ABSTRACT:

Volume fracturing has shown great promise in reconstructing unconventional oil/gas reservoirs effectively, while new problems of frequent casing deformation failure were triggered. In this paper, based on drilling and completion data, rock damage criterion and microseismic surveillance data, and previous studies about relevant influencing factors, 2D and 3D finite element model (FEM) of casing-cement sheath-formation are established to study the mechanism of casing deformation during multi-stage volume fracturing of Z1 tight oil horizontal well. The results show: a) those factors thought by most scholars just cause the cross-section of the casing smaller change, which do not block the bridge plugs pumped by elastic coiled tubing; b) influenced by in-situ stress, natural fractures tend to slip when the stress difference is large enough, and slippage is mostly likely to happen as the angle between the natural fracture and maximum horizontal stress reaches 30° and the shear displacement is usually several centimeters; c) natural fracture slip is accompanied by drastic local casing shrinkage, with slight deformation one side and severe another, as observed from the impression blocks in oilfields. The results demonstrated in this paper can provide the theoretical basis for the prevent treatment of casing deformation failure during the fracturing reconstruction of stimulated reservoir volume of tight oil horizontal well.

1. INTRODUCTION
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