| With the development of the world economy’s increasing demand for oil and gas,and the conventional crude oil is decreasing,easy of conventional crude oil to reduce gradually,increase the exploration and development of unconventional oil and gas resources become the main trend.Currently,the main methods of unconventional oil and gas exploitation in our country are horizontal well combined with large hydraulic fracturing technology.The main mining principle divides horizontal well into several sections and perforating multiple clusters in each section for segmentation fracturing construction.Ground pump truck injects fracturing fluid underground into the wellbore,thus forming gaps in deep well formation and oil flowing from cracks for exploitation.Casing is a production channel in the process of oil and gas exploitation.Because it works under the conditions of high pressure fracturing,perforation,heterogeneous layer,etc.,it is easy to appear deformation and damage in the process of field work,which affects the field fracturing and mining.Therefore,the study of the influence factors and rules of casing deformation in the process of subsection fracturing has a guiding significance for the next step of efficient development of shale oil in our country.This paper aims at the casing loss problem in the development of Jiyang shale oil,a new national development block.The specific research work is as follows:(1)According to the logging and logging data of Jiyang block and the field construction data,the geological structure of the block and the development status of Liye 1XX shale oil well were analyzed,and the rock mechanical parameters and in-situ stress were obtained according to the gamma logging values:The rock elastic modulus is 15 GPa,the bulk density is 2.4 g/cm~3,the vertical geo-stress is 86.9 MPa,the minimum horizontal geo-stress is 90 MPa,the maximum horizontal geo-stress is 98 MPa,and the formation pore pressure is 52.2 MPa.The casing load size under different fracturing displacement is obtained according to the field construction data;(2)According to the cementing quality of Liye 1XX shale oil well in Jiyang Shale,the cement ring shape is simplified into complete and incomplete missing,Through the analysis of the casing stress under the condition of non-uniform in-situ stress and finite element analytical solutions of verifying the rationality of the model.The influence laws of missing Angle,missing depth and mechanical properties of cement ring on casing stress under different states are obtained:when missing cement ring is serious(missing Angle greater than 50°or missing depth greater than 25mm),casing strength will be damaged,and the critical part of missing cement ring is the most prone to casing damage.Casing of the maximum stress decreases with increasing cement ring elastic modulus,but is less affected by Poisson’s ratio;(3)The influence of engineering parameters on casing stress in the multi-stage fracturing process was carried out according to the field construction conditions.Using the finite element software ABAQUS to simulate the stress of casing under the influence factors of perforating parameters,fracturing parameters and fault slip.In order to study the change law of casing stress with the influence of engineering parameters during the fracturing process.The influence degree of different perforating parameters on casing sensitivity is as follows:perforating density>aperture>perforating phase;The influence law of different construction parameters on the non-uniform in-situ stress difference around the casing:the crack width and crustal stress difference increase with the increase of construction displacement;With the increase of injection time,the in-situ stress difference firstly decreases and then increases until it becomes stable,and the injection time is proportional to the fracture propagation length.The interval between fracturing stages is inversely proportional to the change of crustal stress difference.When the fracturing interval is 18m,the method of increasing the fracturing interval to reduce the crustal stress around casing by increasing to inter-fracturing clusters has little effect on the effect of casing stress.Different fault slip parameters effect on the casing stress:As the slip distance increases,the maximum equivalent stress borne by the casing gradually increases,and the deformation of the casing increases linearly;and the shape variable of casing increases linearly.When the fault slip distance exceeds 7.8mm,the large equivalent stress at the fault interface of the inner casing wall exceeds the yield strength.When the dip Angle of the potentially activated fault block is greater than 45°,fracturing should not be performed near the fault;(4)On the basis of the casing deformation analysis in the previous chapter,the defects of the bridge plug size of conventional fracturing tools are pointed out according to the final stress and deformation of the casing.Combined with the actual demand of oil and gas field production,a small size soluble bridge plug is designed,which mainly includes the center mechanism,slip anchoring mechanism and bridge plug seal:The outer diameter of the center pipe is 68mm,the inner diameter is 40mm,and the overall length is620mm.The outer diameter of the slip is 90mm,the inner diameter is 68mm and the length is 60mm.The outer diameter of the sealing mechanism rubber cylinder group is 100mm,the inner diameter is 69mm,and the overall length is 184mm;And the above structure strength check and seal check,can meet the downhole fracturing environment of strength and sealing requirements. |
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