Research On Fracture Formation Mechanism And Forecasting In Volcanic Rock Of Song Liao Basin

The basin has evoluted the complicated palingenic process from Palaeo Asiatic structural system to Pacific-Oceanic structural system on which the structural overlay and reconstruction of the structural movement with different characteristics and different direction have acted, Xiu jia wei zi fault depression is one of the biggest subsidence in the northern SongLiao basin, this fault depression has evoluted three period such as rift period, sag period and rediversion period. The Fangshen 9 well is located in the Xiujiaweizi fault depression with the simple structure and has the areal eastern dip-single slant. Yingcheng formation volcanic rock is one of the explorative objective formations in the rift deep formation. The explorative results show that the Commercial gas stream with high content of CO2 has been occurred in the second section of Yingcheng member. The fracture predetermination pre-drilling operation is difficult due to the complicated evolution of oil-gas distribution with the fractures. It should be essential significant for the volcanic areal fracture genetic mechanism and distribution sequences to the exploration and exploitation of volcanic reservoir.This paper emphasized that the field outcrop, core fracture observation, paleogeomagne- tic direction, microscopic fracture test, three dimensional finite-element digital simulation for the fracture genetic in-situ stress field by means of the multidisciplinary studies such as structural geology, petroleum geology and geophysics, So that the fracture density distribution quantitative predetermination results can be obtained.It has been predicted that the connate fracture has not widely generated and reconstructed by the postal structural stress or by the dissolution just within the research area, the secondary fractures and fractures are mainly the structural fracture. It has been measured that the two groups of macroscopic fracture's dominated direction are NEE-NE and NWW-NW, respectively, by the core pale magnetic direction measurements, the generating direction problem for the Yingcheng formation volcanic reservoir structure has been quantitatively resolved. The core section sheet analyses have shown that the principal horizontal stress direction for the target formation was NNW-SSE collision at the final period of K1 Nenjing structural movement, the principal horizontal stress direction for the target formation was NW-SE collision at the Ming shui period of K system, the principal horizontal stress direction for the present structural stress field is EW direction, so the stronger reversion movement direction for the stress field has been determined at the end of nengjiang group sedimentary period, at the end of Ming shui group sedimentary period as well as early tertiary period. The rifting for the subsidence period is so important that it controls volcanic distribution and postal structural fracture generation. Most of the faults for the Subsidence period and reversion period can't penetrate into the volcanic formation, but the redistribution of the Stress field in the revision period is the main mechanism of the volcanic rock structure fracture in the research area on the basis of outcrop observations and core measurements and statistics combined with microscopic structural testing results, as well as the areal Sedimentary environmental results, well logging evaluation and exploitation results, the comprehensive research results for the areal volcanic rock, facies and its fractures evolution process have shown that the fractures were generated around the volcanic vent which dominate by the inter-brecciated texture fractures and intercrystalline fractures in the volcanic breccia and agglomerate at the eruptive facies. The condensing contractive fractures were generated at the top and bottom base of the overflow facies, at this stage, the laminated volcanic formations were distributed the under water environment, the temperature difference has been generated between the temperature at which the volcanic projection and the temperature un...