非均匀地应力场下水合物储层水平井井周塑性区分布

Distribution of plastic zone around horizontal wells in hydrate reservoir in non-uniform in-situ stress field

为研究非均匀地应力场下水合物储层水平井井周塑性区分布,首先,考虑温度变化、渗流作用和水合物分解作用的影响,结合岩石塑性屈服准则,建立了井周塑性区分布分析模型;其次,求解了井周塑性区域的分布;最后,分析了地质因素和工程因素对井周塑性区域形状和面积的影响。研究结果表明:非均匀地应力场中井周塑性区形状更复杂,可能出现椭圆形、蝶形和X形等形状,井周塑性区形状主要受地应力非均匀程度及水平井眼方位控制,井眼截面上的应力差较大时塑性区主要为蝶形和X形,应力差较小时主要为椭圆形;塑性区面积主要受地应力非均匀程度、井底温压、井眼方位角、水合物分解区面积及分解后的岩石强度影响;当水合物分解区较小时,影响塑性区面积的主要因素为分解区内岩石强度的弱化程度,水合物分解区面积增大,塑性区面积也增大;而当水合物分解区较大时,影响塑性区面积的主要因素为井周应力,塑性区面积将不再随水合物分解区面积变化而变化。

To study the distribution of plastic zone around horizontal wells in hydrate reservoir under non-uniform in-situ stress field,firstly,considering the influence of temperature change,seepage and hydrate decomposition,the plastic zone distribution analysis model was established combined with the rock plastic yield criterion.Secondly,the distribution of plastic zone around the well was solved.Finally,the influence of geological factors and engineering factors on the shape and area of the plastic zone around the well was analyzed.The results show that the plastic zone around the well is more complex in non-uniform in-situ stress field,and oval,butterfly and Xshaped shapes may appear.The shape of the plastic zone around the well is mainly controlled by the inhomogeneity of in-situ stress and the orientation of horizontal hole.When the stress difference on the well section is large,the plastic zone is mainly butterfly and X-shaped.When the stress difference is small,the plastic zone is mainly oval.The plastic zone area is mainly affected by ground stress inhomogeneity,bottom hole temperature and pressure,borehole azimuth,hydrate decomposition zone area and rock strength after decomposition.When the hydrate decomposition zone is small,the main factor affecting the plastic zone area is the weakening degree of rock strength in the decomposition zone and the plastic zone area increases with the increase of hydrate decomposition zone area.When the hydrate decomposition zone is large,the main factor affecting the plastic zone area is the borehole stress and the plastic zone area will not change with the change of the hydrate decomposition zone area.