With the world^’s oil and gas industry developing from conventional oil exploration and development to unconventional oil field, the study of unconventional oil exploration is drawing great attention. Unconventional and conventional oil and gas are substantially different in terms of eight aspects – basic conception, subject system, geological study, exploration method, evaluation of ^“sweet-spot zone,^” technological research, development method and production pattern. The geological theories of unconventional and conventional oil and gas are based separately on continuous hydrocarbon accumulation theory and buoyant trap accumulation theory. Unconventional oil and gas has two key characteristics. One is continuous distribution of oil and gas in a large area without obvious boundaries of traps. The other is no stable natural industrial output. The Darcy seepage is not obvious. There are two key parameters – porosity is lower than 10% and pore throat diameter is lower than 1μm or air permeability is lower than 1mD. As for conventional oil and gas, the above-stated characteristics and parameters are apparently different. The porosity usually ranges from 10% to 30% and the permeability is usually higher than 1mD. Unconventional oil evaluation is focused on six geological properties, such as source rock characteristics, lithologic character, physical property, brittleness, petroliferous property, and stress anisotropy. Conventional oil evaluation is focused on source rock, reservoir, cap rock, trap, migration and preservation as well as the optimum coupling relations of these six characteristics. There are eight elements for evaluation of ^“sweet spot zone^” of unconventional oil and gas abundance, of which three key elements are TOC higher than 2%, high porosity (tight oil and gas higher than 10% and shale oil and gas higher 3%) and development of micro-fractures. Evaluation of conventional oil reservoir is focused on core elements of accumulations and matching of time and space, emphasizing high-quality hydrocarbon source kitchen, favorable reservoir body, scale of trap, and effective conducting system. Unconventional oil and gas is obviously different from and closely related to conventional oil and gas. Unconventional oil and gas has something in common with conventional oil and gas, such as in the same oil and gas system and sharing the same hydrocarbon source system, the same primary migration force and the similar oil and gas components. Based on the substantial relations in genesis and distribution, conventional and unconventional oil and gas are in ^“orderly accumulations,^” related to each other in genesis, and symbiotic in time and space, forming a set of unified oil and gas accumulation system. In accordance with the law that conventional and unconventional oil and gas are in ^“orderly accumulations,^” the two different types of oil and gas resources should be taken into account as a whole in the process of exploration and development for harmonious development.

Reserve and production ratio is the ratio of the yearend remaining recoverable reserve to the annual output. This value is often mistaken for how long the existing reserve can last. The numerator and denominator of the ratio are variables under the influence of many factors. The changes in the oil and gas statistical figures (such as a certain kind of non-conventional oil and gas is included in the reserveproduction ratio) may cause the ratio to rise substantially. Generally speaking, the world oil reserve and production ratio is on the rise. It is 57.5 in 2013. The natural gas reserve and production ratio is also on the rise, reaching 63.1 in 2004, but it has dropped slightly since 2010. The average value is 58.3 in the past four years. China^’s oil reserve and production ratio reached its peak of 19.5 in 1984 and then declined to 12.2 in 2013. The country^’s natural gas reserve and production ratio climbed at the initial stage of rapid development, reaching 66.3 in 2002 and then was on the decline (particularly after 2006), reaching 29 in 2013. Generally speaking, China oil and gas reserve and production ratios are lower than the world^’s average, belonging the same level as the United States. The healthy oil and gas industrial development may be affected when the reserve and production ration is too high or too low. The reserve and production ratio can be lowered slightly if the resources are abundant with the market forces able to be mobilized for exploration in a short period of time. The study indicates that oil and gas used as main energy can last well into the second half of the 21st century.

To analyze the hydrocarbon accumulation law of Zhuyi oil and gas zone in Pearl River Mouth Basin, this paper establishes a halfgraben hydrocarbon accumulation model on the basis of the halfgraben accumulation system in Zhuyi Depression, focusing on structural evolution and accumulation element combination. Based on analysis of the accumulation elements, such as source rock, hydrocarbon migration conditions and reservoir-cap assemblages in the different structural zones of half grabens, it is assumed that the hydrocarbon accumulation pattern of the half-graben ambulation system in the research area can be divided into four types – hydrocarbon accumulation assemblage in gentle slope zone, steep slope zone, sag zone and uplift zone. The main direction of hydrocarbon migration and hydrocarbon distribution patterns are determined by geological structure of rift lake basin, formation occurrence and fluid potential. From the angle of hydrocarbon resources distribution, the half grabens in the research area can be divided into three types of structure, such as gentle slope predominant half graben, steep slope predominant half graben and nearly balanced half graben. These three half grabens have apparently different distribution patterns of hydrocarbon accumulations.

The fine sedimentary rock of semi-deep lake subfacies in Xiagou Formation of Qingxi Depression, Jiuquan Basin is composed of thick argillaceous dolomite and dolomitic mudstone with development of a number of laminations. Optical microscopy, cathodoluminescence microscopy and fluorescence microscopy are used to observe the color, morphology and distribution of laminations and analyze their mineral components. Field-emission scanning electron microscopy is used to inspect the types, sizes, shapes and distribution of reservoir space in the laminations. The pore throat structural characteristics of different laminations are analyzed by means of N2 absorption method and nano-CT technique. There are mainly four types of laminations, such as carbonate lamination (mainly dolomite), siliceous lamination (mainly feldspar and quatz), argillaceous lamination and organic matter lamination, with a thickness of 0.03-0.5 mm. Micro-fractures developed in carbonate lamination and siliceous lamination, usually filled with organic matter. Siliceous lamination contains comparatively coarse mineral grains and is often deformed and disconnected. Argillaceous lamination is in dark color with development of clay mineral interlayer pores, which are filled with organic matter too. Therefore, argillaceous lamination is high in organic matter abundance. Organic matter lamination is distributed in a state of continuity, discontinuity and dissemination. It is an important source rock with a small quantity of fractures distributed on the periphery and in the internal part. From the semi-deep lake subfacies to peripheral fan delta subfacies, the laminations change gradually from the lamination couplets dominated by carbonate components to the lamination couplets dominated by siliceous components with deformations and coarser mineral grains. Formation of laminations is related to climate, property of water body, terrigenous input volume and bioactivity. The paleo-sedimentary environment and formation mechanism of the laminations can be deduced according to the types, shapes and thickness of laminations. The laminations usually lead to different source-reservoir symbiotic relations. The carbonate lamination and siliceous lamination are good in reservoir capability, while the argillaceous lamination and organic matter lamination are associated, thus having a good potential for hydrocarbon sourcing.

A scientific classification scheme of rocks is the basis for study of fine-grained sedimentary rocks. Based on analysis of the mineral components of fine-grained sedimentary rock from Guan-X Well drilled on the second member of Kongdian Formation in Cangdong Depression, this paper comes up with the scheme for classification of fine-grained sedimentary rocks on the basis of X-ray diffraction data. This scheme is a three-unit four-component division system. The three units are carbonate minerals, clay minerals and felsic minerals. Finegrained sedimentary rocks are divided into 12 types of rock in four main categories, such as fine-grained felsic sedimentary rock, carbonate rock, clay and fine-grained mixed sedimentary rock. Meanwhile, with analcime taken as the fourth component, fine-grained sedimentary rocks are named according to the concrete content of analcime. This scheme can unify the classification system of fine-grained sedimentary rocks and promote unconventional hydrocarbon exploration and development in the fine-grained facies zones.

Based on the cluster analysis and cross plot technique, the low-porosity and low-permeability sandstone reservoir of Baikouquan Formation in Mahu Depression of Junggar Basin is divided into four categories. Meanwhile, comprehensive well log, logging and oil testing data are used to develop the multidisciplinary identification method for multi-factor fluid in the complicated reservoir. The reservoir quality classification plot is established on the basis of the physical properties acquired by NMR logging while the calculation model of gas-logging oil-bearing factor and wireline logging oil-bearing factor is created. In addition, with the fluid identification method for Mahu Depression developed, the coincidence rate of mud logging and wireliine logging is improved by 30.6 percent and 28.1 percent. Through the analysis of reservoir renovation results, the distinguishing criteria are established on the basis of the Young^’s modulus from logging, dividing the reservoir in this area into ^“easy to fracture^” and ^“difficult to fracture.^” Based on analysis of the relevant parameters, such as dynamic fractural length and sanding factor, the fracturing prediction model for maximum results of reservoir renovation is established, which improves the fracturing results of Mahu Depression by 32.7 percent.

Yanchang Formation of Honghe Oilfield in Ordos Basin is a lithologic oil reservoir. The main horizons are characterized as low porosity, low permeability and strong heterogeneity, difficult for exploration and development. Distribution of favorable sand bodies is a key factor to restrict exploration and development of Honghe Oilfield. Conventional wave impedance inversion is difficult to predict distribution of reservoirs because the differences of wave impedance from the surrounding mudstone cap rock are very small. Take Chang-81, the main oil layer of Honghe Oilfield, for instance, the natural gamma curve and neutron porosity curve are used to reconstruct a lithologic indicator curve to effectively differentiate sandstone from mudstone. The Chang-81 sand body is predicted on the basis of multi-well constrained sparse pulse inversion and geological statistical inversion. Good results have been achieved, providing the convincing basis for deployment of horizontal wells.

Unconventional oil and gas reservoirs represented by tight sandstone are complicated in porous space, leading to a long period of rock physical measurement at a high cost and making it difficult to quantitatively study the influence of micro parameters on resistivity. Simulation technology for digital core physical properties developed on the basis of the X-ray CT scanning makes up for this deficiency. This paper systematically summarizes the advantages and disadvantages of various kinds of numerical simulation methods for digital core electrical properties, such as Lattice Boltzmann method, Kirchhoff circuit node method, the random walk method and the finite element method. It also discusses four main problems currently existing in numerical simulation study of electrical properties – (1) lack of models for simulation of more micro factors; (2) contradiction between resolution and heterogeneity of reservoir; (3) limitation of image segmentation method; (4) multiple solutions of digital pore network. It also points out four development orientations for digital-based core property simulation – (1) construction of fine 3-D pore network model; (2) image processing based on multiple threshold segmentation method; (3) optimization of electric simulation model; (4) high-performance parallel computing technology based on digital core. This study will help improve numerical simulation of tight sandstone electrical property and lay a solid foundation for exploration and development of unconventional reservoirs.

Seismic reflection signal is a compound signal caused by a number of geological factors under the ground (such as lithologic characters of formation, physical properties, thickness and assemblage). The traditional seismic data are difficult to accurately identify recoverable CBM in No.3 coal measure of Permian Shanxi Formation in Zhengzhuang area of Shanxi. Wavelet decomposition and reconfiguration technique is used to divide conventional seismic data trace into wavelet set of different frequencies. Combined with the results from spectrum analysis of the CBM bearing measure and drilling data in the research zone, the favorable frequency band is determined for wavelet reconfiguration. Comparing the seismic data acquired from reconfiguration with the drilling data for analysis, it is found that the coal measures in this area are obviously characterized as “strong amplitude for high gas content and low amplitude for low gas content.” Such characteristics can be used to effectively differentiate high gas-bearing wells from dry wells and provide the basis and support for determination of well positions in the lateron stage. The technique has achieved good results for application.

Tectonic and sedimentary evolution of the Arabian Plate provided favorable petroleum conditions for Paleozoic hydrocarbon accumulations in Qatar. The analysis shows that a set of high-quality source rock (graptolite hot shale) developed at the bottom of the Silurian System in Qatar, with development of two sets of clastic rock reservoir-cap assemblage. The reservoirs are mainly fluvial-delta facies sandstone with the buried depth usually exceeding 3600 meters. Generally speaking, the reservoir rock is relatively tight and mainly of mid to low porosity and low permeability. However, the ^“sweet spots^” of the reservoirs might develop partially in the region, with a good productivity. The types of Paleozoic traps are mainly anticlines, faulted anticlines, updip pinchout lithologic traps and stratigraphic traps in connection with unconformity. There are three hydrocarbon accumulation patterns. The main pattern is migration and accumulation based on transportation through vertical faults and ^“generated in the lower and stored in the upper part.^” Hercynian tectonic compression and salt uplift have a critical effect on development of Paleozoic traps, which were shaped mainly in Late Permian – Late Triassic, earlier than the hydrocarbon expulsion period of Silurian source rock. The conditions for accumulations were matched desirably. The clastic rock stratum series in Qatar has highquality source rock as its materials basis, favorable reservoir-cap assemblages, favorable areas for accumulation of structural traps and excellent conditions for hydrocarbon accumulations. The stratum series has a great potential for exploration thanks to low extent of exploration. The main favorable areas for potential exploration are the flanks of Qatar Uplift and the Southern Gulf Salt Basin in the eastern part of the country,