Diagenesis Research And Reservoir Evaluation In Quan3 And Quan4 Members Of Northern Songliao Basin

On the basis of completely collecting the test data of Quan3 and Quan4 members of Northern Songliao Basin, we have done more tests and studied the diageneses of the region. Diageneses of mudstones are relatively simple, no more than the transformation of clay minerals and the thermal evolution of organic matter, but they control pH of diagenetic environments and diageneses of sandstones. Diageneses of sandstones in Quan3 and Quan4 members include mechanical compaction, pressure solution, cementation and dissolution. Both compactions and cementations diminish the porosity of the reservoirs, but compaction is more important than cementation in the basin. The pore-fillings of the reservoirs are dominantly clay minerals and carbonate cements. Dissolutions generate secondary pores and enhance the porosity and permeability. Materials dissolved in Quan3 and Quan4 members are feldspars, debris and carbonate cements, but the dissolutions of feldspars are more intense than those of carbonates. Calculation of Gibbs free energy shows that feldspar dissolving becomes easier and easier with the depth increasing, while calcites and laumontites are opposite. Feldspar dissolving is much easier than calcites and laumontites do. Above 3000±m calcite dissolving is harder than laumontites do, otherwise, the result is opposite.Based on the test data of thin sections, SEM, epoxy resin-impregnated thin sections, homogenization temperature of fluid inclusions, Ro, the diageneses of clastic rocks in Quan3 and Quan4 members of Northern Songliao Basin can be divided into stage A and B of early diagenesis, stage A1, A2 and B of middle diagenesis, their bottom depths are 400±m, 900±m, 1300±m, 2350±m and even deeper respectively.Considering the porosity and permeability and other factors of the reservoirs of Quan3 and Quan4 members in Northern Songliao Basin, the reservoirs are divided into four types, typeⅠi s mainly distributed nearly on the edge region of the basin, such as Northern Pitching Area, Northeastern Uplift And Western Slope. From the edge of the basin to center, the quality of other kinds of reservoirs in the same layer also gradually becomes worse. The reservoirs of Quan3 and Quan4 members in the western area of Daqing placanticline are relatively the worst, belonging to typeⅢ-Ⅳ.There exist three anomalously high porosity zones vertically in Quan3 and Quan4 members of Northern Songliao Basin, their depth bounds are 300～700m, 750～1450m, 1500～2350m. The first high porosity zone is formed by leaching of meteoric water, and the others are formed by dissolution of organic acids, and H+ generated in the clay minerals transformations is also important. By means of superposing the sedimentary facies maps and digenetic facies maps, favorable reservoir developing regions are predicted where ID<0.71, diagenetic facies are the early compaction and cementation, dissolution, they almost occurred in the sandstones of channels, delta plains, delta fronts and branch channels.