The Piltun-Astokhskoye field is located off the east coast of Sakhalin Island and has been on production since 1999. Several layers of the reservoir rocks feature high water saturations in the range of 40 to 90%, particularly within the ‘deep layers’. A key uncertainty for the development is the productivity of these layers: how much of which fluid will flow and at what saturation level? This paper looks at the various options for reducing this uncertainty. Ultimately, a wireline formation tester option was chosen, and we cover the execution of the job and the interpretation of the acquired data.