| The Gaotaizi oil field located in the southern part of Changhuan in Daqing is a tertiarystructural belt to the south of the secondary structural belt of Changhuan, Daqing. Thetectonic axis is22degree of northeast, China. The structural high is near to theGao44-Xin31Well. The altitude of the top surface of Pu I group is-932.9m. The inclinationangle of two wings in the eastern and western parts within the oil-bearing area is gentle. Themain structure of the oilfield measured by structure contour as-1000m, close-height is67.1mand close-area is30.6Km2. The lithology of cap rocks is mainly characterized by clay. Thetensile strength measured with two clay blocks turns out to be1.89Mpa and1.5Mpa,1.7MPaas the average. The hydraulic fracturing risk of cap rocks in the zone researched can beevaluated through quantitative analysis of force retention of the20oil wells. Therefore, whenthe pore-fluid pressure comes to about88%of lithostatic pres-sure, force retention is0andhydraulic fracturing risk is relatively high. The trend line of porosity fluid pressure whichshow the critical point where the hydraulic fracture of the cap rocks happens can be drawn upand shows the condition that the critical porosity fluid pressure (Pc) changes with depth. Bystudying the fault sealing of the slope area in Gaotaizi and Xingshugang, the threshold valueof SGR in the closed fault can be defined. When SGR of fault is over30%, most of thereservoirs feature as the oil layer meaning that the fault is closed; when SGR is less than30%,most of the reservoirs are oil-water layer or water layer (fig.3-2), meaning that the permeationrisk of the fault is relatively high. By statistically studying SGR of the section stretching fromthe top of oil layer in footwall--Saertu district to the bottom of oil layer in Gaotaizi, there areextremely few SGR of the section is less than30%, and the relatively great sealing ability canbe seen in fault as a whole. AS the anticline structure is generally characterized in the areastudied, even if the lateral cross-fault permeation of the CO2happens, it is still confined in theanticline structure. The lateral sealing ability of the fault exerts no influence on the storage ofthe CO2. The statistical analysis of stability of the section shows that the234fault slidingstability is inferior to the inflation stability and the minimum activating pressures of thesliding stability and the inflation stability are3.6MPa and14.4MPa respectively which meansthat the fault tends to slide first on the condition that stress fields are the same. The statisticalanalysis of the stability, the section trend and the inclination angle proves that the mostunstable position features towards to east or west with an inclination angle approaching60°.By comparing it with the oil-water interface corresponding to lateral sealing, oil-water withsliding stability is deeper than that with the lateral sealing on any point of the section.The frequency of both oil-water interfaces statistically shows oil column height of the stablesealing is much greater than that of lateral sealing with the same regularity of thecorresponding oil-water interface. The research on fracturing pressure of the general caprocks, fault stability and the crude oil reservoir defines the sealing pressures of the cap rocksand the faults contributing to working out the sealing pressure of Gaotaizi structures as13.6Mpa. With this pressure the density of CO2injected is computed along with the Putaohuareservoir depth of Gaotaizi structures, structural amplitude, geothermal gradient andcompression coefficient of CO2. The geological reserve of CO2in the Putaohua reservoir ofGaotaizi structures is0.3896×108t. |
PDF Full Text Request