Using Automated Pressure Transient Analysis (Auto-PTA) to Understand the Root Causes of Production Impairment

Abstract This article presents the rationale behind the use of automated Pressure Transient Analysis (auto-PTA) to dramatically reduce the time spent on an analysis, to perform the analysis in a consistent and repeatable manner, and to allow more well tests to be included in the solution set. In short, the objective is to employ auto-PTA to increase sample size, improve accuracy and precision, and reduce bias. Several case studies will be presented, covering a variety of different well types, highlighting the time savings/engineering efficiency, as well as the improved consistency of this workflow. The first step in performing a PTA is to ensure that the data includes valid flow rates and bottomhole pressures. Errors in the rates have a direct relationship with the calculated permeability and distances to reservoir limits; errors in the rate and in the bottomhole pressure have direct and indirect relationships with skin. Once the rates and BHPs have been validated, wellbore geometry and reservoir flow regimes must be considered in order to initiate the automated PTA. This will be explained in much more detail in the main text of the paper, but a simple way to think about this is that picking a radial flow period in a conventional vertical well is different than picking linear flow in a fractured horizontal well. Next, an algorithm, expert system, neural network, or AI system may be created to automatically analyze the PTAs consistently. An engineer then needs to spend only a few minutes per test to validate/approve it, so that test can be included in the historic PTA dashboard. Pressure Transient Analysis (PTA), combined with wellbore pressure drop and velocity calculations is the most effective way to determine the location of a production impairment. Other surveillance techniques, such as nodal analysis, productivity tracking or unit step delta pressure (P1hr-Pwf) methods are quite good at recognizing that a well has a problem, but they do not specify what or where the problem is. PTA splits the production impairment delta pressures into losses in the completion, in the reservoir, or in combinations thereof. Automating the PTA process reduces the engineering time spent per PTA from days to minutes and improves the consistency of the results. Once added to the PTA dashboard, the rest of the team can then use that information to draw meaningful conclusions. Automated PTA has been employed for at least fifteen years in conventional wells but has only been recently used for fractured unconventional horizontal wells. This article will also discuss some of the early results from Auto-PTA on shale wells.