Analysis of Shut-in Pressure Decline for Enhancing our Evaluation of Hydraulic Fracturing Treatments

Abstract

The focus of this paper is on the analysis of shut-in data immediately after a fracturing treatment and critical information that can be learnt about the created fracture from the magnitude and rate of pressure decline during this period. The selected example data in this paper had two specific features; frac job was injected in two cycles in several stages, and had long shut-in time (more than 10 hrs) in all stages. Review of this data shows that frac growth in each stage continues at a decreasing rate beyond the end of pumping and how many hours of shut-in was needed for the fracture to reach its ultimate stable condition. In this horizontal well with multiple fractures the data also gives direct measure of the relative complexity of the created fractures in each stage and their conductivity. The paper recommends specific practices that can enhance what can be learnt from the data. These include recording the pressure data continuously during the treatment and for the entire shut-in period, and occasional injection of a small volume of fluid into one or more randomly selected fracture stages to gain better understanding of fracture growth during the stage. An important conclusion of the paper is that the Instantaneous Shut-In Pressure (ISIP) does not provide a reasonably accurate measure of the least in-situ principal within the fractured formation.