How to raise the exploiting efficiency for loose sand reservoirs has been an emphasis for natural gas enterprises world\|wide. In course of the exploitation in Sebei gas field comprising Quaternary loose sand reservoirs, there existed problems such as severe sanding, hard sand\|controlling, bypass channeling, and hard water-controlling. New techniques have been developed to adapt the exploitation of loose sand reservoirs in Sebei gas field, including sand-flux monitoring, sand controlling, sand flushing, zonal withdrawal, and production while water pumping. Applications of these new techniques for several years in Sebei gas field suggest the efficiency in exploitation of loose sand reservoirs.
The division of reservoir flow unit is an important method in the development of remaining oil. A block of an oilfield in the eastern China is characterized as the feature of reservoir heterogeneity, complexity of produced layers between wells, difference of integrated water and complex flow zone under function of depositional environment, diagenesis and structural activity. We setup the sub\|consciousness function, based on 7 parameters of formation fluid factor, sandy ratio, permeability, porosity, onrush coefficient, permeability coefficient, and distribution density of mean interlayer. These 7 parameters are selected from 18 candidate parameters to indicate the depositional environment, diagenesis, tectonic factor, rock microscopic pore structure and reservoir physical property. The reservoir flow unit in the study area is divided into three types. We consider that the type Ⅱflow unit has the good potential for the remaining oil development. The reservoir flow unit division is well fitted with the actual development of remaining oil.
Since there is the ambiguity of well test interpretation and no special technique method for the reliability evaluation of interpreted result, we try to use the well test interpretation and core permeability pattern to examine whether or not the integrated result is reasonable. The relational expression between effective permeability and absolute permeability is deduced by the relative permeability of test data. Then the effective permeability is corrected to the absolute permeability by means of the relational expression. Finally, we compare two kinds of permeability to make the accurate judgment for the effective permeability of the well test interpretation.
Volcanic gas reservoir has become one of the main fields of gas prospecting and development in China. Recently, the volcanic gas reservoir has exceeded 3,000 billion m3 in the basins of Songliao, Zhunger and Bohai bay. We discussed the gas seepage characteristic with different water saturations and the variation of movable gas saturation by means of physics simulation and nuclear magnetic resonance experiment. The result indicates that the relation curves between seepage discharge of volcanic gas reservoir rock and pressure gradient would be concave to line, and the Klinkenberg curve be divided into two seepage states by the critical water saturation. When the water saturation is lower than the critical water saturation, there is no gas start-up pressure gradient; and when the water saturation is higher than the critical water saturation, the start-up pressure gradient of gas exist. The higher the water saturation is, the bigger the start-up pressure gradient is, and the lower the movable gas saturation is. We also discuss the occurrence state of water in pores.
In recent years, large scale gas reservoirs have been found in deep volcanic layer of Songliao basin. The volcanic gas reservoir is characterized as extremely complex geological structure, several volcanic bodies reciprocally superposing in different periods, sharp lateral variations of lithology and lithofacies, various thickness, serious anisotropy, poor continuity, and poor contrast property. There is no successful experience about development of volcanic gas reservoir as a worldwide technological problem. The factor controlling gas productivity during process development of volcanic gas reservoir is a puzzled question. According to feature of the volcanic reservoir mentioned above, we interpreted lithologies, lithofacies, physical property of volcanic reservoir, degree of fracture development, pressure-sensitivity of reservoir, drilled well types as well as reservoir pollution, then got the main factor controlling gas productivity. This result will provide some guides for evaluating the gas productivity of volcanic reservoir and determined the schedule for development of gas volcanic reservoir.
Less attention is paid to flow unit in the domestic and foreign reports. With development of gas reservoir, the change of state equilibrium will affect the distribution of the primitive flowing unit, associated with gas pool pressure, reservoir physical property, and fissure. In this paper, based on factorial analysis and cluster analysis, we used the Xu 2 gas layer of Qiongxi as a case to detect the change of the movable flow unit between twice gas samplings and got the mobile unit information from the fluid within the reservoir, in combination with the similar geochemistry of natural gas in one flowing unit. This technological application can provide the geological evidence for the adjustment of gas produced plan and obtain the maximum economic efficiency.
The low permeability petroleum reservoir, which is controlled by depositional environment, is characterized as low permeability and bad connectivity between sand bodies, associated with big resistance of fluid. The petroleum product pattern for the low permeability reservoir is different with normal permeability reservoir, causing the difficult prediction of petroleum production. In this paper, we introduced 5 predicted production patterns (i.e. double log predict, Weibull, Yuqitai, gray system and fluxionary simulation) to predict the petroleum production in the Gao 5 block. The comparative results suggest that the grey system would have an ability to predict the simple change of petroleum product whereas others provide the complex change. But, there is big error of petroleum product production by using of these five patterns. So we developed a linear pattern of petroleum production prediction that can provide the better prediction of petroleum production.
More than 90% oil and gas reservoirs in the Middle and Upper Ordovician of Tazhong Slope-Break Zone-Ⅰ are related to fractures. The fractures in Ordovician of Tazhong are divided into 2 kinds (diagenesis fractures and structural fractures), including 17 types, by the cross-cutting relation of fractures and features of hydrocarbon inclusions in fracture filler. The structural fractures can be divided into three periods by chronological order of the fracture formation. The features of hydrocarbon inclusions in the vein calcite suggest four periods of hydrocarbon inclusions. Results of carbon, oxygen and strontium isotopes experiments on vein calcites with various hydrocarbon inclusions suggest that the vein calcites were filled in the anadiagenetic stage. Vein calcites containing Ⅰ-OL and Ⅲ-OLG were mixed by the deep Cambrian remelted strontium, whereas vein calcites containing Ⅱ-OL and Ⅳ\|OLG were controlled by the remelted strontium of Ordovician surrounding bed. In the Late Caledonian-Early Hercynian，hydrocarbon sourced from Cambrian source rocks of Tazhong Slope-Break Zone-Ⅰ migrated upwards through the Middle-Upper Ordovician limestone, but didn′t accumulate. In the Late Hercynian, hydrocarbon sourced from the Lower-Middle Ordovician source rocks of Manjiaer depression migrated to carbonate reservoirs of the Middle-Upper Ordovician and accumulated. The contemporaneous hydrocarbon sourced from the Lower Cambrian migrated to the Middle-Upper Ordovician carbonate reservoirs. Ⅳ-OLG formed in Himalayan was familiar in wells of TZ26、TZ24 and TZ62, but not in wells of northwest Tazhong Slope-Break Zone-Ⅰ. Hydrocarbon might migrate from northwest to southeast and formed present hydrocarbon reservoirs. Ⅲ-OLG and Ⅳ-OLG were crucial for huge petroleum accumulation.
Based on data of micro-thin section , scanning electron microscope and image analysis , the porosity evolution of low permeability glutenite body as the deep gas reservoir in the northern slope of Dongying depression was quantitatively described by quantitative inversion , in combination with temperature and depth of reservoir. According to type of reservoir space and feature of pore, the reservoirs were dividedintthree types , i .e. secondary denudation pore type , coexistence type of secondary pore and primary remain pore , and micro-fissure type .Based on effect of physical properties of reservoir , two types of digenesis were classified as const ructive diagenesis (i .e .undercompaction , dissolution , recrystal lization) and destructive one (compaction , bitumen filled and cementation deposit). Then , we use the diagenesis intensity to quantitatively describe the controlling action of diagenesis to the porosity evolution of three types of reservoir. TheⅠtype reservoir was mainly affected by aciddissolution .The Ⅱ type reservoir retained a certain amount of primary porosity due to gypsum-saltlayero verlying .The Ⅲ type was almost not dissolved by later acid solution , because the early strong compaction existed so that the acid water can not come in .
Since the number of rock samples and quality of core constrain the conventional geochemical measurement and hydrocarbon-generated evaluation for source rock, it is difficult to reveal the real spatial distribution of source rock. The logging method associated with the geochemical analysis can carry out the prediction of total organic carbon TOCof source rock and spatial distribution by mean of the high vertical resolution log data. Based on relationship between TOCand hydrogen index IH, the lacustrine source rock in the Jizhong depression can be divided into three class as follows: High quality source rock with TOC>2%, good source rock with TOC=1%-2%, and poor source rock with TOC=0.5%-1%, respectively. The lateral and vertical distribution of paelocene lacustrine source rock was controlled by depositional facies, and the high quality source rock mainly was developed in the depositional center. From the margin to the basinal center, the thickness of the high quality source rock is various from thin to thick. According to evaluation of logging data, distribution and prospect of potential resource, the future favorable exploration area should focus on the buried hill, Paleocene deep lithological layer, shallow and middle complex fault-block structure in the Raoyang sag.
A lot of evidences of oil and gas was discovered, some of them getting the commercial oil and gas flow, suggesting the good petroleum exploration in the Shahejie volcanic rock body.But, the volcanic rock has the complex lithology associated with different types.The depositional facies is mainly composed of extrusion, effusive, outpour and volcanogenic facies, the intrusive faices exists in partial location.In the multiphase volcanic activities, the lithology, facies of volcanic rock and types of volcanic reservoir and pore structure is different for every activity.The almond body hole and grain dissolved pore is the main accumulated space in the volcanic reservoir.And the volcanic reservoir manly distributed in effusive face and outpour face.The fissure is not only the hub between the fissure and pore, pore and pore, fissure and fissure, but also the main reservoir space.The main factor of volcanic reservoir development is tectonic action, weathering and leaching, thermal fluid activity.
The quantitative analysis of point-bar′s inner architecture is essentially computation of lateral mudstone′s attitude and lateral accretion body′s scale. Based on recognition criteria of lateral mudstone on log map, three computing methods are used to quantitatively describe the attitude and the scale. The methods are diplog, twin wells and the horizontal well. The diplog show the attitude directly. And the twin wells can provide the real inclination of mudstone with calculation on well′s data by work of sublayer top laping and angular transformation. The third method is based on the horizontal well, and the attitude is calculated by a formula composed of some horizontal well′s parameters, such as radius of well hole, the hole deviation angle, the stratum dip and the length of mudstone. The length can be obtained by analysis of GR log curve, which is very sensitive to the shale bulk volume. Based on the data of attitude and scale, the architecture elements of point-bar can be quantitatively described. On the analysis of relationship between lateral mudstone and remaining oil, then the enrich zone of remaining oil is forecasted and the corresponding development plan will be carried out.
The research of the complex distribution of gas and water in the upper Triassic Xujiahe Formation of central Sichuan basin is important to the effective development of gas reservoir. Based on gas testing data, logging response and water saturation calculation for more than 80 wells in the 15 gas pools, we successfully used the high definition induction logging and movable water saturation to identify the gas or water layer. According to distribution gas and water of single well and cross section, we considered that there were many vertical gas-water systems in the Xujiahe Formation of central Sichuan basin, the movable water saturation gradually increased from top to bottom in a single gas-water system, suggesting gas accumulated at top and water did at bottom. Three gas-water distributed patterns are followed as: lithological pattern in T3x2 of Hechuan area, fractura-|lithological pattern in T3x4 of Chongxi area, and structura-|lithological pattern in T3x6 of Guang′an area, respectively. In combination with geological background, the distribution of gas and water in the Xujiahe Formation of central Sichuan basin was controlled by high-quality reservoir, including to connectivity of sand bodies, fracture and structure.
The pore texture feature in clastic reservoir is not only a hot topic of the oil and gas exploration and development, but also an important task of fine description of gas reservoir and comprehensive reservoir evaluation. By technical tools such as cast thin section, scanning electron microscope, cast image analysis, high-pressure mercury injection and constant velocity mercury injection, etc, we discussed the pore types, pore combinations and pore textures in the upper Triassic Xujiahe Formation clastic reservoirs in the central part of Sichuan basin. There are six kinds of pores, i.e. remainder intergranular pore, dissolved pores between grains, dissolved pores in grains, mould pore, intracrystalline pore and micro-fissure. The pore structure can be classified for types, such as Ⅰ type of bold skewness double peaking\|large pore with medium-large throat, Ⅱ type of middle skewness double peaking-middle pore with small-middle throat, Ⅲ type of gentle skewness double peaking-small-middle pore with small throat, and Ⅳ type of single peak\small pore with micro throat. The four types of pore structure corresponded to remainder intergranular pore-dissolved pores between grains type, dissolved pores between grains-dissolved pores in grains type, dissolved pores in grains-mould pore type, and microporetype, respectively. Ⅰ and Ⅱ types located in the favorable structure area as middle-high producing petroleum layer are beneficially accumulated for the oil and gas．
In this paper, we proposed the structural trap recovery by mean of denudation value. By recovery of denudation value on the main unconformities caused by tectonic movements, we can identify the paleogeomorphology of the region and integrate the formation and evolution process of the structural trap. In the middle section of west Sichuan depression, there are three main unconformities of the upper Triassic Xujiahe Formation layer. The results of denudation value recovery suggest that the structural traps of Xiaoquan-Xinchang, Hexingchang and Dayi in the Xujiahe Formation layer were formed at the Anxian tectonic movement, the structural traps of Yazihe, Majing and Luodai were formed at the late Indo-Chinese movement. All of these structural traps were activated and uplifted during the Himalayan movement, associated with the formation of Shiquanchang and Fenggu structural traps. Based on these structural traps and preservation conditions, four types of the region were divided.
By the observation of core and analysis of microscopic flakes and scanning electron microscope, the feature of the Carboniferous volcanic rocks in the Luxi district of Junggar basin was discussed, including volcanic lithology, pore type, oil and gas evidence, and diagenesis. The lithology of main volcanic reservoir in the study area is dominated by volcanic lava (basalt and andesite) and pyroclastic rocks (tuff and volcanic breccia). The pore type is dissolution pore and the secondary dissolution. The volcanic lava has a good oil and gas evidence.The volcanic reservoir become a good stored body only after weathering and leaching, fracture and dissolved reformation later. The laumontite filling in the study area would make a positive role of the formation of high quality reservoir. Finally, the pattern of porosity evolution for different types of volcanic rocks was setup.
Based on integration of thin section, X-ray diffraction analysis, scanning electron microscopy, cathodolumi-nescence and mercury injection, we found out that the Permian reservoir under the Kebai fault in the northwestern margin, Junggar basin was formed in the alluvial fan and fan-delta facies. They were comprised of sandy glutenite, glutenite, and pebbled sandstone. During the diagenesis, the rock assemblages went through compaction, cementation and corrosion. The types of the reservoir pore are primary intergranular pore, intracrystalline pore, carbonate cement and zeolite dissolution pore, and micro fractures formed under tectonic action. The reservoir is in the stage B of late diagenesis, most primary pores were destructed after the diagenetic evolution and the secondary pores were mainly formed. Therefore, the diagenesis would control the physical properties of reservoir in this area. Porosity evolution greatly experienced the three phases, including destruction of primary pores, formation of secondary pores and destruction of secondary pores.
Types of petroleum reservoir as a basic and important work are scientifically and practically classified so as to guide the petroleum exploration and development. The classification of reservoir need display the stage and connection between exploration and development. The different stages of exploration and development would focus on the different objects, such as sedimentary and reservoir characteristics, trap type and accumulation, etc. during exploration phase; and reservoir parameter, fluid physical property, percolation and temperature/pressure, etc. during development phase. The feature above is one of references of petroleum reservoir classification at different stages of exploration and development. Therefore, we point out the multi\|elemental and comprehensive classification in order to offer convenient service for petroleum exploration and development. As a case of Santanghu basin, we use the multi-elemental and comprehensive classification of reservoir to classify reservoir types in the Santanghu basin, and discuss the significances of the classification in the petroleum exploration and development.
Based on drill core, logging, hole logging and seismic data, we discerned 8 types of sedimentary facies, such as alluvial fan and fan delta etc. and grouped 4 types of depositional system, including alluvial fan system, river\|delta system, underwater fan-fan delta system, lake-density flow system. The Shiwu rift subsidence was alluvial fan system at early phase. But at the period of Shahezi to Quantou, the depositional system type changed from alluvial fan system to underwater fan-fan delta system in the west fracture belt and the north steep slope belt, and from lake facies to braid delta-river faices in the southeast slow slope belt, and there is multiform sedimentary types in the middle part.
Materials (logging, seismic, core and etc.) are used to reconstruct the paleogeomorphology before the Jurassic deposition by the impression method (the total thickness of Yan 9 Member, Yan10 Member of Yanchang Formation and Fuxian Formation) in Ziwuling area, which shows diverse paleogeomorphic patterns, including high, slope, gully, szyrt and river valley. Based on the relationships between the paleogeomorphology and the formations of Yan 10, Yan 9, Yan 8 reservoirs, it can be inferred that reservoirs are mainly distributed in the slope near high and other relatively high zone. Favorable conditions for petroleum accumulation include the upward migration pathway of hydrocarbon from source rock of Yanchang Formation via the incised valley, the type and distribution size of reservoir sand bodies controlled by the slope, and the relatively high zone of later structural trap formed by differential compaction caused by slope mouth, beam between gullies, and monadnock.
Based on casting thin section, cathodoluminescence, scanning electron microscope, we discuss the lithological feature, petrophysical property and diagenesis of sandstone in the Chang 8 oil layer of Jiyuan area of Ordos basin. The research results show that the reservoir rock consists of feldspathic lithic sandstone and lithic feldspathic sandstone, with low compositional maturity and textural maturity, and average value of Q1/(F1+R1) less than 0.8. The dissolution of feldspar in the reservoir rock was happened under diagenetic fluid and atmospheric water action. There is a lot of clay mineral, authigenic quartz and calcite in the dissolved feldspar brim and developed pores. The feldspar dissolved matters give an influence to reservoir physical property, where the self-kaolinite and authigenic quartz give a positive role to the pore formation and protection of, whereas the carbonate and authigenic illite play a negative action to it.
Stress sensitivity exists in oil-gas reservoir. There is a lot of report about stress sensitivity in porous and fractured reservoirs while less attention is paid to stress sensitivity in the fractured-vuggy reservoir. The fractured-Vuggy carbonate reservoir of Tahe oilfield as a case was subjected to simulate stress sensitivity experiment by choosing natural fractured, artificial fractured, single-cavity and double-cavity core samples. Experimental results from 12 rock samples of 4 groups show that stress-sensitive coefficients of the natural fractured, artificial fractured, single cavity, and double cavity core are 0.64, 0.75, 0.58 and 0.61 respectively, corresponding to the stress-sensitive degree changed from med\|strong,strong,med-strong, and med-strong, respectively. After 60h of samples download, the final return permeability rate of rock samples is 69.84%, 4.36%, 11.86% and 38.75%, respectively. Thus, the existence of cavity would weak the stress\|sensitive degree of fractured reservoir, and the development of cavity also increases the hardness of controlling drill-in fluid loss damage.
Qiongdongnan basin is a Cenozoic petroliferous basin. In this paper, according to analysis of main controlling factors on regional tectonic evolution in the Qiongdongnan basin( i.e. spreading of the South China Sea, Red River Rift, the Pacific plate, etc.), in combination with features of the internal sequences and faults in the Qiongdongnan basin, the tectonic evolution of Qiongdongnan basin in Cenozoic Era can be divided into three stages: Tectonic evolution of multiphase rifting stage from late Cretaceous to late Oligocene, thermal subsidence stage from early to mid-Miocene Epoch, and new tectonic stage in late Miocene Epoch. Based on the tectonic evolution of Qiongdongnan basin, we discuss the correlated function of tectonic evolution to formation of source rocks, reservoirs, cap rocks and traps, an then point out that the structurally adjusted middle area in the Qiongdongnan basin (i.e. Yabei sag, Songxi sag, Lingshui low uplift, Songtao salient, Lingshui sag, Songnan sag, central low uplift, Beijiao sag) would be the profitability of oil and gas accumulation, which is possible to achieve a breakthrough for the future exploration of oil and gas in the Qiongdongnan basin.
The south Qinshui basin is one of the most hot areas in the coalbed methane (CBM) exploitation and the first commercial exploitation of CBM in China. No 3 and No 15 coal seams is the developed seam of CBM, with gas production of 2 000~5 000 m3/d for single well. The permeability is generally about 1.0×10-3μm2 by input or drawdown test. Base on data of CBM production in different blocks, the permeability of coal seam is amended by historical matching of numerical simulation. The amended permeability is in range of (0.47~3.95)×10-3μm2, which is about 6.76 times than that of well test. The positive relationship between CBM production and amended permeability of coal seam exists. The permeability of coal seam in the south of Qinshui basin is high, especially at the Panzhuang and Duanshi areas.
The original permeability, fracturing and reconstructing permeability, surrounding permeability affect the pressure spread contrail in the production process of the CBM vertical wells, and then control the productivity of CBM vertical wells. Based on the raw data of exploration and development of CMB in the Encun mine field, we classified the coal structure into the primary structure coal (Ⅰ), fragmentation coal (Ⅱ) and tectonic coal (Ⅲ and Ⅳ), in combination of curve of logging response and drilling core. According to elasticity theory of rock and state of natural fracture in different coal structures, we set up a model about the azimuth of natural fracture and the direction of the stress, and discussed the main controlling factors about main fractures in different coal structures. Based on azimuth of extended fracture and pressure spread contrail in the production process of CBM vertical wells, we got the relations between the productivity of CBM vertical wells and different coal structures. The production tests showed that under current hydraulic fracturing crafts the fragmentation coal would be the best coal reservoir, then primary structure coal, and the tectonic coal was hardly modified to improve production capacity of CBM vertical wells.
According to physical heterogeneity of coal seam as gas reservoir and type of coalbed gas reservoir, we discuss the relationship between types of coalbed gas reservoir and gas productivity, and find out that the CBM well with high gas productivity (>3 000 m3/d) is distributed in the high permeability coalbed methane reservoir; the well with middle gas productivity (1 500~3 000 m3/d) is in the high saturation and low permeability coalbed methane reservoir. But two types of coalbed reservoirs with high permeability and low saturation, and low permeability and high saturation, respectively, are restricted by permeability and gas content, with low gas productivity.
In view of stress sensitiveness to coalbed methane reservoir, we made the stress sensitiveness experiments of dry and moisture drill cores collected from the coalbed methane reservoir by means of change of peripheral pressure and pore pressure. The experimental data of stree sensitiveness were fitted to obtain the deduced equation of permeability with active pressure after the rock deformation of coalbed methane reservoir was mearured. The results indicated that the existence of water would make the stress sensitiveness of the drill core become stronger. The pattern described by exponential function would offere the experimential reference to the effective and rational development of the coalbed methane.
Gas hydrate formation in well hole will block up oil pipes so as to affect normal production. By reference of documents, we conclude the formation conditions of gas hydrate in gas well hole, controlling factors as well as prediction methods. Based on temperature and pressure in gas wells and simplified Newton thermodynamics prediction methods of gas hydrate formation, we set up a prediction model of gas hydrate formation, and compiled the software to calculate gas hydrate formation in two cases. The calculated results suggested that the model would be a preferable prediction of gas hydrate formation.
Gas hydrate has important research significances in future energy, natural environment and disaster. The thickness of gas hydrate stability zone (GHSZ) shows the possible range of hydrate development and distribution. It is greatly related with geothermal gradient, sea bottom temperature and water depth. Based on hydrate phase equilibrium formula of Dickens and Quinby, we quantitatively calculated the thickness of GHSZ in different conditions of geothermal gradient, water depth and sea bottom temperature. When the two parameters in three parameters are assumed unchanged, the thickness of GHSZ decreases with the increase of geothermal gradient regularly, the thickness of GHSZ increase with water depth, and the thickness of GHSZ decrease with increasing of sea bottom temperature as a good liner relationship. If the temperature of the sea bottom is a constant, the thickness of GHSZ will increase gradually from the regions with the larger geothermal gradient and shallower water depth to the smaller geothermal gradient and deeper water depth. If the water depth is unchanged, the thickness of GHSZ will increase gradually from the region with the larger geothermal gradient and higher sea bottom temperature to the smaller geothermal gradient and lower temperature. In addition, we also discussed the differences among the three hydrate phase equilibrium formulas for calculating the thickness of GHSZ. The maximize result of GHSZ thickness was gotten by Dickens-Quinby′s phase equilibrium formula gets, and the smaller values was done by the two others.
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