Abstract:

Carbonate sequences of the upper Ordovician Lianglitag Formation along the Tazhong 83-Tazhong 16 well blocks，
Slope Break I，Tarim Block is 170-300 m thick and notable as reservoirs of oil-gas．This suite of sedimentary facies from the
platform margin is generally shown as overlapping of reef complexes with 4-5 cycles. Lithological facies as well as enhanced karst and tectonic action onward are considerable factors controlling the trap formation．Based on the analysis of drilling cores, thin sections and logging parameters, types of reservoir space are recognized as cave，intragranularly dissolved pores，intercrystalline dissolved pores，moldic pore，biologic dorsal pore，organic framework pore and micro-fracture．The features of the void structures as well as their associations are catalogued as vug，fracture-vug, and fracture configuration types, respectively，and are in similar abundance. Nevertheless， the perspective of reservoirs with good conditions of porosity and permeability are favorable for spatial distribution from the platform margin of the Slope-break I. Such a model is subtly consistent with reef-bank complexes. Outer setting of the platform margin has ideal lithologiolal facies that experienced multiple reformation phases and show weak filling.The reservoir pattern shows that fracture-vug and vug types are dominant. Therefore, we consider it a potential area for highquality type I andⅡ reservoirs. However, inner setting of the platform margin along the Tazhong 12-Tazhong 16 well blocks is dominated by fractures and high lithological filling during later periods that resulted in type Ⅱ and Ⅲreservoir.

Key words: Reservoirs, Reef complexes, Lianglitag Formation, Upper Ordovician, Slope-break I in Tazhong, Tarim Block, NW
China