The Lower Triassic Feixianguan Formation in the Daxian-Xuanhan region, northeastern Sicbuan is interpreted to be a carbonate platform intermediate between the West Hubei-East Cbongqing marine basin and Guangyuan-Wangc...The Lower Triassic Feixianguan Formation in the Daxian-Xuanhan region, northeastern Sicbuan is interpreted to be a carbonate platform intermediate between the West Hubei-East Cbongqing marine basin and Guangyuan-Wangcang marine basin. Outcrops, well logs and seismic data have disclosed that three sedimentary facies can be identified for the formation： open platform, platform exposed shoal and restricted platform facies. During the early stage of deposition of the Feixianguan Formation, there existed a sedimentary framework all the same as the Late Permian one： open platform in the west, and platform exposed shoal, restricted platform and open platform eastwards. The gradual increase of the shoal area permitted eastward migration of the shoal facies. During the deposition of the third member of the Feixianguan Formation, the study area was invaded by temporary transgressions. Till the deposition of the fourth member of the formation, the study area was prevailed over the unified restricted platform deposits, as indicated by the sedimentary model for the typical carbonate platform shoal deposits. The reservoir rocks in the Feixianguan Formation consist mostly of solution opening dolostone, and the rock types are assembled by oolitic dolostone, residual oolitic dolostone and sucrosic residual oolitic medium- to coarse-grained dolostone. The deep and shallow dual laterologs show relatively high resistivity, clear amplitude differences and time difference saltation of acoustic waves in some intervals. The seismic responses are indicated by low-frequency and highly variable amplitudes and chaotic reflection configurations. The reservoir rocks are characterized by high porosity-high permeability and medium porosity-medium permeability, showing a marked correlation between porosity and permeability. Solution openings are extremely developed in the reservoir rocks, including cast pores, intergranular solution openings, intercrystal pores, intercrystal solution openings, solution openings （caves） and minute fissures. Macropores and coarse pore throats are common. The reservoir rocks are apparently controlled by sedimentary facies in distribution patterns. Vertically, they occur dominantly in the second and first members of the Feixianguan Formation, and laterally in the platform exposed shoals and restricted platforms, where good natural gas potential is expected.展开更多
Dolostones in the Cambrian Longwangmiao Formation have become one of the most significant gas exploration domains in China. Over a trillion cubic meters of gas reservoirs have been discovered in the Gaoshiti-Moxi area...Dolostones in the Cambrian Longwangmiao Formation have become one of the most significant gas exploration domains in China. Over a trillion cubic meters of gas reservoirs have been discovered in the Gaoshiti-Moxi area; however, the origins and distribution of the dolostone reservoirs are not well understood. This work discussed the geology and geochemistry of the dolostone reservoirs in the Longwangmiao Formation to determine their origin and distribution. Two understandings are acquired： firstly, a carbonate ramp provided excellent conditions for grain beach deposition, while the presence of a hypersaline lake was favorable for the contemporaneous dolomitization of grain beach deposits. Petrographic and geochemical evidence further confirm that the Longwangmiao dolostone was formed during the contemporaneous stage. Secondly, the reservoir characteristics indicate that the grain beach sediments provide material basis for the development of the Longwangmiao dolostone reservoirs. Reservoir dissolution simulation experiments show that the porosity of the reservoirs was formed by dissolution during contemporaneous and burial stages. The dissolution pores formed during the contemporaneous stage were controlled by sequence interfaces. The large scale dissolution vugs formed during the burial stage subsequently spread along the pre-existing porosity and fracture zones. This study therefore identified that the development of grain dolostone reservoirs in a shallow water ramp under arid climatic conditions generally met the following conditions：（1） reefal beach deposits lay a foundation for reservoir development;（2） superficial conditions are an important determining factor for reservoir porosity; and（3） burial conditions provide environment for porosity preservation and modification.展开更多
This paper discusses the reservoir space in carbonate rocks in terms of types,combination features,distribution regularity,and controlling factors,based on core observations and tests of the North Truva Oilfield,Caspi...This paper discusses the reservoir space in carbonate rocks in terms of types,combination features,distribution regularity,and controlling factors,based on core observations and tests of the North Truva Oilfield,Caspian Basin.According to the reservoir space combinations,carbonate reservoirs can be divided into four types,i.e.,pore,fracture-pore,pore-cavity-fracture,and pore-cavity.Formation and distribution of these reservoirs is strongly controlled by deposition,diagenesis,and tectonism.In evaporated platform and restricted platform facies,the reservoirs are predominately affected by meteoric fresh water leaching in the supergene-para-syngenetic period and by uplifting and erosion in the late stage,making both platform facies contain all the above-mentioned four types of reservoirs,with various pores,such as dissolved cavities and dissolved fractures,or structural fractures occasionally in favorable structural locations.In open platform facies,the reservoirs deposited continuously in deeper water,in an environment of alternative high-energy shoals（where pore-fracture-type reservoirs are dominant） and low-energy shoals（where pore reservoirs are dominant）.展开更多
1 Introduction Reservoir architecture analysis of distributary channel of Daqing oilfield has drawn consistent interest among development geologists and petroleum engineers over the last decade(Lv et al.,1999;Zhou et ...1 Introduction Reservoir architecture analysis of distributary channel of Daqing oilfield has drawn consistent interest among development geologists and petroleum engineers over the last decade(Lv et al.,1999;Zhou et al.,2008;Zhang et展开更多
Exploration practice has proved that deep and ultra-deep reservoirs consist of mainly matrix-porous dolomite reservoirs and fractured-vuggy karst reservoirs and still will be very important targets for future explorat...Exploration practice has proved that deep and ultra-deep reservoirs consist of mainly matrix-porous dolomite reservoirs and fractured-vuggy karst reservoirs and still will be very important targets for future exploration, in which large oil and gas fields such as Anyue, Yuanba, Halahatang, Fuman and Shunbei have been discovered. This paper systematically summarizes three theoretical and technical achievements in studying deep and ultra-deep carbonate reservoirs in the past decade.(1) The micro-zone and multi-parameter experiment analysis technology featured by determining the “age, temperature, pressure and fluid properties” of carbonate reservoirs, together with experimental simulation of cross-tectonic-period pore formation and preservation featured by the “multi-stage, continuous, visualized and online detection technology”, providing useful tools for studying the pore formation and preservation mechanism of deep and ultra-deep carbonate rocks from the perspective of“forward” and “inversion”.(2) Deep and ultra-deep matrix-porous dolostone reservoirs are still controlled by sedimentary facies,among which reef(mound) and/or beach contribute most. The reservoir space is mainly composed of sedimentary primary pores and supergene dissolution pores and fractures, though some of reservoir spaces are formed by burial dissolution and they tend to develop and may locally concentrate following the pre-existing porous zone. In other words, burial dissolution vugs are inherited rather than newly formed. Early dolomite precipitation(or dolomitization) has a high potential to preserve early pores.(3) The development and preservation mechanism of fractured-vuggy karst limestone reservoirs in deep and ultra-deep realm was analyzed. Pene-contemporaneous dissolution and interlayer and buried-hill karstification control the development of early and late supergene fractured-vuggy reservoirs. Strike-slip faults superimposed with supergene karstification lead to the development of “fence-style” faulted karst reservoirs. Dissolution simulation experiments reveal that the development of karst fracturedvuggy reservoirs is facies-controlled in certain degree, mainly developed in packstone. Rock mechanics analysis reveals that the preservation of caves is under the control of lithology, cave size, and the distance to the unconformity, and caves can be well preserved at 10,000 m. The theoretical and technical achievements provide supports for carbonate oil and gas exploration into ten thousand meters deep.展开更多
Origin of dolostone remained a controversial subject, although numerous dolomitization models had been proposed to date. Because of the dolomitization＇s potential to be hydrocarbon reservoirs, one debatable issue was...Origin of dolostone remained a controversial subject, although numerous dolomitization models had been proposed to date. Because of the dolomitization＇s potential to be hydrocarbon reservoirs, one debatable issue was the role of dolomitization in porosity construction or destruction. Based upon case studies of dolostone reservoirs in various geological settings such as evaporative tidal flat （Ordos Basin, NW China）, evaporative platform （Sichuan Basin, SW China）, and burial and hydrothermal diagenesis （Tarim Basin, NW China）, here we systematically discuss the origin of porosity in dolostone reservoirs. Contrary to traditional concepts, which regarded dolomitization as a significant mechanism for porosity creation, we found two dominant factors controlling reservoir development in dolostones, i.e., porosity inherited from precursor carbonates and porosity resulted from post-dolomitization dissolution. Actually, dolomitization rarely had a notable effect on porosity creation but rather in many cases destroyed pre-existing porosity such as saddle dolostone precipitation in vugs and fractures. Porosity in dolostones associated with evaporative tidal flat or evaporative platform was generally created by subaerial dissolution of evaporites and/or undolomitized components. Porosity in burial dolostones was inherited mostly from precursor carbonates, which could be enlarged due to subsequent dissolution. Intercrystalline porosity in hydrothermal dolostones was either formed during dolo- mitization or inherited from precursor carbonates, whereas dissolution-enlarged intercrystalline pores and/or vugs were usually interpreted to be the result of hydrothermai alteration. These understandings on dolostone porosity shed light on reservoir pre- diction. Dolostone reservoirs associated with evaporative tidal flat were laterally distributed as banded or quasi-stratified shapes in evaporite-bearing dolostones, and vertically presented as multi-interval patterns on tops of shallowing-upward cycles Dolostone reservoirs associated with evaporative platform commonly occurred along epiplatforms or beneath evaporite beds, and vertically presented as multi-interval patterns in dolostones and/or evaporite-bearing dolostones of reef/shoal facies. Con- strained by primary sedimentary facies, burial dolostone reservoirs were distributed in dolomitized, porous sediments of reef/shoal facies, and occurred vertically as multi-intervai patterns in crystalline dolostones on tops of shallowing-upward cy- cles. Hydrothermal dolomitization was obviously controlled by conduits （e.g., faults, unconformities）, along which lenticular reservoirs could develop.展开更多
文摘The Lower Triassic Feixianguan Formation in the Daxian-Xuanhan region, northeastern Sicbuan is interpreted to be a carbonate platform intermediate between the West Hubei-East Cbongqing marine basin and Guangyuan-Wangcang marine basin. Outcrops, well logs and seismic data have disclosed that three sedimentary facies can be identified for the formation： open platform, platform exposed shoal and restricted platform facies. During the early stage of deposition of the Feixianguan Formation, there existed a sedimentary framework all the same as the Late Permian one： open platform in the west, and platform exposed shoal, restricted platform and open platform eastwards. The gradual increase of the shoal area permitted eastward migration of the shoal facies. During the deposition of the third member of the Feixianguan Formation, the study area was invaded by temporary transgressions. Till the deposition of the fourth member of the formation, the study area was prevailed over the unified restricted platform deposits, as indicated by the sedimentary model for the typical carbonate platform shoal deposits. The reservoir rocks in the Feixianguan Formation consist mostly of solution opening dolostone, and the rock types are assembled by oolitic dolostone, residual oolitic dolostone and sucrosic residual oolitic medium- to coarse-grained dolostone. The deep and shallow dual laterologs show relatively high resistivity, clear amplitude differences and time difference saltation of acoustic waves in some intervals. The seismic responses are indicated by low-frequency and highly variable amplitudes and chaotic reflection configurations. The reservoir rocks are characterized by high porosity-high permeability and medium porosity-medium permeability, showing a marked correlation between porosity and permeability. Solution openings are extremely developed in the reservoir rocks, including cast pores, intergranular solution openings, intercrystal pores, intercrystal solution openings, solution openings （caves） and minute fissures. Macropores and coarse pore throats are common. The reservoir rocks are apparently controlled by sedimentary facies in distribution patterns. Vertically, they occur dominantly in the second and first members of the Feixianguan Formation, and laterally in the platform exposed shoals and restricted platforms, where good natural gas potential is expected.
基金granted by the National Major Science and Technology Projects (grant No.2016ZX05004002)PetroChina Major Science and Technology Projects (grant No.2014E-32)PetroChina Science and Technology Projects (grant No.2016B-0402-01)
文摘Dolostones in the Cambrian Longwangmiao Formation have become one of the most significant gas exploration domains in China. Over a trillion cubic meters of gas reservoirs have been discovered in the Gaoshiti-Moxi area; however, the origins and distribution of the dolostone reservoirs are not well understood. This work discussed the geology and geochemistry of the dolostone reservoirs in the Longwangmiao Formation to determine their origin and distribution. Two understandings are acquired： firstly, a carbonate ramp provided excellent conditions for grain beach deposition, while the presence of a hypersaline lake was favorable for the contemporaneous dolomitization of grain beach deposits. Petrographic and geochemical evidence further confirm that the Longwangmiao dolostone was formed during the contemporaneous stage. Secondly, the reservoir characteristics indicate that the grain beach sediments provide material basis for the development of the Longwangmiao dolostone reservoirs. Reservoir dissolution simulation experiments show that the porosity of the reservoirs was formed by dissolution during contemporaneous and burial stages. The dissolution pores formed during the contemporaneous stage were controlled by sequence interfaces. The large scale dissolution vugs formed during the burial stage subsequently spread along the pre-existing porosity and fracture zones. This study therefore identified that the development of grain dolostone reservoirs in a shallow water ramp under arid climatic conditions generally met the following conditions：（1） reefal beach deposits lay a foundation for reservoir development;（2） superficial conditions are an important determining factor for reservoir porosity; and（3） burial conditions provide environment for porosity preservation and modification.
基金supported by the National Major Science and Technology Project (No.2016ZX05030002)
文摘This paper discusses the reservoir space in carbonate rocks in terms of types,combination features,distribution regularity,and controlling factors,based on core observations and tests of the North Truva Oilfield,Caspian Basin.According to the reservoir space combinations,carbonate reservoirs can be divided into four types,i.e.,pore,fracture-pore,pore-cavity-fracture,and pore-cavity.Formation and distribution of these reservoirs is strongly controlled by deposition,diagenesis,and tectonism.In evaporated platform and restricted platform facies,the reservoirs are predominately affected by meteoric fresh water leaching in the supergene-para-syngenetic period and by uplifting and erosion in the late stage,making both platform facies contain all the above-mentioned four types of reservoirs,with various pores,such as dissolved cavities and dissolved fractures,or structural fractures occasionally in favorable structural locations.In open platform facies,the reservoirs deposited continuously in deeper water,in an environment of alternative high-energy shoals（where pore-fracture-type reservoirs are dominant） and low-energy shoals（where pore reservoirs are dominant）.
基金funding support of this project from National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2011ZX05010-002-005)
文摘1 Introduction Reservoir architecture analysis of distributary channel of Daqing oilfield has drawn consistent interest among development geologists and petroleum engineers over the last decade(Lv et al.,1999;Zhou et al.,2008;Zhang et
基金supported by the National Natural Science Foundation of China (Grant No. U23B20154)。
文摘Exploration practice has proved that deep and ultra-deep reservoirs consist of mainly matrix-porous dolomite reservoirs and fractured-vuggy karst reservoirs and still will be very important targets for future exploration, in which large oil and gas fields such as Anyue, Yuanba, Halahatang, Fuman and Shunbei have been discovered. This paper systematically summarizes three theoretical and technical achievements in studying deep and ultra-deep carbonate reservoirs in the past decade.(1) The micro-zone and multi-parameter experiment analysis technology featured by determining the “age, temperature, pressure and fluid properties” of carbonate reservoirs, together with experimental simulation of cross-tectonic-period pore formation and preservation featured by the “multi-stage, continuous, visualized and online detection technology”, providing useful tools for studying the pore formation and preservation mechanism of deep and ultra-deep carbonate rocks from the perspective of“forward” and “inversion”.(2) Deep and ultra-deep matrix-porous dolostone reservoirs are still controlled by sedimentary facies,among which reef(mound) and/or beach contribute most. The reservoir space is mainly composed of sedimentary primary pores and supergene dissolution pores and fractures, though some of reservoir spaces are formed by burial dissolution and they tend to develop and may locally concentrate following the pre-existing porous zone. In other words, burial dissolution vugs are inherited rather than newly formed. Early dolomite precipitation(or dolomitization) has a high potential to preserve early pores.(3) The development and preservation mechanism of fractured-vuggy karst limestone reservoirs in deep and ultra-deep realm was analyzed. Pene-contemporaneous dissolution and interlayer and buried-hill karstification control the development of early and late supergene fractured-vuggy reservoirs. Strike-slip faults superimposed with supergene karstification lead to the development of “fence-style” faulted karst reservoirs. Dissolution simulation experiments reveal that the development of karst fracturedvuggy reservoirs is facies-controlled in certain degree, mainly developed in packstone. Rock mechanics analysis reveals that the preservation of caves is under the control of lithology, cave size, and the distance to the unconformity, and caves can be well preserved at 10,000 m. The theoretical and technical achievements provide supports for carbonate oil and gas exploration into ten thousand meters deep.
基金supported by Major National Science and Technology Project of China(Grant No.2011ZX05004-02)
文摘Origin of dolostone remained a controversial subject, although numerous dolomitization models had been proposed to date. Because of the dolomitization＇s potential to be hydrocarbon reservoirs, one debatable issue was the role of dolomitization in porosity construction or destruction. Based upon case studies of dolostone reservoirs in various geological settings such as evaporative tidal flat （Ordos Basin, NW China）, evaporative platform （Sichuan Basin, SW China）, and burial and hydrothermal diagenesis （Tarim Basin, NW China）, here we systematically discuss the origin of porosity in dolostone reservoirs. Contrary to traditional concepts, which regarded dolomitization as a significant mechanism for porosity creation, we found two dominant factors controlling reservoir development in dolostones, i.e., porosity inherited from precursor carbonates and porosity resulted from post-dolomitization dissolution. Actually, dolomitization rarely had a notable effect on porosity creation but rather in many cases destroyed pre-existing porosity such as saddle dolostone precipitation in vugs and fractures. Porosity in dolostones associated with evaporative tidal flat or evaporative platform was generally created by subaerial dissolution of evaporites and/or undolomitized components. Porosity in burial dolostones was inherited mostly from precursor carbonates, which could be enlarged due to subsequent dissolution. Intercrystalline porosity in hydrothermal dolostones was either formed during dolo- mitization or inherited from precursor carbonates, whereas dissolution-enlarged intercrystalline pores and/or vugs were usually interpreted to be the result of hydrothermai alteration. These understandings on dolostone porosity shed light on reservoir pre- diction. Dolostone reservoirs associated with evaporative tidal flat were laterally distributed as banded or quasi-stratified shapes in evaporite-bearing dolostones, and vertically presented as multi-interval patterns on tops of shallowing-upward cycles Dolostone reservoirs associated with evaporative platform commonly occurred along epiplatforms or beneath evaporite beds, and vertically presented as multi-interval patterns in dolostones and/or evaporite-bearing dolostones of reef/shoal facies. Con- strained by primary sedimentary facies, burial dolostone reservoirs were distributed in dolomitized, porous sediments of reef/shoal facies, and occurred vertically as multi-intervai patterns in crystalline dolostones on tops of shallowing-upward cy- cles. Hydrothermal dolomitization was obviously controlled by conduits （e.g., faults, unconformities）, along which lenticular reservoirs could develop.
