| With the increasing difficulty of exploration and development of major oil and gas fields,it has become an urgent scientific problem to optimize exploration deployment,reduce exploration risk and avoid"high investment and low return",and people need to understand the spatial and temporal distribution of permeability more urgently.Weizhou 12-X oilfield in Weixinan sag of Beibu Gulf Basin is a typical continental complex fault-block oilfield,which mainly develops braided delta front underwater distributary channels and has strong reservoir heterogeneity.Under the condition of similar sedimentary environment,the reservoir porosity of Weizhou 12-X oilfield middle block 3 and 4 Wells is similar,but the permeability varies greatly.In this paper,the basic characteristics of the third member of Weizhou Formation sandstone reservoir in Weizhou 12-X oilfield,Weixinan Sag,were studied by core physical property analysis,thin section microscopic identification,scanning electron microscopy,clay X-ray diffraction and laser particle size analysis,the controlling factors of sandstone reservoir permeability are analyzed,the formation mechanism of anomalously high permeability zone in the third member of Weizhou Formation in Weizhou 12-X oilfield is discussed,the spatial-temporal distribution of diagenetic index of the third member of Weizhou Formation sandstone reservoir is quantitatively simulated,The dynamic model of reservoir permeability prediction before drilling is established,the distribution of plane permeability of Weizhou Formation 3 Member sandstone reservoir is predicted,the distribution of anomalously high permeability zone of Weizhou Formation 3 Member sandstone reservoir in Weizhou 12-X oilfield is described.The results show that:（1）The sandstone reservoir of the third member of Weizhou Formation in Weizhou 12-X oilfield is mainly composed of lithic quartz sandstone and feldspar lithic sandstone,with fine grain size and medium sorting,and most of them are sub-circular to sub-riticular.The average pore throat of the reservoir ranges from 5.00μm to10.00μm,and the pore throat type is fine throat to fine throat.The porosity and permeability of the reservoirs are mainly in the range of 15%～25%and 50×10-3μm2～500×10-3μm2,respectively.（2）The sandstone reservoirs of the third member of Weizhou Formation are mainly in point-line contact and line-point contact,and are generally in medium compaction strength.For a given lithofacies,authigenic kaolinite is positively correlated with porosity and permeability,coated or lined chlorite is positively correlated with porosity and permeability,pore-filled chlorite is negatively correlated with porosity and permeability,and authigenic illite is negatively correlated with porosity and permeability.The diagenetic environment of the third member sandstone reservoir in Weizhou Formation alternates between acid and alkaline diagenetic environment and is in the stage of A11-A21diagenetic microstage dominated by dissolution.（3）Three anomalously high permeability zones are developed longitudially,with depths ranging from 2300m to 2400m,2420m to 2580m and 2650m to2900m.The corresponding diagenetic stages are A11microstage,A12microstage and A21microstage respectively.Due to the effect of clastic grain structure,dissolution and early oil and gas emplacement,there are mainly two genetic mechanisms of anomalously high permeability zones in the study area:increased permeability type genetic mechanism and retained permeability type genetic mechanism.（4）In the study area,clay minerals have a great influence on reservoir permeability,which can be characterized by clay factorβ.Whenβ=0.4,the prediction error of reservoir permeability is minimum.The new permeability prediction model has achieved good results in the predication of distribution of favorable areas of oil and gas Weizhou 12-X oilfield in Weixinan Sag,Beibu Gulf Basin.The absolute error of permeability prediction value varies from 0.01×10-3μm2to 192.65×10-3μm2,with an average value of 38.6×10-3μm2.The relative error varies from 0.00 to 1.00,with an average of0.33.The oil and gas in Weizhou 12-X oilfield are mainly distributed in the anomalously high permeability zone,and the oil and gas are always prefered to distribute in the advanced anomalously high permeability zone when there are multistage anomalously high permeability zones. |
