应用速度场技术预测深水钻井中的浅层地质灾害

随着深水油气勘探开发的逐渐深入和不断发展,浅层地质灾害成为深水钻井作业中面临的一大难题。深水井海底淤泥强度低、欠压实,地层不稳定,地层破裂压力梯度与地层空隙压力梯度之间窗口窄,当量循环密度控制困难,存在浅层气、天然气水合物及浅水流等浅层地质灾害风险。浅层地质灾害源体积小,难以预测;层位浅,灾害常突然出现;压力高,易发生井喷等事故,造成巨大的损失,所以对浅层地质灾害的预测就显得尤为重要。分析发现,地震波速度对浅层灾害的预测起着非常关键的作用,速度场技术结合了横向分辨率较高的地震资料和纵向分辨率较高的井资料,为速度的准确求取奠定了基础,也为浅层地质灾害的预测提供了科学的依据。为此,阐述了深水浅层地质灾害与地震波速度之间的关系,重点分析了速度场建立的方法及步骤,并对荔湾深水气田LW3-1-1井区所建立的速度场进行分析,预测了井区浅层地质灾害存在的可能性,这对后续钻井作业服务具有参考作用。

Application of seismic wave velocity field to predict the geological disasters in shallow strata during deep sea drilling

Along with the deep going and continuous development of deepwater oil and gas exploration and production, geological disasters in shallow strata have become one of the most serious issues in deepwater drilling operations. Deepwater wells are drilled in the unsteady strata with the soft and uncompacted seabed mud; and due to a narrow window between fracture initiation pressure and pore pressure, the equivalent circulating density is difficult to control in drilling and completion activities. As a result, potential risks in shallow strata are caused by shallow gas, natural gas hydrate, shallow water flow, etc. Those sources of geological disasters at shallow strata are extremely difficult to predict because of a small volume. Besides, being at superficial horizons easily results in sudden occurrence. Moreover, being under high pressure is prone to downhole accidents such as well blowout. To avoid the subsequent huge loss, it becomes quite essential to predict such geological disasters at shallow strata. Therefore, an analysis was made to discover that the seismic wave velocity is crucial in the prediction of geological disasters at shallow strata. Thus, a velocity field technology integrated with the high lateral resolution seismic data and the high longitudinal resolution well data not only laid the foundation for the accurate velocity acquisition, but provided the scientific basis for the prediction of shallow strata geological disasters. On this basis, we explained the relationship between seismic wave velocity and shallow strata geological disasters in deep water focusing on the method and procedures of the velocity field establishment. And we analyzed the established velocity field of LW 3-1-1 well block and predicted the possibilities of geological disasters at shallow strata, which is of valuable reference for subsequent drilling services.