Distribution prediction of the glutenite in Member 3 of Triassic Xujiahe Formation in Yuanba area, northern Sichuan Basin

Abstract

Although the Triassic Xujiahe Formation in Yuanba area of northern Sichuan has a large amount of resources, the proportion of proved reserves to the amount of resources is low. Production of most of the pilot production wells is high at the initial stage, but it declines rapidly, mainly due to tight rock properties and strong heterogeneity of Xujiahe Formation. Thus, it is important to investigate the distribution of high-quality reservoirs. The Member 3 of Xujiahe Formation develops sandstone interbedded with mudstone, and its lateral thickness of different sandstone groups varies greatly, so it is a challenge to identify appropriate time windows for seismic attribute analysis, thus, so the prediction effect of the glutenite in the Member 3 of Xujiahe Formation. In this study, through analysis of core data and logging facies, single-well sedimentary microfacies subdivision is carried out. Single-well lithological interpretation is also studied with application of lithological identification technique. Then, lithological associations and its seismic responses at the top and bottom interfaces of each sandstone group in the Member 3 of Xujiahe Formation are well investigated, The lithological association with the glutenite above and the mudstone below the stratigraphic interface respectively, corresponds to a trough in seismic profiles; in this case, when extracting the seismic attributes of sandstone groups above the stratigraphic interface, only the difference of between drilling horizons and seismic horizons needs to be considered. The lithological association with the mudstone above and glutenite below the stratigraphic interface respectively, corresponds to a peak in seismic profiles; in this case, when extracting the seismic attributes of sandstone groups above the stratigraphic interface, influence of which should be eliminated; thus, a method of time window determination for seismic attribute extraction is established. Among amplitude, frequency, and phase attributes, the total peak energy has the good correlation with thickness of the glutenite at well sites and it also can reflect the distribution of distributary channels well. The results show that belt-like glutenite in each sandstone group in the Member 3 of Xujiahe Formation extends in a NW-SE direction and thins out toward the southeast, and the distribution of glutenite has certain inheritance in the longitudinal direction, the glutenite in the third sandstone group in the Member 3 of Xujiahe Formation (TX33) and the first sandstone group in the Member 3 of Xujiahe Formation (TX31) are both developed.