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Jiangyou, China

Kang Y.,Southwest Petroleum University | Huang F.,Southwest Petroleum University | You L.,Southwest Petroleum University | Xu C.,Southwest Petroleum University | Mi G.,Northwest Sichuan Gas Field
Xinan Shiyou Daxue Xuebao/Journal of Southwest Petroleum University

The invasion of drill-in fluid into reservoir formation can lead to a damage zone around the wellbore during the process of over balanced drilling and completion in fractured tight reservoirs, which will strongly affect the production performance of a well. Taking the tight conglomerate reservoir of Jiulongshan structure as the research object, the mathematical model of solute transport in fractured network was established by double continuous medium method; the dimensionless concentration at any time in different position from wellbore was determined by using finite difference method to solve the developed model; the extent of formation damage caused by drill-in fluid loss was quantitatively evaluated, and the numerical results were validated by pressure built-up test analysis and dynamic damage assessment of drill-in fluid. The numerical results show that the depth of drill-in fluid invasion increases over time, and pollutions induced by the drilling fluid loss continuously push and cumulate in depth of the formation with the kill fluid loss; respectively, the radius and equivalent skin factor of damage zone due to lost circulation of drill-in fluid is about 17.0 m and 7.5, the relative errors between the numerical results and the results of pressure built-up test analysis and dynamic damage assessment are less than 10%, which proves the reliability of the model. ©, 2015, Science Press. All right reserved. Source

Gong L.,Northeast Petroleum University | Gong L.,Daqing Petroleum Administration Bureau | Zeng L.,China University of Petroleum - Beijing | Chen S.,Daqing Petroleum Administration Bureau | And 4 more authors.
Geotectonica et Metallogenia

Based on microscopic thin section analysis and in combination with filed observation, core logging, and experimental results, we investigated the genetic types and validity of micro-fractures in the compact conglomerate of the Zhenzhuchong Formation in the Jiulongshan structure in the north of western Sichuan foreland basin, and discussed their contribution to reservoirs. Three types of micro-fractures, i.e. intragranular, gravel edge, and transgranular fractures, are developed in the compact conglomerate reservoirs of the Zhenzhuchong Formation, and their genetic types are dominated by structural micro-fractures, followed by diagenetic micro-factures and pre-existing micro-fractures. Few of these micro-fractures are filled with minerals, so most of the micro-fractures are effective. The validity of micro-fractures is affected by the age of fractures, dissolution and abnormal pressure. The average aperture of micro-fractures is 11.0 μm and the mean areal density is 0.85 cm/cm2, which illustrate that micro-fractures are well developed in the study area. The average porosity of micro-fractures is 0.78%, which accounts for 22.9% of the reservoir total porosity; and the average permeability is 3.18 mD, which reflects that the micro-fractures are the major storage space in the study area. © 2016, Science Press. All right reserved. Source

Gong L.,China University of Petroleum - Beijing | Zeng L.,China University of Petroleum - Beijing | Pei S.,Northwest Sichuan Gas Field | Zhang B.,Northwest Sichuan Gas Field | And 3 more authors.
Scientia Geologica Sinica

Fracture is an important controlling factor for the distribution of tight sandstone gas reservoirs in the second member of Xujiahe Formation in Jiulongshan structure at the north of western Sichuan Basin. Using the data of outcrops, cores, thin sections, image logs and experimental analysis, we analyzed the fracture origin types, development characteristics and formation mechanism. There are two types of fractures in the study area, i. e. tectonic fractures and diagenetic fractures. Among them, tectonic fractures are the dominant. They are mostly shear fractures with three sets of NEE-SWW, NNE-SSW and NW-SE orientations. According to the dip angle, tectonic fractures can be subdivided into shear fractures with high dip angle and horizontal shear fractures. The shear fractures with high dip angle formed under the tectonism of the end of Indosinian, Yanshan and Himalaya stage. The forces that formed tectonic fractures came from horizontal tectonic compression of Longmen Mountain and Micang-Daba Mountain, overpressure caused by deep bury and stress from the uplift. The horizontal shear fractures were related to the thrusting of faults and interlayer sliding under tectonic compression. Source

Gong L.,China University of Petroleum - Beijing | Zeng L.-B.,China University of Petroleum - Beijing | Zhang B.-J.,Northwest Sichuan Gas Field | Zu K.-W.,China University of Petroleum - Beijing | And 2 more authors.
Zhongguo Shiyou Daxue Xuebao (Ziran Kexue Ban)/Journal of China University of Petroleum (Edition of Natural Science)

Based on the data of outcrops, cores, image logs and thin sections, the distribution characteristics and controlling factors of fractures in tight conglomerate reservoirs were discussed. The results show that there are three types of fractures which include trans-gravel fractures, gravel-edge fractures and intra-gravel fractures in the tight conglomerate reservoirs. Among them, trans-gravel fractures are dominant. The development degree of these fractures is controlled by the gravel composition, gravel size, contact relationship between gravels, interstitial material composition and structural location. The fracture development degree in the quartz sandstone gravels is better than that of the chert gravels. The development degree becomes better with the increase of gravel size, contact area and interstitial material, while the content of clay matrix is adverse to the fracture development degree. The favorable areas for fracture development are the high part of structures and the fault areas, which are the favorable areas for natural gas accumulation. Source

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