蒙古国宗巴音凹陷沉积相研究及优质储层预测

Abstract:Little fundamental work on petroleum exploration and production of Zuunbayan Subbasin, Mongolia has been done before because of the backward economy and petroleum industry techniques in this country, which also results in our little knowledge of reservoir characteristics of this area. This paper focused on the sedimentary system, sedimentary facies, reservoir characteristics and their genesis distribution of Zuunbayan subbasin with various drilling, well logging, seismic, coring and outcrop data, aiming at providing significant guidances for the petroleum exploration and production of Zuunbayan area. Therefore, several conclusions have been achieved as follows: ①In Zuunbayan Subbasin, there are two chief source areas with Tarkhyata and Totoshan Uplifts in the southeast and Saykhandulaan Uplift in the west, respectively, while two subsidiary ones in the northeast and southwest of this subbasin. The sedimentary system of alluvial fan-fan delta is formed in the southeast highland, meanwhile braided river-braided river delta develops in the western ramp region and fan delta in the southern palaeohigh. ②There are middle to high permeability reservoirs in the upper Zuunbayan Formation and the upper member of lower Zuunbayan Formation meanwhile low-porosity and permeability to ultra-low permeability ones in Tsagaan Tsav Formation and the middle and lower members of lower Zuunbayan Formation. Combing with sedimentary facies belt, oil sources conditions and tectonic settings, favorable reservoir belts have been proved to be existing in the fan delta front reservoirs of lower Zuunbayan – Tsagaan Tsav Formation in the central uplift faulted zone as well as the braided river front ones of lower Zuunbayan-Tsagaan Tsav Formation in Zuunbayan nose anticlinal structural belts. ③The reservoir lithologic composition is complex and also related to volcanic activities. Generally, the types of lithologic composition in Zuunbayan Subbasin are chiefly feldspathic litharenites with low compositional maturity and high-middle textural maturity. The rock constituents from upper Cretaceous to lower Zuunbayan Formation are mainly metamorphic rocks including cleaving stone, phyllite, quartzite and schist while volcanic tuffs and acidic extrusive rocks are the secondary; and in the Tsagaan Tsav Formation are mainly volcanic tuffs with subsidiary cleaving stone, phyllite, quartzite and schist. ④In this paper, high-quality reservoirs in the upper member of lower Zuunbayan Formation have been discovered in the drilled high production wells of favorable reservoir facies through sedimentary system and sedimentary facies research, which benefits the prospect and also will bring a new life for petroleum exploration and production of Zuunbayan Subbasin. Key words: sedimentary system, sedimentary facies, superior quality reservoir, Zuunbayan Subbasin, lower Zuunbayan Formation