How Do We Achieve Sub-Interval Fracturing?

Abstract

To achieve multiple transverse fractures in a horizontal well, ball-actuated stimulation-sleeve completions were developed as an operationally faster alternative to plug-and-perforate completions. However, ball-actuated stimulation sleeves have reached a physical limit for the maximum number that can be used in a well. Horizontal wells can be divided into approximately 20 independent intervals. The actual maximum number of intervals is dependent on several variables. The goal is to achieve an independent transverse (normal to the wellbore axis) fracture for each interval. Each interval is pumped separately. To attain more transverse fractures per well, multi-entry stimulation sleeves were developed to subdivide the intervals. An interval consists of one traditional ball-actuated stimulation sleeve and one or more multi-entry stimulation sleeves located upstream of the traditional stimulation sleeve. Multi-entry stimulation sleeves are actuated, or opened, with a specific-diameter ball, and then the ball is released and lands on a traditional stimulation sleeve. Each interval is still pumped separately, and the fluid flows in parallel through each sub-interval (sleeve within the interval). The question to be answered is how can sub-interval fracturing be achieved while pumping through multi-entry sleeves in parallel? The ultimate goal is to achieve one transverse fracture per sub-interval. Analysis results are presented that address several issues, specifically, the role of annular isolation between sub-intervals, methods to achieve sub-interval fracturing, and scenarios that result in only one fracture per interval. Several options for the verification of sub-interval fracturing are discussed. Currently, plug-and-perforate completions with multiple clusters are used. The perforation clusters are pumped in parallel. However, there is more to be done to help ensure sub-interval fracturing or verify the effectiveness of the multiple clusters. Strengths and weaknesses of the verification methods for both multiple-cluster plug-and-perforate completions and multi-entry stimulation-sleeve completions are discussed.