Seismic performance analysis of ultra-deepwater jacket platform with external hanging well slot using SACS-based simulation

doi:10.11996/JG.j.2095-302X.2026040874

Abstract

Abstract:

External well-slot extensions for jacket platforms have been widely adopted because they enable the full utilization of existing platforms to develop additional reserves in mature oil and gas fields at relatively low cost. However, most existing studies on external well-slot extensions focus on shallow-water conditions with water depths of approximately 30 m or less, whereas in ultra-deepwater environments the load-transfer mechanism of jacket-integrated systems with external well-slot extensions becomes considerably more complex. To address the limited understanding of the seismic performance mechanism of external well-slot extensions on in-service ultra-deepwater jacket platforms, a design scheme for an external well-slot extension on an in-service ultra-deepwater jacket platform was selected as the case study. A refined finite element model was established in the conventional offshore engineering analysis software SACS (Structural Analysis and Design System), and dynamic response simulations were performed based on a 200-year return-period acceleration response spectrum; additionally, discretized horizontal input directions were considered to evaluate directional effects. Connector stiffness was parameterized by modifying the elastic modulus of the connector material, and structural responses under stiffness multipliers of 0.5, 0.75, 1.0, 1.5, and 2.0 relative to the baseline were analyzed. Stress contour plots and the first five mode shapes were generated using the graphical functions of SACS to visually identify stress-concentration regions and differences in dynamic characteristics. Furthermore, focusing on sensitive members in the connection region, a mixed-effects model was introduced to quantify the relationships between connector stiffness, the maximum Unity Check (UC) value, and the associated stress components, thereby reducing the random influence arising from member-size and location variability. The results indicated that member stress levels in the connection region were significantly higher than those in surrounding areas, and that increasing connector stiffness led to an overall upward trend in the maximum UC of sensitive members, with some members exhibiting UC values exceeding 1.0 at twice the baseline stiffness. The mixed-effects analysis revealed an extremely significant positive correlation between connector stiffness and the maximum UC, and showed that the increase in maximum UC was primarily driven by the growth of shear stress and bending normal stress with increasing stiffness, whereas the effect on axial stress was not significant. Considering the direction-discretization results, seismic inputs perpendicular to the connection direction were more likely to trigger unfavorable structural responses due to displacement incompatibility induced by differences in dynamic characteristics between the jacket and the well-slot extension; excessive connector stiffness may further intensify stress concentration and reduce safety margins. It should be noted that the simulations were based on a single in-service platform design scheme and a linear analysis framework; therefore, the findings mainly reflected mechanisms and trends. Further validation across different regional seismic inputs, platform scales, and structural configurations is required, and nonlinear analyses and detailed modeling are recommended to improve engineering applicability.

Key words: jacket, external hanging well slot, dynamic response analysis, mixed-effects model, SACS

CLC Number:

TP391.9
TE95

XU Mingchao, LI Sunwei, LIU Dongliang, CHEN Yeming, ZHANG Hongning. Seismic performance analysis of ultra-deepwater jacket platform with external hanging well slot using SACS-based simulation[J]. Journal of Graphics, 2026, 47(4): 874-881.

Figures/Tables 11

Table 1 Intraclass correlation coefficients and adjusted r-squared values in each mixed-effects model

因变量	组内相关系数	调整决定系数
最大UC值	0.947 97	0.902 10
轴向应力	0.983 59	0.986 93
剪应力	0.975 72	0.958 34
弯曲正应力	0.993 50	0.991 05

Fig. 1 Q-Q Plots of residuals for each mixed-effects model ((a) Maximum UC value; (b) Bending normal stress; (c) Axial stress; (d) Shear stress)

Fig. 2 Newly built jacket platform with external hanging well slot in a certain sea area ((a) Oblique view of the jacket；(b) Front view of the jacket)

Fig. 3 Mesh refinement of members at the connection

Table 2 Main structural parameters of jacket platform with external hanging well slot

结构部位	重量	桩腿数	总高度/m	底面尺寸/m	设计水深/m
老导管架	27 612	8	127.49	60×55	93.57
外挂井槽	9 347	4	127.49	24×19	93.57

Fig. 4 Spectral amplification coefficient curve for a 200-year return period

Fig. 5 Structural stress contour plot under original stiffness

Fig. 6 Local stress contour plot of structural connection under original stiffness

Fig. 7 Maximum UC values of 15 sensitive members under various stiffness conditions

Fig. 8 First 5 mode shapes of the structure ((a) First-order mode shape; (b) Second-order mode shape; (c) Third-order mode shape; (d) Fourth-order mode shape; (e) Fifth-order mode shape)

Table 3 Results of mixed-effects model analysis

应力类别	系数	标准差	t值	P值
轴向应力	-1.933 54	3.028 57	-0.638 43	0.525 25
剪应力	11.419 23	3.222 15	3.543 98	7.01×10^-4
弯曲正应力	59.475 40	8.214 16	7.240 60	4.24×10^-10

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