PSI - Issue 22

Yihua Dou et al. / Procedia Structural Integrity 22 (2019) 33–42

40 8

Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Under the loading of oil testing conditions such as well opening, shut-in and acid fracturing, it is safe if the maximum equivalent stress in the pipe satisfies equation (3).

   

    

K

s n k n y  ，

(3)

min  



IC

4max

xd

/ 2



s

k

where, s  － Yield stress of casing material, the value is 758MPa for P110 ； ns － Stress safety factor ； k － Stress concentration factor of perforated casing ； KIC － Fracture toughness of casing material with plane strain ； n k － Stress intensity safety factor ；  － Perforated hole diameter ； y － Revised factor of perforation stress intensity. Reference to drill pipe fatigue life estimation method and damaged tubing remaining strength calculation method, according to the theory of stress intensity factor, if the perforation as semi elliptical surface crack, from the flat surface crack on the stress intensity factor, the surface stimulating, correction of unilateral correction, width, elliptical and ballooning effect correction, perforation of the stress intensity factor can be obtained. Table 5 formula for calculating the stress intensity factor of perforated hole The crack stress Cracking orientation formula axial stress a  circumferential along edge of the hole 1 1 ( / 2) ah a K K y     ， 1 2 2 2 e e ky y y  tangential stress t  axial along edge of the hole 1 1 ( / 2) th t K K y     ， 1 2 2 2 e e ky y y  5. Application of perforated casing remaining strength analysis Well YB1 is an exploratory well in Junggar basin, with production casing of 51/2"×9.17 mm P110 casing and depth of 4100 meters. According to the drilling fluid density (1.40 g/cm3) used when drilling the target layer, the pressure in the middle of the test reservoir (4039 m) is estimated to be 55.47 MPa. According to the Well services Design for Layered Fracturing of Well YB1, it is assumed that the bottom hole closing pressure is 76 MPa, and the wellhead pressure value of casing injection fluid during the first stage of fracturing is calculated as shown in table 6. Table 6 pumping pressure table of well YB1 displacement/m3/min Fluid friction/MPa pumping pressure/MPa 6.0 3.34 48.84 7.0 3.88 49.38 8.0 4.74 50.24 9.0 4.82 50.32 10.0 6.15 51.65 According to the casing procedure, fracturing design and oil testing scheme, the risks of using production casing as the channel for operation in this well are: (1) When fracturing with high pumping pressure, the pressure inside the perforated hole is relatively high. And once the remaining burst strength is exceeded, the perforated casing will crack (tear). (2) because the well is an "abnormally high pressure system", if the pressure difference is too large at the later stage of drainage and exceeds the remaining collapse strength, the perforated casing will be collapseed. Considering note ： 1.65 0.5 [1 1.464( / ) ] a c      0 / , y  ； 5 / 1.8 / 1.10 5.2 0.5 ( / ) a c a c a c      2 0.5 1 [(1 1.61 /( )] , e y a Rt   ( R D t   ) / 2 ； 2 0.5 2 [(1 0.32 /( )] , e y a Rt   ( R D t   ) / 2