52nd U.S. Rock Mechanics/Geomechanics Symposium,
2018. American Rock Mechanics Association
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ABSTRACT: The goal of the study is to find the optimal design of slotted liners by 3D finite element analysis and experimental study. Slotted liners are widely used in horizontal wells because of the abilities to ensure wellbore integrity and sand control. During installation and operations, the slotted liners have to be strong enough to hold axial loads and radial compression to prevent excessive buckling and deformation of slots. Experiments were designed to select the grades of materials, diameter/thickness of pipes, slot pattern. Finite element models were developed to decide the slotted liner design under various load conditions. The study showed considerations for slotted liner design and analyzed how much material grades, casing/tubing dimension and slot patterns can be expected to evaluate the risk of slotted liner failure.
Slotted liners are widely used to improve the performance of horizontal wells. They are mainly used for sandstone (Furui, 2012), limestone reservoirs. There are also applications in shale reservoir. However, the openings on the casing/liner can reduce the strength under geotectonic loading, such as axial compression, bending, and radial compression. The structural integrity of these slotted liners should be properly studied to ensure the safety.
Different plain casing/liner were studied by (Morita, 2014, Furui, 2012). According to Furui, axial-compression collapse is a major liner-deformation mechanism, and in horizontal sections, failure is induced by increased axial loading because of cavity deformation.
Slotted liners are manufactured by cutting several rows of slots with width ranging from 0.012in to 0.15in, and length ranging from 1in to 3in depending on the formation's grain size. But if the slots are too long, cause overlapping between offset slots, the structural capacity will be the lowest. (Xie, 2015) In this way, sand production can be prevented while keeping oil/gas production. Although bigger and more slots can ensure maximum production, structural capacity will be reduced. So slotted liner design needs to balance sand prevention, open flow area (OFA) and structural capacity.
Extensive sand production occurred in many wells, means slots deformed a lot. Slot opening can be due to various mechanisms including buckling under axial compression, bending, collapse under external pressure (formation touching).
The primary objective of slotted liner is to assure the structural capacity, sufficient sand prevention, while maintaining enough open flow area (OFA). In addition to base pipe parameters including materials grades, weight, diameter, wall thickness, properties of slotted liners are impacted by slot length, width, slot pattern and density.
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