柴达木盆地阿尔金山前深层基岩气藏储集空间再认识与成储潜力区探讨

Reservoir space and potential reservoir-formation areas in deep bedrock gas reservoirs in Altun forelands, Qaidam Basin: Recognition and discussion

柴达木盆地阿尔金山前深层基岩气藏的发现,拓展了该盆地天然气勘探开发的新领域,自发现以来,一直都认为该类气藏的储集空间是由发育良好的基质孔隙和裂缝双重介质构成的,然而气藏开发的实践却与该认识出现了矛盾。为了深化对该类基岩气藏储集空间及成储主控因素的认识,对基岩的溶蚀増孔特性和受力成缝特性开展了调研,然后基于东坪1、尖探1区块基岩岩心、铸体薄片等资料,分析阿尔金山前深层基岩气藏的主要储集空间类型,进而得出该区域基岩有利目标储集体形成的主控因素,并结合区域地质背景深化了相关地质认识。研究结果表明:(1)该区域基岩气藏岩性为钙碱性火成岩和片麻类区域变质岩,基质孔不发育,并且其发育程度主要受断裂的控制,有效储集空间和渗流通道为构造裂缝与溶蚀缝;(2)有利目标储集体形成的主控因素主要包括岩性的影响、构造作用、风化作用及岩脉侵入,并且基本遵循“优势岩性—应力主导—高点富集”三元共控成储的规律;(3)成储潜力区包括构造应力集中的张扭区、侵入体岩性界面接触带、挤隆抬升的风化带、剥蚀区近围坡积带及假整合或不整合界面5种类型。

The discovery of deep bedrock gas reservoirs in Altun forelands in the Qaidam Basin has expanded a new field of natural gas exploration and development in China. Since then, it has always been believed that the storage space of this kind of gas reservoirs is com- posed of well-developed dual media of matrix pores and fractures, but the practices of such gas reservoir development began to be in con- tradiction with this cognition. In order to achieve a better understanding of the storage space and the main controlling factors of reservoir formation in this bedrock gas reservoir, it is necessary to investigate the dissolved increased pores characteristics and the forced fractures characteristics in the bedrock gas reservoir. Then, based on the data such as cores and cast thin sections in the bedrock intervals in the Dongping 1 and Jiantan 1 blocks, the main storage space types of deep bedrock gas reservoirs in Altun forelands were analyzed, then the main controlling factors of favorable target reservoirs in these blocks were put forward, and in combination with the regional geological background, the geological understandings of favorable target reservoirs and potential reserves were deepened in this study area. The fol- lowing research results were achieved. (1) The lithology of the bedrock gas reservoirs in this area consists of calc-alkaline igneous rocks and gneiss suite regional metamorphic rocks. Matrix pores are not developed, and their development degree is mainly controlled by faults. Main effective storage spaces and permeable channels are structural fractures and dissolution fractures. (2) The main controlling factors of target reservoir formation include lithology, tectonic effect, weathering, intrusive dikes, and on the whole the rule of ternary-control is followed, namely prevalent lithology-dominant stresses-hydrocarbon accumulations in the structural higher parts. (3) The potential zones of reservoir formation include the following 5 types: tectonically stress concentrated tension-torsional zones, contact zones between lithologic interfaces of intrusive body, weathering zones of compressing uplift, slope sediment zones near circumscribed erosion area, pa- ra-conformity or unconformity interface.