Abstract
The feasibility of a normal perforating operation depends on the perforating tubing string, which is the main component of the cluster perforating tool for the exploration and development of unconventional oil&gas reservoirs. To improve the efficiency of cluster perforation in horizontal wells, a passing capability analysis model for the tubing string in a wellbore was established, thereby generating complex equations with coefficients that are solved via geometric analyses and the beam-column theory. This model was based on a comprehensive consideration of the friction between the downhole tools and the borehole wall, fluid resistance, wellbore geometric constraint, pump thrust, axial tension, tool variable cross-section, tension of cable head, and tool elastic deformation. Based on field test data, the pass-through capacity of “1 bridge plug + 4 cluster perforating gun string” in the X206 well and the main factors affecting pass-through ability were analyzed to test the validity of the model. The model presented in this paper can provide an effective tool for analyzing the design and operation of a cluster perforating string.
Highlights
Cluster perforations 1 have resulted in revolutionary developments in perforation technologies 2
During a cluster perforating operation, the tool string is conveyed to the downhole target stratum via a cable; this is followed by bridge plug setting and multi-cluster perforation 3
A large tool string can get stuck, especially under specific well conditions such as irregular well trajectories and a high dogleg degree. This can result in a sudden rise in the pumping pressure, thereby leading to accidents such as premature setting of a composite bridge plug, deformation of perforated tubing strings, wear failure of tubing-casing and strength failure 5
Summary
Cluster perforations 1 have resulted in revolutionary developments in perforation technologies 2. A large tool string can get stuck, especially under specific well conditions such as irregular well trajectories and a high dogleg degree This can result in a sudden rise in the pumping pressure, thereby leading to accidents such as premature setting of a composite bridge plug, deformation of perforated tubing strings, wear failure of tubing-casing and strength failure 5. Existing studies assume that the tool string is stuck at a position of maximum dogleg degree These models are appropriate for rigid tool strings; for tool strings with greater flexibility, including cluster perforating strings, such simplifications and assumptions are significantly different from the actual situation, resulting in a conservative prediction. The model was based on the comprehensive consideration of factors such as the friction force between the downhole tools and wellbore, wellbore geometry limitation, pump thrust, axial tension, string variable cross section, tension of cable head and tool elastic deformation
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