Influence of mechanical characteristics of deep composite salt-gypsum layers on safe drilling of directional wells: a case study of Palaeogene in the Kuqa Piedmont structure, Tarim Basin, China

The directional wells can effectively improve the development efficiency of deep and ultra-deep pre-salt oil gas reservoirs in Kuqa Mountains Tarim basin. Under condition temperature pressure, mechanical properties composite salt-gypsum layers are complex. During drilling process, that salt rock is easy to creep causes drill stick. controlling well inclination, it difficult choose appropriate fluid density resist thus maintain stability wellbore. On basis mechanics experiments, this study established a two-dimensional finite element model considering combination inclined with effect in-situ stress, analyzed influence temperature, differential stress deviation on creep. for preventing sticking calculated, safe chart shrinkage compiled. results show when less than 10 MPa, rate at least times higher Gulf Mexico layers; increases increase an incremental curve; taking highly deviated Bozi area as example, where ratio caused by set be 5%, resistance 45° 60° inclination built, which consistent actual field. provide design selection anti-creep Piedmont layers.