Successful Testing and Sampling the Desired Formation Fluids Despite the Challenging Environment in the Middle East

Abstract

Most of the time a brownfield's formation producibility is no surprise to petrophysicists and reservoir engineers, however, the downhole conditions change continuously in the oil and gas production and injection. Therefore, it is critical to acquire high-quality representative testing and sampling data in real-time despite formation uncertainties and operation constraints.

There are several challenges when acquiring the wireline formation testing (WFT) and sampling services in Middle East. The downhole real time fluid properties must be representative of reservoir conditions and provide fluid fractions, water salinity, contamination, etc. At the same time, there is a big constraint on the operational time limit per station due to the substantial risk of getting stuck. In complex lithologies, it is critical to understand the fluid's connectivity between layers and rock compressive strengths as the expectations may not match reality. To meet the abovementioned challenges the WFT technologies must be equipped operationally and provide a valid instantaneous interpretation.

Current research covered cases across several countries in the Middle East. In low-mobility formation the challenge was on operational ability to continuously pump-out for extended hours. The record-breaking results were achieved with 36 hours of pumping-out, with bubble point as close as 50 psi below formation pressure. Some advanced features were implemented including FT pre-job modeling and real-time support vertical interference tests, which helped to complete the injector well as planned. Many challenges comes in differentiation between formation and filtrate water in real-time. It was solved using the only resistivity sensors available in current WFT setup. For deep tight gas reservoirs, the sampling in tight environment were an issue, nevertheless, getting a single sweet spot allowed to collect representative gas samples. Dealing with retrograde condensate field might be tricky when the condensate precipitation and gas appearance are not known. In presented cases the two scenarios shows the appearance of gas across the zone and appearance of condensate. The results were compared to production logging (PLT) to clarify the unusual multi-phase changes in phase behavior.