Reservoir engineers study a formation’s geology to determine what fluids, proppant concentrations, pressures, and procedures are necessary to optimize production from each zone. Operators in North American drill most wells horizontally to maximize contact with their formation. The primary process for completing wells is called Plug & Perf, which enables the segmentation of horizontal wells to treat individual zones separately. Plug & Perf involves connecting a plug to a wireline bottom hole assembly (BHA) that includes perforation guns and a setting tool, running the BHA to a specific point in the well, setting the plug, perforating the well, and after removing the BHA fracing the zone. The plug must stay anchored and sealed during the frac, so the treatment reaches the formation per the design. The process repeats for each stage of the well. Afterward, a milling operation removes the plugs from the well.
The plug is the most critical equipment in the completion operation; it ensures the frac reaches the appropriate zone. The plug must be easy to connect to the wireline BHA, have no issues while being pumped to the correct location in the well, anchor & seal against a frac that could be up to 10,000 psi. Then, drill up into small pieces in less than 10 minutes. The design and manufacturing of frac plugs shall perform without issues up to 100 times a well. The varied nature of the steps in the process is why the composite plug faces the most formidable challenge of any completion technology.
The first step in the plug & perf operation is connecting the plug to the setting tool. The proper connection ensures the design force is exerted on the plug to set it in the well. If the setting force is too low, the plug will not set fully and slide when it sees pressure. Too much setting force and the plug could break during the process. This connection must be easily repeatable because wireline teams must do it up to 18 times a day, along with all their other responsibilities.
There are two sections in a plug & perf well: the vertical and horizontal sections. The wireline BHA can fall to the transition point (Kick-off point) in the vertical section. When the BHA falls, fluid travels upward around the plug. The accelerating fluid creates a force against and a low-pressure zone around the plug, which must withstand these forces. Once in the horizontal section, the operator will pump fluid to carry the BHA to the proper location. Pumping the BHA isn’t 100% efficient, so now the fluid is traveling past the plug downward. The plug must handle these forces as well.
Also, the plug has the largest OD of the wireline BHA. As it travels down the well, it is dragging against the casing. The materials must withstand this friction without causing a preset during the pump down.
The setting tool applies a force against the plug to lock the slips into the casing and energize the element. The slips anchor the plug to ensure it doesn’t move (up or down), and the element creates a seal to keep fluid from bypassing during the frac.
The plug sees high pressures during the frac, up to 10,000 psi. The assembly must hold its anchor and seal throughout the process, including multiple changes in pressures as the formation breaks down, sand concentrations change, and operations progress.
After the frac operation completes, all the plugs in the well must mill up. They must break into small pieces that are small and lite enough to flow past the milling BHA and out of the well.
Success with plug & perf completion is not about one tool working correctly. It is about 1,000s of plugs meeting the challenges described above. To reduce risk in your operations, you should select a completions provider that understands material properties, design, manufacturing, and field operations. WellBoss has over a decade of experience engineering, producing, and deploying over 600,000 plugs. We understand the entire process and have built our company, products, and team around meeting these challenges to reduce your risk.