Combining carbon dioxide and strong emulsifier in-depth huff and puff with DCA microsphere plugging in horizontal wells of high-temperature and high-salinity reservoirs

Abstract

The profile control and water shutoff are still considered as technical problems for high-temperature and high-salinity reservoirs. A composite technique combining carbon dioxide and strong emulsifier in-depth huff and puff with water shutoff in the horizontal wells of high-temperature and high-salinity reservoirs was proposed. The composite technique comprised a strong emulsifier technique, a water shutoff agent technique, and technical injection of working fluid slug. The strong emulsifier technique included emulsifier screening. The ability of strong emulsifier served as the performance index. The strong emulsifier had two roles. When the strong emulsifier reached the oil, the entire system could be emulsified to activate the plugging system in situ and in real time. During the migration of oil and water, the emulsion system could improve volumetric sweep efficiency and microscale displacement efficiency. Carbon dioxide had a good emulsifying capability. The water shutoff agent technique included research on the high-temperature resistance and high-salinity resistance of polymer microspheres. The residual resistance coefficients of positive injection and back injection of polymer microspheres were still greater than 2. The working fluid included the slug of the system of polymer microspheres, the slug of the strong emulsifier and the slug of the carbon dioxide. Three kinds of slugs could improve volumetric sweep efficiency and microscale displacement efficiency during production. The key process of the proposed technique was the sequential injection of carbon dioxide and the strong emulsifier into the producer well of horizontal well. Upon injecting of polymer microspheres of the water shutoff agent, the microspheres aggregated to physical plugging and bridging by the effect of covalent bonds on one another after reaching the deep reservoir. The carbon dioxide and strong emulsifier were shut by the microspheres in the high-permeability formation. When water (bottom water, edge water, or injected water) approached the oil well along the high-permeability zone, the carbon dioxide and strong emulsifier would be carried by the water into the middle-permeability and low-permeability zone with higher oil saturation during production. Optimizing the injection method of the working fluid slug, a composite technique that combined carbon dioxide and a strong emulsifier with polymer microspheres was also proposed. Laboratory results showed that the rate of enhanced oil recovery increased by 38.50% based on water flooding recovery (10.00%) by using carbon dioxide in-depth huff and puff and polymer microsphere plugging after the first round. The rate of enhanced oil recovery increased by 17.75% based on the water flooding recovery of the first round by using carbon dioxide and strong emulsifier in-depth huff and puff and polymer microsphere plugging. In this paper the results of physical simulation experiments further prove that combining carbon dioxide and strong emulsifier in-depth huff and puff with divinylbenzene-co-acrylamide (DCA) microsphere plugging is a potential technical direction for controlling water cut and increasing oil recovery in horizontal well of high-temperature and high-salinity reservoirs.