Risk assessment method for cementing program considering well integrity

The development of the Jimsar shale oil is found with severe issues of well integrity failure due to fracturing, and the failure position and rate are highly differentiated among different cementing programs. To investigate the effects of cementing programs on well integrity during fracturing, two horizontal well models (Ⅰ and Ⅱ) were built in accordance with the characteristics of the cementing for the horizontal wells with two casing sections in the study area. The same positions of the 1^st and 2^nd casing sections and the solid-fluid interface between the cement sheath and drilling fluids in Well Ⅰ were selected for analysis. The effects of fracturing on the well were simulated using a finite element simulator. In cases of different cementing programs, the stress distribution patterns of the casing and cement sheath along the well during fracturing were clarified, the full-well multi-node failure risks were assessed, and the cementing program was optimized. The results showed that with the B annulus filled with drilling fluids, the Mises stress of the production casing is considerably higher than that with the B annulus occupied by the cement sheath, indicating higher damage risks. The stress of the cement sheath in the B annulus is higher than that in the C annulus. Moreover, the top of the B annulus cement sheath is prone to tensile failure, while the bottom is prone to compressive failure. The Ⅰ cementing program is found with lower risks of well integrity failure, compared with the Ⅱ cementing program. The performed risk assessment and optimization provide guidance for the designs of cementing and well completion of wells to be fractured to deliver safe and cost-effective cementing and well completion programs.