Research on the Shale Reservoir Sensitivity by Using the Mineral Analysis Method.

Shale reservoirs have diverse mineral types, and analyzing the sensitivity of the mineral composition to shale pores is of great scientific and engineering significance. In this paper, first, X-ray diffraction (XRD) experiments on shale mineral compositions are carried out, and the characteristics of pore structure changes after shale mineral compositions interacted with external fluids (slick water and backflow fluid) are elucidated. Then, the effects of quartz, kaolinite, and pyrite on the pore structure and permeability of shale on the susceptibility to slick water are studied. The results show that (a) quartz and clay minerals are the dominant constituents of each core, with some cores containing minor amounts of plagioclase feldspar and rhodochrosite. (b) The composition of the shale changed significantly following the action of external fluids. The average quartz content of pure shale decreased from 31.62% to 29.1%. The average content of quartz in siliceous shale decreased from 36.53% to 33.5%. The average content of quartz in carbonaceous shale decreased from 9.15% to 8.05%. (c) Factors affecting the sensitivity of shale pore structure and permeability to slick water are mainly quartz, kaolinite, and pyrite. The contents of quartz, kaolinite, and pyrite decreased by an average of 5.1%, 4.6%, and 0.9%, respectively, after slick water action.

Experiment on the Scaling Mechanism of Strong Alkaline-Surfactant-Polymer in a Sandstone Reservoir.

Most of the mature oilfields are facing the problem of great difficulty in exploitation currently. Alkaline-surfactant-polymer (ASP) flooding has been widely used in Daqing Oilfield as a tertiary oil recovery technology that can effectively enhance oil recovery (EOR). However, various degrees of scaling appeared in field application tests, which hindered the large-scale application of this technology. The damage and scaling mechanisms of strong alkali-surfactant-polymer (SASP) flooding to heterogeneous reservoirs with high clay mineral content are still unclear. In this study, several sets of experiments have been carried out to determine the core mineral composition and the pore structure. Additionally, the damage mechanism and mineral corrosion with different permeabilities can be explored from a microscopic point of view. The results indicate that the corrosion of SASP reduces the contents of quartz and kaolinite, while the illite/montmorillonite mixed layer increases. In addition, there is chlorite and secondary quartz generation, which do not exist in the original mineral composition. Clay particles and sediment are easy to form bridges or stay on the surface and block the pore throats, which results in core seepage capacity reduction. All our preliminary results have contributed to the present understanding of scaling during ASP flooding. Moreover, it is of great significance to guide ASP flooding field application and prevent scaling.

Laboratory Experimental Optimization of Gel Flooding Parameters to Enhance Oil Recovery during Field Applications.

The profile-control technique is one of the most important enhanced oil recovery (EOR) methods to maintain oil production in the medium and late stages of water flooding. It is necessary to conduct laboratory experiments based on the reservoir parameters from specific oil reservoirs to optimize the operation parameters during the profile-control process. In this work, based on the reservoir properties from Daqing Oil Field (China), we employed three parallel core holders and a square core with one injection well and four production wells to conduct profile-control experiments, and the operational parameters in the field scale were obtained using the similarity principle. The results show that the selected gel system has a good plugging performance and the best injection volume and profile-control radius are 0.3 PV and 6 m, respectively. Additionally, we show the optimized injection speed under different injection pressures when the profile-control radius is in the range of 6-9 m. The optimized displacing radius of the field is in the range of 3-6 m. When the radius is 6 m, the pressure decreases 90% and the corresponding plugging ratio is 81%. The optimized plugging proportion of the fracture length is 50%, and further increase of the proportion has a negligible effect on the production performance. Good field response has been achieved after the implementation of the optimized parameters in the target reservoir. This work, for the first time, systematically studies the operational parameters for the profile-control technique using experimental methods, and it provides the fundamental understandings and implications for enhancing oil recovery in similar types of high-water-cut reservoirs.