SEDIMENTARY SYSTEM ANALYSIS USING SEISMIC MULTI-ATTRIBUTES TECHNIQUE IN AREAS LACKING WELL DATA: AN EXAMPLE FROM SHAHEJIE FORMATION IN BZ3-1 BLOCK OF WESTERN SLOPE OF BOZHONG SAG

The multi-attributes technique has been widely adopted to sedimentary facies analysis recently. The accuracy and resolution of the method depend upon the availability of drilling holes in the area. In the area with enough drilling wells, it is of efficiency and precise enough to use the method of multiple attributes and single-well facies analysis to map the plane distribution of sedimentary facies. However, in the areas with few wells or even no well, the method to optimize seismic attributes and define sedimentary facies remain immature up to date. The well drilling degree is quite low in the BZ3-1 block of the western slope of the Bozhong sag, and few wells have penetrated the Shahejie Formation. In this paper, taking the Shahejie Formation as an example, we studied the distribution pattern of sedimentary systems semi-quantitatively on the basis of seismic multi-attribute analysis, in combination with available palaeogeomorphologic data. Through the study of high-accuracy 3d sedimentary system using the three-dimensional visualization and dissection technique, we discovered that the development of 3rd-order system tracts deposits depended upon their development stage in the 2nd-order sequence. The sequence of SQs₃^l of the lower member of Es3 developed in the LST of the 2nd-order sequence, and the size of fans are larger than those formed in the HST; the sequence of SQs₃^m of the middle member of Es3 developed in the TST of the 2nd-order sequence, so the size of LST fans are equal to HST fans; the sequence of SQs₃^u of the upper member of Es3 developed in the HST of the 2nd-order sequence, and the size of HST delta fans are much larger than those in the LST.