Abstract: The distal gravity flow sedimentary body of Chang 7₃ sublayer in the Ordos Basin is an important target for deep-water oil and gas exploration, but there is still an unclear understanding of its sedimentary scale and spatial distribution law, thus resulting in low drill ratio of sand bodies and high exploration risks in horizontal wells. Using the core, drilling, mud logging and logging data of Chengye 1 pilot well, Chengye 1 and Chengye 2 horizontal well, this paper studies the sedimentary types, distribution characteristics, sand body structure, deposition process and mode of the distal gravity flow of Chang 7₃ sublayer in the Chengye horizontal well region. Four types of sedimentation are developed in the deep-water sedimentary system of Chang 7₃ sublayer:sliding-slumping, arenaceous debris flow, turbidity flow and deep lacustrine mud deposits. The sand bodies are dominated by intermittently distributed arenaceous debris flow tongue-shaped bodies, with the thickness of 0.6-2.5 m for a single stage. The sand bodies have a stable thickness and good continuity along the provenance direction (NE), with a length of up to 800 m; in the direction perpendicular to the provenance (NW), the continuation length is mostly less than 150 m, and pinch out occurs suddenly. The gravity flow deposits in the horizontal well region of Chengye were formed by the instability, detachment and transportation of sediments in the delta front of the southwestern margin of the lake basin. The transportation of the nappe mainly experienced four stages of sliding, slumping, arenaceous debris flow and turbidity flow. The separation body of arenaceous debris flow is transported over a long distance and forms distal gravity flow sand bodies after wholly coagulating in the center of the lake basin. Sliding-slumping and turbidity flow deposits are the products of the interaction between the separation body of arenaceous debris flow and the lakebed and lake water. The structure of gravity flow sand bodies at the distal lake basin is controlled by the occurrence frequency and the single-stage scale of gravity flow events in the delta front. Isolated sand bodies are formed in gravity flow events with low occurrence frequency and large single-stage scale. Continuous superimposed sand bodies are formed in gravity flow events with high occurrence frequency but relatively small single-stage scale. The gravity flow sand bodies superimposed at intervals are the transitional deposits of the former two. Arenaceous debris flow sand bodies and deep lacustrine black shale at the distal lake basin are favorable targets for deep-water oil and gas exploration in Chang 7₃ sublayer of the Chengye horizontal well region. The development zone of fine sandstone in the Chang 7₃ sublayer in wells B522, C81, and C121 distributed in NE direction is a sweet spot for exploration, and the lower sand group of the Chang 7₃ sublayer is a section of the sweet spot. The direction along the provenance is a favorable horizontal drilling direction.

Key words: distal gravity flow, horizontal well, deepwater oil and gas, Chang 7 reservoir, Ordos Basin

摘要： 鄂尔多斯盆地长7₃小层远端重力流沉积体是盆地深水油气勘探的重要目标，但对其沉积规模、空间展布规律认识不清，导致水平井的砂体钻遇率低、勘探风险高。利用城页1井导眼井、城页1水平井和城页2水平井的岩心、钻井、录井及测井资料，对城页水平井区长7₃小层远端重力流的沉积类型、分布特征、砂体结构、沉积过程以及沉积模式进行研究。长7₃小层深水沉积体系发育滑动-滑塌、砂质碎屑流、浊流和深湖相泥质4种沉积类型。砂体以断续分布的砂质碎屑流舌状体为主，单期厚度为0.6~2.5 m。砂体在顺物源方向（NE向）厚度稳定、延续性好，长度可达800 m；在垂直物源方向（NW向）上延续长度多小于150 m，并发生突然尖灭。湖盆西南缘三角洲前缘沉积物的失稳滑脱和搬运形成了城页水平井区的重力流沉积，滑脱体搬运过程中主要经历滑动、滑塌、砂质碎屑流和浊流4个阶段，砂质碎屑流分离体远距离搬运，在湖盆中央整体凝结，形成远端重力流砂体，滑动-滑塌与浊流沉积是砂质碎屑流分离体与湖底、湖水作用的产物。湖盆远端重力流砂体结构受控于三角洲前缘重力流事件的发生频率与单期规模，孤立型砂体形成于发生频率低且单期规模较大的重力流事件；连续叠加型砂体形成于发生频率高但单期规模较小的重力流事件；间隔叠加型重力流砂体为前两者的过渡沉积。湖盆远端砂质碎屑流砂体和深湖相黑色页岩是城页水平井区长7₃小层深水油气勘探的有利对象，沿B522井、C81井和C121井NE向展布的长7₃小层细砂岩发育带是勘探"甜点"区，长7₃小层下砂层组是"甜点"层段，顺物源方向为有利的水平钻井方向。

关键词: 远端重力流, 水平井, 深水油气, 延长组7油层组, 鄂尔多斯盆地