In the dissolved gas studying, the abundance is very important meaning. If reserve is used in the calculation, the abundance value would be deviated greatly, even the dissolved gas remaining recoverable reserves and the abundance show negative if the recovery efficiency is not high. Using the cumulative production of oil and dissolved gas abundances accrued from year to year could eliminate the impact of specific situations, thus allow the dissolved gas abundance more representative. The abundance values of Chinese regions show that that of the northwest area is the highest, the sea area the lowest, and great basins are generally higher than the adjacent smaller basins. However, in the same basin, the abundance values of different units in different fields, or of the same oil (field) exploration and development in different time, may be different considerably, indicating the controlling factors to the abundance of dissolved gas is complex. Generally speaking, the oil dissolved gas abundance is related to the gas-rich regions and also effects to its preservation directly. At present, the research on the dissolved gas in China is still quite weak, but using the dissolved gas has great potential，therefore we recommend appropriate strategies to promote its utilization.
The distribution, the status of exploration and exploitation as well as the reservoir geological characteristics and formation mechanism of low-permeability oil and gas resources were systematically investigated. The main affecting factors of the low\|permeability oil and gas resources are as follows: not easy to identify oil and gas reservoirs, difficult identification of oil and gas layer, low permeability, starting pressure gradient, small elastic energy, slow effectiveness of water injection wells, significant decrease in liquid water production index after water breakthrough, serious water channeling and flooding. Multi\|parameter joint inversion of reservoir prediction technology, fracturing technology, well optimization technologies, advanced water technology, horizontal wells technology, CO2 miscible flooding techniques, microbial enhanced oil recovery technology are special technologies for exploration and exploitation of low\|permeability oil and gas resources.
The characteristics and the research advances of the chemical components and carbon-hydrogen isotope compositions of known abiogenic gas seepages and the deep gas in the Songliao basin are reviewed, combined with our Feisch-Tropsch synthesis in a close-system. The abiogenic gas and the deep gas in the Songliao basin are reexamined in this paper. Attentions should be drawn to the chemical components and the experimental condition. It is suggested that the thermodynamics, thermodynamic equilibrium, post-genetic processes be focused on in the future. Moreover, an integrated study on the deep gas in the Songliao basin needs to be performed to investigate the origin of the deep gas.
Tarim Basin was a typical superimposed basin with large amount of oil and gas, and lots of hydrocarbon accumulations have been discovered in recent years. As a result of complex hydrocarbon accumulation and transformation of the basin, the studies on its hydrocarbon accumulation are of great challenge. At present, there are some disputes on its oil sources, reservoir forming stages and process. To meet the need of present exploration, the conference was held in Lanzhou, July 2009, with the subject of “Complex Oil and Gas Pool Formation, Adjustment and Reaccumulation Mechanism of the Typical Superimposed Basins in the West of China”. In the conference, the scholars have discussed the present research situations and open questions of hydrocarbon accumulation of the Tarim basin, and finally reached the agreements as the following: (1)Correct understanding of oil and gas source was important for resource assessment, the marine oil and gas are mainly from the Cambrian and Ordovician source rocks in the Tarim basin, and the “mixed source oil” was obvious, and the Middle Upper Ordovician source rocks do a greater contribution to the hydrocarbon accumulation. (2)Hydrocarbon accumulation periods are generally related to those significant structural changes. In the Caledonian, the Cambrian source rocks generated and expulsed a large amount of hydrocarbons; in the early Hercynian, the reservoirs were destructed and the Silurian asphaltic sands were formed because of uplifting and exposing; large amount of oil was filled into reservoirs in the late Hercynian and natural gas in the late Himalayan. (3)To study dynamically on hydrocarbon accumulation processes, it is necessary to restore the ancient structures of important pool\|forming periods, and consider the effect of geological events. Only based on comprehensive analysis of some typical reservoirs, the distribution of oil gas could be summarized.
According to the compositions, carbon homolog isotope and light hydrocarbon parameters of natural gas in the Gubei buried hill of Jiyang depression, we conclude that the coal formed gases are mainly from Carboniferous Permian coal measures as the source rock, and the Mesozoic coal measures do some part of contribution. Furthermore, the coal formed gases are mainly preserved in the fourth row of buried hills, as well as the north of second and third rows of buried hills which are far away from the Gubei fault. After identification of the coal formed gases' source, homogenization temperature of the fluid inclusion, as well as hydrocarbon generation kinetics, history of hydrocarbon generation and sedimentation of the source rocks, the conclusion is that there are four periods in hydrocarbon generation of Carboniferous Permian source rocks, among which the Yanshan perio d and Xishan period are the main periods, and the late Xishan period is the main period for the Mesozoic hydrocarbon source rocks. Also, there are two types of coal-formed gas pools in this area, one is the secondary gas pool formed after the primary pool of Carboniferous Permian system, which is destroyed during the Xishan period, the other is that after the secondary hydrocarbon generation of the deep Carboniferous-Permian and Mesozoic coal measure source rocks in the later Tertiary period, among which the second type will be favorable in the natural gas exploration in this area.
The formation time and stage of the deep gas reservoirs in the Bonan and Gubei Areas of Jiyang Depression are ascertained by a set of analysis techniques, including the hydrocarbon generation history, fluid inclusion homogenization temperature, light hydrocarbon characteristic and structure movement analysis. Two periods of different original gas charging are established in the Gubei buried hill belt, coal-formed gas charging in late stage of Ng and oil-formed gas charging in middle stage of Nm. At the same time, there are two accumulation periods which include from late stage of Es1 to late stage of Ed and from the stage of Nm to nowadays in oil-associated gas reservoirs in Bonan sub-sag, the late stage accumulation plays an important part. There are different periods at different structure location and strata. The formation period of gas reservoir at downstructure location is earlier than that of gas pool at upstructure location.
Huanghua Depression, which is located in north-central Bohai Bay basin, belongs to North China basin in structure. It has experienced five tectonic movement stages of Caledonian, Hercynian, Indo-Chinanian, Yanshanian and Himalayanian, and developed four periods of basin-forming function, which are mutually superimposed and reformed in the longitudinal direction. The hydrocarbon rocks in the deep region have experienced evolution process of shallow deposit in early and middle periods and deep deposit in late period, and have a great potential of secondary hydrocarbon generation. Pool-forming types posses a variety of combination characteristics, containing paleo-storage of neogeneration, paleo-storage of paleo-generation, meso-storage of paleo generation, meso storage of neo-generation and so on. This study shows that the region has great potential of deep resources, and exploitation directions are proposed as paleo-storage of neogeneration in buried hills, meso storage of neo-gation in buried hills of central uplift belt, primary reservoir of paleo-storage of paleo generation.
Based on the analysis of rock slides, casting slides, scan electron microscope and X\|ray diffraction etc, the characteristics of diagenetic evolution of clastic sandstone in Quan 4 Formation at Longxi region, Songliao basin are studied. The diagenesis in Quan 4 Formation is in the mesogenetic stage, and is subdivided as A1 and A2 stages. Four types of diagenesis are recognized, including compaction, cementation, dissolution and metasomatism. The compaction and cementation destroy the primary pore structure intensively, and dissolution betters the pore structure effectively. Secondary porosity zones are developed in 1600~2000 meters.
The Tazhong paleo uplift is a multiple oil gas accumulation play, and medium large scale reservoirs have been found in the Carboniferous, Silurian, Ordovician and Cambrian Systems. The achievements in oil-gas exploration and exploitation and the researches on its petroleum geology show that large scale reef flat deposit of Tazhong No.1 slope-break zone, large weathering crust of the karst reservoir are the most important exploration areas for large and oversize oil-gas fields. First, the inherited paleo uplift is the foundation of oil-gas migration and accumulation; Second, multiple charging sites and multistage pump type charging are the key factors for wide distribution and local enrichment of oil and gas in marine carbonate reservoirs of the Tazhong area; Third, multiple pore-cave fracture carbonate reservoirs of high quality are the preconditions for large scale unconventional condensate oil gas fields. In a word, the Upper Ordovician reef flat deposit and the Lower Ordovician weathering crust karst reservoir are important exploration areas, where oil and gas are widely distributed in lateral and vertical directions.
Because of the great change in thickness of the overlying gyprock and the high density drilling fluid in Kuqa depression, it is very difficult to define the boundary stratotype. TDC are used in exploration wells and the temperature at the bottom of well can be measured continuously and the natural gas reservoirs of Eogene-Cretaceous are high pressure reservoirs. Based on this situation and according to the cause and feature of the abnormal high temperature in the natural gas reservoir, we inspected the formation temperature continuously and predicted correctly the change of the formation, defined the boundary stratotype, found the trace of gas and solved the difficulty in work.
According to the systematically testing solid bitumen content of the Lower Paleozoic source rock and reservoir in Tadong, the eastern Tarim basin, we have estimated the cracked gas resources in the paper. On the whole, the Lower Paleozoic source rock has a tremendous hydrocarbon generating potential and generates a great deal of crude oil at one time in Tadong. At the blocks, the solid bitumen content per unit area increases from west to east. In horizons, the solid bitumen is much more in the Middle Cambrian source rock than that in any others. With respect to the stages, the early solid bitumen is more than that in late one. In accumulating position (in reservoir or in source rock), most of solid bitumen, 87%, rests on the source rock, only 13% of them in the reservoir. The amount of solid bitumen content, cracked gas and cracking gas resource are closely interrelated, and their distributing characters are the same with that of solid bitumen. Choosing a sound accumulation coefficient, the Lower Paleozoic cracking gas resource in Tadong is about (2.18~4.37)×1012m3. That is to say, the exploration potential for natural gas is great in the Lower Paleozoic rocks in Tadong.
Low permeability hydrocarbon reservoirs in the Shanle area have two secondary pore zones vertically: Middle Xinshanyao Formation and Sangonghe Formation oil layers. In the secondary pore zones, potassium feldspar is corroded intensely; authigenic kaolinites are well developed with more than 25% relative content and occur as book and vermicular kaolinites between the skeletal grains. The well developed authigenic kaolinites need the diagenetic environment which is an open or half-open flow system. This was also favorable for hydrocarbon accumulation. According to the characteristics of diagenesis and pore evolution, the reservior of Middle Xinshanyao Formation can be divided into three diagenetic facies. We evaluated the development of secondary porosity in condition of mutual action of different diagenesis. Besides, depositional condition controls original physical properties of sand, and fractures generated by late tectonization improves the physical properties, all of them control the enrichment of hydrocarbon in this area. These factors are oil storage mechanism of anticlinal reservior in Xinshanyao Formation of Shanle area.
There are rich sources of CO2 in the marginal basins in the northern of the South China Sea. The genetic types are crustal original, crustal-mantle original，and volcano-mantle original one, due to geologic conditions and controlling factors. The different geologic conditions and controlling factors to the accumulation and migration of CO2 and oil gas among different areas result from the different geological settings and characteristics. Crustal original and crustal\|mantle original type are located at the Yinggehai basin of the northwest margin and controlled by the diapirs up-invasion and thick marine calcic sand shales. Volcano-mantle original type is most located at the Qiongdongnan basin of the northeast margin and the Pear River Delta. Furthermore, the accumulation and migration of CO2 and oil gas of these types of CO2 are controlled by the exhaustion of mantle magma and the transportation of discordogenic faults.
On the basis of the analysis of natural gas geological factors of Upper Tertiary Xujiahe Formation in the middle part of West Sichuan Depression, the gas resources are calculated by reservoir volumetric method. The research results show that the reservoir formation conditions are superior and there are rich gas resources. The Xujiahe Formation has good hydrocarbon\|generating conditions, its source rock is characterized by big thickness, wide distribution, high organic matter abundance, good quality and large gas generating amount. The reservoir rock has low porosity and low permeability and obvious heterogeneity. The sandstone reservoirs mainly lie in the second and the fourth members of Xujiahe Formation, their direct regional caprocks are the third and fifth members of mud shale, respectively and they have wide distribution, big thickness and stable lithology. Trap is abundant and its type is varied in the Xujiahe Formation. There is a good association of source, reservoir and cap rocks. The natural gas resource of Xujiahe Formation in the middle part of west Sichuan depression is 5431.2 hundred million cubic meters. There is material base for forming large to middle gas fields and there are great exploring prospects. The east and west sections of the almost latitudinal direction uplift from Mianzhu to Yanting, the regional slope of the Longmen mountain front and the gentle slope of the east part of the depression are the favourable zones for oil and gas migrating and accumulating.
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The Ma 6 member of the Early Ordovician Majiagou formation distributes broadly along the southern margin of Ordos basin, its thickness increases gradually from north to south, and its rocks mainly of algal limestone, patchy limestone, powder crystal dolomite and grained dolomite. Based on the tectonic setting of the southern margin of the Early Ordovician North China platform, the sedimentary environments and sedimentary patterns of the Majiagou Formation are analyzed. The reservoir-forming factors and their space arrangement are researched using the outcrop data, downhole core data and lithologic combination features. The result shows that reef flat facies deposition is developed in some parts of the Majiagou Formation and they form dolomite reservoirs through later diagenesis and dolomitisation. These dolomite reservoirs and the neighboring muddy intervals form reservoir-forming combination of up generation and down storage, and have a exploration potential.
Amu Darya basin, located in the southeast of Tulan platform and surrounded by eastern European plate, Kazak plate, Arabian plate and Indian plate, is a large oil and gas bearing basin, with Paleozoic basement and Mesozoic caprock. Middle-Lower Jurassic coal bearing formation is the main source rock. Upper Jurassic evaporite, which divides Amu-Darya basin into clastic petroleum system above saline and carbonate petroleum system below saline, is the regional caprock. According to the character of basement structure and caprock, the basin can be divided into many large structural units, such as Amu-Darya Depression, Murgab Depression, Zauzngui Depression, Karakum High, Bakhardok Monocline, Kopet Dag Fore deep and Repetek Salt-Kelif, etc.
In recent years, the difficulty and risk have increased in exploration for the conventional petroleum. With the continuous discovery of the volcanic reservoirs, volcanic-related rock reservoirs have become a new field of hydrocarbon exploration, and have greatly attracted the attention of the petroleum geologists. Former researches mostly focused on the seismic character identification of extrusive igneous rock and extrusive igneous rock-related reservoirs, therefore the study of seismic character identification of intrusive igneous rock and intrusive igneous rock-related reservoirs has an important theoretical and practical meaning in hydrocarbon exploration. Through the comprehensive research of the typical igneous seismic profiles in Qiongdongnan basin, the stocks, laccoliths, sills and dikes were identified from other seismic characters, and their identification characters were also summarized. Finally by the analysis of their implications for hydrocarbon systems, eight kinds of intrusive igneous rock-related traps were proposed.
The surface of Kela 2 gas field is hills, stormed cracks and rivers; it's difficult to collect and process seismic data. Above the reservoir of interest is high and cliffy formation which has variable lithofacies and thickness, and has developed salt bed, gypsum, mud and hi\|pressure aquifer. To prevent leak, check, overflow and blowout, it's necessary to predict geologic position depth accurately. We elaborate the limitation and error of adjacent well position depth correlation method and seismic profile method through examples, and present a method that uses structural diagrams to predict geologic position depth under complex structures. The application of the new method increased the accuracy in predicting complex geologic position depth of the Kela 2 gas field, achieving good results. The method can be for reference in instructing drilling geologic design and drilling trace on other comparable or wide spacing fields.
Measured the element composition of reservoir bitumen in marine strata of Sichuan basin, and chemical compositions and carbon isotopes of its natural gas, the origin of natural gas could be determined and result in the conclusion that the geochemical origin of natural gas is different from the typical coal\|type gas in China, but similar with the oil-type gas. The thermal maturity of natural gas is generally high, reaching at the stages of that between oil and gas cracking. The partial reverse of the carbon isotopic trend of C1—C3 alkanes is observed, i.e δ13C1>δ13C2<δ13C3. The abnormal phenomena are related to the later thermal sulfate reduction (TSR) to hydrocarbons, for the characteristics of the element composition (i.e. C, H, O, N, S) are different between marine and non\|marine reservoir bitumen. The bitumen in non-marine sand reservoirs in the NE Sichuan basin has low sulfur concentration and low bitumen reflectance; whereas the marine carbonate accumulated bitumen contains high sulfur. The bitumen in marine carbonate was formed by both oil cracking and TSR; in contrast, that in non-marine sandstone was generated from oil cracking.
The compositional characteristics of light hydrocarbons, Mango parameter and maturity for 23 crude oil samples in the Tuha basin were studied systematically. The results show that the crude oils are rich in cyclanes, and the straight chain alkanes content is very low, dominated by terrestrial organic matter. The MCHI indicates that the crude oils contain Type Ⅲ kerogen. N61/N51and(N61+N51)/（P2+P3+ N2 ratios of light hydrocarbon compounds have different molecular structural type, suggesting that the crude oils belong to terrestrial oils. Compositional characteristics of C7 light hydrocarbon fractions show that the methylcyclohexane content is higher than 50%, the dimethylcyclopentane content is lower than 9%, the heptane content is lower than 40%. The data is characteristic of coal generated oils and mixed crude oils. The Heptane values and isoheptane values indicate that the crude oils are in the normal mature stage. The maximum generating temperature of the crude oils is between 91.16℃ and 102.22℃.
Based on two pieces of calcilutite from the Sebei Well 1 in Qaidam basin, a systematic analysis of saturation hydrocarbon and aromatic hydrocarbon and nonhydrocarbon is employed to study the complex hydrocarbon charging histories. By GC/MSD, we found the aqualane and MPI (2,6,10,15,19 pentanethyl-eicosane) of the microbial characteristic biomarkers and the unsaturated fatty acid and isofatty acid and trans-iso-fatty acid. In addition, the ground temperature of samples is about 30℃, which is good for microorganisms thriving. Hence there were some microorganisms in the palaeosedimentary environment of the samples. Microorganisms transformed sedimentary organic matters, so they produced the 8,14-secohopane and alkaneones by the degradation of bacterium-germs. With the participation of microbes, the low mature source rocks would change greatly and the macro molecules were partly transformed to the micro molecules and the demethylation was strong and the ratio of C31/32αβ22S/（22S+22R）of hopanes and C29ββ/(ββ+αα) of steranes occurred abnormally. The result shows that the microbial degradation was helpful to generating gaseous hydrocarbon. And the sequences of degradation of low mature source rocks is saturation hydrocarbon>aromatic hydrocarbon> nonhydrocarbon.
The geothermal water in Weihe basin contains abundant soluble hydrocarbon gas with the main composition of methane, whose content is commonly about 10% and the highest of 82.44%. Carbon isotope analysis results of methane gas show that the carbon isotope of hydrocarbon gas features with positive carbon sequence, and the value of δ13C1 increases with the carbon number of gas. This indicates that hydrocarbon gas dissolved in geothermal water is organic gas. Gas from the Huxian-Xi′an Cenozoic depression is biological gas characterized withδ13C1less than -55‰. However, gas from other areas of geothermal water is pyrolysis gas with δ13C1 of -38.7‰~-27.2‰. Zhangjiapo Formation, a set of deep lacustrine deposition with good organic material and appropriate temperature and environment conditions for biological gas formation, is the important source rocks of biological gas. The Palaeozoic sediments of the basin basement, distributed in the north Weihe Fault, and the equivalent Palaeozoic carbonate and coal series occurred in the southern margin of Ordos basin, are the main source rocks of pyrolysis gas.
The essence of deep basin gas accumulation is gas saturated feature in the basin center, which may present several hundred meters of gas in a well bore without water, and generally include coal bed absorbed gas, shale fracture gas, and sandstone void gas. Basin centered gas accumulation could easily happen in a basin with plenty of coal formation, moderate burial depth, tectonic constancy, and a mega temperature evolution history. Most of deep basin gas accumulations are sealed by tight reservoir water in updip direction and involve everlasting gas supply, but this is only one of deep basin gas styles. Mutual dissolution of water vapor and methane in the ancient HTHP situation and the formation of bound water in reservoir bed compaction lithogenesis led to the absence of water layers in deep basin gas accumulation.“Acid dew” which has lower salinity than formation water will present along with mutual dissolution vapor condensation during the cooling and shrinking stage of deep basin gas accumulation. Deep basin gas accumulation may have the subpressure or surpressure characteristics in different evolutionary phases. Deep basin gas accumulations are available in Songliao basin, Qinshui basin and other coal basins in Northwest China.
According to the characteristics of deep basin gas pools in the North America and Welson's theories about the lithogenesis of the hydrocarbon bearing and water-bearing strata, this article presents that deep basin gas pools form when a relative dry zone is created between the water saturation zone and gas water transitional zone after lithogenesis of the reservoirs evolves into a certain phrase. On the basis of well hole and seismic data, combined with the physical properties of the Pingshi sandstone in Anpeng Zhaowa Region, this article analyses formation conditions and characteristics of the deep-basin oil-gas pools, and points out that the nonmarine deep\|depression region in the lake basin also boasts positive geologic background for deep-basin gas pools.
The identification of hydrocarbon′s microseepage from its macroseepage could improve the accuracy of interpretation on anomaly geochemical exploration, so we summarize the present research progress about identification marks and pointe out that the indicators, namely soil microbes, headspace gas, acid extraction of soil hydrocarbon and soil gas, appear to be responded differently towards macroseepage and microseepage respectively. The anomalous points of these indicators are linear distribution, high hydrocarbon concentration, more C6+, high alkane alkene ratio where the macroseepage is detected; where the microseepage is presented, the anomalous points of soil microbes are random distribution and seepage hydrocarbon is low concentration, little or no C6+, low alkane alkene ratio. Further investigation on Changling Longwanggou area of Zhenba block of Nandaba fold thrust belt located in western China Sichuan basin show that Longwanggou anomaly zone is of fault macroseepage and may not be vertically above the reservoir, while Changling synclinoria anomaly zone is caused by the microseepage and is vertically above the reservoir. The anomalous samples of soil butane oxidating bacterias andC1—C4from acid extraction of soil are linear distribution, C1—C4 of anomalous samples are highly concentrated (>1 000×10-6）, the alkane/alkene ratios are also high(>10) in Longwanggou anomaly zone while the anomalous samples of soil butane oxidating bacteria are random distribution, values of C1—C4 are low(<1 000×10-6）, the alkane/alkene ratios also are low(<5) in Changling synclinoria anomaly zone.
To get a right knowledge of the effectiveness of the geochemical exploration technique in searching for subtle reservoirs and to summarize the successful exploration cases of such reservoir types are essential for the exploration of subtle oil and gas reservoirs at present. A subtle fault block oil reservoir in the Linnan area, Bohai Bay basin was chosen as an example, and the characteristics of the geochemical fields of both the acid\|extraction methane and the heavier hydrocarbons were studied and characterized in detail by using the intensive geochemical exploration technique. The results show that both the acid-extraction methane and the heavier hydrocarbons have stable geochemical field in the study area; and the geochemical fields of the two kinds of acid-extraction hydrocarbon indicators coincide very well, both effectively indicating the underground subtle fault block oil reservoir with stable ring\|like anomaly patterns. The results also show that there are causal relationship between the hydrocarbon seepage (both the microseepage and the macroseepage along Xiakou fault) from this subtle oil reservoir and the anomaly of the two acid-extraction hydrocarbon indicators. The other exploration cases from Odors basin and Junggar basin demonstrate that the fundamental base for the geochemical technique to be used effectively in exploring the subtle fault block oil reservoir is comprehensively combining various factors together, including choice of the geochemical methods, selection and combination of the effective geochemical indicators, extraction of the integrated anomaly information, and recognition of the related petroleum geological conditions. The study results of Linnan area and the geochemical exploration cases of Ordos basin and Junggar basin indicate that the geochemical exploration technique can play important roles in the exploration for subtle oil reservoirs.
Because of the great change in thickness of the overlying gyprock and the high density drilling fluid in Kuqa depression, it is very difficult to define the boundary stratotype. TDC are used in exploration wells and the temperature at the bottom of well can be measured continuously and the natural gas reservoirs of Eogene-Cretaceous are high pressure reservoirs. Based on this situation and according to the cause and feature of the abnormal high temperature in the natural gas reservoir, we inspected the formation temperature continuously and predicted correctly the change of the formation, defined the boundary stratotype, found the trace of gas and solved the difficulty in work.
Fracture-pore tight sandstone gas reservoirs are characterized by low porosity and permeability, high capillary pressure, fracture development, water wettability, and high irreducible water saturation. In the course of drilling, completion and development, filtrate intrusion would lead to water saturation increase and gas permeability decline near wellbore area, and result in aqueous trapping damage. Aiming at the geological characteristics, this paper studied different aqueous trapping damage models during drilling and development in fracture pore network system, and researched the aqueous trapping damage forming process and damage mechanism owing to operating fluid and edge and bottom water intruding into the matrix and fracture system. Then, it presented the measures to control aqueous trapping damage while drilling, completion, workover, production and development, such as temporary shielding techniques, underbalanced drilling, optimizing treatment fluid, enlarging flowback pressure difference, decreasing interfacial tension, evaporating or heating to reduce water saturation, drainage gas recovery, and equivalent development. With these treating, aqueous trapping damage can be effectively prevented.
Based on the fluid theory and analysis of the advantages and disadvantages of existing models, this paper studies the characteristics of fractured horizontal wells and the distribution of fracture production in formation. According to the principle of Dupuit formula of finite conductivity vertical wells, it calculates the effective wellbore radius of production formula for horizontal wells. With the effective wellbore radius, it sets up a productivity formula group for a horizontal well with N fractures. With three fractures as examples, it analyzes the production dynamic characteristics, and gets the relationship among some parameters, including formation parameters, horizontal well fractures geometry parameters and physical parameters. This paper also studies the the impact of fractures number, spacing and other factors on flow distribution for the horizontal well fracture. It shows that this method can guide the low permeability fractured horizontal well optimization.
The complexity of gas water distribution in the low permeability sandstone gas reservoir is decided by the reservoir characteristics of low porosity, low permeability, strong heterogeneity. The complicated structure and collocation of pore throats results in the complexity of gas\|water distribution in low permeability high water saturation sandstone gas reservoirs. The reasons for the complicated structure and collocation of pore throats are analyzed thoroughly, and the cause of high water saturation is explained. Combined with the gas\|water distribution of the Xujiahe Group reservoir, three gas water distribution models were concluded. Among the three models, the model of gas\|water distribution controlled by reservoir unit is the primary one in the areas of plain structure and strong heterogeneity. Then the main factors of controlling gas water distribution were analyzed from macro scale to micro scale, all to part according to the reservoir characteristics of gas water distribution, structure, and heterogeneity: the area structure background dominates the macro distribution of gas water, the reservoir heterogeneity controls the partial distribution, and the space match between pore types and throat structures affect the micro differentiation of gas and water.
The factors of production decline are different at the reservoir development stages, and water cut is more influence on the production at the flooding stage. Based on the trend analysis of the product of the three, water cut, oil bearing, and cumulative production fluid, we form a new forecasting method of reservoir production at the flooding stage, combining the calculation of reasonable injection production ratio and the water cut optimization of the stage. This method supports the development of adjustment for reservoir without numerical simulation in practice.
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