鄂尔多斯盆地延长区上古生界储集层地质特征及天然气勘探前景

Geological characteristics and exploration prospect of Upper Paleozoic reservoirs in Yanchang area,Ordos Basin

鄂尔多斯盆地东南部延长区天然气勘探程度低,对该区古地理格局、沉积相类型及展布特征、储集层岩石特点及其储集条件进行分析,进而预测该区上古生界山西组、下石盒子组天然气勘探前景。延长区气源岩及盖层条件良好,广泛发育了主要产气层山西组、下石盒子组的三角洲前缘、三角洲平原、滨浅湖等沉积;储集层以石英砂岩为主,次为岩屑砂岩,具低孔、低渗特点。根据储集层岩石特征、物性特征、孔隙结构特征,将延长区上古生界储集层划分为4类,工业气流一般都形成于Ⅰ至Ⅲ类储集层,Ⅳ类储集层基本不具备储气能力。不同类型储集层分布比较分散,是本区普遍含气却产量偏低的原因之一。研究区子长—延川—延长一带,多期河道叠加发育,砂体厚度大,已见到较好的含气显示和工业气流井,是极富希望的天然气勘探区。

The degree of exploration is low in Yanchang area, SE Ordos Basin. The paper analyses its paleogeographic format, sedimentary facies and their distribution characteristics, rock characteristics, and reservoir conditions, and forecasts the exploration prospect for gas in the lower Shihezi and Shanxi Formations. The conditions of gas source and cap rock are favorable in the area, where develop the main gas productive reservoirs of the lower Shihezi and Shanxi Formations located on the delta front facies, delta plain facies and littoral-shallow lake facies. Quartzose sandstones and litharenites are the primary and secondary reservoirs respectively, and are of low porosity and permeability. Based on rock characteristics, physical property and pore configuration, the reservoirs are divided into four types. Industrial gas is formed in types I to Ⅲ, and type Ⅳ doesn＇t contain industrial gas. The low production rate results from the dispersed distribution of reservoirs. The area of Zichang-Yanehuan-Yanehang, which has muhiple- phase channel deposits and thick sandstones, is a promising gas exploration area.