基于初至旅行时差的微地震速度模型反演

Microseismic velocity model inversion based on moveouts of first arrivals

为精确定位微地震震源,需已知压裂井和监测井所在工区准确的地层速度模型。常规速度建模方法需用射孔记录中P波和S波初至旅行时信息校正地层速度,这要求已知准确的射孔起始时间。然而受施工条件等因素影响,实际监测过程中射孔的起始时间很难准确测量。因此,本文基于Levenberg-Marquardt反演算法,提出一种利用初至波旅行时差信息替代旅行时进行速度模型反演的方法,该方法可在射孔起始时间未知的情况下反演出地层速度模型。利用该方法分别对模型数据和实际资料进行试处理,从处理结果可以看出:虽然受观测系统布设位置及初至拾取精度等因素影响,反演出的速度模型存在一定误差,但利用该模型可将射孔位置定位到其真实位置附近,表明该速度模型可用于微地震震源定位。

In order to accurately locate microseism sources,velocity models between treatment wells and monitoring wells are needed.For conventional approaches,such velocity model building needs exact perforation origin times,so that travel times of P-wave and S-wave first arrivals can be estimated to calibrate velocities.However perforation origin times are very difficult to be precisely measured in the practice.So in this paper,we develop a new method to invert the velocity model without knowing the perforation origin time.Instead of the travel times,our method adopts first arrival moveouts to invert velocity models based on Levenberg-Marquardt inversion algorithm.So it can overcome the limitation of conventional approaches when perforation origin times are unavailable or inaccurately measured.Both model and field dataset tests indicate that velocity models inverted by our method can locate the perforation shots back to their expected positions,although velocity models have some discrepancies,which could be caused by many factors such as monitoring deployment positions and first arrival picking errors.So the inverted velocity models can be used to locate microseism sources.