Abnormal Pressure Distribution Rule And Tectonical Control Mechanism In Bide-santang Basin

It is necessary to study the distribution rule and formation mechanism of coal reservoir pressure for which influences development technology, completion method and production capacity of CBM wells. The distribution rule of reservoir pressure was analyzed according to water-head height of hydro-geological borehole, CBM well test data and measured gas pressure in Bide-Santang basin of Zhina coal field in Guizhou province.The quantitative evaluation of medium and small faults complexity was done adopting fractal theory. The characteristic of stress field was analyzed accoding to the results of in-situ stress test and hydraulic fracturing test. Based on the reservoir physical properties, the hydro-geological condition and geological tectonic characteristics, the control mechanism of tectonic characteristics and tectonic stress field to abnormal pressure was discussed.Research shows that: the reservoir pressure belongs to stress gas under pressure type. The data of equivalent pressure and well testing pressure reveal that reservoir pressure is mainly low and normal pressure, and there is abnormal high pressure in some local areas. Water burst with a mass of gas in the synclinal shaft and fold hinge zones indicates that the abnormal high pressure system in which hydraulic pressure plays a supporting role is mainly composed of gas pressure. The faults formed in multiple compression stress field are closed. The pressure coefficient near conversion depth of stress field is higher. The upward bending curve of closure pressure and pressure coefficient declares that reservoir pressure is composed of groundwater hydrodynamic field contribution and geostatic transmission. Discrete surface pressure coefficient with buried depth and stable deep reservoir pressure coefficient show there is one or more confined water system in deep determining the reservoir pressure while in-situ stress has a little influence. The formation mechanisms of abnormal high pressur e divide into reservoir self trap and confined water sealing type. The former is represented by Wulunshan well field in Shuigonghe syncline and Agong and Zhucang synclines are on behalf of the latter. The abnormal low pressure is mainly caused by tectonic uplift, erosion and formation temperature decrease.