Seismic Acquisition Techniques for Loess Area in Western China

Abstract

Abstract The obduction zone of Kunlun mountain foreland in southwest Tarim basin in China is covered with thick loess whose thickness changes from several decade meters to 500m, even up to 600m in some area, so, the S/N of seismic data acquired in this area is very low due to serious absorption and attenuation of seismic wave and develops strong secondary interference. Being extruded and compressed by Kunlun Mountains, the topography of this area changes rapidly, the subsurface structure is steep and complex, and the faults are very developed, which lead this area to be one of the most difficult areas to do seismic exploration in the world. The conventional seismic exploration techniques used previously can't meet the requirements of the oil/gas exploration any more, and in the area since 1978, after the Kekeya oilfield was discovered, there has been no breakthrough made. Since 1999, several seismic technique tackling studies on Kekeya edge have been carried out, and wide line receiving and source array with deep holes have been applied, but the effects are not good. In recent years, on the basis of the previous rounds of seismic exploration tackling results in the thick loess area, new research has been conducted, and seismic data with relatively high S/N been acquired, which can meet the requirements for geological interpretation. Moreover, aimed at this thick loess area, seismic acquisition technique series have been developed, and great breakthroughs have been obtained for seismic exploration in loess area, and the first-grade rate of the seismic data increased by about 20%, all of which made a solid foundation for seismic exploration of loess area in southwest Tarim, and these technique series have some reference values for seismic exploration in the similar areas. The paper introduces some new technical achievements and knowledge for seismic acquisition in loess area of southwest Tarim basin, mainly including: (1) wide-line survey technique with high fold and long receiving spread is applied to increase the effective fold on the target horizons, and improve the quality of the seismic section; (2) source array technique with long pattern length and small charge size is applied to enhance the downgoing energy of the seismic wave; (3) long array receiving technique is applied to suppress the lateral interference and improve the signal sensitivity.