Being made of quartz, feldspar and rock fragment,sandstone reservoirs of the third member of the Hetaoyuan Formation are major oil layers in the Shuanghe oilfield, whose diagenetic evolution can be divided into early and middle diagenesis period. Filtration, hydration and mechanical compaction were the main mechanisms in early diagenesis period and the immature stage of middle diagenesis period; on the other hand, cementation, dissolution, replacement, pressure solution and recrystallization were the main mechanisms in the low-mature stage, mature A stage, mature B stage of middle diagenesis period. Pore evolution is genetically related to diagenetic evolution, and diagenesis results in a pore-evolutionary process that includes the decreasing of primary pore, the increasing and the reducing of secondary pore. Being more stable and having more types than primary pore, though its reservoir capacity has big difference because of its complex structure, secondary pore is the main part of pore system that is made of both primary pore and secondary pore. With big pore space,intergrain pore is the principal pore of secondary pore. Sandstone reservoirs of the third member of the Hetaoyuan Formation have very good reservoir capacity.
