昭通地区龙马溪组浅层页岩气储层特征及可开发性

CHARACTERISTICS AND EXPLOITABILITY OF SHALLOW SHALE GAS RESERVOIR IN LONGMAXI FORMATION,ZHAOTONG AREA

昭通地区龙马溪组是典型的浅层、中浅层页岩气储层,研究储层特征及可开发性对于浅层页岩气开发具有重要意义。本文以云南昭通龙马溪组页岩为研究对象,利用X射线衍射实验、场发射扫描电镜、氮气吸附等实验进行储层孔隙结构表征;将浅层页岩气储层与川南典型深层页岩气储层进行对比,归纳浅层特征,分析可开发性。结果表明昭通地区龙马溪组有机质丰度高,有机质类型好,属于过成熟阶段;具有低孔低渗的物性特征。矿物成分主要为石英、长石等,主要发育细粒混积岩以及长英质页岩。页岩储层主要发育粒间孔、粒内孔、有机质孔和微裂缝4种类型;孔隙形态以板状孔和柱状孔为主,比表面积与孔容均较大,发育孔径介于1~2 nm之间的微孔,以及2~4 nm之间、8~9 nm之间的介孔;其中有机质孔含量高,连通性较好。页岩气储层可开发性是指页岩气储层具有优越的有机质特征、矿物含量特征、储层物性特征、孔隙结构特征、含气性特征、脆性特征和地应力特征,能够通过储层改造进行开发的性质。本文通过将不同深度的龙马溪组页岩气储层进行对比分析,结果表明不同深度龙马溪组矿物组成基本一致,有机质孔发育形状基本一致,但昭通地区埋藏较浅,较小的地层压力与含量较高的长英质矿物导致其小于0.1μm的孔隙得到更大程度的保存;昭通地区龙马溪组主要含气类型为吸附气,储层脆性和所处地应力条件与深层相似。昭通浅层龙马溪组可开发性较好,是有利的页岩气开发方向。

Longmaxi Formation in the Zhaotong area is a typical shallow and middle-shallow shale gas reservoir.It is of great significance to understand the reservoir characteristics and its potential exploitation for the next phase of shallow shale gas extraction.In this paper,the shale gas reservoir of the Longmaxi Formation in Zhaotong,Yunnan Province,was studied.The pore structure of the reservoir was characterized by X-ray diffraction experiments and nitrogen adsorption experiments under a field emission scanning electron microscope.Through investigation and image recognition,shallow shale gas reservoirs were compared with deep shale gas reservoirs in southern Sichuan,summarizing shallow shale gas characteristics and analyzing exploitability.The results show that the total organic carbon of the Longmaxi Formation in the Zhaotong area has high abundance,good organic matter type,and over-mature thermal evolution.It is characterized by low porosity and low permeability.The mineral composition is mainly quartz,feldspar,calcite,and clay minerals,with mainly developed fine-grained mixed stone and felsic shale.Shale reservoirs are mainly divided into four types:intergranular pores,intragranular pores,organic pores,and micro-fractures.The pore morphology is dominated by plate pores open on four sides and cylindrical pores open on both ends.The specific surface area and pore volume are large.Micropores with pore sizes ranging from 1 nm to 2 nm and mesoporous pores ranging from 2 nm to 4 nm and 8 nm to 9 nm are developed.The content of organic pores in organic matter is high,and the connectivity is good.The exploitability of the shale gas reservoir refers to the characteristics of the shale gas reservoir with superior organic matter characteristics,mineral content characteristics,reservoir physical characteristics,pore structure characteristics,gas-bearing characteristics,brittleness characteristics,and in-situ stress characteristics,which can be exploited through reservoir reconstruction.In this paper,the shale gas reservoirs of the Longmaxi Formation at different depths are compared and analyzed.The results show that the mineral composition and organic pore development shape of the Longmaxi Formation at different depths are basically the same.However,the Zhaotong area has a relatively shallow burial depth,and the lower formation pressure and the higher content of feldspathic minerals lead to a greater degree of preservation of pores smaller than 0.1μm.The main gas type of the Longmaxi Formation in the Zhaotong area is adsorbed gas,and the reservoir brittleness and in-situ stress conditions are similar to those in deeper layers.The shallow Longmaxi Formation in Zhaotong has good exploitability and is a favorable direction for shale gas exploitation.