| In recent years,the object of tertiary oil recovery in block a has been changed from class I oil layer to class II oil layer,in which the S?1-9 oil layer was developed independently as a group of development reservoir.At present,it has been transferred to the chemical flooding of the secondary upper return strata in this interval.Because shales above S?4 are developed and have poor stability,they are frequently damaged by casing,and a large amount of casing damage has occurred;In the development process of chemical flooding second time back to block A,it was found that the injection rate difference between S?1-4 and S?5-9 was large,the production was poor,and the effect was slow.In order to prevent and control casing damage,it is necessary to control reservoir pressure and injection production pressure difference;On this basis,reasonable reservoir pressure and injection production pressure difference are transformed into reasonable injection intensity for different layers and well groups;At the same time,in order to ensure the overall development effect of chemical flooding,it is necessary to further optimize the injection parameters and measures optimization design standards on the basis of casing damage prevention and control,so as to ensure the horizontal and vertical balanced mining and achieve the purpose of improving efficiency.In this paper,CMG software is used to trace the history of A block's ASP flooding stage.From December 2014 to the end of June 2019,the stage recovery degree is 11.41%,and the calculated recovery degree is 54.40%.The distribution of pressure field in each target layer and the change of injection production pressure difference in ASP flooding stage are given,and the change trend of injection production pressure difference and target layer pressure in block a is also given.The potential is almost the same.From May 2015 to April 2017,the injection production pressure difference increased from 14.5 MPa to 20.0 MPa,and the pressure of the target layer increased from 11.8 MPa to 17.2 MPa.At present,the injection production pressure difference of block A is 18.9 MPa and the pressure of the target layer is 16.2MPa.Based on the analysis of casing damage layer and type in block A,combined with injection production pressure difference and target formation pressure change in block A,the causes of casing damage are as follows:the larger the injection production pressure difference between oil and water wells is,the greater the pressure gradient between wells is;a large number of sudden stress concentration occurs in a short distance,and the local capacity of the well section is prone to sharp bending and fault,leading to fault casing damage.The second reason for casing damage is that high-pressure injection agent is easy to cause the change of injection volume,which leads to the rise of formation pore pressure and the tendency of stress concentration in long well section,but the stress concentration section is relatively long,which causes casing deformation and casing damage.Based on the statistical analysis of injection production pressure difference in block A and the casing damage in block A,the reasonable control limit of injection production pressure difference in block S?1-9 is obtained:18MPa.In block A,the most serious casing damage block A-S is matched with the history of ASP flooding.The recovery degree of ASP flooding is 6.55%,the calculated recovery degree is 51.17%,and the recovery degree is 3.23%lower than that of block A;Based on the statistical analysis of injection intensity of different well groups(class I,class II,class III and class IV)in block A-S and block casing damage,the reasonable injection intensities of S?1-4 and S?5-9 are obtained as follows:class I,6.0 m~3/d·m for S?1-4,7.5 m~3/d·m for S?5-9;class II,5.5 m~3/d·m for S?1-4,7.0 m~3/d·m for S?5-9;class III,5.0 m~3/d·m for S?1-4,and 6.5 m~3/d·m for S?5-9;class IV,4.0 m~3/d·m for S?1-4 and 5.5 m~3/d·m for S?5-9.Under reasonable injection intensity,the optimal injection scheme of ASP flooding in block A-S is:prepolymer slug,polymer concentration 1700 mg/L,slug size 0.040 PV;main slug of ASP system,alkali concentration 1.2wt%,surfactant concentration 0.3wt%,polymer concentration 2000 mg/L,slug size 0.35 PV;sub slug of ASP system,alkali concentration 1.0wt%,surfactant concentration 0.15wt%,polymer concentration 2200mg/L,slug size 0.20 PV;post polymer slug,polymer concentration 1800 mg/L,slug size 0.20 PV.According to the prediction results of the optimal injection scheme of ASP flooding,the recovery degree of ASP flooding is 17.44%,the final recovery degree is 62.06%,and the EOR is 15.91%higher water flooding.Under the reasonable control of pressure system and the optimal injection scheme,the fracture parameters,fracture length and fracturing opportunity of S?1-4 in 125m well spacing A-S block are optimized.The optimal fracture length is 45m for injection well and35m for production well under 125m well spacing.The optimal fracturing opportunity is 45m for injection well and 35m for production well.The optimal fracturing opportunity is that the injection well should be fractured during the period of water cut decreasing.For production of class I and class II It is better to fracture the wells in the initial stage and water cut decline stage,while the fracturing time of the wells in the third and fourth categories should be later,and it is better to fracture the wells in the water cut decline stage and water cut low value stage. |
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