Sensing element for the formation fluid refractometer on the basis of total internal reflection

When developing oil fields, there is an urgent task to quickly determine the type of pumped formation fluid, which includes formation gas, formation oil and formation water. In this paper, we propose a new type of a sensor element designed for flow refractometry of formation fluid based on the effect of total internal reflection. The sensor element is a taper tip of a conical shape made of sapphire and is 20 mm in length and 20 mm in diameter. The original shape of the sensor element is determined by a modified ray tracing method, taking into account analytical relations that determine the conditions for providing a larger dynamic range of measurements under specified physical, technological and design constraints. The conversion dependence of the tip is obtained for the wavelengths of 405 nm, 1064 nm and 3300 nm and allows determining the type of formation fluid (gas/water/oil). The proposed method enables the development of conical sensor elements based on the total internal reflection for downhole monitoring systems and optical threshold sensors of the refractive index.