Perforation Efficiency Estimation Through Soft Shutdown Results in Multi-Stage Slickwater Stimulated Wells
Authors: Alghanim Halah , Alowaid Abdulrahman , Baki Sohrat , Alsulaiman Nouf 
Published: March 2023

One of the key parameters in identifying the success of fracture placement is to determine the number of perforations contributing to creating fractures from each hydraulic fracturing stage. One of the popular methods of estimating perforation contribution and near-wellbore pressure frictional losses is by performing step-down tests (SDT). The only drawback of this methodology is that the rate has to be dropped in a step-wise fashion, which introduces operational constraints. At the area of the implementation, frac treatment designed rate is 92 barrel-per-minute (bpm) and is reduced to zero to shut-in the well in step-wise fashion. The objective of this paper is to exploit the opportunity of utilizing the common practice of soft shutdown (SSD), where rate is dropped to 60 (bpm) then to zero at the end of the stage frac job to act like a mini SDT as a practical alternative solution.

The proposed methodology entails conducting a tailored rate SDT on one well, and utilizing the shutdown period as a substitute to SDT on another well, specifically selected to be of the same conditions in terms of formation landing zone, stimulation treatment design and perforation count. A typical SDT is conducted by dropping the pump rate gradually in step-wise decrements. In this particular approach, two SDTs were performed within a single frac job, one at the beginning of the job before the introduction of proppant, and the other at the end after the flush period. Whereas in the SSD test approach, rate is dropped in only two steps at the end of the job and no time interval is specified. Pressure and rate are then selected as data points from each step, with instantaneous shut-in pressure (ISIP) considered as the final data point. It is important to keep as many variables fixed as possible in order to have the pressure response contributed by wellbore and perforation frictional components only. The selected data points are then plotted as pressure versus rate and matched with frictional losses and number of open perforations. The methodology capitalizes on the availability of SSD data, and evaluate its feasibility as a substitute to SDT.

By performing this type of analysis, an estimate of perforation efficiency from both methodologies was achieved. Although two different results were retrieved from the SDT obtained from the beginning and the end of the frac job, the one performed at the flush stage was the focus of this study as it mimics the most realistic setting of perforation efficiency post treatment. Although lower number of data points are obtained from the SSD approach, it did not obscure matching the calculated pressure to the selected pressure-rate data points. In fact, the results from the SSD indicated a variance of as low as 2% when compared to SDT results from a mirror stage. This small variation demonstrated the technical and practical feasibility of utilizing SSD as a strong substitute to SDT, promoting the effectiveness of this robust methodology.

Novelty of this approach lies within the utilization of readily available data retrieved from the original practice to substitute SDTs that could be operationally time consuming. The results from SSD tests validated the results from SDT, which allowed for the extrapolation of this approach to future wells within the same field without the necessity of performing any additional data acquisition.