The Lower Paleozoic dolomite is widely distributed in Tarim Basin with a large thickness and good conditions for source-reservoircap assemblage. It is the important exploration field in the basin. Great exploration efforts have been focused on Lower Paleozoic dolomite since Tarim Basin was brought under exploration and development, but no significant discoveries have been made in this field. Based on a better understanding of the stable reservoir-cap assemblage and the accumulation conditions for palaeohigh, the exploration mindset was changed around 2010, being concentrated on the Tazhong successive palaeohigh. With application of 3D seismic assessment technology, Zhongshen-1 Well was drilled, which made a breakthrough in Cambrian subsalt dolomite and turned a new page of Cambrian dolomite exploration. Two sets of oil and gas horizons of the Middle-Lower Cambrian series were found at Zhongshen-1 Well. One set is located in Awatage Formation of the Middle Cambrian series in the form of low-density wax-containing light crude oil, while another set is located in Xiaoerbulake Formation of the Lower Cambrian series in the form of dry gas reservoir. The breakthrough of Zhongshen-1 Well is of great significance to oil and gas exploration of Tarim Basin. It is the first time to find inner-curtain dolomite hydrocarbon reservoirs in the basin, confirming the petroleum geological conditions for large-scale hydrocarbon accumulations in Cambrian subsalt dolomite and locating a new strategic replacing field which has an extensive area of nearly 30×10⁴km². Meanwhile, discovery of Cambrian subsalt hydrocarbon reservoirs at Zhongshen-1 Well indicates that Cambrian source rock is likely to be the main hydrocarbon source rock in the platform-basin area of Tarim Basin. This discovery exerts a far-reaching influence on exploration of the platform-basin area of the basin.

With introduction of the fluid compartment theory, this paper discusses the relations between abnormal pressure and fluid compartment and establishes the fluid compartment model. Based on analysis of source rock buried history, structural thermal development history, secondary porous and fractural development history, diagenetic trap history and natural gas migration and accumulation history and combined with the homogenization temperature of gas-liquid inclusions and authigenicillite K and Ar isotopic dating data, the time for development of He-8 and Shan-1 gas reservoirs of Sulige Gas Field in Ordos Basin is determined as Late Jurassic – Early Cretaceous. The paper also summarizes the natural gas accumulation and development pattern in the study region on the basis of the above-mentioned conclusion. It makes a comprehensive study of the natural gas accumulation elements in the study region, such as sourcing, reservoir, capping, sealing, migration and storage. The summarized natural gas abundance law indicates that sourcing intensity controls natural gas abundance degree while the favorable migration channels are the basic paths for natural gas migration. The physical properties of reservoir are the key factors to influence natural gas abundance.

As for the increasingly complicated exploration situation in the old oil areas in East China, this article proposes an ^“oil-assumed deduction^” assessment method, which is a backstepping evaluation of exploration targets based on the fundamental principle for oil and gas accumulation system. The process of the method is focused on the targets of traps in mature exploration of basins while centering the main factors controlling oil and gas accumulations, thus making comprehensive analysis and study of the petroleum geological conditions. The relative oil and gas accumulations model is established to fulfill the objective for gradual reduction of exploration risks and attainment of marginal effects. As compared to the traditional method, this method not only improves exploration of oil and gas abundant zones and evaluation efficiency for potential targets but also gets rid of restrictions from the past exploration experiences, offering an effective measure for exploration of increasingly complicated oil and gas abundant sags. The mindset of basckstepping evaluation is also suitable for settlement of exploration bottlenecks in the ^“oil and gas enriched sag^” field. With this method used to identify the main factors controlling oil and gas accumulations, breakthroughs have been made in basement exploration of Anfutun and Gaosheng buried hill areas, opening up the new field of lithological stratigraphic oil and gas exploration.

Division and comparison of basement carbonate rock formations of Damintun depression in Liaohe Basin has been remained controversial. One of the controversies is about whether Paleozoic exists in this set of formations. Another is the issue of partition attribution– whether this set of formations belongs to Liaoxi area or Liaodong area. Based on a comprehensive study of the data concerning lithological characters of drilling section, paleontology, seismic survey, logging and geochemistry, this set of formations can be divided into Dapashan formation and Kangzhuangzi formation of the Proterozoic Changcheng system, the Lower Paleozoic Cambrian – Ordovician system, the Upper Paleozoic Carboniferous – Permian system and a number of lithologic sections. The basement carbonate rock strata are located on the northeastern periphery of the table land in North China. The stratigraphic sequence and lithologic characters of the strata can be compared to those of Panhe formation, but there are some differences. Proterozoic bedrock, mainly Changcheng system, can be compared to Changcheng system in Panhe formation. The main difference is that the Paleozoic missing in the near surface can be found in the northern basement of Damintun depression. The Middle Cenozoic is located at the intersection of Tanlu fault in Bohai zone, belonging to Lower Liaohe formation zone.

Field seismic acquisition is the source of seismic work. The seismic acquisition observation system holds the key to high-quality seismic data and is related to exploration cost. With seismic exploration continually extending to development, seismic data are required to meet the demand of technological application for pre-stack imaging, reservoir prediction and oil and gas inspection so that the new targets can be set to optimize the acquisition plan. This article elaborates the technological conception and method for seismic acquisition design of surface pre-stack imaging and reservoir prediction. Based on the underground geological characteristics, surface absorption and attenuation as well as analysis of petro-physical properties, the geophysical parameters are acquired from the target zone to focus on the concrete seismic exploration task and geological target. Following the technological demand for pre-stack imaging and reservoir prediction, the key parameters are selected and optimized, such as the surface elements of the observation system, times of coverage, density of shots and traces, and line spacing. The design of seismic exploration and acquisition is also optimized to provide more effective basic data for pre-stack imaging and reservoir prediction.

The ancient buried hill hydrocarbon reservoir found and proven in Niudong buried hill structural zone in Baxian sag of Jizhong Depression was Cambrian carbonate rock reservoir of Paleozoic erathorn. The reservoir space is mainly composed of vugs and fractures, with the physical property varying horizontally. The study of pre-stack elastic inversion was made in the light of the bottleneck that buried hill and buried hill inner curtain carbonate rock reservoir is has a strong heterogeneity. The pre-stack elastic impedance inversion technology and AVO attribute analysis technology were adopted in combination with post-stack wavelet decomposition and restructure technology to predict and describe the space distribution law of the fracture and vug system of the reservoir, divide the favorable development zones of the reservoir and clarify the fractural development zone and hydrocarbon abundance zone. The drilling results in this region show the carbonate rock reservoir of Niudong buried hill structural zone sees development of fractures with a good prospect for oil and gas, confirming effectiveness of the technology for prediction of characteristics of carbonate rock reservoir.

The geological structure is complicated in the eastern peripheral region of Junngar Basin. Only a few studies were focused on exploration of the region. The quality of 2D seismic data was poor. Synthetic seismograms, geological outcrop, seismic characteristics, interval velocity and non-seismic data were used to identify the geological level of 2D seismic data in the study region. Based on the regional structural background, the paper makes description of the main faults in the region. The interpretation of 2D seismic data shows that the eastern peripheral region of Junggar Basin is in the pattern of a ^“chessboard^” structure, with development of structural elements, such as sag zone, foothill zone and uplift zone. The scope of Shiqiantan sag and Mulei sag is revised, enlarging the area and identifying the scope of Qitaizhuang foothill zone. The current sags in the study region are Middle Paleozoic remained sags. The formations of sag zone and foothill zone developed in the region with the thin remained formations in the uplift zone. The multi-element calibration can help identify the geological level and be used for interpretation of 2D seismic data for the area where exploration degree is low and no exploration well is drilled.

Karst topography is common in Guizhong mountainous area in Guangxi. Near surface and subsurface structure are complex and varied in the area. Most of rock is carbonate rock directly cropping up with development of karst and fractures, causing a number of disadvantages, such as poor conditions for excitation and acceptance, low original signal-to-noise ratio, serious static correction problems and difficult structural imaging. Based the study and experiment, the bin stack information of adjacent gathers is used for wide line survey method and all kind of interference is suppressed effectively while the quality of seismic section is improved substantially. Under the special geological conditions of Guizhong mountainous areas, the crooked wide-line acquisition technique is an effective method to suppress interference and improve the signal-to-noise ratio of seismic section. With good results for acquisition achieved in application, this method can be widely used in the similar low signal-to-noise ratio regions.

The 6^th member of Yanchang Formation of Jurassic System in the northern region of Shaanxi is an important layer for oil exploration and development. High natural gamma sandstone is widespread in this layer. Such reservoir is different from conventional one in terms of logging response characteristics, thus causing some difficulties for calculation of physical property parameters and water saturation logging for the 6^th member of the formation. Based on comparison and analysis of logging characteristics between the high gamma reservoir and its neighbor conventional reservoir, the formula is established to calculate porosity, permeability and mud content for the 6^th member of Yangchang Formation. This paper also further discusses the horizontally oil-bearing property of such reservoir. High gamma reservoir is nor obviously different from its neighboring conventional reservoir in terms of core analysis of saturation. However, high gamma reservoir is quite different from its neighboring conventional well in terms of water saturation calculated by using logging data, because the resistivity value of high gamma reservoir decreases significantly. Therefore, the saturation calculation formula of high gamma reservoir is revised. Based on classification of reservoirs, this paper regards changes of resistivity and porosity of high gamma reservoir as the main factor to affect saturation calculation of the 6^th member of Yanchang Formation in the northern region of Shaanxi. The formula is further perfected for saturation calculation of the complicated 6^th member of Yanchang Formation in this region.

Muglad and Melut are the two basins richest in oil and gas resources in the Central African rift system. CNPC has found a large number of large oil fields in the two basins since its involvement in Sudan^’s oil and gas exploration in 1995. Currently, the two basins are in their mature exploration stage and need to have a new pattern of exploration to keep the oilfields for stable and sustainable development. Based on the petroleum geological conditions of Muglad and Melut basins and exploration activities, this paper elaborates on the necessity of exploration transformation in the two basins. Meanwhile, based on analogy with the similar domestic rift basins like Bohai Bay Basin and Songliao Basin, a new series of strata, lithological oil and gas reservoirs, offshore subaqueous fan, fan delta and deep-layer natural gas are clarified as the key areas in the two basins for potential oil exploration and development. Transformation of exploration in the two basins can be realized in three ^“shifts^” – shift from the main producing horizons to non-main producing horizons for multi-layer exploration, shift from structural oil reservoir to lithological oil reservoir for diversification of exploration targets to fully tap underground resources, and shift from single-reservoir exploration to overall deployment for deep-layers for unified appraisal on oil and gas reservoirs. The analogy research makes CNPC confident about exploration of Muglad and Melut basins and clear about the future exploration targets.

Commercial development of shale oil and gas in North America has drawn great attention from the world. China’s energy companies also eye overseas shale oil and gas market. Therefore, it is of great importance to learning the geological characteristics and resources potential of overseas shale oil and gas blocks. The shale oil and gas reserves and production conditions are the basic contents for assessment if overseas blocks in the favorable exploration zone are brought under rapid appraisal without enough related data. The analysis of TMS (Tuscaloosa Marine Shale) shale oil resources in X area of North America indicates that TMS shale has a number of characteristics, such as large thickness of shale rock, high content of organic carbon, organic matter under the sourcing peak stage, appropriate buried depth of shale rock, appropriate content of clay minerals, the top and bottom of shale reservoir kept desirably, and a great exploration potential for shale oil. Using the multi-layered fuzzy judgment method, the favorable shale oil exploration area can be divided into five types. The first-class area, with the comprehensive evaluation factor higher than 0.75, is the most favorable zone, which is distributed mainly in the central part of the study region. Of the 25 small geographic blocks, Block V is the most potential block for shale oil exploration. The P1 block is the highest in potential abundance for shale oil exploration.

Take the shale section from a shale gas well in Sichuan Basin for instance. The XRF-measured element content and XRD-measured mineral content are used to establish the math calculation method for transformation from elements to minerals. It can calculate seven kinds of mineral in the rock, including clay mineral (kaolinite, chlorite, montmorillonite and illite), quartzes, feldspar and calcite. The calculated value of mineral content is compatible with the actually-calculated value. In addition, the content of elements is used to divide three components of the rock – muddy, sandy and ashy matters. Use of sandy/(muddy + sandy + ashy) matter appraisal of brittleness of shale is of great reference to implement transformation of shale reservoir.