论文部分内容阅读
为了保证在超压区安全而经济的钻井,需要准确地了解地层的压力情况。利用地震资料来预测地层孔隙压力是众所周知的事情,但所使用的地震速度常常是利用低分辨方法得出的,这种速度是一种基于地震孔径上的平均速度。这样的速度资料可能会导致孔隙压力估计不准确,尤其当地震速度存在横向变化的时候,精度更低。反射地震层析成像可得到具有较高空间分辨率的地震速度,因此,利用层析速度可得到更可靠的钻前孔隙压力预测结果。然而,地震速度受岩性变化和孔隙流体成分以及孔隙压力的影响(也就是说,地震速度的变化并不完全是由孔隙压力引起的,岩性和孔隙流体也会引起速度的变化)。对于海洋来说,利用放置于海底的四分量检波器可接收到P波和S波信息。S波速度资料有助于减少钻前压力预测的多解性,即可区分纵波速度的变化到底是由孔隙压力的变化引起的,还是由岩性和流体成分的变化引起的。
In order to ensure safe and economical drilling in the overpressure zone, accurate understanding of the pressure in the formation is required. It is a well-known fact to use seismic data to predict formation pore pressure, but the seismic velocities used are often derived from low-resolution methods based on the average velocity at the seismic aperture. Such velocity data may lead to inaccurate estimates of pore pressure, especially when seismic velocity changes laterally. Reflected seismic tomography can obtain seismic velocities with high spatial resolution. Therefore, more reliable pre-bore pore pressure prediction can be obtained by using tomographic velocity. However, the seismic velocity is affected by changes in lithology and pore fluid composition and pore pressure (that is, changes in seismic velocities are not solely due to pore pressure, and lithology and pore fluids also cause changes in velocity). For the oceans, P-wave and S-wave information is received using a four-component geophone placed on the seafloor. S-wave velocity data can help to reduce the multiplicity of predictions of pre-drill pressure, and can distinguish whether the change of P-wave velocity is caused by the change of pore pressure or by the change of lithology and fluid composition.