Real-Time Analysis of Formation-Face Pressures in Acid-Fracturing Treatments

Knowledge of fracture-entry pressures or formation-face pressures (FFPs) during acid-fracturing treatments in real-time mode can help in evaluating the effectiveness of the treatment and improve the decision-making process during execution. In this paper, methods and tools used to generate FFPs in real-time mode with the help of bottomhole-pressure (BHP) data are discussed in detail. The horizontal wells selected for the study were drilled and completed in the North Sea with permanent BHP gauges that enabled constant monitoring of downhole pressures. The tool in discussion uses the combination of treatment data such as surface pressure, fluid density, injection rates, fluid type, wellbore details, and wellbore deviation, along with bottomhole-gauge pressures, to calculate fracture-inlet pressures just outside the casing at active perforation(s) depth. The tool performs the calculations in “live” mode during treatment execution and simultaneously generates a dynamic array of data that assists in “on-the-fly” evaluation and the decision-making process. Several acid-fracture treatments were analyzed using the tool and led to important conclusions related to fracture-propagation modes, acid-exposure times, and the effectiveness of given acid types. The results had a direct influence on the modification of treatment designs and pump schedules to optimize treatment outcomes.