阿姆河右岸区块深水低能缓坡礁滩分布综合预测

土库曼斯坦阿姆河右岸区块别什肯特坳陷带由于具有特殊的低能深水缓斜坡沉积背景,目前地质认识程度低,天然气勘探难度大。为了加快对该坳陷带的天然气勘探进程,在分析中上侏罗统卡洛夫阶—牛津阶沉积特征的基础上,开展了基底古地貌特征分析;再从地球物理方法入手,通过礁滩体厚度识别、非连续性地震属性提取和基于波动方程的模型正演等手段,开展深水低能缓坡礁滩特征研究及礁滩地震识别,落实礁滩分布,并形成了一套适用于该坳陷带的地震地质综合礁滩识别方法。研究结果表明:①该坳陷带卡洛夫阶—牛津阶岩石类型以泥晶颗粒灰岩、颗粒泥晶灰岩及泥晶灰岩为主,卡洛夫期主要为中—外缓坡沉积环境,牛津期主要为上斜坡—下斜坡沉积环境,低能缓斜坡沉积特征明显;②该坳陷带基底古地貌发育3个次级古隆起,具有西北高—东南低的古地貌特征,为后期礁滩发育奠定了地貌基础;③通过三维地震资料识别出面积大于1 km~2的礁滩体68个,总面积为187.3km~2,其中该坳陷带北部及中—南部为礁滩较发育的有利区;④地质地震综合解释该坳陷带北部的G22井区、T21井区以及中南部的B21—H21井区及其周缘地区为有利区带,部署实钻2口井均获得了高产气流。结论认为,所形成的深水缓坡盐下小规模礁滩地震地质综合识别方法应用效果好,助推了该坳陷带碳酸盐岩气藏勘探取得重大突破,可以为类似气藏的勘探提供参考。

Integrated prediction on the distribution of reef beach in the depositional environment of low-energy deepwater slopes in the Amu Darya Right Bank Block

The Beschkent Depression in the Amu Darya Right Bank Block of Turkmenistan has a special depositional environment of low-energy deepwater gentle slopes where the geological understanding has been so little known currently that natural gas exploration there is quite difficult. In order to speed up the natural gas exploration in the Beschkent Depression, this paper analyzed the depositional characteristics of Callovian and Oxfordian of Middle–Upper Jurassic and the basal palaeogeomorphology. Then, from the perspective of geophysics, the characteristic investigation and seismic identification of reef beach in the depositional environment of low-energy deepwater slopes were carried out by means of reef-beach body thickness identification, discontinuous seismic attribution extraction and forward modeling based on wave equation, and accordingly the distribution of reef beach was confirmed. Finally, an integrated seismic and geologic identification method suitable for the Beschkent Depression was developed. And the following research results were obtained. First, in the Beschkent Depression, the rock types of Callovian–Oxfordian stage are mainly micrite grainstone, grain micrite and micrite. The depositional environment is mainly middle-outward gentle slope facies in the Callovian stage, and upper-lower slope facies in the Oxfordian stage, presenting obvious depositional characteristics of low-energy gentle slope. Second, three sub-palaeouplifts are developed in the basal palaeogeomorphology of the Beschkent Depression and the palaeogeomorphologic characteristics of being high in the northwest and low in the southeast are presented, which lays a geomorphologic foundation for the development of reef beach in the later stage. Third, based on 3D seismic data, 68 reef-beach bodies larger than 1 km2 are identified in the study area, with a total area of 187.3 km2. The northern and central-southern parts of the Beschkent Depression are the favorable zones for the development of reef beach. Fourth, it is revealed from the integrated geologic and seismic interpretation that Well block G22 and T21 in the northern part of Beschkent Depression and Well block B21–H21 in the central-southern part and its periphery zone are favorable zones. Two wells deployed and drilled in the favorable zones produce high-yield gas flow. In conclusion, this proposed integrated seismic and geologic identification method for subsalt small-scale reef beach in the depositional environment of deepwater gentle slope presents remarkable application effects. It promotes the significant breakthrough in the exploration of carbonate gas reservoirs in the Beschkent Depression and also provides some reference for the exploration of similar gas reservoirs.