| The main production layers in Yanchang Oilfield of Ordos Basin include Chang 6reservoir,Chang 2 reservoir of the Yanchang Formation,and Yan 9 reservoir of the Yan'an Formation.Most of the oilfields related to the above production layers have entered the stage of water injection development.In terms of water injection effects,these three types of production layers show large differences,and the reasons causing these differences are still not clear,which leds to the blindness in the adjustment of water injection development for these three types of reservoirs.In order to resolve these problems,this paper focus on the Zhenjiamao Chang 6 reservoir,the Haojiaping Chang 2 reservoir and the Laozhuang Yan 9reservoir,and conducts a comprehensive study of reservoir characteristics including structural features,sand body connectivity,reservoir characteristics and oil-bearing properties.And the relationship between the reservoir characteristics,well pattern,well spacing,and water injection method are researched.Based on the above studies,we discussed the water injection development and adjustment measures of different types of reservoirs.The main conclusions are listed as follows:1.Different geological characteristics of Chang 6,Chang 2 and Yan 9 reservoirs?1?Structural features:The structural range of Chang 6 reservoir and Yan 9 reservoir is quite different,in which the structural range of adjacent Wells of chang 6 reservoir is generally 2m and show small structural scale.The structural range of adjacent Wells in Yan 9reservoir can reach 6m and show large structural scale.The structural range of Chang 2reservoir is between two of the above layers,and is generally 2m?4m,and show medium structural scale.?2?Characteristics of sand body connectivity:The difference of the sand body connectivity between the Chang 6 oil layer and the Yan 9 oil layer is large.The single layer of Yan 9 oil reservoir can reach 15m with a fast lateral variation.Single layer of Chang 6 oil layers is thin,only 3m?4m,with a poor lateral connectivity.The single sand body thickness of Chang 2 oil layer is generally 7m,with a good lateral connectivity.?3?Characteristics of reservoir property:The permeability of Chang 6 reservoir is the smallest,the average permeability of each small layer is between 1.8×10-3?m2 and2.1×10-3?m2,and the permeability of the inner and interlayer changes greatly.The permeability of Chang 2 reservoir is medium,and the average permeability of each small layer is between 7.7×10-3?m2 and 8.4×10-3?m2.The reservoir permeability of Yan 9 is the largest,and the average permeability of each small layer is between 10.6×10-3?m2 and10.7×10-3?m2,and the permeability of the inner and interlayer is basically unchanged.?4?Characteristics of oil saturation:The oil saturation of Yan 9 reservoir is the highest,generally 45%?60%.The oil saturation of high structural site is higher than that of low structural site.The oil saturation of Chang 6 reservoir is 35%?55%.There was no difference in oil saturation between high and low parts of the structure.The oil saturation of Chang 2 oil layers is the smallest,generally 30%?50%.2.The reasonable relationship between the characteristics of the three reservoirs,well pattern,well spacing,and the intensity of water injection.?1?The areal injection pattern used by Yanchang oilfield is suitable for the Chang 6reservoir with a small structure range,but not to the Yan 9 with a large structure range,high oil saturation and local Chang 2 reservoir with many tectonic structures.This kind of well spacing may led to remaining oil in Chang 2 and Chang 9.?2?The 250m well spacing used by Yanchang is suitable for the Yan 9 and Chang 2 with a large thickness of sand body,good connectivity,and high reservoir property.But this well spacing is not suitable for the Chang 6 with a small thickness of sand body,bad lateral connectivity,and bad reservoir property.This kind of well spacing may led to inner and inter layers of remaining oil.?3?The 15m3/d single well daily injection water used in each oilfield is applicable to the Chang 2 oil reservoirs with medium reservoir property,but not applicable to Chang 6 and Chang 9 oil reservoirs with bad and good reservoir properties.Due to the high intensity of water injection in Chang 6 reservoir,inner and inter layer may contains remaining oil.However,due to the slow speed of water injection,the uneven between recovery and injection led to inner layer remaining oil.3.Development strategies and effect of Chang 6,Chang 2 and Yan 9 reservoirs?1?The adjustment of Chang 6 reservoir should focus on adjusting well spacing and water injection amount based on the method of areal water injection.The well spacing should reduce between 180m and 200m,whereas the daily amount of water injection for single well should reduce to 10 m3/d.After this adjustment,the daily crude oil production of Zhenjiamao oilfield increased from 249t to 344t,and the natural decline rate dropped from 9.2%to-10.9%,showing obvious effects.?2?The adjustment of the structural gentle region of Chang 2 reservoir should mainly use the mode of areal water injection.And the area of micro structure in nose-shaped uplift should adopt water injection at low structure part,whereas recovery oil at high structure part.The well spacing should reduce to 200m,whereas the daily amount of water injection for single well should reduce to 15 m3/d.After this adjustment,the daily crude oil production of Haojiaping oilfield increased from 113t to 147t,and the natural decline rate dropped from6.8%to-16.6%.?3?The adjustment of the Yan 9 reservoir show keep the well spacing as 250 m.And adopt the edge water injection with injecting water at low structure part,and recovering oil at high structure part.The daily amount of water injection for single well should increase to 25m3/d.After this adjustment,the daily crude oil production of Laozhuang oilfield increased from 145 t to 203 t,and the natural decline rate dropped from 13.0%to-17.6%. |
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