Study on Fine Time-Depth Calibration in Petroleum Exploration
Hou, Jiang B.; Li, Huiyong; Jiang, Liqun; Fan, Jianhua; Li, Deyu
Fine time-depth calibration has important significance in petroleum exploration, especially for deep strata exploration, low amplitude structure exploration and subtle reservoir exploration. Relative to the shallow strata exploration and conventional structure exploration, they gradually become the key and difficulties for petroleum exploration of Bohai oilfield, the precision and veracity of the time-depth calibration restrict the exploration of these fields. Regarding the theoretic time-depth relationship as the standard, this paper analyses the difference between VSP and migration section with the theoretic time-depth relationship, which is very important for fine time-depth calibration and reservoir prediction.
Due to the time-depth calibration involves VSP relationship and migration section. In order to discuss the difference between them, this paper introduces the concept of theoretic time-depth relationship.
According to the Marine VSP measurement principle, this paper discusses the difference between VSP time-depth relationship and theoretic time-depth relationship in condition of vertical well, and infers calculation formula of VSP time in tilted stratum. In order to validate the size of VSP time error, also forward VSP time of models which have different angels, layers and speed by the wave equation forward modeling method, forward modeling results also validate our understanding. Making clear that the VSP time error which caused by tilted stratum is the main one out of all the influence factors.
According to the pre-stack time migration principle, this paper also analyses the reasons which cause migration section time error, determines the sources including inaccurate longitudinal velocity pickup, seismic phase change, anisotropies and migration method difference. And realize that migration section time error is the main reason for time-depth adjustment. At the same time, inaccurate longitudinal velocity pickup is the main source of migration section time error.
From the study, we make clear the reasons and main controlling factor of time-depth adjustment, which can prevent the blindness of time-depth adjustment and improve the accuracy and precision of reservoir prediction. This research is well applied in horizon calibration and reservoir prediction of Bohai oilfield, and plays a very positive role in the deep strata exploration, low amplitude structure exploration and subtle reservoir exploration.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013