Study on the effectiveness of fractures is of great significance for understanding reservoir types and properties, identifying reservoir seepage mechanisms and delineating the reasonable development technologies and p...Study on the effectiveness of fractures is of great significance for understanding reservoir types and properties, identifying reservoir seepage mechanisms and delineating the reasonable development technologies and policies. In this paper, the Changxing reef-flat facies reservoirs in the Yuanba area, Sichuan Basin, was taken as an example. After the characteristics of natural fractures were evaluated, the effectiveness of different types of fractures was investigated by using core, thin section, imaging logging and production performance data. Then, the main geological factors that influence fracture effectiveness were analyzed, and the development significance of effective fractures was illustrated. The following results are obtained. (1) Structural fractures and diagenetic fractures are mainly developed in Changxing Fm carbonate reservoirs in Yuanba area. Structural fractures include shear fractures and extensional fractures, and diagenetic fractures include dissolution fractures, structural-dissolution fractures and pressure-solution fractures. (2) High-angle structural fractures are the most effective, followed by horizontal fractures and then oblique fractures, and pressure-solution fractures are the least effective. (3) Among structural fractures, those of NW–SE and nearly E–W oriented are more effective than those of the NE–SW oriented. (4) The earlier the fractures are formed, the more likely they are to be filled with calcite or dolomite and become invalid. (5) The fractures which are formed before or during the oil and gas charging tend to be filled with organic matters and become invalid. The late fractures which are formed after oil and gas charging are mostly effective and their contribution to the reservoir is the greatest. (6) The fractures nearly parallel to the maximum principal stress direction of current ground stress present good effectiveness with large opening. It is concluded that the opening and filling features of natural fractures help determine if fractures are effective or not, and the development degree, distribution and combination features of effective fractures and the matching relationship between fractures and pores further dominate the development significance of effective fractures;that when the effective fractures are more developed and are connected with each other to form a large-scale fracture network, separated and isolated pores and dissolved fractures and cavities can be connected, as a result, the physical properties of reservoirs are improved and high production rates of gas wells are realized.展开更多
Microbes and microbial carbonates in reef-flat and coral community dynamics and submarine geomorphologic features in reef crest and fore reef of Yongxing Island,the Xisha Islands,South China Sea,were studied by means ...Microbes and microbial carbonates in reef-flat and coral community dynamics and submarine geomorphologic features in reef crest and fore reef of Yongxing Island,the Xisha Islands,South China Sea,were studied by means of scuba diving,underwater investigation,and line intercept transect survey.Studies indicate a very high coral mortality with few living corals in the reef flat of Yongxing Island.Moreover,macro algae,sea grass and cyanobacteria are common in reef flat.Microbes and microbially induced carbonates occur in reef flat.Living corals grow mainly in the reef crest and fore reef,but are also declined dramatically.From coast to off shore,the southeast reef flat of Yongxing Island can be divided into beach,inner reef flat,outer reef flat,reef flat front(reef crest and fore reef),and fore-reef slope settings.Sedimentary facies include coast,reef flat,reef crest and fore reef,and fore-reef slope.Reefal carbonate sediments are composed of coral skeletons and framework,coral fragments,bioclasts,and lime mud.With the deterioration of environment and water quality,the coral communities tend to be distributed in the reef crest and fore reef with clean sea water,well circulation and moderate water energy.Reef flat is occupied mainly by the macro algae and Heliopora coerulea communities.The coverage statistics on the reef crest demonstrate that the coverage of Acropora cytherea is more than 28% and represents a dominant species with wave-resistant ecological type.Sedimentary characteristics and geomorphologic features are different between the southeast and northwest reef-flat fronts(reef crest and fore reef) of Yongxing Island.The former shows discontinuously tidal channels in outer reef flat and different dimensional and deep reef ponds in reef crest and fore reef,and the latter presents a typical spur-and-groove system.Microbes(cyanobacteria Lyngbya sp.) occur generally in the inner reef flat and reef ponds of reef crest with restricted water circulation.Widely algae growth indicates a eutrophic environment,and the common microbes on the coral surface in the reef flat and reef ponds also demonstrate eutrophication in seawater and deteriorated water quality.展开更多
基金Project supported by the Sinopec Ministry of Science and Technology Project “Fine Modeling and Production Stabilization Strategy by Water Control for Reef-Flat Facies Gas Reservoir” (No.: P15050).
文摘Study on the effectiveness of fractures is of great significance for understanding reservoir types and properties, identifying reservoir seepage mechanisms and delineating the reasonable development technologies and policies. In this paper, the Changxing reef-flat facies reservoirs in the Yuanba area, Sichuan Basin, was taken as an example. After the characteristics of natural fractures were evaluated, the effectiveness of different types of fractures was investigated by using core, thin section, imaging logging and production performance data. Then, the main geological factors that influence fracture effectiveness were analyzed, and the development significance of effective fractures was illustrated. The following results are obtained. (1) Structural fractures and diagenetic fractures are mainly developed in Changxing Fm carbonate reservoirs in Yuanba area. Structural fractures include shear fractures and extensional fractures, and diagenetic fractures include dissolution fractures, structural-dissolution fractures and pressure-solution fractures. (2) High-angle structural fractures are the most effective, followed by horizontal fractures and then oblique fractures, and pressure-solution fractures are the least effective. (3) Among structural fractures, those of NW–SE and nearly E–W oriented are more effective than those of the NE–SW oriented. (4) The earlier the fractures are formed, the more likely they are to be filled with calcite or dolomite and become invalid. (5) The fractures which are formed before or during the oil and gas charging tend to be filled with organic matters and become invalid. The late fractures which are formed after oil and gas charging are mostly effective and their contribution to the reservoir is the greatest. (6) The fractures nearly parallel to the maximum principal stress direction of current ground stress present good effectiveness with large opening. It is concluded that the opening and filling features of natural fractures help determine if fractures are effective or not, and the development degree, distribution and combination features of effective fractures and the matching relationship between fractures and pores further dominate the development significance of effective fractures;that when the effective fractures are more developed and are connected with each other to form a large-scale fracture network, separated and isolated pores and dissolved fractures and cavities can be connected, as a result, the physical properties of reservoirs are improved and high production rates of gas wells are realized.
基金supported by National Natural Science Foundation of China (Grant Nos.40976030,41006029),Projects of International Cooperation and Exchanges of National Natural Science Foundation of China (Grant No.41210104029)Knowledge Innovation Program of Chinese Academy of Sciences (Grant No.SQ201114)
文摘Microbes and microbial carbonates in reef-flat and coral community dynamics and submarine geomorphologic features in reef crest and fore reef of Yongxing Island,the Xisha Islands,South China Sea,were studied by means of scuba diving,underwater investigation,and line intercept transect survey.Studies indicate a very high coral mortality with few living corals in the reef flat of Yongxing Island.Moreover,macro algae,sea grass and cyanobacteria are common in reef flat.Microbes and microbially induced carbonates occur in reef flat.Living corals grow mainly in the reef crest and fore reef,but are also declined dramatically.From coast to off shore,the southeast reef flat of Yongxing Island can be divided into beach,inner reef flat,outer reef flat,reef flat front(reef crest and fore reef),and fore-reef slope settings.Sedimentary facies include coast,reef flat,reef crest and fore reef,and fore-reef slope.Reefal carbonate sediments are composed of coral skeletons and framework,coral fragments,bioclasts,and lime mud.With the deterioration of environment and water quality,the coral communities tend to be distributed in the reef crest and fore reef with clean sea water,well circulation and moderate water energy.Reef flat is occupied mainly by the macro algae and Heliopora coerulea communities.The coverage statistics on the reef crest demonstrate that the coverage of Acropora cytherea is more than 28% and represents a dominant species with wave-resistant ecological type.Sedimentary characteristics and geomorphologic features are different between the southeast and northwest reef-flat fronts(reef crest and fore reef) of Yongxing Island.The former shows discontinuously tidal channels in outer reef flat and different dimensional and deep reef ponds in reef crest and fore reef,and the latter presents a typical spur-and-groove system.Microbes(cyanobacteria Lyngbya sp.) occur generally in the inner reef flat and reef ponds of reef crest with restricted water circulation.Widely algae growth indicates a eutrophic environment,and the common microbes on the coral surface in the reef flat and reef ponds also demonstrate eutrophication in seawater and deteriorated water quality.
