogene Minghuazhen Formation (12.2–2.0 Ma) and Neogene Guantao Formation (16.6–12.0 Ma). The Bozhong sag expelled the most hydrocarbons, followed by the Liaozhong, Qikou, and Huanghekou sags.

Assessment of the CO2Storage Potential in the Deep Saline Formation of Offshore Bohai Basin, China

Regions of China have generated large CO2 emissions, and investigating the means for reducing them has become a priority. The geological storage of CO2 is one technique gaining interest, and the offshore Bohai Basin is believed to be a promising option to aid emissions mitigation. The Cenozoic sedimentary rocks, which measure more than 10,000 m in thickness and have diverse depositional system and good reservoir-seal assemblage, appear to offer the most favorable circumstance for CO2 storage in the offshore Bohai Basin. The Minghuazhen Formation of the Pliocene-Miocene consists of thick and extensive mudstone, especially its lower member, and is regarded as an excellent regional seal cover. The Miocene sandstone, including the lower member of the Minghuazhen Formation and the Guantao Formation, has high porosity and permeability and is a preferred target storage reservoir. The Dongying Formation and the Shahejie Formation of the Oligocene-Eocene are also storage options. Based on the pore volume method suggested by USDOE, the effective storage capacity of the Cenozoic sedimentary rocks in the offshore Bohai Basin is calculated. The mean storage capacity is approximately 192 Gt, a huge capacity on a par with that of the Pearl River Mouth Basin, and potentially offering storage capacity for hundreds of years of CO2 emissions from the Circum-Bohai-Sea Region. Considering the storage capacity and risk, the Bozhong Sag area may offer the most promising early CO2 storage option in the Basin.

Hydrocarbon migration pathways in the Neogene of Laixi structural belt, southern Bohai Sea, China

Characteristics, distribution, temporal and spatial configuration, and effectiveness of hydrocarbon migration pathways have been investigated through geochemical and formation pressure analysis etc, to further reveal hydrocarbon accumulation patterns in the Neogene of the Laixi structural belt, southern Bohai Sea of China. Firstly, three factors, faults, carrier rocks (beds) and mud caprocks of the transporting framework in the Neogene were examined to find out its feature and space configuration and made static state evaluation. It is found that besides the Guantao Formation – lower Minghuazhen Formation No. V oil layers, the No. I – III oil layers in the lower Minghuazhen Formation are also the dominant oil and gas carrier beds. Cutted by the adjustment faults and sealed by mudstone capcocks, the two carrier layers are combined into a “layered cake” type hydrocarbon migration framework. Then the hydrocarbon passage pathways were tracked dynamically and described using nitrogen compounds concentration, formation pressure, fluorescence logging and sand bodies description, which shows that the “T03-T02-T01 mudstone cap layers” separate the Neogene hydrocarbon migration pathways into upper and lower units. The massive sandy conglomerate reservoirs in the Guantao Formation – lower Minghuazhen Formation No. V oil layers are the carrier bed of the lower hydrocarbon migration pathway, while the north-south trending overlapped and connected channel sandbodies in lower Minghuazhen Formation No. I – III oil layers are the carrier bed of the upper unit. Hydrocarbon migrated laterally along the two passage ways, accompanying with differential accumulation.

Evolution regularity of the Neogene shallow water delta in the Laibei area Bohai Bay Basin, northern China

According to the characteristics of sedimentary microfacies, unique vertical depositional sequences and well logging response, the authors propose that a shallow water delta was widely developed in the Neogene of the Laibei area, Bohai Bay Basin of northern China. Based on seismic minimum amplitude slices, well logging data, test analytical data and so forth, detailed research on the evolution of the shallow water delta of the Neogene Lower Member of Minghuazhen Formation was conducted. The results indicate that the third-order sequence base level controls sandbody types. During a period of low base level, a distributary channel sandbody of shallow water deltaic plain was developed. With base level rising, the sandbody type gradually changed into a subaqueous distributary channel sandbody and a sheet sand can be found as well. The fourth-order sequence base level controls medium–short term evolution of the sandbody. Within a sequence, due to the rising and falling of base level, the sandbody assemblages are identified as an upward-coarsening type, an upward-fining and a compound type respectively. Regionally, from the Laibei Low Uplift to the Huanghekou Sag, the shallow water delta evoluted from a dendritic shape, to a cuspate shape and finally to a sheet shape.

Hydrocarbon Accumulation Dominant Factors and Modes of Minghuazhen Formation in Chengdao Area

Chengdao area is a multiple hydrocarbon accumulation belt with the typical tectonic background, and its main target stratum is Neogene. However, the exploration and recognition level of Minghuazhen Formation is still at the primary stage. Based on the comprehensive analysis of seismic, well-logging, logging and geochemical data, and combined with its structural characteristics, intensity of fault activity and reservoir-caprock assemblage, this paper systematically analyzed the dominant factors of hydrocarbon accumulation in Minghuazhen Formation, and clarified that the tectonic setting controlled where the hydrocarbon enriched, intensity of fault activity influenced how much of hydrocarbon enriched and the reservoir-seal assemblage dominated hydrocarbon accumulation strata. Then two types of hydrocarbon accumulation models, that is, main fault-sand body and main fault-secondary fault–sand body were established.

Charging of the Penglai 9-1 oil field, Bohai Bay basin, China: Functions of the delta on accumulating petroleum

The Penglai 9-1 (PL9-1) oil field, which contains China's third largest offshore oil accumulation (in-place reserves greater than 2.28 × 108 ton or 1.49 × 109 bbl), was found in shallow reservoirs (700–1700 m, 2297–5577 ft) within the most active fault zone in east China. The PL9-1 field contains two oil-bearing series, the granite intrusions in Mesozoic (Mz) and both the sandstone reservoirs in Neogene Guantao (Ng) and Neogene Minghuazhen (Nm) Formation. The origins of the PL9-1 field, both in terms of source rock intervals and generative kitchens, were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples. The Mesozoic granite intrusions, which hold more than 80% of the oil reserves in the field, were charged in the west by oil generated from the third member (Es3) of the Shahejie Formation in the Bodong depression. The Neogene reservoirs of the PL9-1 field were charged in the west by oil generated from the third member (Es3) of the Shahejie Formation in the Bodong depression and in the south by oil generated from the first member (Es1) of the Shahejie Formation in the Miaoxibei depression. Interactive contact between the large fan delta and the mature source rocks residing in the Es3 Formation of the Bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the PL9-1 field, which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east China.