Long-Term Productivity Monitoring of Multistage Wells with New Quantum Dot Technology and its Application in Xinjiang Oilfield

Abstract

Traditional production logging uses cable or coiled tubing for productivity measurement. Such measurement normally requires well to be shut-in, which brings risks for field operation, especially for directional or horizontal wells; it affects normal field production management. Besides, the result only reflects production profile at one time point. The later production system adjustment or changes of water production value need to be measured again, eventually increasing the total cost. Productivity monitoring technology based on ‘Quantum Dot’ tracers uses nano-size quantum dots to make micron-size quantum signature codes or marker-reporters. As the basic monitoring particle, the quantum signature code can be made to flake quantum dot monitoring tape through polymer materials, this special tape is wrapped around pipe or screen and placed at target location in the borehole. For different layers and fluid phases, quantum monitoring tapes with different codes and affinity properties are utilized to distinguish them. When monitoring tapes come into contact with different fluids such as oil or water in formation, diffusion channels will be generated, from which quantum monitoring particles (marker-reporters) are released and adsorbed on the surface of the material. As fluid flows, quantum monitoring particles in monitoring tapes will be continually released and adsorbed on tapes surface and carried to the wellbore, this achieves a release process proportional to flow rate. The produced liquid collected at wellhead is mixed with quantum monitoring particles with various codes, which can be separated by laboratory analysis. By counting the percentage of marker-reporters with different codes, the production rate percentage of different intervals can be obtained, and then for each stage, oil, gas, and water production can be obtained according to the total wellhead production. The quantity of quantum monitoring particles is massive, and its release rate is in a positive correlation to flow rate. Under normal circumstances, unlimited production monitoring can be achieved within 3 years. Traditional production logging measure formation and production parameters such as temperature, pressure, density, resistivity, flow rate, water cut etc. logging tools and packers are combined to measure flow volume from each stage and fluid types are identified at wellhead. Main disadvantage of this method is the requirement for wellbore shut-in and the risk of unsuccessful RIH the tools as the wellbore faces common issue – wellbore deformation. In addition, it is not normal using packers to isolate other zones while allowing only one stage to produce. Also, production logging can only obtain inflow profile at a specific time or short period of time. If one needs to get information such as later production data or water cut value when producing system is adjusted or changed, logging operation must be done again. It results in higher costs. How to monitor production profile of each stages any time during normal production process and utilize these data to make timely adjustment is of great significance in terms of operation and efficient development of single well or for a whole block.