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Igneous rocks are widely distributed in the world and have a big impact on oil and gas exploration. In order to discover the relationship between igneous rocks and oil and gas accumulation, starting from the whole process of oil and gas accumulation, the effect of igneous rocks on basin evolution, oil and gas generation, reservoir development, seal conditions, trap formation, oil and gas migration, and oil and gas reservoir preservation were analyzed, and the patterns were summarized. The study results show that igneous rocks are rich in minerals, which provide material conditions for the reproduction of hydrocarbon-generating rocks, increases the geothermal gradient and accelerates the hydrocarbon-generating procession, the metal elements carried can improve the hydrocarbon-generating transformation efficiency of the source rocks. Igneous rocks have positive and negative effects on the reservoir. It has a constructive role as reservoir, transforming reservoir and changing paleo morphology, which is beneficial to carbonate rock deposition. It has destructive effect of baking the reservoir to make it dense and occupying the reservoir space. Tight igneous rocks can act as effective seals and fluid segmentation layers. During the spilling and eruption of magma along the volcanic channel, various types of structures can be formed, which enriches the types of traps. The thermodynamic effect on surrounding rock during the igneous eruption process produces a large number of faults and fractures, which are conducive to the migration of oil and gas. The igneous rocks developed in the early stage or at the same time with hydrocarbon generation have constructive effects on oil and gas accumulation, and the igneous rocks in the later stage have destructive effects on early oil and gas reservoirs. The formation and evolution of oil and gas in igneous rock-bearing basins were closely related to that of igneous rocks. We should dialectically recognize its positive and negative effects in oil and gas exploration, which requiring targeted theoretical innovations and methodological improvements.
Pressure gradient method is based on the principle of connectedness, using formation pressure test data to character pressure gradient curves of reservoir fluids and distinguish oil water contact. The greatest advantage of this method is Intuitive identification of oil and water contact depth. It provides basis for fine reservoir description and progressive exploration and development. According to the data of single well test, the regional water pressure curve is fitted. The difference between the hydrostatic pressure curve and the hydrostatic pressure curve is defined as the overburden pressure. The depth of test point and test pressure, formation water density and crude oil density are established to calculate the depth of oil-water contact. Well Che 47 Block, because of many times of vertical volcanic cycle, complex lithology and lithofacies, and strong heterogeneity of secondary reservoirs, multiple lithologic shielding bodies can be identified. By using the pressure gradient method and combining the reservoir geological characteristics of the industrial area, it is revealed that at least 3 relatively independent reservoir units in the Well Che 47 Block, and the corresponding depth of oil-water contact is −2786 m, −2848 m and −2912 m respectively. According to the relationship between the depth of the oil and water contact and the position of the test point, it is conservative to predict that the lowest oil layer is at least 200 m of the oil column height, and the prospect of rolling is good. The application of the pressure gradient method to identify the oil-water interface in complex reservoirs is more in line with the actual underground conditions. This method, combined with seismic and log data, can provide an important basis for the fine evaluation of complex volcanic reservoirs.
The Junggar Basin is the basin with the richest exploration results of volcanic reservoirs among petroliferous basins in China. The oil test data and production data show there also exhibit good hydrocarbon displays in the Kebai Fault Zone where the paleo-weathering crust is not developed. In this study, we utilized core data and thin sections to investigate volcanic reservoir rocks lacking paleo-crusts of weathering in Carboniferous deposits in the western Junggar Basin, Northwestern China. The studied interval is dominated by seven types of volcanic rocks, two types of metamorphic rocks and three types of sedimentary rocks, which are grouped into six lithofacies. From northeast (NE) to southwest (SW) of study area, the dominant rock type changes from sedimentary rock, to pyroclastic rocks, tuffites, and then to welded pyroclastic rock, lavas, respectively volcanic rocks. And the corresponding dominant lithofacies changes from delta facies, to volcanic-sedimentary facies, explosive facies, and then to sub-volcanic facies, and effusive facies. Fault-induced fractures and dissolved pores are the dominant reservoir space types. Faults and lithology jointly played a significant role in controlling the macro-distribution, physical properties, and hydrocarbon accumulation in volcanic reservoirs. The geological setting controlled the influences of primary and secondary processes. This study also reveals that the volcanic lavas with high-angle fractures of effusive facies located in SW of the study area are favorable lithofacies for hydrocarbon accumulation. This study highlights the differences in volcanic reservoir rocks with and without paleo-crusts of weathering in terms of reservoir spaces, controlling factors and hydrocarbon accumulation. This study also reveals that volcanic reservoir lacking paleo-crust of weathering can have a high hydrocarbon potential.
The BZ19-6 deep buried-hill structural belt in the southwest of Bozhong Sag, Bohai Bay Basin, is a newly discovered super-giant oil and gas bearing area. The study on its reservoirs is still in the early stage, and the characteristics and control factors of reservoir development are not understood deeply. In this paper, cores, sidewall cores, rock sections were analyzed and described. Then, based on regional structural setting, mud logging and logging data, the buried-hill reservoirs in this area were analyzed from the aspects of petrological characteristics, reservoir space types and physical properties, the inherent factors influencing the development of the reservoirs were discussed, and distribution laws of the reservoirs were investigated. And the following research results were obtained. First, the deep buried-hill reservoirs of this belt are a pan-buried hill reservoir system composed of the Palaeocene–Eocene Kongdian Fm glutenite in the upper part and the Archean buried-hill metamorphic granite in the lower part. A multi-layer reservoir structure of glutenite pore zone, weathering crust dissolution fracture zone and inner fracture zone is formed. These reservoirs are complex in genesis and diverse in type. Second, the Archean buried-hill metamorphic granite reservoir can be vertically divided into weathering crust, inner fracture zone and tight zone, and it presents the dual characteristics of porous and fractured media. Third, the buried-hill weathering crust is mainly affected by strong dissolution and leaching superimposed with fracturing, forming fractured-porous reservoir space. The reservoir of inner fracture zone is mainly controlled by the superimposition of three-phrase fractures, which forms the main development period of buried-hill fractures since the Yanshanian. Fourth, the glutenite of Kongdian Fm is a typical sieve deposit and it is mainly controlled by the late dissolution. Fifth, migmatization and supercritical fluid cryptoexplosion play a constructive role in the development of the reservoirs. In conclusion, the understanding of buried-hill glutenite and metamorphic reservoir system developed in this belt is conductive to determining the target and direction of next oil and gas exploration in this area. Keywords: Bohai bay basin, Bohai sea area, BZ19-6 deep buried-hill structural belt, Archean, Deep metamorphic granite reservoir, Paleogene, Glutenite reservoir, Dissolution, Structural fracture
This paper wants to present an overview on the origin of porosity in volcanic gas reservoirs from main sedimentary basins of China, with an emphasis on volcanic gas reservoirs discovered during the last thirty years in China. A classification scheme and facies model based on the integrated diagenetic patterns-compositions-structures model is available for the deep volcanics in the Songliao Basin. However, we found that according to the models, various types of porosity formed in each location during complex diagenetic processes, and we show that it could be used as criteria for gas reservoir exploration.
The first work of its kind, Volcanic Reservoirs in Petroleum Exploration summarizes the current research and exploration techniques of volcanic reservoirs as a source of oil and gas. With a specific focus on the geological features and development characteristics of volcanic reservoirs in China, it presents a series of practical exploration and evaluation techniques based on this research. Authored by an award-winning petroleum geologist, it introduces exploration and outcome prediction techniques that can be used by scientists in any volcanic region worldwide. Volcanic reservoirs as new sources of petroleum resources are a hot topic in petroleum exploration. Although volcanic rock cannot generate hydrocarbons, it can serve as a reservoir for hydrocarbons when conditions permit. This book explains the differences between volcanic reservoirs and other major reservoir types, and describes effective methods for examining volcanic distribution and predicting volcanic reservoirs, providing a framework for systematic studies throughout the world. Includes an entire section dedicated to current trends in volcanic prediction and evaluation technology More than 90 full-color photos illustrate the text in greater detail Case studies conclude each chapter, helping scientists apply the book's concepts to real-life scenarios. © 2013 Petroleum Industry Press Published by Elsevier Inc. All rights reserved.
Based on 112.5 km2 of 3-D seismic data and data of 8 prospecting wells drilled volcanic rocks in the 3rd member of the Paleogene Shahejie Formation in Hongxing area of the Eastern Sag of the Liaohe Depression, Bohai Bay Basin, three levels of volcanic interfaces (stage→edifice→lithofacies) of the intermediate-mafic volcanic formation are identified to reveal favorable prospecting facies through comprehensive studies on geology, well logging and seismic data in single well and multiple wells following the seismic volcano stratigraphy principle. According to stage interfaces, three volcanic stages were identified in the 3rd member of Shahejie Formation. One or more volcanic edifice-seismic facies were identified in each volcanic stage and volcanic facies-seismic facies were identified in each volcanic edifice-seismic facies. Based on single well points, we described volcanic edifices on well-tie seismic sections; identified volcanic bodies by extracting coherent seismic attribute (superimposed volcanic edifices) taking the volcanic stages as the units; then identified volcanic edifices and volcanic lithofacies by extracting waveform classification properties. Volcanic facies mapping were completed by constituting the relationship between the volcanic facies and the seismic facies in drilling wells, seismic cross sections and mappings. There are two types of plane volcanic facies sequences in the intermediate-mafic volcanic facies of this study area: volcanic conduit facies→extrusive facies (→explosive facies)→effusive facies→volcanic sedimentary facies, volcanic conduit facies (→explosive facies)→effusive facies→volcanic sedimentary facies. Among them, the near crater assemblage (volcanic conduit, extrusive and explosive facies) has better hydrocarbon shows and is the most favorable target of hydrocarbon exploration. © 2016 Research Institute of Petroleum Exploration & Development, PetroChina.
Volcanic lithofacies of Kalagang Formation in Santanghu Basin mainly consisted of volcanic explosive facies and effusive facies, yet volcano-sedimentary facies was poorly found. By using of wireline logging, geology and seismic data, logging response pattern for volcanic lithology identification was built, and then seismic inversion was runned restricted by the single-well facies in order to make clear of the areal distribution of volcanic lithofacies. The research results revealed that the main type of volcanic eruption was crevice eruption and crater was arrayed heatedly along the basement faults; effusive facies that mainly consisted of andesite was spreaded like bedded. The results can effectively guide the exploration and evaluation for the volcanics of Kalagang Formation, and also provide the idea of the research can be used as a reference of volcano rock facies.
According to occurrence, lithological association of volcanic rocks and volcanic facies composition in the Early Cretaceous Yingcheng Formation of Songliao Basin, the volcanic edifice was classified into three kinds of cracter-near cracter facies belt, proximal facies belt and distal facies belt. The reservoirs characteristics in each facies belt of volcanic edifice were analyzed using the parameters of porosity, permeability and mercury-injection capillary pressure curve from 304 drilling samples. The reservoir in the crater-near crater facies belt is characterized by big pore, wide and long fracture, big pore-throat radius and pore-throat well-sorted. The measured porosity ranges from 2% to 25%, and the average value is 7.74%. The range of permeability is from 0.01 × 10-3 μm2 to 100 × 10-3 μm2, and the average value is 1.99 × 10-3 μm2. In the crater-near crater facies belts, most reservoir is charaterized by middle porosity and high permeability, the local parts are the reservoir with high porosity and high permeability. The reservoir in the proximity facies belt is of the properties of middle pore, narrow and small crack, middle pore-throat radius and pore-throat slightly well-sorted. The range of porosity is from 1% to 15%, and the average value is 7.47%. The range of permeability is from 0.01 × 10-3 μm2 to 20 × 10-3 μm2, and the average value is 0.95 × 10-3 μm2. The proximal facies belt mostly is the reservoir with middle porosity and permeability. Some part of the belt is the reservoir with middle porosity and high permeability. The distal facies belt is the reservoir with middle-small pore, wide and long crack, small pore-throat radius and pore-throat bad-sorted. The range of porosity is from 1% to 10%, and the average value is 6.95%. The range of permeability is from 0.02 × 10-3 μm2 to 1.0 × 10-3 μm2, and the average value is 0.13 × 10-3 μm2. The distal facies belt is the reservoir with middle-small porosity and low permeability. The crater-near crater facies belt is the preferable target for volcanic reservoir exploration.
With the deepening of exploration and development, volcanic gas shows the feature separate reservoir of volcanic edifice. The non-homogeneous characteristics of volcanic formation are obvious. For meeting the need of meticulous study of exploration and development, improving the level of volcanic gas reservoir comprehensive study and achieving a understanding, in the Xujiaweizi depression dense well pattern-three dimensional seismic area of Songliao basin, the authors research the seismic volcanic edifice anatomy under geological prior model constraint. Three kinds of volcanic edifices can be identified as layered, dome, and funnel-shaped. The overlying mode is in three kinds of shoestring, superimposed mosaic type. Volcanic edifice type and overlying mode are controlled by fault systems.
The oil-gas reservoirs in igneous rocks have notably differences at the petrologic and fluids properties from the traditionally normal reservirs of classic rocks. The original pores in the igneous rocks didn't undergo strong compaction during cooling down. The formation and evolution of the secondary pores are very important to the development of the igneous reservoirs. Water-rock interaction is one of the major driving forces in the formation and evolution of the secondary pores. Researches on this issue are important for understanding and predicting the igneous reservoirs. However, previous studies on the igneous reservoirs mainly focused on descriptions of surface characters and the geological surroundings, few of details about the water-rock interactions within the igneous rock reservoirs. To better understand formation and evolution of secondary pores in the reservoir of igneous rocks, new conceptions and techniques are much needed in comprehensive water-rock interaction studies on the igneous rock reservoirs.
A new oil field with a reserve of more than 100 million tons has been found in the Penglai 9-1 buried hill, consisting of Paleoproterozoic metamorphic rocks and Yanshan granites. The granites surrounded by Paleoproterozoic metamorphic rocks are distributed in central valley floor of the buried hill. The oil pool mainly accumulates in the reservoirs of granite weathered crust located in the valley floor of the buried hill. The granites can be classified into granodirorite and adamellite. Paleoproterozoic metamorphic rocks mainly consist of phyllite, schist, metasandstone, quartzite and mylonite. Although both metamorphic rocks and granites have experienced similar weathering and deformation, differences in mineral constitution, mechanical property and weathering ways between metamorphic rocks and granites result in alternative development of high quality reservoirs in the granites. The reservoirs in metamorphic rocks belong to porosity types and development of secondary porosity is quite limited, no effective reservoirs may be formed in the metamorphic rocks. The reservoirs in granites are characterized by development of porosity and fissure, high quality reservoirs mainly develop in the sandy, pebbly weathering zone and fissured zone, in which the reservoirs in fissured zone are the thickest. Except for intensity of hypergenic karstification and tectonic deformation, lithologic constitution and lithofacies of the granites play a controlling role in development of high quality reservoirs in granite weathered crust. The factors such as weathered intensity, deformation, lithologic constitution and lithofacies, etc. contribute to vertical zonation characteristics of weathered crust reservoir at the granite buried hill, the reservoir types changed from porosity to fissure from the top of the weathered crust to the bottom. The various secondary porosity and fissure are the most important reservoir spaces in buried hill granite reservoirs.
Based on the rock texture, volcanic edifices of Yingcheng Formation and Huoshiling Formation in Songliao Basin were classified into 3 types. They were pyroclastic volcanic edifice, lava volcanic edifice and compound volcanic edifice. According to the chemical composition of rocks, every type was classified into acid subtype or intermediate-basic subtype. Based on the number of cones the volcanic edifices were classified into 16 basic types. Most volcanic edifices of Huoshiling Formation are intermediate and basic lava's. And most of volcanic edifices of Yingcheng Formation are acid compounds. On the basis of 544 samples of acid volcanic edifices, the lava's average of porosity and permeability was bigger, and the pyroclastic's was smallest. The discovered gas pool of volcanic rocks revealed that productivity of acid volcanic edifices were higher than intermediate and basic's. The gamma average value of intermediate and basic edifices is less than 80 API, and that of the acid edifices is more than 110 API. More than 70% of the lengths of lava edifices loggings are low amplitude-box shape with smooth-microjagged. More than 70% of the length of pyroclastic edifice loggings are middle-high amplitude box or bell shape with jagged-microjagged. The other part is compound volcanic edifice. According to logging response of volcanic edifices, the logging recognition model of texture is built with variance, variation root, stair slope, down slop, relative difference value between stair slop and down slop. The component of volcanic edifices is recognized by using gamma log. It provides evidence for logging recognition and evaluation of volcanic edifices.
Volcanic edifices of the Yingcheng Formation and the Huoshiling Formation in the Songliao basin are classified into 3 types. They are pyroclastic, composite and lava volcanic edifices. According to chemical composition of rocks, each type is subdivided into acid subtype or intermediate-basic subtype. Most of volcanic edifices of the Yingcheng Formation are acid subtype. The percentage of acid lava volcanic edifice is 33% in northern basin and 38% in southern basin. The proportion of intermediate-basic volcanic edifices in northern basin is more than that in southern basin. The volcanic gas pool of Songliao basin isstructural-lithological type. The depth of gas-water interface changes greatly. Internal characteristics of gas pools are controlled by volcanic edifices type. The shape of gas layer within acid pyroclastic volcanic edifice is sill or tabular, and the thickness changes little. The shape of gas layer within acid composite and lava volcanic edifice is mound or sill, and the thickness changes little. The shape of gas layer within intermediate-basic lava volcanic edifice is mound or wedge, and the thickness changes rapidly. The volcanic gas pool forming in Songliao basin is controlled by effective source rocks, faults of communicating source rocks, porosity and permeability. The industrial gas pool of Songliao basin is accumulated in acid lava volcanic edifices, which contributes 50% in northern basin and 38% in southern basin. The efficiency of gas pool formation of intermediate-basic volcanic edifices in northern basin ishigher than that in southern basin. The acid composite edifices have the maximum productivity of single well. The productivity of acid volcanic edifices is higher than intermediate-basic. The volcanic exploration direction should be focused on the targets with effective source rocks and faults of communicating source rocks. Firstly, aim at the acid volcanic edifice. Secondly, find the intermediate-basic volcanic edifice.
Carbonate mineral is an important mineral component in the YingCheng formation volcanic reservoir of the Changling rift, and calcite is the main authigenic carbonate mineral. On the basis of isotopic analyses of C and O in the calcite, the genesis of authigenic carbonate mineral in this volcanic reservoir was studied. The results show that the δ 13C V-PDB values of calcite in samples collected from the volcanic reservoir of the Changling rift range from - 12.7‰ to 0.4‰; that these samples are characterized by high δ 18O values of from 3. 8‰ to 12‰; and that the calculated δ 13C values of CO 2 gas equilibrium with calcite range from -16.0‰ to 2.2‰. The large variation of carbon and oxygen isotope compositions indicates that mineral-forming material may derive from multiple sources. The δ 13C-δ 18O diagram of calcite suggests that the calcite-forming CO 2 gas originated from both inorganic and organic sources, mantle and magma are major sources and sedimentary organic matter is the secondary source. The inorganic and organic CO 2 gases and organic acids produced by the thermal evolution of organic matter dissolved in the fluid to form an acidic fluid. Finally, this fluid reacted with silicate mineral in the volcanic reservoir to form carbonate mineral.
In order to get a clear understanding about the influence of volcanic rock composition on erosion in creating porosity during deuteric processes, 32 fresh igneous rock samples are picked out and sorted according to their whole rock alkaline. An indoor eroding experiment is employed to simulate the rocks' pore changing processes. Pore distributions are observed on cast thin sections before and after erosion and their porosity and permeability are also detected. Combining with the reservoir characteristics of igneous samples from drilling wells under natural erosion, the difference of different alkali content igneous rocks are compared and studied. The experiment show the strong alkaline igneous rocks have an absolute pore growth by more than 5% in average after erosion, and the values are 4.6% and 2.1% for alkaline and calc-alkaline igneous rocks respectively. The result indicates that the contents of alkali in igneous rocks act as one of the important internal factors in forming high-quality weathering crust reservoirs. By regression analysis of major elements and rock pore increasing value, it is revealed that the contents such as K, Na, Ca, Mg have good correlations with the pore increasing ability under erosion condition. Because of relatively more active components, the alkali-rich igneous rocks have a stronger ability to develop better reservoir than the calc-alkaline ones under the same acid erosion environment.
The common belief among many petroleum geologists that regions of volcanic and metamorphic rocks are generally to be avoided as potential hydrocarbon reservoirs has greatly slowed the research and exploration efforts on hydrocarbon potential in volcanic and metamorphic rocks. However, many hydrocarbon-bearing basins containing volcanic and metamorphic rocks have been found in convergent margin settings and in rift basins. This article describes the reservoir lithofacies and wire-line logs and elucidates the parameters controlling reservoir-quality evolution of Archean metamorphic and Jurassic volcanic rocks from the Xinglongtai buried hill, western depression of the Liaohe basin, China. Four lithofacies (pyroclastics, lavas, volcaniclastics, and volcaniclastic-epiclastics) have been identified in the Jurassic volcanic reservoir rocks, each having different pore types and variable porosity and permeability values and, thus, different reservoir potentials. Pore types in the volcanic rocks include voids, fractures, fissures, weathering cracks, interstices, and vesicles. The volcanic-rock reservoir evolution is primarily controlled by the burial-thermal diagenesis. Plastic deformation and alteration of the biotite during the eogenetic phase led to the considerable loss of primary pores. Destruction of the primary porosity by compaction was limited by the presence of eogenetic carbonate and zeolite cement formation. Dissolution during the deep-burial mesogenetic phase and during near-surface leaching and erosion in the intervening volcanic eruptions enhanced the permeability and increased reservoir quality.
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