A group of researchers from China University of Petroleum and M.V. Lomonosov Moscow State University created a new chemical agent capable of simultaneous preventing sand formation failure and decreasing water in-flow to producing wells. This is an important achievement for producing oil from loose sand reservoirs, where low cohesion of rock particles results in their fall-out with the flow, thus clogging the equipment and drastically decreasing the recovery efficiency.
This new polymer received a lab designation as PDKM. It was synthetized from four monomers – acrylamide, methacryloyloxyethyl trimethylammonium chloride, styrene and organo-silicone compound KH570. It is a supramolecular material capable of self-assembly and environmental adaptation. During the trials, PDKM demonstrated reliable bonds with the surface of sand grains forming a firm lattice pattern, which prevented sand grains fall-out with the flow. When contacting with water, polymer chains expanded creating an additional barrier and closing-off permeable conduits, and when interacting with oil – on the contrary, shrank not interfering with its filtration. Such mechanism allows for simultaneous consolidation of rock and for regulating the movement of fluid in the reservoir decreasing the water in-flow while maintaining stable continuous oil flow. The trial showed that the polymer remained stable under the temperatures of up to 263 °C and did not degrade in the standard petroleum stratum conditions.
To determine the limits of its efficient application, the researchers developed and patented their own methodology of trials capable of reproducing real working conditions of oil wells. It allowed for simulating the high-speed fluid movement – up to 100 milliliters per minute, which is similar to the modes at off-shore oil fields. Previously, the lab tests were performed at the speed three times slower and did not reflect the real operating conditions, e.g., as in Bohai Gulf. In the course of the experiments, the scientists measured temperature and salinity of the stratum water, oil viscosity and rock permeability, defining at which factors and which combinations of factors the polymer maintains its properties.
As the result, it was defined that the optimal concentration of PDKM was circa 5 grams per 1 liter of solution. Given this proportion and the temperature up to 90 °C, the agent almost completely prevents sand fall-out: the loss does not exceed 0.05 g/l of fluid, which is in line with the highest industry standard. Simultaneously, the share of water in the produced fluid is decreased by 10-12%, which is evidence of the noticeable enhancement of oil recovery and a confirmation of the unique water shut-off properties of the new polymer. The limits of the stable performance of the new polymer were also defined: the stratum water salinity should not exceed не должна превышать 21 g/l, oil viscosity – up to 50 mPa·s, and the difference in permeability between the layers – not more than double.
The achievement of Russian and Chinese scientists opens up the possibility for creating a new system of selecting chemical agents for specific types of reservoirs. Now engineers will be able to calculate the well parameters in advance and to define the performance of PDKM for each individual oil field.
