Stress Analysis Of Casing In Unconsolidated Formation

The casing damage in oil and gas wells has always restricted the extraction of oil fields,which has seriously affected the economic benefits of the oil and gas industry at home and abroad.In order to prevent casing damage and improve the economic benefits of oil and gas industry,scholars have done a lot of experimental research on casing damage,but few studies have focused on casing mechanical behavior after unconsolidated formation changes.In this paper,based on the mechanism of unconsolidated formation changes,the unconsolidated formation changes are divided into unconsolidated formation sand production and dense formation-unconsolidated formation interlayer slip.And the mechanical theoretical model of the casing in the stratum after the above two changes is solved and analyzed.When a small area of cavity occurs in the formation,the stress on the outer wall of the casing at the same well depth will have a sudden change in stress under different conditions of the well wall(complete formation,cavity formation),and the casing will produce a peak stress at this location.Reasonably reducing the water injection pressure in the surrounding wells,reducing the internal pressure of the casing and increasing the steel grade of the casing can effectively prevent the casing from being damaged at this place.When large-scale cavity occurs in the formation,reducing the water injection pressure and fracturing pressure of the surrounding wells,reasonably reducing the borehole internal pressure,and increasing the casing steel grade and wall thickness can effectively prevent the casing from being subjected to vertical and horizontal bending forces.When the interlayer slip occurs in the dense-unconsolidated formations,the reasonable setting of the borehole pressure can reduce the uneven distribution of stress on the outer wall of the casing;increasing the steel grade of the casing while increasing the wall thickness can reduce the peak stress of the outer wall of the casing Below the yield stress of the casing;in dense formations near the junction of the formation,the open hole of the casing will also help reduce the possibility of the casing being damaged by shear.Only by taking into account the various changes in the formation status of the unconsolidated formation,can the completion production design be based on this to avoid damage to the casing in the borehole and improve the production efficiency of the oil and gas field.