膏盐层蠕变致套管变形损坏机理及对策——以四川盆地北部X区块为例

四川盆地北部三叠系海相地层已发现20余口井套管存在不同程度的变形损坏，变形井段主要集中在雷口坡组和嘉陵江组，该井段含有大量膏盐，其中嘉四段膏盐含量高达58%。为此，针对该区域的X区块A1井海相地层套管变形检测结果及膏盐层的蠕变特性，采用有限元方法建立了非均匀外挤载荷反演模型，反演得到了海相地层套管所受的非均匀外挤载荷最大、最小值分别为98.93 MPa、92.85 MPa；通过建立海相地层套管受力分析模型，模拟得到了非均匀外挤载荷状态下Φ177.8 mm套管等效应力分布，计算出作用在套管上的等效外挤载荷为119.68 MPa，而被检测的变形套管抗挤强度仅有89.8 MPa，不能满足抗挤要求，定量揭示出了引发该区套管变形损坏的原因是膏盐层蠕变产生的非均匀外挤载荷。结合该区非常规井身结构应用情况，进一步计算了对应Φ190.5 mm和Φ215.9 mm井眼尺寸的Φ168.28 mm、Φ193.68 mm和Φ 177.8 mm套管的等效外挤载荷，推荐了这3种尺寸的套管选型，其抗挤强度分别大于119.24 MPa、124.29 MPa和119.68 MPa，为该区域海相地层套管柱设计提供了参考数据。

Mechanism of casing deformation caused by gypsum-salt layer creep and relevant countermeasures : A case study of Block X in the northern Sichuan Basin

Casing deformation and damage of different degrees occurred at the interval of Triassic marine strata in over 20 wells in the northern Sichuan Basin, and most of which focuses in Leikoupo and Jialingjiang Formations, which contain a large amount of gypsums salt, with a content up to 58% in the 4^th member of Jialingjiang Formation. Based on the casing deformation test results of marine strata in Well A1 and the creeping properties of gypsum-salt layers, a non-uniform external collapse load inversion model was built by finite element method. It is presented that the maximum and minimum non-uniform external collapse loads acting on the casings in marine strata are 98.93 MPa and 92.85 MPa respectively. The force analysis model of marine strata casings was established to simulate the equivalent stress distribution onΦ177.8 mm casing under the state of non-uniform external collapse load. The calculated equivalent external collapse load acting on casings is 119.68 MPa, but the measured collapsing strength of deformed casings is only 89.8 MPa, which can't meet the requirement. It is quantitatively revealed that casing deformation and damage in this block is caused by non-uniform external collapse load which is generated by gypsum-salt creep. Equivalent external collapse loads were calculated forΦ168.28 mm,Φ193.68 mm andΦ177.8 mm casings inΦ190.5 mm andΦ215.9 mm boreholes with the configurations of unconventional wells in this block taken into account. The collapsing strengths of these three types of casings are over 119.24 MPa, 124.29 MPa and 119.68 MPa respectively. This study provides an important reference for casing string design of marine strata in the northern Sichuan Basin.