Title : Field diagnosis and operational mitigation of casing deformation during hydraulic fracturing: A case study of a multi-layer deep shale-gas development pad in the Daan Block, sichuan Basin
Abstract:
Casing deformation is a recurring well-integrity challenge during multistage hydraulic fracturing of deep shale-gas horizontal wells, particularly on multi-layer development pads where wells targeting vertically stacked reservoirs are stimulated within a limited area. This paper presents a field-based diagnosis of casing deformation on the Daan 1H21 Pad, a representative multi-layer development pad targeting the deep Wufeng-Longmaxi shale succession in the Daan Block, southern Sichuan Basin, China. The analysis integrates multi-finger caliper surveys, well trajectories, cement-bond logs, fracturing-pressure records, interwell pressure responses, microseismic monitoring, and seismic discontinuity interpretation.
Seventeen deformation points were identified across the pad, nine of which displayed distinct step-like shear signatures. The deformation points were mainly located near interpreted fracture corridors or mechanically contrasting stratigraphic interfaces. Comparison with dogleg severity and cement-bond quality showed no systematic relationship, indicating that trajectory curvature and cement quality were not the dominant causes. In contrast, several deformation intervals coincided with anomalous microseismic energy release and rapid pressure responses in offset wells, including responses over relatively long interwell distances. Pressure communication was also observed between wells targeting different vertical intervals. These observations suggest that injected fluid entered connected natural fractures, increased fracture pressure, and induced localized slip that transferred shear loading to the casing. The vertically stacked well arrangement and closely spaced fracturing sequence further increased interwell stress interference.
Following the deformation events, the stimulation sequence and operating parameters were adjusted. Continuous adjacent-well zipper fracturing was replaced by a more separated sequence, and pumping intensity was reduced near suspected risk zones. The remaining stages were subsequently completed successfully. The case study demonstrates that integrating casing diagnostics with pressure and microseismic surveillance provides an efficient means of identifying fracture-reactivation-related deformation and supporting timely operational decisions. The results offer a practical workflow for reducing casing-deformation risk on multi-layer shale-gas development pads.
Keywords: Casing deformation; Multi-layer development pad; Deep shale gas; Hydraulic fracturing; Fracture reactivation; Wellbore integrity
