Subtle Reservoirs Research Articles

Unsupervised machine learning-based multi-attributes fusion dim spot subtle sandstone reservoirs identification utilizing isolation forest

Subtle sandstone reservoirs are difficult to identify due to their weak seismic responses. Here, we propose to identify subtle sandstone reservoirs by an unsupervised machine learning-based multi-attribute fusion scheme using prestack seismic data. The proposed scheme carries out seismic attenuation gradient analysis and prestack simultaneous inversion to obtain the attributes that are sensitive to subtle channel sands, and uses them as the selected multiple attributes, and further employs a state-of-the-art unsupervised machine learning algorithm, called isolation forest, for the multi-attribute anomaly detection and analysis to identify subtle sandstone reservoir. To the best of our knowledge, this is the first time to introduce the isolation forest unsupervised anomaly detection algorithm in the reservoir identification. Prestack simultaneous inversion can use multi-angle and multi-scale information as constraints, and the attenuation gradient reflects the body response of the reservoir. For the field seismic data from a subtle channel sandstone reservoir in the western Sichuan basin, China, we found that the proposed scheme has good application effect in identifying subtle reservoirs. The application example demonstrates that the identified results are highly consistent with the actual development results, illustrating the feasibility and effectiveness of this scheme on the characterization for dim spot subtle sandstone reservoirs. This study is hoped to be useful as an aid for reservoir identification for dim spot subtle sandstone reservoirs, as well as to provide a new technical idea and method for reservoir characterization.

Improved fixed-point seismic inversion constrained by instantaneous phase

Some subtle reservoirs are hidden in the weak reflection areas and thin layers in seismic profiles, and they cannot be identified easily. Thus, the thin layer interpretation and the subtle reservoir prediction are the essential in reservoir management plan while field development and production stage. To improve the recognition capability in the weak reflection areas and resolution, the fixed-point (FP) algorithm is employed to obtain the inversion results since the conventional FP seismic inversion (CFPSI) is sensitive to the weak changes in seismic signals. However, the CFPSI suffers from low convergence. Therefore, the new iterative equations of pre- and post-stack FP seismic inversion are designed to improve the computational efficiency and convergence. Besides, a new constraint, which is derived from the instantaneous phase of the seismic trace, is also sensitive to the weak changes of the seismic signal. The instantaneous phase constraint is then involved in the objective function, contributing to a significant improvement of identification capability in weak reflection areas and the resolution of inversion. Additionally, the initial model constraint is introduced into the objective function to weaken the multi-solution and noise sensitivity. The synthetic examples demonstrate that the computational efficiency, recognition capability in the weak reflection areas and resolution of the proposed approach are higher than those of the CFPSI. The field examples suggest that the subtle reservoirs and thin layers, which are hidden in the weak reflection areas in the field data, are accurately identified using our method. Thus, the proposed method is useful for improving the recognition capability in weak reflection areas and resolution of the inversion results.

Subtle reservoirs and implications for hydrocarbon exploration in terrestrial lacustrine fan-delta deposits: Insights from the Triassic Baikouquan Formation, Mahu Sag, Junggar Basin, western China

Petroleum reserves are abundant in the large-scale lacustrine fan delta reservoirs containing mixed oil in the Baikouquan Formation (MA131 Block, Junggar Basin). However, detecting such subtle reservoirs in the lacustrine foreland basins is challenging. High-resolution sequence stratigraphy, sedimentary basin evolution, and reservoir models are established by integrating the results obtained via wireline log data, cores, thin sections, and seismic data. A fifth-order sequence stratigraphic framework for the Baikouquan Formation is established, which enables the reconstruction of the sedimentary basin evolution and further detailing of the reservoir model, such that the correlation to multistage progradation and retrogradation of the fan delta complex can be determined. The study of core samples led to the identification of eight microfacies, of which sandy debris flows and distributary channels dominate approximately 80% of the depositional system. Stratal slices enable the characterization of the northern Xiazijie and eastern Madong fan-delta systems. The northern Xiazijie fan delta is widely distributed throughout sequences SSQ1–SSQ6, whereas the Xiazijie fan delta underwent, in general, gradual retrogradation during the formation of sequences SSQ6 and SSQ7. The eastern Madong gravity flow fan-delta system only developed during the formation of sequences SSQ1–SSQ5 at the location of an abrupt slope break. There are nine categories of reservoir models in the study area based on the source rocks, faults, and reservoirs. Geomorphology and climate are crucial in controlling the sedimentary infill. Deep faults and an unconformity between the Permian and the Triassic of the Mahu Sag played a decisive role in controlling the hydrocarbon migration pathways. The faults, source rocks, and microfacies together exert considerable control on hydrocarbon accumulation. Within the nearshore fan-delta front, variable reservoir quality can be observed. Crucial factors in improving reservoir quality are fine-grain size and relatively low clay content. This study may facilitate subtle reservoir characterization in other basins.

Frequency-dependent AVO analysis

A method for generalizing the conventional amplitude variation with offset model from an isolated interface to a scattering reservoir interval is presented. The advantage of this new method is that it can provide enhanced detection of subtle reservoir and pore fluid properties. First- and second-order expressions for the reflected compressional wave energy from a specified heterogenous interval are given. These expressions are applied to two problems of interest for reservoir description. One application is discriminating low versus higher saturations of hydrocarbons, and the other is detecting the extent of vertical stratification within a reservoir. The first-order expression is used for determining hydrocarbon saturations, and the second-order expression is used for detecting the magnitude of fine-scale layering within a reservoir. Synthetic models and field data examples are used in demonstrating the applicability of the proposed method.

Distribution and controls of petroliferous plays in subtle traps within a Paleogene lacustrine sequence stratigraphic framework, Dongying Depression, Bohai Bay Basin, Eastern China

The characteristics of petroliferous plays in subtle traps within a sequence stratigraphic framework in the Dongying Depression are investigated in this study. Sand bodies within lowstand systems tracts (LSTs) of sequences, comprising incised-channel fills, sublacustrine fans, deltas in LSTs, controlled by syndepositional normal faults, and sand bodies within transgressive systems tracts (TSTs) to early highstand systems tracts (HSTs), consisting of beach bars, and turbidites, controlled by the prodelta slope, paleorelief, and syndepositional normal faults, are good subtle reservoirs. Mudstones and shale of deep lake subfacies in TSTs to early HSTs of sequences are source and cap rocks. Abnormal overpressure is the dominant dynamic factor for hydrocarbon migration from source rock to the subtle traps. Normal faults, sand bodies, and unconformities function as conduit systems. Sand bodies distributed in the abnormal overpressure source rocks within LSTs to early HSTs are petroliferous plays in lithologic traps. The petroliferous plays in stratigraphic traps are controlled by unconformities at margins of the Depression.

Automatic Identification of Sedimentary Facies Based on a Support Vector Machine in the Aryskum Graben, Kazakhstan

The Aryskum Depression in the South Turgay Basin has shown improving exploration prospects for subtle reservoirs, due to investment in the exploration workload and more comprehensive geological research. Among them, lithologic stratigraphic reservoirs have gradually become one of the focuses of oil and gas exploration. At present, deduction of the sedimentary characteristics of the target layer through core wells using artificial exploration has become an urgent problem to be solved. We selected 16 artificially interpreted coring wells in the Aryskum Graben for this study. Using the parameters of the gamma-ray (GR) curve of coring wells and support vector machine (SVM) classification algorithms, we developed an automatic identification model of sedimentary facies in the study area. The application of the SVM includes the following steps: Firstly, using the GR curve of 16 coring wells, six quantitative indexes defined as standard deviation, relative gravity, curve amplitude ratio, average median, average slope, and mutation amplitude, are selected to quantify the logging curve in the study area, thus realizing the description of the logging curve form. Secondly, training samples are selected to establish an SVM classification model. Finally, a quantitative discrimination model based on the SVM algorithm is established to realize the classification of depositional facies. Field application shows that this solution can be effectively used in uncored wells to identify depositional facies with a rate of accuracy approaching 70%. Our results provide new methods for the identification of sedimentary facies in the study area. The results will also provide a theoretical basis, as well as data basis, for further fine division of microfacies in the study area.

Genetic Quantitative Techniques Combined with Continuous Electromagnetic Profiling to Identify Subtle Oil and Gas Reservoirs

Subtle reservoir exploration could not be commonly carried out by costly conventional methods especially when subtle reservoirs are becoming smaller in surfaces and reserves. The epochal genetic quantitative techniques were proved to be suitable for the subtle reservoir prospecting, but the anomaly grade classification method did not match the quantitative data qualitative dividing. And the combination of genetic quantitative techniques and geophysical exploration methods to the prospecting application for subtle reservoirs still need more studies. For the questions, 194 topsoil samples and 237.05 km continuous electromagnetic profiling (CEMP) lines were arranged in typical subtle reservoirs in the Suganhu Basin. The realtime-PCR technique was used to get methanotrophic, propanotrophic functional gene pmoA and prmA quantitative data. The results showed that the classification method using cumulative probability distribution curves with regression analyses could be used to classify the genetic quantitative anomalies by the equation of y = az. The genetic quantitative anomalies and source strata thickness showed positive correlation along the section lines in the east of study areas. Integrated studies between genetic quantitative anomalies and CEMP results in the stereoscopic direction indicated three promising areas in the Suganhu Basin. This research is expected to be extended to the same type of reservoirs prospecting work.

Detection of subtle differences in seismic amplitude using convergence rate of the logistic map

Subtle reservoir is a key target of oil and gas exploration in the future. The high similarity of seismic amplitude between the reservoir and surrounding rock presents a challenge to detecting the reservoir boundary and its distribution. We have developed a global measurement of the distance between each sample value of seismic data and the stable fixed point of the data, i.e., the seismic convergence rate defined by the logistic map, and use it to highlight subtle differences in seismic amplitude. The logistic map is a fixed-point iteration system with one control parameter. To establish the relationship between seismic data and the logistic map, we define the stable fixed point of seismic data based on the Banach contraction principle and Cauchy convergence theorem, and we derive an equation for adaptively searching for the optimal control parameter of the logistic map based on the data’s stable fixed point. According to such an equation, we design a workflow to automatically generate seismic convergence rate for an input data. The seismic convergence rate is essentially the stable fixed-point image of seismic data, which is characterized by a fine structure and interpreted as the data’s invariant set. We use numerical experiments to illustrate the characteristics of seismic convergence rate, and we use the Marmousi model experiment to demonstrate the effectiveness of the seismic convergence rate on detecting subtle edges of seismic data. Then, we use real data from two typical carbonate exploration areas in China, the Central Tarim Basin and the Ordos Basin, respectively, to show the abilities of the seismic convergence rate in detecting hidden seismic facies and in detecting subtle edges in high-coherence zones, as well as in extracting the seismic invariant set.

The Synthesis and Decomposition of Signals and Its Application in Subei Basin Exploration

Subei basin is the most promising onshore oil and gas bearing basin in South China. With the deepening of exploration, subtle hydrocarbon reservoirs have gradually become the major target of exploration. Seismic record often shows low signal to noise ratio (SNR), resulting that conventional seismic records have three shortcomings in the identification of subtle reservoirs: difficult to identify small faults; difficult to show the distribution law of sand body; and difficult to find traps. In order to solve this problem, we conducted the research on signal synthesis and decomposition. The research results showed that seismic record of different frequency bands can be restored from original seismic record and both of them contain real stratigraphic information. Based on this, when a certain band or several bands in the original seismic record is affected by noise and result in the reduction of SNR of seismic record, seismic information seriously affected by noise can be abandoned, leaving only less affected seismic information to obtain seismic record with higher SNR. In the collection of actual seismic record, the low and high band seismic information is seriously affected by noise, while medium-band seismic information is less affected. Therefore, based on this, the medium-band seismic information can be restored from the original seismic record to be new record, which is called predominant frequency band seismic record. In this paper, based on the research result, the predominant frequency band seismic record was applied to the two areas of Subei basin and the result showed the research result can be used as a good instruction on well placement and the improvement of drilling success rate.

Research Progress in the Petroleum and Natural Gas Geological Theory of China

AbstractThe Chinese landmass, as a composite region, consists of multiple small continental blocks, such as Sino‐Korea, Yangtze, Tarim, etc., and orogenic belts. Because of its distinctive tectono‐sedimentary evolution, China's oil/gas‐bearing regions differ remarkably from that elsewhere in the world. For instance, in comparison to the Middle East oil/gas‐bearing regions which are characterized by Mesozoic‐Cenozoic marine oil/gas‐bearing beds, early oil and gas discoveries in China are distributed mainly in Mesozoic‐Cenozoic continental sedimentary basins. Generation of oil from terrestrial organic matter, or terrestrial oil generation, and the formation of large oil/gas fields in continental sedimentary basins were previously the major characteristics of petroleum geology of China. However, in the past 20 years, a series of major oil and gas discoveries from marine strata have been made. Marine oil/gas fields in China are mainly distributed in the Tarim, Sichuan, and Ordos basins, which are tectonically stable and covered with Mesozoic‐Cenozoic deposits. In these basins, hydrocarbon‐bearing strata are of old age and the oil/gas fields are commonly deeply‐buried. Cumulatively, 995 oil/gas fields have been found so far, making China the fourth largest oil‐producing country and the sixth largest gas‐producing country in the world. In terms of petroleum and natural gas geology, theories of hydrocarbon generation from continental strata, such as terrestrial oil generation and coal‐generated hydrocarbons, etc., have been established. Significant progress has been made in research on the sequence stratigraphy of continental strata, formation mechanisms of ultra‐deep clastic reservoirs, and hydrocarbon accumulation in the continental subtle reservoir. Regarding research on the marine petroleum geology of China, with respect to the major characteristics, such as deeply‐buried reservoirs, old strata, and multiple phases of transformation, important advances have been made, in areas such as the multiple‐elements of hydrocarbon supply, formation of reservoirs jointly controlled by deposition, tectonic activities, and diagenetic fluid‐rock reactions, and oil/gas reservoirs formed through superimposed multi‐stage hydrocarbon accumulation. As more and more unconventional hydrocarbon resources are discovered, unconventional oil and gas reservoirs are under study by Chinese petroleum geologists, who endeavor to come up with new discoveries on their formation mechanisms.

Mechanism of diagenetic trap formation in nearshore subaqueous fans on steep rift lacustrine basin slopes—A case study from the Shahejie Formation on the north slope of the Minfeng Subsag, Bohai Basin, China

Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those traps were formed is not clear, which inhibits further exploration for this type of reservoir. In order to solve the problem, we take as an example nearshore subaqueous fans in the upper part of the fourth member of the Shahejie Formation (Es4s) on the north slope of the Minfeng Subsag in the Dongying Sag. Combining different research methods, such as core observation, thin section examination, scanning electron microscope (SEM) observation, fluid-inclusion analysis, carbon and oxygen isotope analysis of carbonate cements, and analysis of core properties, we studied the genetic mechanisms of diagenetic traps on the basis of diagenetic environment evolution and diagenetic evolution sequence in different sub/micro-facies. Conglomerate in Es4s in the north Minfeng Subsag experienced several periods of transition between alkaline and acidic environments as “alkaline-acidic-alkaline-acidic-weak alkaline”. As a result, dissolution and cementation are also very complex, and the sequence is “early pyrite cementation / siderite cementation / gypsum cementation / calcite and dolomite cementation—feldspar dissolution / quartz overgrowth—quartz dissolution / ferroan calcite cementation / ankerite cementation / lime-mud matrix recrystallization / feldspar overgrowth—carbonate dissolution / feldspar dissolution / quartz overgrowth / pyrite cementation”. The difference in sedimentary characteristics between different sub/micro-facies of nearshore subaqueous fans controls diagenetic characteristics. Inner fan conglomerates mainly experienced compaction and lime-mud matrix recrystallization, with weak dissolution, which led to a reduction in the porosity and permeability crucial to reservoir formation. Lime-mud matrix recrystallization results in a rapid decrease in porosity and permeability in inner fan conglomerates in middle-to-deep layers. Because acid dissolution reworks reservoirs and hydrocarbon filling inhibits cementation, reservoirs far from mudstone layers in middle fan braided channels develop a great number of primary pores and secondary pores, and are good enough to be effective reservoirs of hydrocarbon. With the increase of burial depth, both the decrease of porosity and permeability of inner fan conglomerates and the increase of the physical property difference between inner fans and middle fans enhance the quality of seals in middle-to-deep layers. As a result, inner fan conglomerates can be sealing layers in middle-to-deep buried layers. Reservoirs adjacent to mudstones in middle fan braided channels and reservoirs in middle fan interdistributaries experienced extensive cementation, and tight cemented crusts formed at both the top and bottom of conglomerates, which can then act as cap rocks. In conclusion, diagenetic traps in conglomerates of nearshore subaqueous fans could be developed with inner fan conglomerates as lateral or vertical sealing layers, tight carbonate crusts near mudstone layers in middle fan braided channels as well as lacustrine mudstones as cap rocks, and conglomerates far from mudstone layers in middle fan braided channels as reservoirs. Lime-mud matrix recrystallization of inner fan conglomerates and carbonate cementation of conglomerates adjacent to mudstone layers in middle fan braided channels took place from 32 Ma B.P. to 24.6 Ma B.P., thus the formation of diagenetic traps was from 32 Ma B.P. to 24.6 Ma B.P. and diagenetic traps have a better hydrocarbon sealing ability from 24 Ma B.P.. The sealing ability of inner fans gradually increases with the increase of burial depth and diagenetic traps buried more than 3,200 m have better seals.

Application of Seismic Prediction Technique on Complex Lithological Reservoir in SL Oilfeild

In recent years, the proven reserves of lithological reservoirs account for a little more than two-thirds of the total proven reserves in SL Oilfield. The seismic predication technique as the key exploration method of lithological reservoirs focuses on identifying and describing reservoirs, especially on sand bodies. For the lacustrine faulted basin with various complex lithological reservoirs, based on the different geological characteristics of the reservoirs, a series of techniques suitable for channel sand, sandy conglomerate, turbidite and beach bar reservoirs have been developed and applied in the lithological reservoir identification and description and have made great progress in the actual exploration.PrefaceSince 1990s, the exploration in SL Oilfield has already developed to that of subtle reservoirs. The proven reserves of lithological reservoirs account for nearly 70% of the total reserves. The seismic predication technique as the key exploration method of lithological reservoirs focuses on identifying and describing reservoirs, especially on sand bodies. For lithological reservoir exploration in complex geologic conditions, lots of studies have been completed in order to obtain great success in many areas [1-7]. With the increasing degree of exploration, lithological reservoirs will become the key role in the future. It is very important to apply geophysical data for identification and description of lithological reservoirs. It has significant effect to improve exploration benefit and the production.

Stratigraphy and reservoir quality of the turbidite deposits, western sag, Bohai bay, China P.R.

Stratigraphic and subtle reservoirs such as pinchouts, sand lenses and unconformities have been discovered in Bohai basin. These reservoirs occur in sub-basins and sag structures called depressions. A prolific depression is the Liaohe depression that has been filled with rapidly changing mixed alluvial fan deposit of the Cenozoic age. Attempts made at recovering residual hydrocarbon from the subtle reservoir have necessitated the re-evaluation of available data to characterize and model the prolific Shahejie Formation turbidite deposit occurring as pinchouts and sand lenses for hydrocarbon assessment, reservoir quality and possible recovery through enhanced methods. Methods employed covered well logs analysis, clustering analysis for electrofacies and fuzzy logic analysis to predict missing log sections. Stratigraphic and structural analysis was done on SEGY 3D seismic volume after seismic to well tie. Stochastic simulation was done on both discrete and continuous upscaled data. This made it possible to correctly locate and laterally track identified reservoir formation on seismic data. Petrophysical parameters such as porosity and permeability were modeled with result of clustering analysis. Result shows that electrofacies converged on 2 rock classes. The area is characterized by the presence of interbeded sand-shale blanket formations serving as reservoir and seal bodies. The reservoir quality of the formations as seen on the petrophysical analysis done is replicated in simulation volume results. Reservoir rocks have porosity between 0.1 and 0.25, permeability between 1 and 2mD and hydrocarbon saturation as high as 89%. Lithofacies are observed to be laterally inconsistent, sub-parallel to dipping and occurring as porous and permeable continuous beds or pinchouts hosting hydrocarbon. The stochastic stratigraphic model depicts rock units in associations that are synsedimentary. The prevalent configuration gotten from the model gave an insight into exploring and developing the field for enhanced oil recovery of the heavy hydrocarbon of this area.

Study of real-time LWD data visual interpretation and geo-steering technology

LWD (logging while drilling) data has been used to explore complex subtle reservoirs by real-time visual interpretation and geo-steering. The method comprises of computer communication, well log data processing, formation recognition, reservoir modeling and model updating in real time. We studied the key technologies related to real-time LWD data visual interpretation and geo-steering and developed computer software with Chinese intellectual property rights covering the following important aspects: 1) real-time computer communication of well site LWD data; 2) visualization of geological model and borehole information; 3) real-time interpretation of LWD data; 4) real-time geological model updating and geo-steering technology. We use field application examples to demonstrate the feasibility and validity of the proposed technologies.

The Depositional System of Dongying Formation and Subtle Reservoir Exploration in Sha’nan Structural Belt Qikou Sag of Bohai Bay Basin, China

The subtle reservoir has become an important exploration target within the Bohai Bay Basin, especially in the Qikou sag. In order to guide subtle reservoirs exploration in offshore area geological analysis to Sha’nan structural belt is carried out in this paper. Qikou sag has large thickness, high abundance, ideal type hydrocarbon source rock. By unconformity recognition technique and paleotectonic analysis technique, results show that tectonic uplift had provided sedimentary source to the depression around it after Es1. By 3-D seismic interpretation technique and Seismic facies analysis, the sedimentary facies was confirmed. Geological analysis results show that sand bar, subaqueous fan is developed around it in Ed3. With the new geological analysis data sedimentary model of Sha’nan structural belt has been built in this paper. The sand bar and subaqueous fans showed a good reservoir potential, which are advantageous to oil accumulations. The southern part of Sha’nan structural belt has good hydrocarbon exploration potential.

Impact of arid surface megacracks on hydrocarbon reservoir properties

The megacrack pattern of the ephemeral north Panamint dry lake, California, United States, is characterized by variably sized polygons with diameters ranging from hundreds of meters to meters. The evolution and subsurface extent of this polygonal pattern and a probable tectonic link are examined by ground resistivity measurements and surface mapping. Crack development is initiated by the shrinking of clays caused by changes in water content near the surface. For crack evolution, the following processes are proposed: Cavities develop at approximately 1-m (3-ft) depth during a subsurface phase, followed by the collapse of the overburden into the existing cavities to form the surface cracks. Cracks are filled by wind-blown sand and dried-out lake sediments from collapsing crack walls. Following burial, differences in competence between crack-fill and surrounding playa-lake sediments provide zones of structural weakness that might channelize stress release and faulting. Ground resistivity measurements confirmed the extent of the cracks to a depth of more than 3 m (9 ft). The megacrack pattern is compared to a Rotliegende (Upper Permian) tight gas field, located in the southern Permian Basin of northwestern Germany, situated in a comparable geologic setting. There, a multidirectional polygonal pattern is recorded on horizon slices of three-dimensional seismic data and compares well to our observations from the Panamint Valley. The Rotliegende pattern is associated with low-offset faults, which are proposed to be responsible for subtle reservoir compartmentalization.

Yinggehai basin gas exploration: Comparison with Jiyang depression

Yinggehai (莺歌海) basin and Jiyang (济阳) depression experienced similar tectonic evolution, which is mainly controlled by the strike-slip faults. The strike pull-apart basins are characteristic by multiple deposition cycles, migration of deposition and subsidence center, and diversity depositional systems. Furthermore, both basins show abnormal formation pressure. Compared with the oil and gas-rich Jiyang depression, Yinggehai basin developed the similar geological background that is favorable to the formation of funnel-shaped meshwork-carpet subtle reservoirs. Overpressure diapir body is the core of hydrocarbon accumulation in central diaper zone of Yinggehai basin. Driven by high pressure, oil and gas migrate along the funnel-shaped passage system into the overlying low-potential zone formed. The overlying sand bodies of overpressure diapirs are the favorable gas exploration zone.

Research on Main Constraints in Sustainable Development of China Oil-Gas Upstream Industry

Though the long term exploration and development of China oil and gas resources, the yield and consumption have been increasing, but there are also many problems, including low grade oil reserve account for large percent in the future oil-gas replacement reserve, subtle reservoir exploration measures are immature, reservoir monitoring and management level need to be improved, oil-gas exploration and development advanced technologies are shortage, and so on. so, it must fully understand to these many problems in China oil-gas resources exploration and development, moreover, the effective implementation and completion our country oil-gas resources development targets must depend on the reasonable planning .This article is based on the analysis to present China oil-gas reserve, and point out that the current our country oil-gas resources station and problems in oil-gas resources exploration, development and utilization, meanwhile, the relative suggestion are put forward.

Hydrocarbon Detection Techniques on Subtle Reservoir Exploration in Qiongdongnan Basin

Subtle reservoir is an important area of hydrocarbon exploration in Qiongdongnan basin. The reservoir hydrocarbon-bearing potential is one of the cores of this research, and the geophysical technology is the main research tool. In this paper, AVO, AVD, DR and seismic attenuation gradient techniques are carried out to evaluate the hydrocarbon-bearing ability. Taking the JY area of eastern Qiongdongnan basin as a case study, the results show that the characteristics of gas-bearing reservoir in JY area are the 3rd AVO anomaly, high AVD and DR, and low attenuation gradient. Furthermore, multi-information fusion technique is used to qualify the gas resource scale and provide decision-making advice for the future exploration. It shows that the seismic anomaly sand body of the first member of Sanya Formation in JY area has large gas resource potential and good exploration prospect.

Sequence boundaries and regularities in the oil–gas distribution of the low swelling slope belt in the continental rift basin

Where are the zones more enriched in sand deposits in the down slope and deep depression of the low swelling slope belt? Are there any screening conditions for oil and gas there? These are the chief geological problems to be solved during exploration of a region. Taking the Paleogene system developed along the east slope belt of Chengdao as an example the concepts of sequence stratigraphy and sedimentary sequenc are applied. A new research method likened to a way “to get a melon by following the vine” is proposed to determine the direction for exploring within un-drilled or less-drilled areas. This is the process: “the characteristics of the sequence boundary → the forming mechanism of the stratigraphic sequence → the conditions of oil and gas accumulation → the distribution zones of oil and gas”. The relationship between the dynamic mechanism of stratigraphic sequence and the forming conditions for oil and gas accumulation establishes that the tectonic disturbance of the slope belt has significant responses as denudation and deposition. Above the stratigraphic sequence boundary there are large scale sand bodies of the low stand system tract (LST) that have developed in the low swelling slope belt and its deep depression. Below the sequence boundary there are the remaining sand bodies of the high stand system tract (HST). On the slope there is a convergence of mudstone layers of the extended system tract (EST) with the mudstone of the underlying strata, which constitutes the screening conditions for the reservoir of the down slope and deep depression. The distribution regularities in preferred sand bodies on the surface of the sequence boundary, and in the system tract, indicate the ordering of oil–gas deposits. From the higher stand down to the depth of the slope there are, in order, areas where exploration was unfavorable, major areas of stratigraphic overlap of oil–gas reservoirs, unconformity screened oil–gas reservoirs, and, finally, sandstone lens oil–gas reservoirs. The low swelling slope belt of Chengdao was tectonically active, which is typical for a continental rift basin. The methodology and results of the present paper are significant for the theory and practice of predicting subtle reservoir and selecting strategic areas for exploration.