Differences of natural fracture characteristics and their development significance in Chang 6, Chang 7 and Chang 8 reservoir, Ningxian-Heshui area, Ordos Basin
Zhao Xiangyuan1, Zeng Lianbo1, Wang Xiaodong2, Wang Fei1, Zhang Yangyu3, Jiao Jun4, Weng Jianqiao1
1. College of Geoscience, China University of Petroleum, Beijing 102249;
2. Research Institute of Drilling and Oil Production Technology, Changqing Oilfield Company, PetroChina, Xi'an 710021;
3. CNOOC, Research Center, Beijing 100027;
4. Exploration and Development Research Institute of Changqing Oilfield Company, PetroChina, Xi'an 710018
Based on the outcrops, cores and logging data, fractures developing characteristics of Chang 6, Chang 7 and Chang 8 reservoir in Ningxian-Heshui area were compared and their development significances were discussed. There are two kinds of fractures in Chang 6, Chang 7 and Chang 8 reservoir in Ningxian-Heshui area, i.e. tectonic fractures and diagenetic fractures, but the occurrence, scale and development degree of fractures in each reservoirs are of great difference. Chang 6 reservoir develops nearly E-W and S-N tectonic fractures. In Chang 7 reservoir the fractures in the direction of NEE-SWW are developed the best, followed by the E-W and S-N. In Chang 8 reservoir, the NEE-SWW fractures are dominant, followed by the nearly E-W and NWW-SEE. The tectonic fractures in each reservoir are all mainly high-angle, while Chang 6 reservoir also develops low-angle mudstone slippage fractures with relatively high percentage. On the development degree and the scale of fractures, Chang 7 reservoir is of the best development degree with relatively small scale and Chang 8 reservoir is of the worst degree with a big scale. The situation in Chang 6 reservoir is between the two. Because of the different fracture characteristics above, fractures of different occurrence in each reservoir have different opening pressure values under the action of present ground stress. Therefore, reasonable water injection parameters should be determined in order to avoid large-scale open fractures which were caused by high water injection pressure being formed during water flooding development. Moreover, the calculation results of brittleness index of each reservoir showed that Chang 7 reservoir has relatively high values. With the high rock brittleness index and well-developed fractures, Chang 7 reservoir is suitable for volumetric fracturing to modify the reservoir.
. Differences of natural fracture characteristics and their development significance in Chang 6, Chang 7 and Chang 8 reservoir, Ningxian-Heshui area, Ordos Basin[J]. Chinese Journal of Geology, 2015, 50(1): 274-285.