Determining reservoir pressure and confirming fluid type in development wells is of major interest to many reservoir engineers. Because of the high costs and operational risks of having a wireline formation tester (FT) stuck downhole, operators seek reliable technologies that not only deliver the information they need but also mitigate the chances of losing the tool downhole. A new generation of slim, light-weight FT technologies can help make production-management decisions, especially in the often complex geometry of development wells.
The Sirikit field Onshore Thailand is an extensively faulted and heterogeneous reservoir, therefore continuously updated pressure profiles have become the key in refining reservoir models. Productive zones are typically thin, but highly permeable. Traditional open hole (OH) log evaluation is insufficient to distinguish fluid types and formation fluid identification (FID) is required in every zone before completion. Because wireline FTs often have thick bodies which are pressed against the borehole wall and sampling takes at least one hour of pump out, they present an increased risk of getting stuck.
A smaller diameter FT was evaluated whose body equally centralized in the well during a test in order to dramatically reduce the risk of differential sticking. However it was not clear whether the new tool could similarly distinguish between hydrocarbons and water in a synthetic based mud (SBM) environment using capacitance and resistivity sensors. Four wells with various trajectories and fluid types were selected to benchmark the new tool. Both traditional and new slim FTs were run in the hole (RIH), monitored in real time and the capabilities of the two tools were cross-checked against each other. The results showed that both tools required a similar pump out volume to reach a clean sample. Despite the oil-base mud environment, the slim tool was able to distinguish the transition from mud filtrate to formation hydrocarbons, and in wells where water-base drilling fluids were used, formation water could be similarly recognized. All water samples were directly drained at surface to verify the in-situ real time measurements and oil samples were sent to the lab. The results showed a remarkable consistency in most cases and during trial tests the slimmest sampling tool exhibited a tremendous value in the first stage of field development and it is continuously used nowadays in newly drilled wells.
A slim testing and sampling tool shows good reliability for basic fluid identification and is especially suitable for wells with differential sticking issues. Globally, this tool may provide a solution of future wireline pressure and sampling, which can help operators to make proper reservoir-management decisions, especially in complex geometry wells or challenging geological formations.
