Problems and solutions for velocity modeling during natural gas exploration in South China Sea

Abstract

Velocity forecast and model building has always been difficult and key problems of geophysical work in the natural gas exploration. Especially for new exploration area or exploration area with fewer wells, the accuracy of velocity prediction is very difficult to obtain, and there may be large errors. The errors are caused by less existing exploratory wells and the misunderstanding existing in the velocity forecast process. Firstly, in this paper, three cases of velocity forecast and model building in Ying-Qiong basin are analyzed. And every case raises an unusual but pressing problem. Secondly, considering mentioned misunderstandings and existing problems, research method and solving thoughts are proposed, mainly including processing velocity with geological model for guidance, establishing regional stratigraphic statics velocity correction templates, using along-horizon velocity interpretation in assistance, establishing forward modeling to assist velocity interpretation, correcting velocity model with information of drilled wells, horizons and geologic zonation, and building the high precision velocity volume. Finally, through the research in this paper, the existing problems of velocity prediction during natural gas exploration are solved and the corresponding solutions which have been applied in the production practice are given.