65 / 2023-07-06 21:53:22

浅层海相页岩含气性特征及其主控因素——以昭通太阳区块龙马溪组为例

浅层页岩气；龙马溪组；含气性特征；控制因素；太阳区块

摘要：近年来，随着中国乃至全球对油气资源的需求不断增加，非常规油气开发领域迅速发展，其中页岩气作为一种大规模、连续型、低丰度的非常规油气资源，已成为油气勘探开发领域中的热点。虽然我国近年来页岩气产量逐年增加，但勘探开发主要集中在埋深1500~3500m并逐步向深层发展，与中深层页岩气相比，浅层（埋深<1500m）页岩气因具备开发成本低、建产速度快等优点受到了广泛关注。目前国外的浅层页岩气的勘探在美国部分盆地已经得以实现，我国昭通国家级示范区经实践证明具有良好的天然气显示，而太阳区块浅层页岩气开发成功在我国尚属首例。目前对于昭通国家级示范区的研究主要集中在黄金坝—紫金坝区块，对于昭通太阳背斜区块浅层页岩气的研究较少，而昭通太阳区块龙马溪组页岩气经实践证明具有埋深浅、高含气量的特点，显示出良好的勘探潜力。前人有对昭通太阳背斜区块的沉积环境、保存条件、储层特征及甜点展布进行研究，提出“三元控藏”规律，但对于太阳区块的含气性特征及主控因素并未进行详细阐述。

本文以昭通太阳区块为研究区，利用太阳区块龙一₁亚段页岩样品的分析测试资料及相关钻井数据对其含气性特征及主控因素进行分析。结果表明，（1）昭通国家级示范区太阳区块浅层页岩气（埋深<1500m）具有良好的勘探开发前景，龙一₁亚段页岩总含气量平均2.27m³/t。垂向上看，总含气量以底部的龙一₁¹小层最高，平均为2.74m³/t，随深度的减小大致呈现逐渐降低的趋势。平面上，各小层页岩含气量总体具有类似的分布特征，呈现出南北高中间低的规律，其中页岩气最富集区域位于研究区的北部；（2）研究区龙一₁亚段页岩的有机质含量、矿物组成及储层物性对其含气性均有一定的控制作用。TOC、硅质矿物含量、孔隙度与页岩含气性呈正相关关系，TOC、硅质矿物含量、孔隙度的发育对页岩气的生成、储集及开发具有促进作用。其中TOC是研究区龙一₁亚段页岩含气量的最主要控制因素，有机质是生成页岩气的原始物质，同时其生烃裂解形成的有机质孔为页岩气提供大量的储存空间；孔隙度和硅质矿物含量的控制作用稍弱；研究表明，海相页岩的孔隙类型多样，在有机质、脆性矿物及粘土矿物等基质中均可见孔隙发育；页岩气主要以吸附气和游离气两种状态赋存，有机质孔的发育大多呈蜂窝状连续密集分布，能够大大增加比表面积^[29-30]，对页岩游离气和吸附气均有积极作用^[31]，而粘土矿物粒间孔中多赋存水分，不利于页岩气的储存，脆性矿物粒间孔中则主要赋存游离气。高含量的脆性矿物有利于储层裂缝的形成以及后期页岩气的压裂开发^[27-28。（3）研究区优质的顶底板条件及微超压—超压为浅层页岩气的富集成藏提供了有利条件。研究区龙一₁亚段顶底板地层岩性致密，封闭性良好，表现微超压—超压特征，减少页岩气逸散，勘探前景广阔。

Abstract:In recent years, with the increasing demand for oil and gas resources in China and around the world, the field of unconventional oil and gas development has developed rapidly, among which shale gas is a large-scale, continuous, low-abundance unconventional oil and gas resource, has become a hot spot in the field of oil and gas exploration and development . Although the production of shale gas in my country has increased year by year in recent years, the exploration and development are mainly concentrated in the burial depth of 1500-3500 m and gradually develop to deep layers. It has received extensive attention due to its advantages of low development cost and fast production speed. At present, the exploration of shallow shale gas in foreign countries has been realized in some basins in the United States. my country's Zhaotong National Demonstration Area has been proved to have good natural gas performance by practice, and the development of shallow shale gas in the Taiyang block has been successful in This is the first case in my country. At present, the research on the Zhaotong National Demonstration Zone is mainly focused on the Huangjinba-Zijinba block, and there is less research on the shallow shale gas in the Zhaotong Taiyang anticline block. It is proved that it has the characteristics of shallow burial depth and high gas content, showing good exploration potential. The predecessors have studied the depositional environment, preservation conditions, reservoir characteristics and distribution of sweet spots in the Zhaotong Taiyang anticline block, and put forward the law of "three-element control of reservoirs". The characteristics and main controlling factors are not elaborated.

In this paper, the Zhaotong Taiyang block is taken as the research area, and the gas-bearing characteristics and main controlling factors of the shale samples from the Long 1 subsection of the Taiyang block are analyzed and tested using the relevant drilling data. The results show that (1) the shallow shale gas (buried depth <1500m) in the Taiyang block of the Zhaotong national demonstration area has a good prospect for exploration and development. Vertically, the total gas content is the highest in the S₁l₁¹ at the bottom, with an average of 2.74m³/t, which generally shows a decreasing trend with the decrease of depth. On the plane, the shale gas content of each sublayer has similar distribution characteristics as a whole, showing a pattern of high in the north and south and low in the middle, and the most enriched area of shale gas is located in the north of the study area; (2) Long 1 subsection of the study area The organic matter content, mineral composition and reservoir physical properties of shale all have a certain control on its gas-bearing properties. TOC, siliceous mineral content and porosity are positively correlated with shale gas-bearing properties. The development of TOC, siliceous mineral content and porosity can promote the generation, storage and development of shale gas. Among them, TOC is the most important factor controlling the gas content of the shale in the Long 1 subsection of the study area. The organic matter is the original material for generating shale gas, and the organic matter pores formed by the cracking of hydrocarbon generation provide a large amount of storage space for shale gas; The control effect of shale and siliceous mineral content is slightly weaker; studies have shown that marine shale has various pore types, and pores can be seen in organic matter, brittle minerals, clay minerals and other matrices; shale gas is mainly composed of adsorbed gas and free gas. The two states exist, and the development of organic pores is mostly honeycomb-like continuous and dense distribution, which can greatly increase the specific surface area, and has a positive effect on the free gas and adsorbed gas in shale, while the clay mineral intergranular there is more moisture in the pores, which is not conducive to the storage of shale gas, while free gas mainly occurs in the intergranular pores of brittle minerals. High content of brittle minerals is beneficial to the formation of reservoir fractures and the fracturing development of shale gas in the later stage. (3) The high-quality roof and floor conditions and micro-overpressure—overpressure in the study area provide favorable conditions for the enrichment and accumulation of shallow shale gas. The top and bottom strata of the Long 1 subsection in the study area are tight in lithology and good in sealing, showing the characteristics of micro-overpressure—overpressure, reducing shale gas escape, and having broad exploration prospects.