Analysis from How Fluid Flow Influences the Fault Sealing: a Case Study of Wx Fault Belt, Junggar Basin of China
WX fault belt is located in the northwest margin of Junggar basin. Many faults in the area suffered multistage tectonic activities and were always the places of active fluid flow. Along the fault belt, a lot of anomalies were shown to reflect fluid movement, such as changes in mineral petrology, temperature and pressure anomalies. The fluid flow near fault zone enhances the transportation, transition and deposition of dissolved matter and influences the fault sealing. In WX belt, many wells drilled through faults and the mineral depositions were particularly common in cores in the fault belt. Fractures were mainly filled with calcite, cemented densely. However, unsealed faults often displayed higher porosity and permeability. When underground water with high salinity migrated through faults, oil became dense and blocked pores. Permeability decreased because of the dissipation of light component or oxidation and degradation of oil, which was well proved by the fact that a great number of fractures in drilling cores were filled with asphalt in WX area. Analysis of the rock samples showed that the average porosity near fault zone was below 5% and the permeability was even lower than 0.2µm2. The increase of cementation near fault zone exhibited negative correlation with the porosity and permeability. Although the formation of faults facilitated the fluid flow, this activity often led to the mineralization, cementation, oxidation and asphaltization in the late period, reducing the permeability of fault belt. Ultimately, it resulted in the enhancement of the fault sealing and prevented oil to migrate along the fault belt.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009