鄂尔多斯盆地杭锦旗地区泊尔江海子断裂以北有效圈闭的识别

Identification of effective traps north of Boerjianghaizi Fault, Hangjinqi area, Ordos Basin

鄂尔多斯盆地泊尔江海子断裂以北地区是该盆地上古生界致密含气区的北部边缘区带,储集体为近物源的辫状河砂体。该区砂体物性以低孔低渗为主,明显好于盆地内部。低渗透河道砂体与低幅构造叠置所产生的气水分异现象,使得圈闭评价和气水关系识别复杂化。通过构造、测井和地震波形差异分析,对下石盒子组盒1段小型背斜气藏进行解剖,明确了在圈闭内部存在气水界面及其识别方法。盒1段圈闭的砂体—构造叠置关系为宽河道+小背斜,圈闭面积小、数量少;而盒2,3段圈闭的砂体—构造叠置关系为窄河道+不闭合构造,多是构造—岩性复合圈闭,圈闭数量多、面积较大。复合圈闭有效范围的落实除需要综合评价砂体、构造和封堵条件等因素外,更重要的是对气水界面的位置加以论证。

The area to north of the Boerjianghaizi Fault is on the northern edge of the tight-gas bearing area in the Upper Paleozoic in the Ordos Basin. A near-source braided river sand body serves as the main reservoir. Sand bodies in this area have low porosity and low permeability, which is nevertheless better than those in the basin.The gas-water differentiation caused by the superposition of a low-permeability channel sand body and a low-amplitude structure complicated trap evaluation and gas-water relationship identification. Through the difference analysis of structure, logging and seismic waveform, a small anticlinal gas reservoir was dissected in Member 1 of Shihezi Formation. The gas-water interface in the trap was made clear and an identification method was proposed.The sand-structural superposition relationship in Member 1 is a wide channel ＋ a small anticline, with small trap area and volume. However, the sand-structural superposition relationship in members 2 and 3 is a narrow channel ＋ a non-closed structure, mostly structural-lithologic composite traps, with a large number of traps and a large trap area. Besides the comprehensive evaluation of sand body, structure, sealing conditions, etc., it is also important to demonstrate the location of the gas-water interface.