Resource Potential and Exploration Techniques of Stratigraphic and subtle Reservoirs in China

The onshore oil and gas exploration has stepped into a new stage in China, with equal attention paid to both stratigraphic and subtle reservoirs and structural reservoirs. In the past few years, the increases in oil reserves in most basins were found mainly in the stratigraphic and subtle reservoirs. Latest resource evaluation shows that the onshore stratigraphic and subtle reservoirs in China account for 42% of the total remaining resource, the highest in the four major exploration regions. Therefore, these reservoirs will be the most practical, potential and prevalent fields for long-lasting oil and gas exploration in onshore China. Among PetroChina's annual oil geologic reserves of 4.3 × 108t^4.6× 108t, the stratigraphic and subtle reservoirs account for more than 50%. In such basins as Songliao, Ordos, Bohai Bay, Junggar, Tarim, Sichuan and Erlian basins, stratigraphic and subtle reservoirs with geologic reserves ranging from 5×107t to 3×108t were discovered, including Ansai, Jing'an, Daqingzijing, Liuxi, well-21 area in Shinan, and Hadexun. Stratigraphic and subtle reservoirs in the four types of inland basins differ from each other in the formation conditions and the distribution patterns. While continental basins are controlled by unconformity surface, maximum flooding surface and fracture surface, the Paleozoic marine basins are influenced by paleouplift, unconformity surface, and fluctuation of the sea level. Through exploration practices and research, PetroChina has formed its own technique series focused on 3-D seismics and sequence stratigraphy.

Complex Exploration Techniques for the Low-permeability Lithologic Gas Pool in the Upper Paleozoic of Ordos Basin

The Ordos basin is a stable craton whose late Paleozoic undergoes two sedimentary stages: from the middle- late Carboniferous offshore plain to the Permian continental river and lake delta. Sandstones in delta plain channels, delta-front river mouth bars and tidal channels are well developed. The sandstones are distributed on or between the genetic source rocks, forming good gas source conditions with widespread subtle lithologic gas pools of low porosity, low permeability, low pressure and low abundance. In recent years, a series of experiments has been done, aimed at overcoming difficulties in the exploration of lithologic gas pools. A set of exploration techniques, focusing on geological appraisal, seismic exploration, accurate logging evaluation and interpretation, well testing fracturing, has been developed to guide the exploration into the upper Paleozoic in the basin, leading to the discoveries of four large gas fields: Sulige, Yulin, Wushenqi and Mizhi.

Major Breakthroughs in Geological Theory, Key Techniques and Exploration of Tight Oil in China

In recent years,U.S.tight oil exploration and development have achieved significant progress,with rapidly increasing production,which has significantly changed the U.S.A.energy supply pattern（Fig.1）.Compared with the North American marine to marginal marine-continental transitional facies,China’s tight oil（Fig.1）

Key strategies for predictive exploration in mature environment: model innovation, exploration technology optimization and information integration

Prediction has become more and more difficult in mineral exploration, especially in the mature exploration environment such as Tongling copper district. For enhancing predictive discovery of hidden ore deposits in such mature environment, the key strategies which should be adopted include the innovation of the exploration models, application of the advanced exploration techniques and integration of multiple sets of information. The innovation of the exploration models should incorporate the new metallogenic concepts that are based on the geodynamic anatomization. The advanced techniques applied in the mature exploration environment should aim at the speciality and complexity of the geological setting and working environments. The information synthesis is to integrate multiple sets of data for giving a more credible and visual prospectivity map by using the geographic imformation system(GIS) and several mathematical methods, such as weight of evidence and fuzzy logic, which can extract useful information from every set of data as much as possible. Guided by these strategies, a predictive exploration in Fenghuangshan ore field of Tongling copper district was implemented, and a hidden ore deposit was discovered.

Research Advances and Exploration Significance of Large-area Accumulation of Low and Medium Abundance Lithologic Reservoirs

In recent years, a series of large low and medium abundance oil and gas fields are discovered through exploration activities onshore China, which are commonly characterized by low porosity-permeability reservoirs, low oil/gas column height, multiple thin hydrocarbon layers, and distribution in overlapping and connection, and so on. The advantageous conditions for large-area accumulation of low-medium abundance hydrocarbon reservoirs include： （1） large （fan） delta sandbodies are developed in the hinterland of large flow-uncontrolled lake basins and they are alternated with source rocks extensively in a structure like ＂sandwiches＂; （2） effective hydrocarbon source kitchens are extensively distributed, offering maximum contact chances with various sandbodies and hydrocarbon source rocks; （3） oil and gas columns are low in height, hydrocarbon layers are mainly of normal-low pressure, and requirements for seal rock are low; （4） reservoirs have strong inheterogeneity and gas reservoirs are badly connected; （5） the hydrocarbon desorption and expulsion under uplifting and unloading environments cause widely distributed hydrocarbon source rocks of coal measures to form large-area reservoirs; （6） deep basin areas and synclinal areas possess reservoir-forming dynamics. The areas with great exploration potential include the Paleozoic and Mesozoic in the Ordos Basin, the Xujiahe Formation in Dachuanzhong in the Sichuan basin, deep basin areas in the Songliao basin etc. The core techniques of improving exploration efficiency consist of the sweetspot prediction technique that focuses on fine characterization of reservoirs, the hydrocarbon layer protecting and high-speed drilling technique, and the rework technique for enhancing productivity.

New Progress in High-Precision and High-Resolution Seismic Exploration Technique in Coal Industry of China

In the past twenty years, the proportion of coal in primary-energy consumption in China is generally between 71.3% and 76.5%. The output of coal was 1.374 billion tons in 1996, and 1.21 tons in 1998, which ranked first in the world. Now coal is mined mainly with mechanization in China, which is planned to reach 80% in major State-owned coal mines in 2000 according to the planning of the government (Li et al., 1998; Tang Dejin, 1998).

Lithium:A review of applications,occurrence,exploration,extraction,recycling,analysis,and environmental impact

The energy transition challenges faced by modern civilization have significantly enhanced the demand for critical metals like lithium resulting in improved methods to explore,extract,and utilize these metals.In this comprehensive review,we discuss the different types of lithium resources,factors,and mechanisms controlling lithium enrichment in various geological settings including terrestrial and marine environments.Diverse exploration strategies including geological,geophysical,mineralogical,geochemical,and remote sensing techniques including drone-based techniques for lithium exploration studies in different terranes are summarized.An overview of the mining techniques,including beneficiation and extraction,and their principles,mechanisms,operations,and comparison of the various approaches and compatibility with different types of lithium deposits for obtaining maximum yield are evaluated.Lithium isotopic studies are useful in understanding geological processes such as past weathering events and riverine input into the oceans,as well as in understanding the source of lithium in diverse types of deposits.We also highlight the recent developments in other areas such as recycling,environmental impact,and state-of-the-art analytical techniques for determining lithium in different lithium ore deposits and other geological materials.Our overview provides the latest developments and insights in the various sectors related to lithium and prompt further developments to meet the growing demand for this valuable metal as the world transforms to clean energy.