| With the development of Daqing oil field,more and more casing damage in oil and water wells appears.With the development of Daqing Oilfield,casing protection and effective treatment of casing damaged wells have become an important subject of oilfield development management.Sazhong Zone is one of the early development blocks in Daqing Oilfield,and it is also a block with many casing damaged wells.Since the discovery of the first casing deformation well in 1963,there have been five peaks of casing damage.Each peak of casing damage has the characteristics of many damaged wells,strong regional and long duration.This paper discusses in detail the casing damage,production and operation,causes and mechanism of casing damage,casing damage countermeasures and overhaul construction measures in Sazhong Zone,Daqing Oilfield,and focuses on the selection of the western area of the first South Zone as a typical block.In recent years,the number of casing damage wells in Sazhong Zone has been increasing year by year.After proper overhaul measures are taken,the repair rate also shows an overall trend of steady and rising.The casing damage parts are mainly divided into standard layer casing damage and oil layer casing damage.This paper also discusses the mechanism of casing damage in Sazhong Zone,and points out that the mechanism of casing damage in the standard layer of oil shale is the combined mechanism of pressure difference and stress,while the mechanism of casing damage in the oil layer is the mechanism of sand body deformation and interlayer sliding.With the gradual recovery of the fluid in the porous sandstone and the gradual decrease of the pore pressure,the formation will be compacted and the ground stress will be redistributed.When the scale of the rock mass is large enough,the deformation of the overlying strata will occur and the casing of oil and water wells in the sliding surface will be damaged.The critical value of regional pressure difference for casing damage of standard oil shale formation in Sazhong Zone is about 0.7MPa.When the differential stress is greater than the shear strength of the mudstone in the interlayer,under the action of the differential stress,the skeleton of the local sand body will be deformed,and the sand body will slide from the high-pressure area(expansion area)to the low-pressure area(contraction area),and shear dislocation will occur with the overlying strata,causing damage to the casing.In oilfield development,when the injection pressure is more than 10 MPa,the number of casing damage wells increases significantly.In order to improve the repair rate of casing damage,this paper also makes a detaileddiscussion and research.Through timely reflecting the key node status and construction progress in the operation process of casing damage control plan,through the combination of prevention and maintenance,the application of new workover technology,optimization of workover plan and process control,the workover efficiency and success rate of overhaul wells are significantly improved.Finally,according to the systematic analysis and discussion of this paper,some measures for casing damage prevention and control are put forward:(1)casing protection is mainly based on prevention and control;(2)pressure system adjustment is the key content of casing protection;(3)centralized "close control inspection" of water injection wells in standard casing damage area is an effective means for casing damage prevention and control,and the earlier the investigation of water injection wells in standard casing damage area The effect of casing damage control is better;(4)casing damage in oil layer is mainly related to pressure holding in small layer,so it is particularly important to control abnormal high pressure layer;(5)optimization of workover plan design and adoption of new technology are effective guarantee to improve workover success rate;(6)optimization of work flow and implementation of different well classification workover can effectively improve operation efficiency and quality. |
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