阿尔及利亚韦德迈阿次盆地438B区块泥盆纪层序-岩相古地理特征

泥盆系是富含油气的阿尔及利亚韦德迈阿次盆地西北部438B区块重要的含油层位之一,可划分出2个三级层序,仅下部的SQ1层序保存较完整;泥盆系属于快速海侵缓慢海退的沉积旋回,由海侵、早期高位和晚期高位3个体系域叠加组成。在SQ1层序中相当体系域级别的地层单元在区域上具有良好的等时性,仅在研究区东、南部外侧构造隆起区明显变薄或局部缺失海侵体系域地层。各体系域中,早期高位体系域的障壁砂坝在纵向上具有更好的可比性,反映该体系域障壁砂坝砂体的发育层位和沉积厚度更稳定,砂体连通性和储集性更好,但上部的SQ2为仅保存部分海侵体系域沉积记录的残余层序。选择SQ1层序各体系域为等时地层单元编制层序-岩相古地理图,编图结果表明:438B区块泥盆纪具备向南东方向弧突的,由浅海陆棚、障壁岛、潟湖、潮坪组成的海湾地貌和分带性沉积格局;在各体系域继承性发展演化的分带性沉积格局中,以早期高位系域中的障壁砂坝和冲溢扇为最有利储层发育的层位、相带和部位。

Characteristics of Sequence-lithofacies and Paleogeography of Devonian in Block 438B of Oued Mya Basin,Algeria

Block 438B is located in the northwest of Oued Mya Basin, Algeria. Devonian stratum is one of the important oil-bearing formations in Block 438B.The stratum is divided into 2 three-order sequences, and only SQ1 sequence in the lower part is intact; Devonian stratum is rapid transgression-slow regression cycles, and is composed of TST, EHST and LHST. The stratigraphic units for the equivalent system tracts are very isochronous in SQ1 sequence, the structural high only outside the east and south part of the research area is thin or lose TST stratum. The comparability of barrier sand bank for EHST is better in vertical for all the system tracts, so the developing stratum and deposition thickness of barrier sand banks for EHST are more stable, and the connectivity and reservoir property of sandbodies are better, but SQ2 in the upper part is residual sequence only recording part sedimentary of TST. All the system tracts of SQ1 sequence are taken as isochronous stratigraphic units in order to draw the paleogeography map of sequence-lithofacies. The results show that there are estuarine physiognomy and zonation sedimentary, which distribut from northwest to southeast and is composed of shallow-sea continental shelf, barrier island, lagoon and tidal flat, during Devonian of Block 438B; barrier sand bank and washover fan in EHST are the most favorable reservoir facies in the zonation sedimentary pattern with inherited evolution of all the system tracts.