Study on Technology for Protecting Loose Sandstone Reservoir in Bayan Oilfield

The reservoirs in the Bayan oilfield are weakly cemented sandstone reservoirs with medium and low permeability. Those reservoir formations are buried deep and are strongly water sensitive. Fresh water based drilling fluids have long been used to drill the wells, and because of the poor inhibitive capacity of the drilling fluids, the reservoirs are contaminated by the change in the salinity of the formation waters. Oilfields with the same buried depth and the similar reservoir physical properties in China are rarely seen, and a new micrometer sized reservoir protection additive is needed for drilling the loose sandstone reservoirs. Based on the analyses of the factors related to the reservoir damage in the Bayan oilfield, a micrometer sized emulsion reservoir protection agent with both filming and clay swelling inhibitive capacity was developed. The capacity of the reservoir protection agent to plug fractures with wide size distribution and the synergistic effect of the reservoir protection agent is verified using laser particle size analyzer, sand-bed plugging tester, PPA plugging filtration tester and SEM. The particle size of the reservoir protection agent D₅₀ is ≤ 2.17 μm, and the D₉₀ is ≤ 7.05 μm. The percent reduction of the linear swelling of cores tested with the reservoir protection agent is 51.35%. Compatibility of the reservoir protection agent with the drilling fluids in which it is used is satisfactory. The reservoir protection agent, combined with acid soluble materials, forms an integrated reservoir protection fluid capable of protecting reservoirs with various properties. Laboratory experimental results show that using this technology, percent permeability recovery of cores made with rock samples from weakly cemented reservoir sandstones can be 90% or higher. In field supplication, skin factor measurement and well production data all demonstrate the good reservoir protection capacity of this technology.