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Pressure transient analysis (PTA) is one of the best tools to estimate critical well and reservoir parameters. Some of those are reservoir properties, reservoir size and shape (i.e. permeability, fracture properties, reservoir model, distance to boundaries, etc.), completion efficiency (i.e. skin, fracture performance…etc.), tubing performance (i.e. optimum tubing design and artificial lift requirements) and well (i.e. fracture performance, skin, etc.), and reservoir characterization (i.e. dual porosity, layered reservoir, composite, etc.). Therefore, proper interpretation of PTA is crucial to acquire critical parameters for field development and well optimization. Pressure transient analysis technology has improved over the time. However, real-life examples of pressure data to fit a given idealized model are often nonexistent. In addition, well test interpretation suffers from a variety of uncertainties that combined, to reduce the confidence of the analyses. This paper attempts to summarize the uncertainties associated with well test analysis, shows examples of pitfalls in well test analysis, and provides the methods that proposed to identify the uncertainties. The first phase of the project, a detailed analysis of several PTA interpretations collected from various oil and gas fields in Petroleum Development Oman (PDO), compiled and analyzed to identify the main areas of uncertainty. In the second phase of project, best practices for well test interpretation methods were developed to achieve a consistent interpretation approach across the company. In the third phase of project, five main sources causing an uncertainty on PTA interpretation were investigated, analyzed and demonstrated with relevant actual examples, as well as demonstrating the pitfalls in well test analysis. The study proposed and developed a six-step PTA interpretation Work Flow including QA/QC steps and the study identified five main uncertainty areas, developed techniques to evaluate each of these, and presented the pitfalls of each uncertainty. Those key uncertainty areas are: The uncertainty in reservoir properties The non-uniqueness of the PTA model responses The limitation of the data set The physical error in the pressure / rate data (including non-reservoir effects on pressure gauges response such as gauge drift) and the human effect The implications of well bore storage effect This document provides a summary and characterizes the five main sources of PTA uncertainties through actual data from PDO in the Sultanate of Oman. This document will also cover the best practices and workflow that have been developed & proposed in order to achieve a step change in the quality and reliability of the PTA interpretations. The implementations of the workflow are presented for a variety of reservoir types and field examples of its implications on well optimization and field developments will be shared. |
