Geological Characteristics Of Carbonated Sandstone Reservoir And Acidification Optimization Technology

The target area of Es2 and Es3 formation in block Z of Shengli oilfield is a complex lithologic carbonated sandstone reservoir,which reaction rate and etching form of the reservoir are not only different from that of the carbonate rocks,but also not same with ordinary sandstone.Unevenness etching is easy to be produced in the acidification of carbonated sandstone.Thus,suitable choice of acid working fluid and acidification process can achieve better acidizing purpose.Z block’s data show that the average content of quartz is about 41%,the average content of feldspar is about 16%,calcite and dolomite are about 37%,and this oil field belongs to the carbonated sandstone reservoir with complex lithology.According to microscopic characteristics of the core were studied by X ray diffraction,thin slice identification,scanning electron microscope and energy spectrum analysis,the reservoir is mainly composed of taupe oil soaked conglomerate sandstone,and with feldspar and calcite cemented.Core sensitivity tests show that the cores of block Z have no velocity sensitivity,no water sensitivity,no salt sensitivity,weak mud acid sensitivity and weak to moderate weak hydrochloric acid sensitivity.Based on previous acidification measures,acidified mineral characteristics and acidizing seepage analysis,the initial acidification of sandstone matrix acidizing is formulated.Conventional mud acid and organic retarded mud acid were selected as the research object.Through the laboratory physical simulation,the acid system suitable for the study layer of block Z was selected,suitable main acid(7.5%HCl+5%HAC+1.5 ~ 2.0%HF)and additives(corrosion inhibitor 2%ZX-01 and 3%CT1-3+0.5%OP-7,anti-swelling agent 1%TX-1,cleanup additive 0.5%OS-15 and 0.5%CH-06,ferrous stabilizer CA,oil detergent 5%JHJ and 5%BN-5)were selected and optimized through laboratory evaluation.Then,compatibility and synergy of the working fluid system were analyzed comprehensively,and the performance was good.On the basis of the "maximum displacement pressure difference method",the appropriate displacement was determined to carry out the acidification,and the field construction effect was evaluated,the effect of field injection improved obviously,water injection quantity increased,and the effective period of water injection increased.The optimum acidification design is formed,and the optimum acid system and process plan are optimized for acidification effect in the field,which is of certain reference significance for the acidification scheme design of the same kind of carbonated sandstone reservoir.