Study on In-Situ Stress in Paleogene Gypsum Mudstone in Yubei Area

Complex and atrocious geological conditions result in high formation pressure and abnormal in-situ stress in Paleogene,which were causes of casing collapse in several wells.In order to clarify the creep characteristics of gypsum mudstone,considering the tectonic evolution and the fault distribution in Yubei Area, Huang’s "seventh-five" model was used.With actual drilling and logging data,this model could determine vertical and horizontal maximum and minimum principal stress in gypsum mudstone layers.Based on the relations among three principal stresses,the types and distribution of faults and fault zones were identified.In addition,in-situ stress characteristics of each well were analyzed.Finally,the distribution of in-situ stress and gradient of abnormal in-situ stress were obtained in Paleogene,which may help guide future well deployment,optimization of casing program and the drilling program.