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.

Discussion of the Mode and Mechanism of Oil and Gas Accumulation in the Nanbaxian Pool in the North of the Qaidam Basin

Because of the difference ofoil and gas accumulation condition between the hanging wall and the footwall of a fault, there is a peculiar accumulation mechanism that oil and gas mainly exists in the hanging wall of the basement fault, but in the footwall of the shallow detachment fault in the Nanbaxian pool. The oil and gas of the Nanbaxian pool came from the mature Jurassic hydrocarbon source rock of the Yibei depression located at the south of the Nanbaxian pool. Firstly, the oil and gas accumulated in the traps of the hanging wall of the basement fault by way of the unconformity and the basement faults, and turned into some primary deep pools; and then, the shallow detachment fault that formed in the later tectonic movement broke into the deep primary pools, which caused the oil and gas migration upwards along the basement faults and the shallow detachment faults and the evolvement into some secondary oil and gas pools later. The history of the Nanbaxian oil and gas accumulation can be summarized successively as the syndepositional upheaval controlled by faults; single hydrocarbon source rock; unconformities and faults as migration channels; buoyancy, overpressure and tectonic stress as dynamic forces; multistage migration and accumulation of oil and gas; and finally an overlapped double-floor pattern of oil and gas accumulation. The most important explorative targets in the north of the Qaidam Basin are traps connected with the primary pools in the footwall by shallow detachment faults.

Formation Laws of Inorganic Gas Pools in the Northern Jiangsu Basin

In the Northern Jiangsu basin there are high pure CO2 gas pools, low condensed oil-containing CO2 gas pools, high condensed oil-containing CO2 gas pools and He-containing natural gas pools, with the δ13Cco2 (PDB) values ranging from ?2.87%o to ?6.50%o, 3He/4He 3.71 × 10?6 to 6.42 × 10?6, R/Ra 2.64 to 4.5, 40Ar/36Ar 705 to 734, belonging to typical mantle source inorganic gas pools which are related to young magmatic activity. The gas layers occur in two major reservoir-caprock systems, the terrestrial Meso-Cenozoic clastic rock system and the marine Meso-Palaeozoic carbonate rock-clastic rock system. Controlled by the difference in the scale of traps in the two reservoir-caprock systems, large and medium-scale inorganic gas pools are formed in the marine Meso-Palaeozoic Group and only small ones are formed in the terrestrial Meso-Cenozoic strata. Inorganic gas pools in this basin are distributed along the two deep lithospheric faults on the west and south boundaries of the basin. Gas pools are developed at the intersected part of the ENE-trending faults that control the half graben and the E-W tenso-shear faults, mainly distributed near the Es1, Ny1 and Ny2-Q basalt eruption centres.

Penetration control by weld pool resonance during gas tungsten arc welding

Presents penetration control by weld pool resonance which occurs when the natural frequency of weld pool is equal to the frequency of sine wave current while the weld pool is excited into oscillation by superimposing sine wave current with definite frequency or regular frequency on DC current, and experiments carried out on detecting resonance signals during both stationary and travelling arc welding with variant frequency pulse current, and concludes with experimental results that penetration control can be realized by weld pool resonance when welding speed is lower than 80mm/min, and this control method is applicable to welding thin (0.5～3.0 mm) plates of carbon steel, low alloy steel, high strength steel and superhigh strength steel, and suitable for alternating polarity welding of stainless steel, titanium alloy steel and aluminum alloy.

Effects of Nitrogen Application Rate to Late Rice on Greenhouse Gas Emissions and Soil Carbon Pool During the Growing Season of Winter Chinese Milk vetch

It is of important referential values for the further understanding of the effects of fertilization on greenhouse gas emissions and the effects of winter green manure on soil carbon pool to study the effects of fertilization on the greenhouse gas emissions and soil carbon pool during the growing season of winter Chinese milk vetch in the process of rice cultivation.This study investigated the effects of nitrogen application in late rice season on the yield of the succeeding Chinese milk vetch and greenhouse gas emissions as well as the soil carbon pool characteristics after the winter planting of Chinese milk vetch with the winter idling of no nitrogen application as the control.The results showed that the yield of Chinese milk vetch was the highest under the nitrogen application of 225 kg/hm^2 in the late rice season,reaching up to 18 388.97 kg/hm^2,which was significantly different from other treatments( P <0.05).Nitrogen application in late rice season increased the emissions of N_2 O,CH_4,CO_2 and global warming potential( GWP) in the growing season of Chinese milk vetch.Compared with the winter idling treatment,winter planting of Chinese milk vetch significantly increased the soil organic carbon and soil carbon pool management index.The yield of Chinese milk vetch was significantly positively correlated with N_2O and CH_4 emissions( P < 0.05),while it presented extremely significant positive correlations with CO_2 emissions,GWP,active organic carbon,and carbon pool management index( P < 0.01).Nitrogen application in the late rice season increased the emissions of N_2 O,CH_4,CO_2,and enhanced the greenhouse gas emission potential during the growing season of Chinese milk vetch.Therefore,without reducing the yield of rice,reducing the amount of nitrogen fertilizer in rice could reduce the greenhouse gas emissions in the growing season of succeeding Chinese milk vetch.

GEOTHERMAL EVOLUTION AND TECTONOSEDIMENTATION OF THE NORTH CHINA CRUSTOBLOCK AND THEIR EFFECTS ON THE FORMATION OF OIL/GAS POOLS

The geothermal history of North China can be divided into at least four stages, i. c. Archaean (much hisher geothermal) stage, Paleoprotcrozoic (hish geothermal)stage, which resulted in four geotectonic stages (pregeosynehoe, geosyncline, platform and diwa stage) in the region. The geothermal field consists of three subgeothermal fields, theupper subgeothermal field with its depth of less than 2000 m, the middle subgeothermal field ranging from 2000 m to 5000 m in depth and the lower subgeothcrmal field locating at more than 5000 m in depth in North China. Sis thermostructural layers are recognised in North China, i. e. the mantle, the lower erust with its heat generation ratc of 0. 6 HGU. Oeothermal field is Corresponding to tectonosedimentary divisions in North China, controlling the tectonosedimentation, the evolution of souree rocks and the formation oF the oil/gas pools.

Conditions for the Formation of Oil and Gas Pools in Tertiary Volcanics in the Western Part of the Huimin Sag, Shandong and Their Distribution

Conditions for the Formation of oil and gas pools in Tertiary volcanics in the western part of the Huimin sag, Shandong and then (?)stribution have been studied based on the geological, seismic and well-logging information. In this paper, the types and lithofacies of the volcanic rocks in the western part of the Huimin sag are described; the relationship between rocks and electrical properties, the seismic reflection structures, the development and distribution of the volcanic rocks are expounded; and the fourfold role of the volcanic activities in the formation of the oil and gas pools is also dealt with. It is considered by the authors that the volcanic activities were not destructive to the formation of oil and gas pools but a factor favourable to the accumulation of organic matters and their conversion to hydrocarbon. The volcanic rocks might have served as reservoir rocks and cap rocks, or as a synsedimentary anticline. The prerequisites and important factors for the formation of oil and gas pools and their distribution are pointed out in the paper.

Formation Mechanism and Controlling Factors of Natural Gas Reservoirs of the Jialingjiang Formation in the East Sichuan Basin

The Lower Triassic Jialingjiang Formation reservoirs are distributed widely in the East Sichuan Basin, which are composed mainly of fractured reservoirs. However, natural gas with high concentration of H2S, ranging from 4% to 7%, was discovered in the Wolonghe Gas pool consisting primarily of porous reservoirs, while the other over 20 fractured gas reservoirs have comparatively low, tiny and even no H2S within natural gases. Researches have proved the H2S of the above reservoirs are all from the TSR origin. Most of the Jialingjiang Formation natural gases are mainly generated from Lower Permian carbonate rocks, the Wolonghe gas pool＇s natural gases are from the Upper Permian Longtan Formation, and the natural gases of the Huangcaoxia and Fuchengzhai gas pools are all from Lower Silurian mudstone. The formation of H2S is controlled by the characteristics and temperature of reservoirs, and is not necessarily related with gas sources. The Jialingjiang Formation in East Sichuan is buried deeply and its reservoir temperature has ever attained the condition of the TSR reaction. Due to poor reservoir potential, most of the gas pools do not have enough room for hydrocarbon reaction except for the Wolonghe gas pool, and thus natural gases with high H2S concentration are difficult to be generated abundantly. The south part of East Sichuan did not generate natural gases with high H2S concentration because the reservoir was buried relatively shallow, and did not suffer high temperature. Hence, while predicting the distribution of H2S, the characteristics and temperature of reservoirs are the necessary factors to be considerd besides the existence of anhydrite.

Welding Deviation Detection Algorithm Based on Extremum of Molten Pool Image Contour

The welding deviation detection is the basis of robotic tracking welding, but the on-line real-time measurement of welding deviation is still not well solved by the existing methods. There is plenty of information in the gas metal arc welding（GMAW） molten pool images that is very important for the control of welding seam tracking. The physical meaning for the curvature extremum of molten pool contour is revealed by researching the molten pool images, that is, the deviation information points of welding wire center and the molten tip center are the maxima and the local maxima of the contour curvature, and the horizontal welding deviation is the position difference of these two extremum points. A new method of weld deviation detection is presented, including the process of preprocessing molten pool images, extracting and segmenting the contours, obtaining the contour extremum points, and calculating the welding deviation, etc. Extracting the contours is the premise, segmenting the contour lines is the foundation, and obtaining the contour extremum points is the key. The contour images can be extracted with the method of discrete dyadic wavelet transform, which is divided into two sub contours including welding wire and molten tip separately. The curvature value of each point of the two sub contour lines is calculated based on the approximate curvature formula of multi-points for plane curve, and the two points of the curvature extremum are the characteristics needed for the welding deviation calculation. The results of the tests and analyses show that the maximum error of the obtained on-line welding deviation is 2 pixels（0.16 ram）, and the algorithm is stable enough to meet the requirements of the pipeline in real-time control at a speed of less than 500 mm/min. The method can be applied to the on-line automatic welding deviation detection.

Three-Dimensional Reconstruction of Welding Pool Surface by Binocular Vision

Current research of binocular vision systems mainly need to resolve the camera’s intrinsic parameters before the reconstruction of three-dimensional(3D)objects.The classical Zhang’calibration is hardly to calculate all errors caused by perspective distortion and lens distortion.Also,the image-matching algorithm of the binocular vision system still needs to be improved to accelerate the reconstruction speed of welding pool surfaces.In this paper,a preset coordinate system was utilized for camera calibration instead of Zhang’calibration.The binocular vision system was modified to capture images of welding pool surfaces by suppressing the strong arc interference during gas metal arc welding.Combining and improving the algorithms of speeded up robust features,binary robust invariant scalable keypoints,and KAZE,the feature information of points(i.e.,RGB values,pixel coordinates)was extracted as the feature vector of the welding pool surface.Based on the characteristics of the welding images,a mismatch-elimination algorithm was developed to increase the accuracy of image-matching algorithms.The world coordinates of matching feature points were calculated to reconstruct the 3D shape of the welding pool surface.The effectiveness and accuracy of the reconstruction of welding pool surfaces were verified by experimental results.This research proposes the development of binocular vision algorithms that can reconstruct the surface of welding pools accurately to realize intelligent welding control systems in the future.

Vision sensing of P-GMAW weld pool using narrow band filters with different center wavelengths

The selection of narrow band filter＇s center wavelength has an important influence on the quality of the weld pool image captured in passive vision mettmd for controlling arc welding process. In this paper, 29 narrow band filters with different center wavelengths ranging from ultraviolet to near infrared wavelength were used to capture images of weld pool during both the peak current period and the base current period of P-GMA W （ pulsed gas metal arc welding）. The experimental results showed that the filters with near infrared center wavelength could weaken the arc most during the peak current period, while during the base current period the entire weld pool could be seen with the filters with wavelength above 600 nm. The camera spectral response and the radio of arc to weld pool emission were considered to analyze the phenomenon of experimental results.

Formation conditions and exploration direction of large natural gas reservoirs in the oil-prone Bohai Bay Basin, East China

The Bohai Bay Basin is a typical oil-prone basin, in which natural gas geological reserves have a small proportion. In this basin, the gas source rock is largely medium-deep lake mudstone with oil-prone type Ⅱ2-Ⅱ1 kerogens, and natural gas preservation conditions are poor due to active late tectonic movements. The formation conditions of large natural gas fields in the Bohai Bay Basin have been elusive. Based on the exploration results of Bohai Bay Basin and comparison with large gas fields in China and abroad, the formation conditions of conventional large-scale natural gas reservoirs in the Bohai Bay Basin were examined from accumulation dynamics, structure and sedimentation. The results show that the formation conditions of conventional large natural gas reservoirs in Bohai Bay Basin mainly include one core element and two key elements. The core factor is the strong sealing of Paleogene "quilt-like" overpressure mudstone. The two key factors include the rapid maturation and high-intensity gas generation of source rock in the late stage and large scale reservoir. On this basis, large-scale nature gas accumulation models in the Bohai Bay Basin have been worked out, including regional overpressure mudstone enriching model, local overpressure mudstone depleting model, sand-rich sedimentary subsag depleting model and late strongly-developed fault depleting model. It is found that Bozhong sag, northern Liaozhong sag and Banqiao sag have favorable conditions for the formation of large-scale natural gas reservoirs, and are worth exploring. The study results have important guidance for exploration of large scale natural gas reservoirs in the Bohai Bay Basin.

Weld pool vision sensing and image processing for GMAW

It is difficult to acquire satisfied weld pool image by CCD sensor during gas metal arc welding（ GMAW） , for arc disturbs violently, welding current is great and working frequency is high. By using CMOS vision sensor to GMA W process, the vivid weld pool image is collected at any time, furthermore, whose gray compression ratio is controllable by sensor hardware circuit developed. Acquired weld pool image is firstly pre-processed by using Wiener filter and Ostu threshold segmentation algorithm. Subsequently separation between weld pool image and cathode mist region is conducted by means of mathematical morphological algorithm, and the edge of weld pool image is extracted by using Prewitt algorithm.

Characteristics of carbonate gas pool and multistage gas pool formation history of Hetianhe gas field, Tarim Basin, Northwest China

Hetianhe is a big carbonate gas field which isfound and demonstrated in the period of 'Chinese NationalNinth 5-Year Plan'. The proved reserve of Hetianhe gas fieldis over 600 ×10~8 m^3. Its main producing layers are Carbon-iferous bioclastic limestone and Ordovician carbonate com-posed of buried hill. The former is stratified gas pool withwater around its side, and the latter is massive gas pool withwater in its bottom. The gases in the gas pools belong to drygases with normal temperature and pressure systems. Basedon the correlation of gas and source rock, the gases aremainly generated from Cambrian source rocks. According tothe researches on source rock and structure evolution, andthe observations on the thin section to reservoir bitumen andthe studies on homogenization temperature of fluid inclu-sions, the gas pool has been identified and divided into threeformation periods. The first is Late Caledonian when the oilgenerated from the Cambrian source rocks and migratedalong faults, as a form of liquid facies into Ordovician carbonate res-ervoir and accumulated there. After that, the crustuplifted, the oil reservoir had been destroyed. The second isLate Hercynian when condensate gases generated from theCambrian source rocks and migrated into Ordovician res-ervoir, as a form of liquid facies. Since the fractures hadreached P strata, so the trap might have a real poor preser-vation condition, and the large-scale gas pool formation hadnot happened. The third gas reservoir formation period oc-curred in Himalaya. The fractures on both sides of Hetianhegas field developed violently under the forces of compression,and thus the present fault horst formed. The dry gases gen-erated from Cambrian source rocks and migrated upwardsas the form of gas facies into Ordovician and Carboniferousreservoirs, and the large gas pool as discovered at presentwas formed finally.

Characteristics of China’s oil and gas pool formation in latest geological history

The structural activities took place extensively in the Asia continent during the Cenozoic era owing to the strong continent-to-continent collision and continuous compression between the India Plate and the Eurasia Plate. Huang Jiqing called such structural activities Himalayan movement. China’s sedimentary basins developed and took shape mainly during the Himalayan movement period. It is also the main period for formation and development of the oil and gas reservoirs. Of 366 large and medium-sized oil and gas fields currently found in China, 212 reservoirs were formed in the Neo- gene-Quaternary period. The proportion is as high as 68.2%. The oil and gas migration and accumu- lation in the latest geological period, which were controlled by the times, properties, styles and strength of the Himalayan movement, took place mainly in eight regions, such as the low uplift area of Bohai Sea, the onshore faulted sag area of Bohai Bay, anticlinorium zone in Daqing, the foreland fold-and-thrust belt in West China, the tilted structural zone in West China, the cratonic palaeohigh in the Tarim Basin, the zone of fault and fold belt in the East Sichuan Basin, and the biological gas zone in the East Qaidam Basin. The oil and gas pool formations in those regions have their own charac- teristics. With the great potential and broad prospect, those regions are the main exploration areas in China in the future.

The generation and accumulation of natural gas from Yinan 2 gas pool in Kuqa Depression

By using the methods of hydrocarbon generation kinetics and carbon isotope kinetics, combined with geological background of natural gas pool formation, the generation and accumulation of natural gas from Yinan 2 gas pool was studied in Kuqa Depression of the Tarim Basin. Natural gas of Yinan 2 gas pool is mainly derived from Middle and Lower Jurassic coal-bearing source rocks, and generally belongs to long time-accumulated gas. It is suggested that Yinan 2 gas is chiefly accumulated in the last 5 Ma, its Ro ranges from 1.25% to 1.95%, and the loss rate of natural gas is about 25%-30%. This work not only complements and reduces the deficiency of formation model of natural gas pools which traditionally depends on the matching relationships between source rock, reservoir, cap rock, and trap, but also is a useful reference in the study of other gas pools.

Petroleum Exploration of Craton Basins in China

Craton basins are a significant petroliferous provenance. Having undergone multiple open- dose tectonic cycles and strong reworking of the late Cenozoic tectonic movement, the craton basins in China are highly broken. This has resulted in multi-source and multiphase hydrocarbon generation and later hydrocarbon accumulation so that a complicated spatial assemblage of primary, paraprimary and secondary oil-gas pools has been formed. The primary factors controlling hydrocarbon accumulation include hydrocarbon-generating depressions, paleouplifts, paleoslopes, unconformity surfaces, paleo-karst, faults and fissure systems as well as the later conservation conditions. In consequence, the strategy of exploration for China＇s craton basins is to identify the effective source rocks, pay attention to the different effects of paleohighs and late reworking, enhance studies of the secondary storage space, attach importance to the exploration of lithologic oil-gas reservoirs and natural gas pools, and approach consciously from the secondary oil pools to the targets near the source rocks. At the same time, a complete system of technologies and techniques must be built up.

CO_2 gas pools from the earth interior in Jiyang Depression

The Jiyang Depression is an intercontinental extensional basin formed on thePaleozoic craton by the interaction among the Eurasia, Kula-Pacific and Indian platessince the Triassic Period. In that depression there are a number of CO2 gas poolsrepresented by the Pingfangwang gas-cap, Pingnan buried hill gas-cap, wells Hua-17,