考虑射孔方位的出砂预测模型

Sand production prediction model considering perforation azimuth

以往的射孔完井出砂预测模型都不能计算和分析不同方位角下的出砂临界压差。针对这一问题,采用岩石力学理论和分析方法,根据应力坐标转换理论和线-弹性力学基本理论,并将直井中的射孔孔道换位看作是特殊情况下的水平井(井眼半径极小),在分析射孔孔道受力的基础上,将Drucker-Prager强度准则作为出砂判断准则,建立了一种考虑射孔方位角、新的射孔完井出砂预测模型。实例计算和分析表明,在射孔完井的直井中,射孔孔道壁上各点的出砂临界压差各不相同,差异较大。出砂总是首先发生在孔道壁的最薄弱处,此处对应的出砂临界压差最小;方位角有规律地影响射孔孔道的出砂临界压差,而2个水平主应力的不均等是造成方位角影响射孔孔道出砂临界压差的最根本原因;水平地应力非均匀系数越大,射孔孔道出砂临界压差随方位角变化的趋势越明显。因此,应根据水平地应力非均匀系数的大小和它对射孔孔道出砂临界压差的影响程度,决定是否使用定向射孔技术。

The conventional sand prediction model for perforated completion wells could not calculate and analyze the critical drawdown in different azimuths. In order to solve this issue, the stress analysis flu＂ a perforated tunnel is derived by using the conception and analytical approach in feld of rock mechanics, the stress coordinate transfer and the line-elasticity theory and by treating the perforated tunnel in a straight well as a special horizontal well. Based on this stress analysis, a new sand prediction model considering azimuth for perforated completion wells is established by taking the Drucker- Prager strength criteria as sanding criteria. The calculation and analysis on two cases indicate that azimuth can regularly influence the critical sanding drawdown of the perforated tunnel remarkably vary in a straight well and sanding always firstly occurs on the most weakness point where the minimal critical sanding drawdown has. Azimuth can regularly influenee the critical sanding drawdown of the perforated tunnel and the primary reason induced this influence attributes to the difl~＇renee of ttle two horizontal in suit stresses; the larger the anisotropic coefficient on two horizontal in suit slresses is, the bigger variation trend of critical sanding drawdown along with azimuth will be. Therefore, whether oriented perforating technology should be used depends on the size of anisotropie coefficient on two horizontal in suit stresses and its influence on critical sanding drawdown for a perforated tunnel.