The exploration based on foreign cooperation has been carried out many rounds in Yangjiang sag of the Pearl River Mouth Basin, but only a few oil and gas shows are discovered and no commercial oil and gas discovery is achieved. Recently, the petroleum geological conditions in Yangjiang East sag were analyzed systematically based on a great amount of new drilling, geochemical and seismic data. It is indicated that Yangjiang East sag can be divided into 4 subsags, including Yangjiang 24 subsag, Enping 19 subsag, Enping 20 subsag and Enping 21 subsag. There are 3 kinds of subsag structures, including composite half graben, double-fault graben and single half graben. In Paleogene Wenchang Formation, the intrabasinal middle-and small-sized provenances are dominant and the source rocks of semi-deep lake facies are widely developed. Among them, Enping 20 subsag has the earliest and longest subsag controlling faulting activity and generates Wenchang Formation which is complete and vertically superimposed stably. It is favorable for the formation of high-abundance source rocks of semi-deep lake facies to provide the rich hydrocarbon generation potential. By using the fluid detection technique, combined with the new understandings on source-fault controlled reservoir, Enping 20 structural belt of faulted anticline was selected to deploy Well Y10-1 preferentially. Owing to its deployment, a middle-sized oil field is discovered with daily industrial oil production over 1000 m³ during the testing, which means the important breakthrough of oil and gas exploration in Yangjiang sag and displays the promising exploration prospect in this area. In conclusion, the exploration discovery in Yangjiang sag opens up a new oil area in the Pearl River Mouth Basin, and the keys to the breakthrough of large- and middle-sized oil and gas fields in the new areas are focusing on the detailed information, enhancing the basic researches and standing on the value exploration.

For a deeper understanding of China's oil production situation, it is necessary to investigate the composition of the reserves-production system and its changes, especially the proved developed estimated ultimate recovery (Proved Development EUR) and the corresponding Proved Developed Reserves and production in large oil fields or basins. The study results indicate that China has almost achieved the goal of the second round of oil and gas exploration, and the Proved Developed Reserves and production began declining. To keep sustainable and stable production, it is necessary to tap the potential of old oilfields, and more importantly, to find strategic replacement in new areas. Such new areas include deep strata in large basins, offshore Pre-Cenozoic marine strata, the Tibetan Plateau, and the Upper Paleozoic of the "Southern Intercontinental Zone of Central Asia" in northern China. In addition to technical challenges, oil and gas exploration and production are currently suffering the impacts from insufficient investment and slow progress in institutional reforms.

Cambrian Fujunshan Formation inside the buried hills in Jizhong depression was investigated to the structure, lithofacies palaeogeography, reservoirs, caprocks, hydrocarbon sources and traps using drilling, seismic, well test and laboratory data. The study results show that Cambrian Fujunshan Formation includes good dolomite reservoirs, and two sections of stable and effective caprocks (Cambrian Mantou Formation and Xuzhuang Formation; Qingbaikou mudstone), which constitute the most favorable reservoir-caprock-isolator assemblage; There are five types of hydrocarbon transport systems:vertical hydrocarbon migration from deep source along faults, lateral hydrocarbon migration from near source along faults, hydrocarbon migration inside source along unconformity, hydrocarbon migration along faults and unconformity, and step-like hydrocarbon migration along fault and effective reservoir; 4 types of traps developed:layered fault trap, bedding unconformity slope trap, adverse unconformity slope trap, and fault-unconformity trap. It is concluded that favorable reservoir-transport system-caprock configuration (isolator) is a key factor for hydrocarbon accumulation inside buried hills. Finally, 3 class I and 2 class Ⅱ exploration zone are proposed, and several buried hill belts are selected for future exploration, including Hexiwu buried hill belt, Wen'an slope west buried hill belt, Nanmazhuang buried hill belt and Changyangdian buried hill belt.

The exploration practice in recent years shows that not only sedimentary facies exist in the oxidized environment but also in the semi-reduced and reduced environment in the early stage of the faulted basin. In order to find out the relatively complete sedimentary sequence and its petroleum geological significance in the early stage of the faulted basin, taking the lower Es₄ (the fourth member of Shahejie Formation) in Bonan sag as an example, comprehensive analysis has been carried out on drilling, logging and experimental data. The results show that in the early stage of the faulted basin, in addition to the alluvial fan and the braided river understood traditionally, river delta, fan delta and lake were deposited. Original sedimentary boundary restoration and sedimentary center analysis indicate that the primary direction of the alluvial fan and the braided river in the lower Es₄ is NNE; the braided river delta formed by the braided river into the lake is in the NW banded lake basin; and under the control of the "source-sink" system, a relatively complete sedimentary sequence of alluvial fan-braided river-braided river delta-lake could be developed in the early stage of the faulted basin. The re-understanding of the alluvial-lake sedimentary system not only makes the originally "barren" red layer have a certain potential for hydrocarbon generation, and the newly identified braided river delta may provide favorable reservoirs and traps, thus expanding the exploration space of the "red layer".

Linhe depression in the Hetao Basin has been less explored. No significant oil and gas discoveries were made until some breakthroughs recently. Wells S5 and Jh2X delivered commercial oil flows of 62.6 m³/d and 10.26 m³/d, respectively, from Oligocene Linhe Formation during the production tests. In this study, the correlation between oil and source rock of Wells S5 and Jh2X was systematically analyzed from prospective of organic geochemistry, in order to determine the oil-source correlation and thereby facilitate the selection of exploration targets. Crude oil in Wells S5 and Jh2X is less mature to mature, generally reflecting the characteristics of a high-salinity and anoxic lacustrine environment. The source rocks in Lower Cretaceous Guyang Formation and Oligocene Linhe Formation are saline lacustrine facies, and less mature to mature locally with abundant organic matters, good kerogen types and high hydrocarbon-generating potential. The oil-source correlation reveals that the oil in Well S5 was originated from the source rock in Linhe Formation, and the oil in Well Jh2X might derive from the mature source rock in Guyang Formation. In conclusion, Linhe depression has a good exploration potential for its rich oil and gas resources, with Guyang and Linhe Formations as the key exploration targets.

The risk of overseas oil and gas exploration projects is quite high, so it is crucial for exploration decision making to develop a set of scientific and complete risk assessment method. In this paper, a set of risk assessment method was innovatively constructed by using the Monte Carlo probability method, and its reliability and practicability were verified by means of specific examples. When there are multiple exploration opportunities, it is recommended to firstly estimate the success probability, resource extent with risk probability and expected moneytary value of multiple traps by using this newly established method, then analyze the effects of three key factors (i.e., success probability dependency, drilling sequence and well quantity) on resource extent with risk probability, success probability, economical success probability and expected moneytary value, and finally discuss deeply the strategies for the final bidding decision making. It is indicated that rational assessment on the project's expected moneytary value is the key to win the bid in the link of exploration bidding, and expected moneytary value is the comprehensive embodiment of success value and failure value. To select the final decision making point, it is necessary to consider the success probability and the effect of the affordability to failure value comprehensively, instead of blindly seeking to maximize the expected moneytary value.

Many wells have achieved new breakthrough in Jurassic in Mahu sag of the Junggar Basin. The characteristics and favorable conditions of Jurassic hydrocarbon accumulation in Mahu sag were studied systematically based on the geological, core, experimental analysis and seismic data of existing exploration wells. Then, based on the main factors controlling hydrocarbon accumulation, the favorable areas for hydrocarbon accumulation were predicted. Finally, the following exploration directions and deployment suggestions of Jurassic in Mahu sag were proposed. It is indicated that two kinds of oil and gas reservoirs (i.e., primary and secondary oil and gas reservoirs) are developed in Jurassic in Mahu sag, and secondary faulted block and fault-lithologic oil and gas reservoirs are dominant. The oil reservoirs are characterized by small burial depth, moderate thickness and moderate physical properties. The conditions of fault controlling migration, nose-like salient controlling accumulation, sufficient sources and developed reservoirs are favorable for Jurassic hydrocarbon accumulation in Mahu sag. It is concluded from the comprehensive evaluation that the favorable areas for the Jurassic oil and gas reservoirs in Mahu sag are mainly distributed in the nose-like salient developed in the slope around the sag and they are superimposed with the favorable areas of the principal producing formations in Permian and Triassic, Mahu sag. It is recommended to take Jurassic as the shallow efficient field for concurrent exploration.

The formation and development of carbonate reservoirs in 4^th member of Shahejie Formation (Es₄) in Gaosheng area, western sag in Liaohe depression, are mainly controlled by sedimentary facies, burial dissolution and tectonic fractures. Whether microscopically or macroscopically, the reservoirs are strongly heterogeneous and controlled by many factors, and the porosity and permeability are very complex. In order to avoid the deviation caused by single factors, and less drilling and logging data when evaluating regional carbonate reservoirs, the Relief F algorithm for feature selection was used to analyze the thickness, porosity, permeability, brittleness index and fracture density of the carbonate rock and the grained limestone (dolomite), and their weights; then the feature plans were overlapped to create a multi-factor probability map; and finally a reservoir evaluation map was built by dividing the probability. In addition, considering the structural and sedimentary facies characteristics in research area, the carbonate reservoirs in Es₄ were investigated and evaluated. The evaluation results are in good agreement with the results from field exploration. Based on the results, favorable exploration zones were predicted.

The Dunhuang Basin is generally superimposed on Dunhuang block in the eastern part of Tarim plate. So far, it has been less explored and investigated. Understanding the basin structure, including fault distribution, structural pattern and basement depth, can provide a geological basis for further comprehensive study on exploration. Based on the physical properties of outcrops, drilling/logging results and other geological data, the variations of rock, formation density and electrical properties were identified. The layered model was combined with the continuation technique to eliminate electric distortion caused by terrains, thus deriving more accurate electromagetic inversion results. The gravity linear-gradient zones were extracted from gravity data using the total horizontal gradient technique to enhance the linear characteristics of faults within the basin. The basement depth was analyzed with the Parker inversion method. The results show that:in the Dunhuang Basin, there are three sets of density and electrical layers. The regional faults control the structural pattern of alternate uplifts and sags. And Wudun sag has the deepest basement, which is the most favorable depocenter.

The reversed anticline is one of the most important hydrocarbon-bearing structures in the mountainous area in western China. Many wells drilled in the steep and complicated structures failed, largely due to insufficient understanding on the geological and seismic reflection characteristics of the reversed anticlines. Based on surface geology, drilling and well logging data, different modes of reversed anticlines were established, then the seismic response features of different types of reversed anticlines were analyzed through forward modeling and migration, and finally the reversed anticlines were recognized based on seismic sections. This method is helpful to identifying the forms of the reversed anticlines. For the complicated mountainous structures with seismic data with high SNR, pre-stack depth migration sections can clearly show the forms of the reversed anticlines. If the normal limb of the reversed anticline is less denuded and moderately buried, it may be a good hydrocarbon trap. If the limb is steep and faults are developed, the conditions for hydrocarbon accumulation may be poor. The buried anticlines beneath the reversed limb have good preservation conditions favorable for hydrocarbon accumulation, so they are promising targets for hydrocarbon exploration.

North Tluwa and Zanazor oilfields under the Aktobe project are located at the eastern margin of the Pre-Caspian Basin. The low-porosity and low-permeability reservoirs in the oilfields are exploited by horizontal wells. To increase the single-well production, the horizontal section is extended from about 400 m to more than 1000 m. However, complicated geological structures and large variations of the boundary and thickness of target layers result in low ROP and footage, only 2.36 m/h and 335 m on average, when a rotary steering tool with an edge detector is used during drilling. In order to improve the drilling efficiency, the BHA (bottom hole assembly) and the rotary speed were optimized depending on the damages of drill bits and the downhole vibration behaviors, and a ROP enhancement technology was developed with a BHA consisting of high-performance PDC bit, rotary steering screw, and near-bit single centralizer or double-centralizer. This technology has been applied in five wells. For four wells, the rotary speed was 60 r/min, the downhole stick-slip index was less 80%, and the drill bits were worn or partially broken. For the rest one well, the rotary speed was 70-80 r/min, the downhole stick-slip index was above 80%, and teeth breaking was mostly observed in bit core. Compared with Well H814, the drilling cycle in the horizontal sections was reduced by 57.7% from 22.5 days to 9.6 days, the average ROP was enhanced by 266.1%, and the average footage was increased by 195.5%.

CBM (coalbed methane) reservoirs are usually developed by hydraulic fracturing stimulation. However, it is less effective to improve the natural fracture system in coalbeds and results in lower production of vertical CBM wells. By applying intense repeated short pulses to the liquid-solid interface, coal rock can be broken and fractured due to the fact that solid is more prone to break than liquid. It is worthy to focus on how intense repeated pulsed wave can improve the natural fracture network in coalbeds. In this study, intense repeated pulse wave was applied to stimulate CBM reservoirs, and the results were evaluated by considering well test interpretation on the improvement of matrix permeability, fracture system and fracturing stimulation. Field tests show that intense repeated pulse wave plays an active role in increasing coal rock permeability and improving induced fractures. It is an effective method for stimulating CBM reservoirs.