西藏措勤盆地郎山组沉积特征及其石油地质条件

西藏措勤盆地的下白垩统郎山组是在海侵不断扩大背景下的前陆盆地碳酸盐浅海相沉积，主要沉积相类型有碳酸盐浅海、礁、水下浅滩、近岸碳酸盐潮下带、陆缘碎屑潮坪等，在革吉、洞措和色林错坳陷发育了巨厚的浅海泥晶灰岩，成为3个沉积中心。浅海相灰岩为主要的烃源岩，向沉积中心方向加厚，有机质类型以腐泥型为主；主要的储集空间和油气运移通道为裂缝；沉积相类型对孔隙的发育有一定的控制作用。该组中缺乏有利的区域盖层。但其中、下部的潮坪相泥岩、泥灰岩可形成局部较为有利的盖层。

Depositional Features and Petroleum Geological Conditions of Langshan Formation in Coqen Basin, Tibet

The Lower Cretaceous Langshan Formation is most important in the exploration of oil and gas within the Coqen basin, Tibet. It consists of marine facies carbonate rocks formed with the relative rise of sea level during marine molasse deposition in the foreland basin, and comprises neritic facies, reef facies, shoal facies, nearshore carbonate subtidal facies etc. There are three depocenters around Ge'gya, Dongcuo and the Selin Lake. Hydrocarbon source rock in Langshan Formation is mainly limestone of neritic facies, whose thickness increases toward the depocenters. The organic matter is mainly of sapropel type. Major accumulation locations are earlier-formed fractures. Facies types control to some extent the development of reservoir pores. The Langshan Formation lacks regional overlying formation. Nevertheless, mudstone or marl of nearshore subtidal facies may be effective local overlying formation.