薄盐层套损防控技术及其在河套盆地的应用OA

Aiming at the uneven casing collapse caused by the creep of thin salt layers in Hetao Basin,considering the wellbore integrity and economy,a targeted research on casing damage prevention and control was conducted.The laboratory creep experiments on salt rock revealed the creep behavior of high-temperature,deep,and thin salt rock.The experiments showed that the steady-state c reep strain(0.69%)of salt rock at 150℃is 4.6 times of that(0.15%)at room temperature.A formation-cement sheath-casing composite mechanical model was established,introducing uneven load factor Kp to improve the calculation method for casing collapse resistance under uneven loads.It was clarified that the main cause of casing damage is that the external collapse force from salt rock creep exceeds the casing's collapse strength under uneven in-situ stress.Based on these findings,a comprehensive casing damage prevention and control technology system adapted to the thin salt layers in Hetao Basin was developed.In the thin salt layer interval,casing with an outer diameter of Ø206.36 mm,steel grade 140HC,and wall thickness of 17.25 mm was adopted,which significantly enhanced the collapse resistance and bending stiffness of the wellbore.Combined with a reaming process to increase the annular clearance,the cementing job quality in the thin salt layer interval was improved.This technology has been applied in five wells,including Well X11-15 in Hetao Basin,effectively guiding the selection of salt-sealing casing.The mixed casing string was run smoothly,the cementing job quality in the salt layer intervals after reaming met the standards,and no casing damage occurred within 1 to 3 years after completion.Moreover,this technology effectively addresses the challenge of casing damage in thin salt layers,without adjustment of the original wellbore configuration,offering significant advantages in controlling drilling costs and shortening the drilling operation cycle.It can provide theoretical reference for the safe and efficient development of similar sub-salt oil and gas reservoirs.