Research On CDG In-depth Profile Modification Eor Technology

Through a systematic analysis of the in-depth profile modification technology, an applicable new profile improvement methodology has been developed to increase the successes in the application of such technology in oil fields. This paper describes the process which starts from the synthesis of the cross-linker to the evaluation of properties of the weak gel system and the mechanistic simulation to the evaluation the field performance to investigate each steps of the application of the technology。On theoretical basis, a high concentration aluminum citrate was synthesized. The high concentration of aluminum in the cross-linker has long-term stability and low freezing point which is suitable for use in severe climate conditions。In the evaluation of the gel properties, it was found that the transition pressure method is more reliable to determine the gel quality. However, it is found that due to the differences between laboratory and reservoir conditions, simple test results in laboratory cannot represent gel properties in the reservoir. Viscosity characteristics of polymer solutions show the similar type of conclusions. For example, laboratory shows that polymer and cross-linker would not form gels in the produced brine but, field results showed that gels have been formed effectively in the reservoir with the produced brine. Therefore, new laboratory techniques have to be developed to test gel properties under the same conditions。Laboratory core flood test using the gel system we developed showed that under the same condition and same concentration of polymer, newly prepared colloidal dispersion gel or CDG has lower resistance factor (RF) than the polymer solution but the residual resistance factor (RRF) of the CDG is several time higher than the polymer。Adsorption data showed that twice as much of polymer in the CDG solution has been retained in the pore throat than the polymer solution and further indicated that such properties can adjust the distribution of fluid flow through the high, medium, and low permeability porous media and increased the recovery efficiency above 7% over polymer flooding in a heterogeneous reservoir。Several field test results show that the performance of CDG in the field is similar to the laboratory coreflood。The increase of injection pressure in the CDG process is more gradual than the polymer solution initially. The increase in pressure after about 0.1 PV of injection, the CDG process is about the same as the polymer solution. However, the injectivity of CDG is less than polymer in the late stage of the process, approximately after 0.35PV of injection. These results show that the effectiveness of the polymer solution occurs in the early stage of the process and the injection pressure decreases sharply with the rapid increase for water-cut after the starting of water drive and, on the contrary, the effectiveness of the CDG process lasted much longer, as shown in the lower pressure decrease after water drive and the slow increase of the water-cut, even the initial pressure increase is slower than polymer flood.The injectivity index of polymer solution decreases in the first two years of injection and reaches the lowest point when the water-cut reaches the lowest level. Then the injectivity index will gradually increase to 8.9% above the injectivity index prior to polymer injection. After the injection changes to drive water, the injectivity index continues to increase and reaches 33.1% above prior to polymer injection。The injectivity index of the CDG solution will also decrease gradually and reaches the lowest level after 1.5 years of injection. Then the injectivity index remains stable until the beginning of water drive but will remain below the level prior to CDG injection。In the same area with similar reservoir conditions and same volume of fluid injection, CDG flood would increase over 3% incremental recovery over polymer flood.Field test also showed that the CDG solution prepared with produced brine is also effective to improve the oil recovery, particularly the pressure increase in using CDG after polymer flood which explains that CDG can be formed in the reservoir to block off the low viscosity water channeling。In order to be effective, the minimal CDG slug volume would be 0.35PV. The large volume of CDG injection with high polymer adsorption and effectiveness of oil recovery proves that the CDG solution can be formed in-situ and also be transported through the reservoir。...