Successful Well Test Operations in Complex Reservoir Fluids: Lessons Learned and Best Practices Over 40 Years of Worldwide Operations

Abstract

Today many exploration, appraisal and development welltest operations are performed in new frontiers. These include extreme environmental conditions and reservoirs bearing complex reservoir fluids, such as heavy oil, or fluids with a high concentration of H2S, CO2, high wax and asphaltenes content, which have rarely been tested in the past. Many failures and operational issues have hindered the interpretability of data, significantly increased the total costs of such well tests or led to severe HSE incidents. Currently, such operations are often designed and executed on a case-by-case basis, and there are no practical recommendations available that would summarise the well testing experience in such environments to guide the operating companies through the process of efficiently planning welltest operations. Consequently, operations are often planned on a "copy-paste" basis, with potentially disastrous consequences. This paper describes in detail the challenges associated with safety, flow assurance, safe handling and disposal of produced fluids, and data quality during current welltest operations with complex reservoir fluids or challenging environmental conditions. Complex reservoir fluids, including highly corrosive fluids, introduce unique challenges that need to be addressed at the design stage of the test, each requiring an appropriate design of surface well test spread and DST string, as well as the overall job operation and equipment planning to incorporate "what-if" scenarios. To address these issues, we summarize the best well-testing practices, and for each of the cases outlined illustrate proven welltesting techniques. Examples show that it is nearly impossible to perform the well test and handle complex reservoir fluids at surface using a traditional approach and standard well test equipment. Novel well testing equipment such as new generation welltest separators equipped with Coriolis mass flow meters, new generation burners and others, in combination with recently developed well testing techniques, allowed us to overcome these challenges. The paper provides practical recommendations, supported by case studies, highlighting the results and lessons learned from successful operations around the worlds in the following well test areas: –Heavy oil testing–Well test operations in high H2S and CO2 environment–Well test operations in reservoir fluids with high wax or Asphaltene content–Deepwater welltest operations with a high risk of hydrate formation–Well test operations with production of foamy oil–Heat management–Viscous fluid management–Contingency planning Recipes for success are provided to ensure that safe operation can be performed in the challenging environment while keeping the cost in line with the AFEs.

An Overview of Recent Developments and Understandings of Unconventionals in the Vaca Muerta Formation, Argentina

“…Extensive research has been conducted to assess the effectiveness of various fracturing techniques, including sliding sleeve and plug-and-perf approaches [28,29]. Post-fracturing operations focus on wellbore clean-up, flowback management [30][31][32], and reservoir pressure maintenance, often leveraging enhanced oil recovery (EOR) techniques, like CO 2 or gas injection, to improve ultimate recovery [33][34][35][36].…”