The Linhe depression of Hetao Basin is a Meso-Cenozoic strike-slip pull basin. The early stage wells were mainly concentrated in the slope zone, which had oil and gas shows but no substantial breakthroughs. Recently, new and old data including gravity, magnetic, electric, seismic, drilling and geology data were used to investigate the basin property, structural characteristics, resource potential and reservoir-cap combination. It is understood that the depression is a strike-slip pull depression, which is zoning east-west and blocking north-south. Two major source rocks in the Lower Cretaceous and Oligocene respectively are confirmed. Three sets of source-reservoir-cap are identified. Indepth comprehensive analyses of the trap-source relationship and the oil and gas accumulation models showed that the Jilantai buried hill is favorable for oil and gas accumulation for its adjacency to the northern deep sag hydrocarbon generation area with Langshan piedmont fault as the main channel for oil and gas migration providing good lateral oil supply conditions. The Jilantai buried hill and its periclinal fault structural belt were selected to deploy Well JHZK2, Well JHZK7 and Well Jihua 2x. All of the three wells have obtained industrial oil flow, which was a great discovery of Linhe depression and demonstrated a broad exploration prospects. With the attention of PetroChina Company and the support of Changqing Oilfield Company as the basis, the innovative geological understanding and scientific deployment and decision-making as prerequisites, the thought-transform and key point-selecting as the key and the selection of economically applicable technologies as the guarantee, the Linhe Depression successfully achieved rapid exploration.

After entering highly mature exploration, the Liaohe oilfield should be finely explored in the middle and shallow reservoirs to improve exploration efficiency. In recent years, to adapt the conditions such as highly explored middle and shallow reservoirs, small fault blocks, thin sandstone layers and complex reservoir development in the Liaohe depression, a series of work have been carried out, involving selection of good zones, innovation of geological understanding, fine target characterization, fine interpretation of micro-relief structures instead of massive structures, combined pre-stack and post-stack seismic inversion instead of post-stack seismic inversion, multi-disciplinary research on exploration potentials, rapid production capacity construction through integrated exploration and development. The implementation of the measures above made new discoveries of several high-quality reservoirs with reserves at 10 million-ton scale in the surroundings and new formations of old fields. Exploration practice shows that to make more discoveries in the middle and shallow reservoirs is important for efficient exploration.

After more than 50 years of exploration and development in the Boxing subsag in the Jiyang depression, eight oil and gas fields such as Purification, Boxing and Jinjia were discovered, and their cumulative proven geological reserves exceed 4×10⁸ tons, but they are all highly explored. In the process of efficient exploration in the Boxing sag, advances of scientific and technological theory and transformation of exploration ideas have been the mainstream. For example, the slope-controlling sandstone theory greatly enhanced the confidence of finding oil in subsags, and realized the transfer from structural reservoirs to lithologic reservoirs in subsag belts; the focus on brackish lake basin and shallow-shore lake beach increased the confidence of subsags full of oil, and revealed that oil in the Boxing subsag should be full and continuous; the order and continuity of oil and gas distribution promoted the overall 3D exploration to multi-layer and multi-type reservoirs in the subsag, and a large number of "red-layer" oil and gas reservoirs and marginal stratigraphic reservoirs have been discovered, expanding the exploration field; at low oil prices, the concept of refined and efficient exploration can ensure the discovery of high-quality and producible reserves in the future.

The Xingning-Jinghai sag is a Mesozoic-Cenozoic superimposed sag lying at the ultra-deep water transitional crust, and a new Mesozoic oil and gas exploration target in northern South China sea. Based on fine interpretation of 2D and 3D seismic data, the structural characteristics, structural evolution history and source rocks feature of the Mesozoic-Cenozoic sag are analyzed comprehensively. The study results show that the Xingning-Jinghai sag has gone through three tectonic evolution stages:the Mesozoic compression and denudation, the stretching rift and thermal subsidence since the Cenozoic. Under the control of the structural evolution, three sets of Mesozoic source rocks, the Triassic, Jurassic and Cretaceous, are developed, of which the Mesozoic marine mudstone is dominant; two sets of favorable reservoir-caprock assemblages are formed:one is the Jurassic and Cretaceous shallow marine and lacustrine sandstone-mudstone interlayers, and the other is the Cenozoic Enping Formation shallow marine and delta sandstone and the Zhuhai Formation marine mudstone; and several types of traps are developed, of which the traps near the sag are favorable exploration targets.

Exploration in the volcanic rock zone in South Bohai Sea has been facing many challenges:poor seismic data, difficult characterization of target traps, deeply buried reservoirs, less researches on the development mechanism of high-quality reservoirs, complex geological conditions, and unclear hydrocarbon accumulation mechanism. Systematical 3D quantitative description of the Cenozoic volcanic rock and structural correction imaging with variable interval velocity have restored the original structure under the volcanic rock and provided a reliable basis for fine structural interpretation. Based on fine delineation of the hydrocarbon accumulation conditions in the volcanic rock zone, it is proposed that the combined control of faulting and magmatic activities determines the formation of the slope-bulge belt and the development of large-scale traps; the orderly spatial-temporal distribution of magmatic activities is conducive to the development of deep reservoirs; and the orderly spatial-temporal configuration of "fault and magma" controls the differential hydrocarbon accumulation. Guided by these understandings, the first large-scale high-quality oilfield, BZ34-X, was discovered in the volcanic rock zone of the southern slope in the Huanghekou sag.

To determine the effect of tectonism on shale gas formation and preservation, the regional tectonic evolution, key periods of tectonic activities and structural styles, etc., were analyzed, and based on which a classification system of "three belts and three zones" was proposed for shale gas preservation, and the characteristics of shale gas accumulation were discussed in the Wulong area, southeastern Chongqing. The results show that the shale gas preservation was influenced by the key periods, intensity of tectonic activities and structural styles. The key periods and intensity of tectonic activities affected hydrocarbon generation, later uplifting destroyed the shale gas preservation conditions, but appropriate uplifting is favorable for shale gas development. The influence of structural styles on the formation and preservation of shale gas is the jointing result of multiple factors, so that simple structural classification can't reflect the shale gas preservation conditions, and the preservation conditions in any tectonic style can be divided into "three belts ad three zones", under which the differences of the preservation conditions in different regions could be comprehensively compared. It is found transitional zone and internal unicom zone are favorable for shale gas development. The eastern flank of the Wulong area is an open slope where the transitional zone and internal unicom zone are small, so the beneficial exploration target should be around the structure center. The western flank of the Wulong area is a continuous slope with fine preservation conditions, where the transitional zone and internal unicom zone are larger, so shallow layers are suitable for shale gas exploration.

In recent years, the rapid growth of tight oil production in the United States has attracted extensive attention all over the world, but the evaluation standard of the permeability of tight oil hasn't been unified at home and abroad. Based on the analysis of reservoir productivity, relative core permeability, core displacement pressure and the relationship between core porosity and permeability, and considering applicable standard and the relationship between overburden permeability and ground permeability, it is suggested that 1mD ground permeability can be the critical value to distinguish tight oil reservoir from conventional reservoir, differences between tight oil reservoir and conventional ultralow-permeability reservoir are analyzed in pore space, porosity-permeability relationship and irreducible water saturation, and finally two auxiliary characterization methods for tight oil reservoirs are proposed:one is seepage rate and the other is pore throat radius.

To demonstrate the feasibility of CO₂ flooding development of the heavy reservoirs in Well Ji7 of Changji oilfield in the Junggar Basin, experiments on injecting CO₂ into crude oil and slim-tube displacement were carried out to investigate the solubility of CO₂ in heavy oil. The experiment results proved that:(1) When injecting CO₂ at 50mol/mol at present 16.41MPa underground pressure, the viscosity of the crude oil was reduced by 42.3%-66.7%, the density was reduced from 0.9011g/cm³ to 0.8428 g/cm³, the volume factor was increased by 20%, the expansion factor was increased to 1.13-1.24, the gas-to-oil ratio increased by 6.3-8 times, and the saturation pressure increased by 140%-306%. (2) The oil recovery increased with injection pressure, and gas breakthrough was delayed. When the injection pressure was 45MPa, the oil recovery was 46.68%, and non-miscible displacement worked. (3) CO₂ effectively reduced the viscosity and made the crude oil expand in the study area. All these results above show that CO₂ flooding technology is effective for the development of deep heavy oil reservoirs in the study area.

Plenty of geological and geophysical data show that shallow-water deltas were developed during the late Oilgocene rifting stage in the Sunda Basin, Indonesia, of which deltaic plains were dominant, but deltaic fronts and prodeltas were less developed. Controlled by shallow basin, gentle slope and rapid current, primary hydrodynamics influencing the shallow-water deltas are surface divergent runoff and vein traction flow dominated by seasonal meandering rivers and braided rivers. Distributary channel and natural levee are main depositional microfacies with abundant sandstone. The former acts as an unloading terminal and a passing channel. The latter gradually accumulates and replaces the inter-river sand bar while transporting. Marsh and coal seam strata are more developed, but they are difficult to shape during gravity deposition. The climate is an important factor affecting the shape of the shallow water delta sand bodies in the late rifting stage. Under the action of thermal diffusion and condensation, the periodic exposure alternating with the rising of the water in the lake basin caused frequent bifurcation, diversion and superposition of the river channels, and developed typical patterns of delta sand bodies, such as leave, teeth, branch, strip.

Based on casting thin sections and FE-SEM (field emission scanning electron microscope), the reservoir space of tight sandstone in the 3rd member of the Hetaoyuan Formation in the Biyang sag is divided into three types, including intergranular pores, intragranular pores and fractures. The former two, intergranular pores and intragranular pores, are primary reservoir space. According to the mineral composition, the intergranular pores are divided into quartz and feldspar intergranular pores, quartz and feldspar grain-boundary pores, and intergranular carbonate pores; the intragranular pores are divided into dissolved quartz and feldspar pores, intragranular carbonate pores and intercrystalline clay pores, which are relatively developed between 3023 m and 3035 m. Theses pore types are quantitatively calibrated based on a highresolution and large-view FE-SEM splicing technology. The results show that the surface porosity of the tight sandstone in the 3rd member of Hetaoyuan Formation is 3.75%, of which intergranular pores, intragranular pores and fractures account for 2.35%, 1.38% and 0.02%, respectively. In various types of reservoirs, the pore diameters have some differences, the intergranular pores of quartz and feldspar mainly ranging from 50 to 100 nm account for 42.4% and 30% respectively, and the grain-boundary quartz and feldspar pores mostly from 100 to 200 nm account for 30% each. Although the intergranular pores larger than 1000 nm account for less than 6%, they contribute more to total pore volume, of which the intergranular quartz and feldspar pores larger than 1000nm account for 95% of each pore volume. The intragranular pores in the range of 100 to 200 nm are dominant; quartz and feldspar dissolution pores are slight different from other types, and the pores between 200 and 500 nm are dominant, and account for more than 35% of each total pore volume.

The penetrating direction of a horizontal well is opposite to real stratigraphic sequence, so that the interface information reflected by synthetic records is inconsistent with real seismic sections. A practical and effective method for making and calibrating synthetic records is proposed for horizontal wells. First, the AC and density curves are calculated from the bottom of a horizontal well upward, based on the horizontal section logging curve, and an imaginary vertical well is made at the bottom of the horizontal well, then the reverse AC and density curves are imported to the vertical well after dip transform, and acoustic impedance and reflection coefficient are calculated. Second, seismic data are flattened along the bottom of the inclined layer, and based on which seismic wavelets are extracted and convoluted by the reflection coefficient to make a synthetic seismic record. Finally, well-seismic calibration is done by comparing the synthetic seismic record with the seismic trace near the imaginary vertical well. The method has been applied to make and calibrate the synthetic record of Well 202-Ping 1 in the Zhanhua sag in the Jiyang depression. The result defines the corresponding relationship between the members of the Mesozoic formation and thick oil layers on the seismic section, achieving the purpose of reservoir calibration in the horizontal well.

Low-permeability reservoirs are generally developed by injecting water. In the process of waterflooding development, due to the heterogeneity of the reservoir and the microscopic randomness of the pore structure, it is common to cause fingering phenomenon, and it would become serious with continuing water injection. To make reasonable development decisions for low-permeability reservoirs, it is necessary to accurately understand the variation law of viscous fingering and its influencing factors. A viscous fingering model was established with a starting pressure gradient, for waterflooding low-permeability reservoirs, and a concept of small fingering tumors was introduced. The migration distance of small fingering tumors was used to characterize fingering change. After solving the model, the effects of permeability, density difference, formation dip, waterflooding rate and the ratio of oil-to-water viscosity were analyzed on viscous fingering. The results show that, in the process of waterflooding low-permeability reservoirs, the presence of starting pressure makes fingering phenomenon serious, but gravity can effectively slow down the phenomenon; the greater the permeability, density difference and formation dip, the less serious the fingering phenomenon; the greater the waterflooding rate and the ratio of oil-to-water viscosity, the more serious the fingering phenomenon. In order to slow down the fingering, it is suggested to inject water at the bottom of the reservoir, and the waterflooding rate should be kept reasonable.

Noise suppression is an important step in seismic data processing. However, the applicable denoising methods cannot remove noise effectively, or process nonlinear or unstable signals. The Empirical Wavelet Transform (EWT) developed recently is an adaptive decomposition algorithm which has better adaptability and more complete mathematical theory than the Empirical Mode Decomposition (EMD). The EWT algorithm is introduced into seismic data for noise suppression. Firstly, a suitable wavelet function is selected which adaptively decomposes target seismic signals to get intrinsic mode functions at different frequency scales. Secondly, a threshold range is set based on the dominant frequency and the intrinsic mode functions whose dominant frequencies are within the threshold range are selected to reconstruct signals and finally get denoised signals. Application of the EWT algorithm to numerically simulated data and real seismic data has proved effective separation of signals from noises, and the result is better than those from conventional denoising algorithms.