麻黄山西区北部延长6～4+5油层沉积相特征及演化规律

Characteristics and evolution of sedimentary microfacies of Chang 6-4+5 layer in the northern area of western Mahuangshan

麻黄山西区长6～4+5油层组油气显示普遍,但试油水多油少,砂体展布及连续性不清。为搞清研究区的沉积微相展布及演化规律,通过岩心详细观察描述,结合测井资料,识别出6种沉积微相、10种沉积构造,总结出10种微相接触样式和5种沉积层序模式,分别代表不同的沉积相带。垂向表现为以反旋回为主,兼有短期正旋回的沉积特征;侧向河口坝(或分流间)与水下分流河道相间发育,河道砂体下部为"多而小,窄而薄",上部为"少而大,宽而厚"。采用"单因素分析多因素综合"的研究方法,将该区划分为三角洲内前缘、三角洲外前缘和前三角洲3个亚相带,内前缘以水下分流河道、河口坝和水下分流间湾微相为主;外前缘以远砂坝和席状砂微相为主;前三角洲以滨浅湖泥微相为主。根据现代沉积相模式,推测该区为建设性辫状河道-湖泊三角洲,其演化表现为3个阶段:初始发育期(长63),以前三角洲和三角洲外前缘相带为主;早中发育期(长62和长61),以三角洲内前缘及外前缘相带为主,各微相多为单期发育,交互沉积;中后发育期(长4+52和长4+5),主要发育三角洲内前缘相带,水下分流河道表现为多期叠加样式。

There are widespread indications of oil and gas in the Chang 6-4＋5 layer of western Mahuangshan, while it proves that there is more water and less oil by well test. Furthermore, the distribution and continuity of sand aren＇t clear. To understand the distribution and evolution of sedimentary microfacies in the area, six kinds of sedimentary microfacies and eight kinds of sedimentary structures were identified and ten kinds of micro-contact patterns and five kinds of sedimentary sequence models were summarized by detailed core observation and description and logging data. Each model represents different sedimentary facies. Reverse cycle is dominant and normal short-term cycle also exists in the vertical direction; distributary mouth bar and subaqueous distributary channel are developed alternately in the lateral direction. The lower channel sands are ＂many but small, narrow and thin＂, while the upper channel sands are ＂a few but large, wide and thick＂. The ＂single-factor analysis and multifactor comprehensive＂ research method was used to divide this area into three phase belts-delta inner front, delta outer front and predelta. Subaqueous distributary channel, distributary mouth bar and interdistributary deposits are prevailing in the delta inner front. Distal bar and sand sheet are dominant in the delta outer front and predelta mud is dominant in the predelta. According to modern sedimentary facies model, the area is a constructive braided river-lake delta. Its evolution shows three stages： the initial development period （Chang 63 ）, the main facies belts are the predelta and the delta outer front; the earlymiddle development period （Chang 62-Chang 61 ）, the main facies belts are the inner delta front and the delta outer front and each micro-facies is a single phase and is deposited alternately; the middle-late development period （Chang 4＋52-Chang 4＋5i ）, the main facies belt is the delta inner front and the subaqueous distributary Channel shows a multi-phase stacking pattern.