The Meso-Neoproterozoic strata dated back to 1800-541 Ma are the oldest sedimentary strata in China. Petroleum geologists never thought that hydrocarbon could be found within the Meso-Neoproterozoic strata, or took them as exploration targets since no reliable early lives and associated fossils were identified in these strata until the 1950s. In recent decades, however, paleontologists have made great achievements in the fundamental research on early Proterozoic lives, and petroleum geologists and geochemists also found numerous oil seeps, asphalts and source rocks with rich organic matters. These organic matters are in immature to over-mature phases, even still in the "liquid oil window" in some zones, so that dozens of primary Meso-Neoproterozoic oil and gas fields have been found with large amount of oil/gas reserves and high oil/gas flows, indicating that the Meso-Neoproterozoic strata have favorable conditions for generation and accumulation of large-scale petroleum resources.

It is quite difficult to explore offshore oil and gas reservoirs, and especially the offshore lithologic reservoirs in middle and shallow layers. And the exploration difficulties are mainly how to identify and describe the lithologic pinch-out boundary when the superimposed relationship of sandbodies is diverse and the resolution of conventional seismic profile is lower and how to discover large-scale reserves of lithologic reservoirs practically and effectively. Huizhou sag in the Pearl River Mouth Basin is a relatively mature exploration area, and it was taken as an example to systematically summarize the distribution characteristics of middle-shallow lithologic reservoirs in this area. And accordingly the exploration strategy for lithologic reservoirs in mature explorations areas was put forward. The exploration practice of lithologic reservoirs in Huizhou sag shows that they are usually distributed near the hydrocarbon rich sub-sags, co-existed with structural reservoirs controlled by marine flooding mudstone, and accumulated in the main hydrocarbon migration paths. Based on these characteristics, the exploration strategy of integrated exploration and development was put forward according to the overall-planning exploration principle with geology, geophysics and economic evaluation as a whole. This exploration strategy takes high-quality seismic data as the base, detailed geological cognition as the guidance and advanced geophysical technology as the method. It provides the important guidance for the discovery of new lithologic reservoirs in the periphery of Huizhou 21-A and Huizhou 25-B oil fields in Huizhou sag.

After more than 50 years of exploration, the Dagang Oilfield faces many challenges such as difficulty in locating wells, difficulty in increasing reserves, difficulty in upgrading reserves, difficulty in producing reserves, and difficulty in enhancing efficient production. With high-quality resources, abundant data, sophisticated equipment and facilities, and great potentials for reserve increase in the Danggang oilfield, valid reserves have been discovered in the surrounding zones by actively dealing with challenges, enlarging potentials and establishing new development models based on new data; efficient reserve increase has been realized by breaking through old ideas and pre-exploring new layers; and new reserve targets have been found by re-recognizing old reservoirs and innovating processes, which make the oilfield active again and provide new ways to increase reserves. It has been proved that these practices are "gold keys" to increasing reserves, and good ways to break through difficulties and keep sustainable and healthy development of mature oilfields.

Based on spatial distribution, petrophysics, hydrocarbon generation, reservoir conditions and hydrocarbon retention, the geological characteristics of the Chang 7 lacustrine shale oil in the Yanchang Formation in the Fuxian area of the Ordo Basin was studied for evaluating the exploration potential, and selecting favorable targets. The study shows that the Chang 7 shale is widely distributed, the sandy laminae in the shale is developed, and the black shale containing silty laminae is the optimal lithofacies for shale oil. The statistics of geochemical parameters (pyrolysis S₁, chloroform asphalt "A", TOC, R_o, free hydrocarbon content, etc.), reservoir conditions, hydrocarbon-bearing properties indicate that lacustrine shale has the conditions for shale oil enrichment and accumulation. The shale oil resource calculated with pyrolysis S₁ is 12.94×10⁸ tons. According to comprehensive evaluation on the oil potential, reservoir capacity, shale oil mobility, etc., the favorable exploration area is up to 452 km².

The commercial development of marine shale gas has been successfully realized in China, but the exploration and development of lacustrine shale oil and gas is in dispute all the time and one of the important evaluation indexes is the TOC lower limit of shale oil and gas. Firstly, continental shale oil and gas was investigated and analyzed. Then, the freshwater lake facies of Jurassic Da'anzhai member in the Sichuan Basin was taken as the research object to analyze the geological conditions for the formation of shale oil and gas from the aspects of rock type, mineral composition and geochemical characteristic of lacustrine shale. After abundant pyrolysis data of organic carbon in shale, the relationship between shale gas producing interval and TOC and the relationship between shale oil producing interval and TOC were analyzed comprehensively, the TOC lower limit of shale oil and gas of freshwater lake faces was preliminarily determined to be 1.5%, which is in line with the practical exploration value. It is indicated that the determined TOC lower limit of lacustrine shale oil and gas is reasonable. Finally, the distribution of Da'anzhai high-quality lacustrine shale (TOC>1.5%) was delineated accordingly. The research results indicate the direction for the exploration and development of lacustrine oil and gas in the Sichuan Basin.

Based on the comparison of hydrocarbon accumulation conditions of inner buried hills among the Huanghua depression, Jizhong depression and Liaohe depression, the exploration potential of the inner buried hills of Cambrian to Meso-Neoproterozoic in the Huanghua depression, Bohai Bay Basin, was analyzed, and its exploration direction has been confirmed. The study results indicate that the Cambrian to Meso-Neoproterozoic in the Huanghua depression has lower exploration degree, the inner buried hill has good geologic conditions for hydrocarbon accumulation, with various types of buried hills and extensive distribution area, thus it is a much favorable exploration region. By evaluating the major traps of the Huanghua depression, it is concluded that the favorable (type I) traps accounts for 48% of the total trap area, and are chiefly distributed in the Qikou sag; they have the favorable conditions for forming large-scale reservoirs in inner buried hills. Especially, most traps are distributed in trough regions, with better developed deep-large faults, then the high-quality dolomite reservoirs in Cambrian to Meso-Neoproterozoic and the major source rock in the third member of the Shahejie Formation (Es3) can connect laterally, thus larger inner buried hill reservoirs with hydrocarbons being generated in younger strata and stored in older strata can be formed. Therefore, it is proposed that the No.1 trap (the Yangerzhuang buried hill) in the Yangerzhuang buried hill belt is the preferred exploration risk target.

Deep-water fan fed by large canyon in passive continental margin is a typical type of deep-water fan. Deep understanding of the sedimentary and hydrocarbon accumulation characteristics is of significance for other deep-water fans of the same type in the world. Analysis of survey data indicates that the Quaternary Congo fan is superimposed by dissected northern, southern and axial fans, and each fan has a variety of turbidite systems. In the east-west direction, the fan is dominated by marine progradation and the depocenter of the channel systems in the fan migrated about 100km. In the south-north direction, the fan migrated from north and south to center, so the turbidite system migrated counterclockwise in the northern fan, clockwise in the southern fan, and from SE to NW in the axial fan. The architectural elements are mainly composed of channel levee and frontal lobe, which present a branch-leaf network. Allogenic factors such as source system, climate and salt rock deformation, control the fan development. Further analysis shows that the ancient Congo fan has similar sedimentary characteristics with the Quaternary Congo fan. The Congo fan has good hydrocarbon accumulation conditions based on statistical analysis. The source rock is the Cenomanian-Maastrichtian marine shale; the reservoir is composed of the Oligocene-Miocene channel or complex sandstone; and the hydrocarbon is blocked locally by the shale interlayer and accumulates in the stratigraphic-structural and stratigraphic traps. At present stage, exploration is suggested on the incised channels on the shelf margin and net crevasse channels in the upper fan on the canyon edge.

As a number of heavy oil reservoirs have been discovered in Paleogene and Neogene of the Sanhecun sag, Jiyang depression, Bohai Bay Basin, it is of great significance for the future oil and gas exploration to figure out the hydrocarbon genetic mechanism and accumulation process in this area. Therefore, the tectonic evolution history, burial history, thermal evolution history and hydrocarbon accumulation stages were combined to reproduce the accumulation process of the heavy oil reservoirs. The results show that the heavy oil reservoirs of Paleogene and Neogene have completely different genetic mechanisms and accumulation processes. At the end of the sedimentary period of the Dongying Formation of the Paleogene, the low-mature crude oil from the source rock of the Shahejie-4 Member in the Bonan depression migrated laterally to Sanhecun sag along the unconformity transport layer between the Shahejie-3 Member of Paleogene and the Pre-Paleocene, then accumulated in the stratigraphic overlap traps of Shahejie-3 Member in Paleogene, forming the original heavy oil reservoirs. During the sedimentary period of the upper member of the Guantao Formation and the Minghuazhen Formation, the mature crude oil from the source rocks of the Shahejie-3 Member and Shahejie-4 Member in the Bonan depression migrated to the Kenxi fault horst first, then migrated vertically along Kenxi fault to the Guantao Formation of Neogene, and finally entered the Sanhecun sag through the skeleton sand bodies and faults of Guantao Formation and accumulated in the tectonic-lithologic traps or stratigraphic overlap traps of the Guantao Formation, which turned into secondary heavy oil reservoirs because of strong biodegradation in late stage. Joint exploration of heavy oil reservoir and shallow gas reservoir will be the new domain to increase reserves and production for Jiyang depression.

Based on the fluorescence property of petroleum, the conventional fluorescence spectroscopy was adopted to quantitatively describe the fluorescence spectrum of oil inclusions. The hydrocarbon charging events can be identified conveniently and effectively based on its attribute parameters (e.g. main peak wave length (λ_max), red-green entropy (Q) and QF₅₃₅) and the relationship between λ_max and QF₅₃₅. 9 samples of fluid inclusions taken from Gaotaizi tight oil reservoir of Qingshankou Formation, Upper Cretaceous in Qijia area were tested. It is indicated that the oil inclusions of three fluorescent colors (i.e., yellow, yellow-green and blue-green) are developed in Gaotaizi oil reservoir. λ_max and QF₅₃₅ of oil inclusions in Gaotaizi oil reservoir are distributed in three regions. The QF₅₃₅ decreases gradually from yellow fluorescence region to yellow-green fluorescence region and to blue-green fluorescence region, reflecting the gradual increase of the maturity of crude oil entrapped in oil inclusions. Then, combined with the studies on burial history, hydrocarbon generation history and homogeneous temperature of inclusions, it is concluded that Gaotaizi oil reservoir in Qijia area has experienced 3 hydrocarbon charging events in the period of geological history. The early charging of crude oil occurred in the late stage of Cretaceous Nenjiang (79-77 Ma), corresponding to the first event of charging, and the late charging occurred in the Mingshui period of Late Cretaceous (69-65 Ma), corresponding to the second and third events of charging.

The Bashijiqike Formation of the Keshen 8 gas reservoir in the Kuqa depression contains ultra-deep fractured-porous tight sandstone reservoir. Systematic researches on reservoir properties and modeling provide a geological basis for locating development wells with high and stable production and establishing a development plan in the Keshen 8 gas reservoir. Comprehensive analysis based on thin section observation, scanning electron microscopy, laser confocal microscope and electron probe shows that the Bashijiqike reservoir is dominated by lithic feldspar sandstone, pores are mainly intergranular pores and less intragranular dissolved pores. Based on structural and lithofacies modeling, the matrix porosity model was established by sequential Gaussian simulation method, and the matrix permeability model was established by using the pore-permeability curve equation, and three matrix porosity-permeability zones were divided. The tectonic fractures in the Keshen 8 gas reservoir were mainly formed with the near SN tectonic compression caused by the Himalayan movement. They are dominated by upright shear fractures and high-dip tensile fractures, and appear as parallel combination and skewed combination on image logs. Some high-dip tensile fractures are filled with minerals such as anhydrite and dolomite. Based on the finite element numerical simulation of the tectonic stress field, the numerical simulation of tectonic fracture parameters was carried out, and based on this, the tectonic fracture property model was established through sequential Gaussian simulation, and four high-porosity areas and five high-permeability areas were identified. Finally, the reservoir matrix property model and the tectonic fracture property model were added to establish a dual-medium property model, three high and stable production areas, Wells KS807, KS8-5 and KS8-8-KS806, were divided on plane, and in the vertical direction, the third sandstone group was proposed as a high and stable production interval. They should be given priority in future development.

In the Shakan oilfield, the productivities of the carbonate reservoirs are very different in different intervals and different wells, making petroleum geologists very confused. It is urgent to solve how to evaluate the reservoirs, and how to identify the high-production reservoirs. Analysis of cores taken from well test intervals, conventional physical properties, casting sections and regional geological data indicates that fractures are developed, and the logging value of uranium is abnormally high in a peak shape in the high-production reservoirs, but the fractures are less developed and the logging value of uranium is low in the low-production reservoirs. According to the geological structures, formation water and reservoir microscopic characteristics, the relationship between uranium and reservoirs has been analyzed, and the result shows that uranium is rich in fractured reservoirs, and the high uranium value is positively correlated to the fracture development. Based on natural gamma ray spectrometry curves and conventional logging data, it is possible to accurately identify high-production fractured reservoirs, and predict favorable reservoirs in the Shakan oilfield. This conclusion has been verified in Wells S -10 and S-12. It is an economical and practical method for looking for high-production fractured reservoirs.

In order to study the effect of temperature on the heavy oil and water relative permeability during the thermal recovery process of heavy oil in Well J7, Changji oilfield, and provide basic data for establishing a reasonable development plan and predicting the oil and water distribution, heavy oil/water relative permeability experiments on the cores with permeability of 56.38mD, 126.54mD and 224.98mD, respectively, were carried out at 50-200℃. The experimental results show that:(1) at 50-200℃, the irreducible water saturation increases with increasing temperature, and the residual oil saturation decreases with increasing temperature; (2) at the same water saturation, the oil relative permeability increases more obviously with increasing temperature; however, with the increase of water saturation, the relative increase of the oil relative permeability decreases gradually; (3) when the permeability is 50-200 mD, the change of the core permeability doesn't influence the relationships between temperature and water saturation, residual oil saturation, and oil/water relative permeability.

Dawangzhuang oilfield is in the late stage of development, so it is very important to find out the distribution of remaining oil. Saturation logging method alone can't meet the requirements of fine interpretation and evaluation. Pulsed neutron full spectrum saturation logging, integrating C/O spectrum, chlorine spectrum, neutron lifetime and oxygen activation logging technology, can record several logging curves in one trip and identify water-flooded zones accurately under low salinity and high shale content. The principle, technical characteristics and data interpretation principle of pulsed neutron full spectrum saturation logging are introduced, and the full spectrum saturation logging data are creatively combined with conventional logging data, the intersection interpretation chart of different layers in Dawangzhuang oilfield is compiled, and the new interpretation standard is set to significantly improve the coincidence rate of full spectrum logging interpretation. The interpretation results can reflect the variation of remaining oil saturation in reservoir accurately, providing reliable basis for identifying watered-out zones, searching potential zones and figuring out the distribution law of remaining oil. It will be a handy and reliable tool in tapping remaining oil and increasing oil reserves.