China was late in tight oil exploration and development. Based on comprehensive analysis, tight oil is the realistic exploration and development field of non-conventional oil and gas resources. In recent three years, PetroChina has made tenacious efforts for the theoretical study of tight oil exploration and development and clarification of the resources, prepared for technological breakthrough and positioned tight oil exploration and development. As a result, the company has established three zones, each with the reserves exceeding 100 million tons, and six new discoveries in the six main basins like Erdos Basin, Junggar Basin and Songliao Basin. PetroChina has also created and improved four key technological families for prediction of the tight oil sweet-point zones as well as seismic prediction and logging evaluation targeted at improvement of single-well production, and developed two initial theories on China^’s onshore tight oil accumulations. However, China^’s tight oil development is still under the preliminary stage. The analysis shows there are four challenges, such as how to enhance theoretical study, how to make breakthrough in key technology, how to bring about high-efficiency development, and how to reduce the cost. Thanks to China^’s complicated onshore tight oil geological conditions, it is proposed that the State formulate more preferential policies to support this industry while focusing efforts for technological study and application, highlighting the discoveries, reducing the cost and improving the economic performance. Those suggestions are of great significance to acceleration of China^’s tight oil development and the security of the country^’s oil and gas supply.

Jizhong Sag of Bohai Bay Basin has good geological conditions for buried hill hydrocarbon accumulations and abundance. A series of large and medium-size buried hill oil and gas fields (reservoirs), such as Renqiu buried hill, have been discovered. With the oil and gas exploration degree improved and the exploration technology upgraded, the active efforts for initial exploration of subtle deep buried hill and buried hill inner curtain hydrocarbon reservoirs led to discovery of a number of subtle abundant high-yield buried hill hydrocarbon reservoirs, such as Niudong-1 super-high temperature deep buried hill hydrocarbon reservoir and Chang-2 buried hill inner-curtain hydrocarbon reservoir, revealing a bright prospect for exploration of this field. Less influenced by the buried depth, the carbonate rock deep buried hill reservoir is good for its physical properties and characterized in early hydrocarbon infill, long-period infill and high-pressure infill, with favorable conditions for accumulations. There were a number of reservoir-cap assemblages in the buried hill inner curtain, forming a variety of sourcemountain contact patterns, conducting systems, and coupling relations of conductivity and physical properties of buried hill inner-curtain reservoir to control hydrocarbon accumulations. Discovery of subtle deep buried hill and buried hill inner-curtain hydrocarbon reservoirs is benefited mainly from ideological emancipation, careful study, creative pattern and technological progress.

Qianjiang Formation of Qianjiang Sag in Jianghan Basin is a typical continental salt lake deposit. Salt rock sedimentation developed most in the lower fourth member of Qianjiang Formation (Eq4x) with a thickness of 1500 meters. Currently, there are few results for analysis and study related to stratigraphic division of salt rock sequences. No effective sequence model was established. The study targeted at the Eq4x deposit is based on the cores logs and seismic data, which analyzed stratigraphic sequences of salt-lake basin, controlling factors of deposit and development model. According to the study, the sequential development of the Eq4x deposit was less controlled by the climate during the sedimentary period while paleotopography and sedimentary source recharge exerted main influence on the deposit. Siltstone and evaporite were distributed in the Eq4x deposit. The sequences of the Eq4x can be divided into transgressive system tract (TST) and lake regressive system tract (RST) according to the position and role of salt rock in the sequential development of the Eq4x deposit in the northern area of Qianjiang Sag. Meanwhile, two sequence models were put forth -- fault slop-break model, flexure slop-break model.

A large quantity of Ordovician krast caves in Lunguxi (LGX) region of Tarim Basin act as krast vugs to hold oil and gas, exerting a great influence on the productivity in this region. The drilling results showed that oil and gas in this region were distributed mainly less than 50 meters below the top surface of buried hill. However, krast caves are seriously packed in this area. On the conventional seismic profile, the caves both packed and unpacked show ^“beaded^” reflective characteristics. It is difficult to identify the effective reservoir by means of a single geophysical method. Based on observation of cores from a number of wells in the operational zone and combined with the geophysical response characteristics and forward model, the packed krast caves under different cap-rock conditions were distinguished. The reflective characteristics of effective reservoir can be identified with the help of frequency spectrum analysis technology. This method has achieved good results in actual application.

Based on core analysis and a large quantity of logging and log data as well as analysis of sedimentary characteristics, it is believed that two main subfacies, namely delta plain and delta front, developed in the 4th member of Quantou Formation in Yingtai-Da^’an Area of Northern Songliao Basin. They can be further divided into six microfacies, such as distributary channels, interdistributory bays, subaqueous distributary channels, subaqueous interdistributary bays, mouth bars and sheet sand. According to the study, the sedimentary microfacies had a controlling effect on the physical properties of reservoir and determined the sedimentary subfacies and oil and gas distribution. The results show that the different sedimentary facies and zones were quite different in physical properties and oil and gas properties. The subaqueous distributary channels and mouth bars were good in terms of physical properties and acted as the main facies and zones for oil and gas accumulations. They are the favorable targets for future oil and gas exploration.

The Upper Paleozoic in Erlian Basin has a promising prospect for exploration. However, the existing old seismic data are weak in reflection signal and low in signal-to-noise ratio resolution. To solve this bottleneck, a series of processing methods are developed, which are focused on model constrained static correction, prestack noise suppression, prestack amplitude compensation for deep signals, well controlled velocity modeling, and anisotropic prestack time migration with curved ray tracing. The re-processed seismic profiles show an improved imaging for interpretation of buried depth, configuration and inner structures in the Upper Paleozoic, laying a technological and data foundation for study of the geological characteristics.

PetroChina has just launched two important projects – ^“4th PetroChina Oil and Gas Resource Assessment^” and ^“Study of Global Oil and Gas Resource Assessment and Application^”. It is required to establish a unified assessment method to link the appraisal results to the international convention. To bring the projects smoothly under way, it is necessary to make an analysis of the oil and gas resource assessment methods and compare their application characteristics. This paper makes briefings about the study progress and characteristics of three methods – the simple Pareto model (SP), the shifted truncated Pareto model (STP) and the lognormal discovery process model (LDP). The research method for effective key parameters is proposed, namely using iteration to determine the largest oil reservoir and distribution of oil reservoirs in SP distribution model and using least squares to obtain the median number of oil reservoirs, standard variance and distribution of oil reservoir in the STP distribution model. The paper also describes the application process of the three above-mentioned models, summarizing their applicable scope and comparing the results of those methods in predicting the largest oil reservoir (S), quantity of oil reservoirs (N) and total resources (R). It is concluded that the prediction results of STD distribution model are good when the exploration degree is high with the data meeting the requirements of the model. The SP distribution model is superior when the exploration degree is low with less data made available. The LDP model has a wide application scope and is superior for the area where the exploration degree is at high and middle levels. The SP model can forecast S and R very well but with an extremely large N; The STP model can forecast S very well, but gives large errors on N and R; The LDP model can forecast N and R very well with a worse estimate of S.

The main series of strata of Jinzhounan Oilfield is the Archean buried hill. The accuracy of fractured reservoir prediction is directly related to development of buried hill oil reservoir. To bring about accurate prediction of fractured reservoir, the efforts were focused on seismic prediction technology and study method of medium- and high-angle fractures in the pattern of offshore narrow azimuth angle seismic acquisition. With combination of geological and structural characteristics of the study zone, the in-depth study was made on the quantitative relations between fracture development degree and seismic response features in the pattern of narrow azimuth angle acquisition. Based on those efforts, the vertical wave azimuth anisotropy fracture prediction technology, far and near offset distance seismic anisotropy fracture prediction and pre-stack stress field fracture prediction technology were brought under application analysis and study. Finally, a magnitude of information was used to merge and process the results of three prediction methods, thus making comprehensive prediction of buried hill fractured reservoir on the basis of various methods. With the multi-solution possibility for single-method prediction reduced, the development well confirmed that the conformity of prediction exceeded 80 percent, providing the data for exploration and development of the oilfield in the next stage. Meanwhile, a set of fracture prediction technology series was summarized for adoption of offshore seismic data.

Chad^’ s Block H and Niger^’ s Block A, Block T and Block B are the onshore blocks located in the western section of the Central- Western African Rift System. They are the largest risk exploration blocks CNPC have ever acquired overseas. Facing a series of challenges, such as low exploration degree, high geological risks, short contract period and complicated operational environment, CNPC located the main play and exploration zones and belts in the region on the basis of geological study and reserve assessment. Meanwhile, it also formulated the comprehensive strategic exploration plan for the whole western African region while focusing on economic performance to optimize the targets of exploration wells. CNPC also enriched and developed the theory on passive rift oil and gas accumulations, adopted the applicable and latest exploration technology, created the management pattern of exploration projects, and made the general deployment in the light of the overseas characteristics. With the productivity construction pushed ahead in harmony with exploration progress, CNPC has made remarkable achievements in oil and gas exploration and development in the region.

Rich in hydrocarbon resources, the Arctic petroliferous domain covers an extensive area in the north Arctic Circle. Based on the tectonic evolution of Arctic region and combined with the stratigrahic characteristics as well as the distribution and development characteristics of basins, the study was made of hydrocarbon geologic conditions in the area. With the elements and process of giant oil and gas fields in this domain analyzed, this paper uses a series of oil and gas theories to study formation and distribution of giant oil and gas fields. The study indicated that the tectonic evolution of the Arctic region controlled formation and development of oil and gas basins in this domain. Moreover, development of giant rifts, buildup and breakup of Pangea and formation of the North Atlantic endowed the domain with the superior hydrocarbon geological conditions. Therefore, Mesozoic is the most important horizon developed as source rock, reservoir and cap rock in the area, while the second important horizon is Cenozoic. The domain includes giant gas fields. The type of trap is mainly structural one. Oiland gas were accumulated mainly in the Jurassic Period but the migration peak basically took place after the Cretaceous Period. Giant oil and gas fields are mostly distributed in the Cretaceous System in terms of quantity and recoverable reserves, and next is the Jurassic System. The domain is very low in exploration degree. There is still a large of resources in the region that is to be developed or remain undeveloped. However, the risk for oil and gas exploration and development in the region is high because of many uncertainties. It is necessary to make a further study of the distribution law of giant oil and gas fields in the domain.