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.

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.

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.

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 Models and Distribution of Oil and Gas Pools in Tarim Basin, China

This article reports the main formation models and distribution of the oil and gas pools in Tarim basin, China, including （1） occurrence of the found oil and gas pools, （2） main formation models of oil and gas pools, and （3） distribution law of oil/gas pools. Petroleum is distributed widely in the strata of Tarim basin from the Sinian at the bottom to the Neogene at the top. However, the found oil and gas fields are mainly distributed in Shaya （沙雅） uplift, Tazhong （塔中） uplift, and Kuche （库车） depression. This article presents 4 main formation models, namely, early formation and long-term preservation, early formation and late reformation, middle-late multiphase-multisource formation, late single-stage formation. Tarim basin is very rich in petroleum resources. Long-term inherited intrabasinal paleohighs and slope zones are the most favorable areas for accumulation of hydrocarbons, but the types of oil and gas pools are different from area to area. The control of unconformities and faults on hydrocarbon accumulating is prominent in Tarim basin. Preservation conditions are of utmost importance. Formation of some oil and gas pools is the result of reforming and re-accumulating of early accumulated hydrocarbons.

Origin and distribution of carbon dioxide gas pools in eastern China

Carbon dioxide gas pools occur widely in the basins of eastern China.CO_2 gas-bearing beds are from the Teritary to Ordovician,and reservoirs are sandstone,carbonates and volcanics.The gases from these gas pools contain CO_2 of 62.86 ‰ —99.55 ‰.In the Mesozoic-Cenozoic extensional basins,such as Songliao,Bohai Bay,Subei,Sanshui and Zhujingkou,the δ^(13)C_(CO_2)values of CO_2 gas pools range from-2.65‰ to-8.83‰,mainly from-3.5‰ to-6.0‰,~3He/~4He ratios are 2.65R_a to 4.96R_a.The regression equa- tion of CO_2 content and helium isotope ratio is CO_2(%)=61.3852+7.9745R/R_a,correlation coefficient r is 0.9430,CO_2 is mainly mantle-derived and magmatic origin.δ^(13)C_(CO_2)value of CO_2 gas from Well X in Yinggehai Basin is-3.80‰.~3He/~4He ratio is 0.07R_a,CO_2 is metamorphic origin.Mantle-derived and magmatic CO_2 gases are discharged from the cross areas of northeastern trending and northwestern trending faults in these Mesozoic-Cenozoic extensional basins,in the shallow level,the CO_2 gases migrate and accumulate along northeastern trending extensional faults.The activity of the Neogene to Quaternary northwestern trending tectonic-magmatism zones in eastern China is another important discharge event for mantle-derived and magmatic gases,which have great contribution to the CO_2 gas pools in this area.Metamorphic CO_2 in the Yinggehai Basin is released by the dynamic metamorphism of shear fractures.

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.

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.

Numerical simulation of influence of nozzle structure on arc characteristics of GPCA-TIG welding

This work mainly articulated the effects of nozzle structure on arc characteristics in gas pool coupled activating TIG （GPCA-TIG） welding process by using Fluent Software. Different models were set up to adapt the different torch structure during computer progress. The specific configuration of the welding torch made the gas flow in outer gas passage constrained. The nozzle structure has great influence on outer gas distribution because of the changing of coupling region between the outer active gas and molten pool surface. When the coupling degree is reduced or the outer gas passage become smaller, the oxygen in outer gas penetrates into the arc plasma and spreads to the arc region more easily. Owing to its cooling effects, the morphology of arc is contracted, and the arc temperature is increased. When the inner wall and the outer wall of outer gas passage are not parallel, the wide top and narrow bottom nozzle shape can bring more oxygen into the arc plasma, the arc is contracted and the peak temperature of arc rises a little more comparing to the narrow top and wide bottom one.

A Study of Thin Sandstone Reservoirs by High-resolution Seismic Inversion

In this paper seismic inversion was used as a key technique and the seismic wavelet most suitable to the actual underground situation was extracted with the higher-order statistics algorithm. The wavelets extracted in this way and the wavelets extracted with the seismic statistics techniques were used separately for inverting the seismic data of the southern part of Tahe oilfield, Tarim basin. The results showed that the resolution of the wavelet inversion with the higher-order statistics method was greatly improved, and the wavelet-inverted section could better distinguish the thin sandstone reservoirs of the upper and lower Carboniferous and their lateral distribution, providing a reliable basis of analysis for the study of thin sandstone reservoirs.

Magmatic Network Structure of Volcanic Rocks in the Shengli Oilfield, Eastern China

Abstract: Types of polymerized molecular network structure and degree of bond breakdown for glass phases of magmatic inclusions and glassy matrix in volcanic rocks from the Shengli oilfield have been defined by the laser Raman spectroscopic investigation. There are significant differences in types of polymerized molecular network structure and degree of bond breakdown of the magmatic glass phases between the non-CO2 and CO2 gas pools: magmatic glass phases of fluid inclusions and matrix in volcanic rocks from the CO2 gas pool contain more sheet network molecules and have a greater degree of bond beakdown than those from the non-CO2 gas pool; and when gas bubbles occur in evolving magma, magma saturated with volatile components has more sheet network molecules. The results suggest the magmadegassing mechanism of the formation of CO2 gas pools in the Shengli oilfield.