Characteristics of fractures from borehole walls of gas-hydrate drilling holes in Muli region
Yang LI1,2,3, Dong-Ming LIU1,2,3(), Zhen-Zhou LIN1,2,3, Yu-Hang WANG1,2,3, Ding-Yu JIA1,2,3, Yang OU1,2,3
1. Institute of Geophysical and Geochemical Exploration, CAGS, Langfang 065000, China 2. Eelectromagnetic Detection Technology Key Laboratory of Ministry of Natural and Resources, Langfang 065000, China 3. National Modern Geological Exploration Technology Research Center, Langfang 065000, China
Well-developed faults and diversified lithology constitute the features of Sanlutian well field, and the drilling results reveal that gas hydrate mainly occurs in the fractures of reservoirs. Therefore, the acoustic image logging data are used specifically to study the structural fractures from borehole walls of gas-hydrate drilling holes in Sanlutian well field. In this paper, the response characteristics of fractures in acoustic image logging were confirmed and the linear density, dip angle and dip direction of fractures were discussed. Some conclusions have been reached: ① Fractures are developed in the borehole walls of gas-hydrate drilling holes. In these fractures, high-angle fractures are dominant, followed by low-angle fractures, and the vertical and horizontal fractures are rare. ②The main strike of fractures is basically consistent with the fault strike or oblique-crossing at small angles. The distribution of fractures is controlled distinctly by faults. ③It is unfavorable for the assembly of hydrocarbon gases as the fractures of the study area are dominated by high-angle fractures, which is one of the possible reasons why gas-hydrate is rare.
Pang S J, Su X, Yang X , et al. Sedimentological features of middle jurassic strata revealed by scientific drilling boreholes of natural gas hydrate in Qilian Mountain permafrost[J]. Geological Bulletin of China, 2011,30(12):1829-1838.
Deng C X, Pan H P, Fang S N . Fracture identification and the response characteristics of fracture in the third drilling hole of WFSD project[J]. Geological Science and Technology Information, 2015,34(5):184-189.
Liu D M, Lin Z Z, Gao W L , et al. The interpretation of ultrasonic imaging logging data obtained in drill hole ZDSD-1 of the zedang scientific drilling in Tibet[J]. Geophysical and Geochemical Exploration, 2017,41(4):672-677.