The Junggar basin is abundant in coalbed methane (CBM) resources, of which the predicted resource of CBM with a burial depth of less than 准噶尔盆地煤层气资源丰富，其中埋藏深度小于2000 m is 3.11 × 米的煤层气预测资源为3.11×10¹² m³, and the southern margin of the Junggar basin (，准噶尔盆地（SJB) has the best preservation conditions for CBM）的南缘对煤层气具有最佳的保存条件[1]. The main coal-bearing strata in the 。SJB are lower-middle Jurassic, and the sedimentary environment mainly includes alluvial fans, fan deltas, braided river deltas, and shore shallow lakes主要含煤地层为中侏罗纪下部，沉积环境主要包括冲积扇、扇形三角洲、辫状河流三角洲和岸边浅湖[1，2，3]. The 。SJB has characteristics of thick and multiple coal seams developed with a laterally widely distribution and frequent interbedded sandstone, shale, and coal seams in the vertical direction which is favorable for the co-accumulation of coal measure gases具有厚厚多煤层的特点，横向分布广泛，纵向层层叠层砂岩、页岩、煤层频繁，有利于煤计量气的共积[4，5，6，7，8，9，10](（CMG, including CBM, coal measure tight sandstone gas and coal measure shale gas). The precedent of successful development in the Ordos basin ，包括煤层气，煤测量致密砂岩气和煤测量页岩气）。鄂尔多斯盆地成功开发的先例[5，11，12]and the maturation of 和CMG symbiotic accumulation theory 共生积累理论的成熟[7，8] have made the industry aware of the great potential in 使业界意识到CMG development. The reservoir quality is crucial for the efficient development of coal measure tight sandstone gas, and regional differences in diagenetic environment and tectonic events lead to different factors affecting reservoir quality 发展的巨大潜力。储集层质量对煤量致密砂岩气的高效开发至关重要，成岩环境和构造事件的区域差异导致影响储集层质量的不同因素[13，14，15，16，17，18，19]. In order to efficiently develop the abundant tight sandstone that is contained in the coal measures in the 。为了有效开发SJB, it is necessary to conduct research on the petrological characteristics and reservoir quality of coal measures sandstone.煤措施中所含的丰富致密砂岩，有必要对煤措施砂岩的岩石学特征和储集层质量进行研究。

The tight sandstone reservoirs generally undergo a complex diagenesis process, resulting in progressive tightness during burial and thermal evolution 致密砂岩储集层通常经历复杂的成岩过程，导致埋藏和热演化过程中逐渐致密[13，14，15，16，17，18]. The effects of reservoir quality include sedimentary, diagenesis and epigenesis, and the specific influencing factors include clastic composition, depositional environment, sedimentary facies, burial temperature and pressure 。储集层质量的影响包括沉积、成岩作用和表观成因，具体影响因素包括碎屑岩组成、沉积环境、沉积相、埋藏温度和压力[19，20]. Sedimentation controls the grain size, sorting, and arrangement of particles, as well as the mineral transformation and sedimentary structure 。沉淀控制颗粒的大小、分选和排列，以及矿物转化和沉积结构[16，21，22，23]. The influence of diagenesis on the sandstone is mainly in terms of tem。成岩作用对砂岩的影响主要表现在温度、perature, pH, pressure, etc., and is presented in the form of compaction, dissolution, cementation, and metasomatism H值、压力等方面，表现为压实、溶解、胶结、变质[19，21，24]. Compaction is one of the main factors leading to the reduction of porosity and permeability 。压实是导致孔隙率和渗透率降低的主要因素之一[25], and the reservoir quality is particularly affected by the degree of compaction and the content of plastic particles (such as lithic fragments, mica, argillaceous debris) and matrix ，储层质量尤其受到压实程度和塑料颗粒（如碎石碎片、云母、泥质碎片）和基质含量的影响[19，26]. Cementation generally leads to the plugging of pore throats and seriously reduces permeability 。胶结一般会导致孔喉堵塞，严重降低渗透率[27、28、29、30、31，32], but at the same time, it can also restrain the deterioration of reservoir quality to a certain extent: The inter-crystalline pores formed by the clay minerals cementation can provide storage space for sandstones ，但同时也能在一定程度上抑制储集层质量的恶化：粘土矿物胶结形成的晶间孔隙可以为砂岩提供储物空间[31，33，34]]; the clay film covering the particle surface resists compaction and inhibits the development of other types of cement 覆盖颗粒表面的粘土膜抵抗压实并抑制其他类型的水泥的发展[13，35], thereby preserving residual pores，从而保留残留的孔隙; the clay film coating the particle surface can resist compaction and inhibit the development of other types of cement; the quartz cementation and carbonate cementation in the eodiagenesis can improve the compaction resistance ability of sandstone 粘土膜覆盖颗粒表面，可以抵抗压实，抑制其他类型的水泥的发展;渗氮中的石英胶结和碳酸盐胶结可以提高砂岩的抗压实能力[15，36，37]. By analyzing the sedimentary environment, composition, and diagenesis characteristics of the coal measure sandstone, the reservoir quality control factors of the coal measure sandstone in the Xishanyao formation can be clarified and the formation and evolution process of the coal measure sandstone reservoir can be explained.。通过分析煤测砂岩的沉积环境、组成和成岩特性，可以阐明西山尧组煤测砂岩储集层质量控制因素，解释煤测砂岩储集层的形成和演化过程。

The coal seams of the Xishanyao formation on the southern margin of the Junggar basin are mainly in the low-medium coal rank, with frequent interbedding of sandstones, mudstones and coal seams 准噶尔盆地南缘西山瑶组煤层以中低煤层为主，砂岩、泥岩、煤层交织频繁[1]. The diagenesis of coal measure sandstone is strongly influenced by the thermal evolution of coal seams and dark shale 。煤测量砂岩的成岩作用受到煤层和深色页岩热演化的强烈影响[7，8]. Previous studies on sandstone reservoirs have mainly focused on the mechanism of pore throat formation, quantitative characterization of pore throats, and the relationship between oil and gas intrusion and reservoir diagenesis of sandstone reservoirs in different zones or layers within the basin 。以往砂岩储集层的研究主要集中在孔喉形成机理、孔喉定量表征、盆地内不同区间或层层砂岩储集层油气侵入与成岩作用的关系[38，39，40，41，42，43]]. However, studies on the coal-bearing sandstones of the Middle Jurassic Xishanyao formation have also focused on the evolution of the sedimentary environment, the classification of reservoir types, and the classification and evaluation of reservoirs 然而，对中侏罗统西山尧组含煤砂岩的研究也集中在沉积环境的演化、储集层类型的分类、储集层的分类与评价等方面[2，4，44，45，46，47]. As the understanding of the diagenetic sequence of the coal measure sandstone reservoirs in the Xishanyao formation, and the influence on reservoir quality is not comprehensive enough, it is urgent to carry out relevant work. This paper combined techniques including casting thin section observation, scanning electron microscope (。由于对西山瑶组煤测砂岩储集层的成岩层序了解，且对储集层质量的影响不够全面，亟待开展相关工作。本文结合浇注薄片观察、扫描电镜（SEM), XRD experiment, high-pressure mercury intrusion, low-temperature nitrogen adsorption, and Ro test of coal measure shale to conduct research on the following contents: (1) Determine the characteristics of coal measure sandstone in the Xishanyao formation; (2) clarify the diagenetic evolution sequence of coal measure sandstone in the Xishanyao formation; (3) clarify the controlling effect of sedimentation and diagenesis on the reservoir quality of coal measure sandstone. This study is expected to provide a reference for the exploration and development of tight sandstone gas in the Xishanyao formation coal measures.）、XRD实验、高压汞侵入、低温氮气吸附、煤测量页岩Ro试验等技术，对以下内容进行研究：（1）确定西山尧组砂岩的特性;（2）明确了西山尧组煤测砂岩的成岩演化序列;（3）明确了沉积和成岩作用对煤测量砂岩储集层质量的控制作用。本研究有望为西山尧组煤措施致密砂岩气的勘探开发提供参考。

2. Geology Background地质背景

The Junggar basin is located in the northern part of Xinjiang准噶尔盆地位于新疆北部; it is a large-scale Mesozoic-Cenozoic depression basin with an area of about 13.4 × 它是一个大型的中生代- 新生代坳陷盆地，面积约为13.4×10⁴ km公里² and an approximately triangular shape in the plane, with a width of 平面呈近似三角形，东西宽1120 km from east to west and 800 km from north to south 公里，南北宽800公里[1，2，3]. Since the Late Paleozoic, the Junggar basin has experienced Hercynian, Indosinian, Yanshan and Himalaya tectonic movements, and the superposition of multi-phase stress fields has led to its structural complexity 。自古生代晚期以来，准噶尔盆地经历了海西、印度支那、燕山和喜马拉雅的构造运动，多相应力场的叠加导致了其结构复杂性[2，44，48]. The Junggar basin can be divided into six structural units: the Luliang uplift, the Ulungu depression, the northern Tianshan piedmont thrust belt, the western uplift, the central depression, and the eastern uplift 。准噶尔盆地可分为六个构造单元：吕梁隆起、乌伦古洼地、北天山皮埃蒙特冲断带、西部隆起、中央洼地和东部隆起[3，49] (Figure （图1A). The A）。SJB is located in the northern Tianshan piedmont thrust belt, which elongates east-west direction with a north-south width of nearly 位于天山北部的皮埃蒙特推力带，东西方向伸长，南北宽近200 km (Figure 公里（图1B). The northern Tianshan piedmont thrust belt is a multi-phase superimposed and inherited structural belt, and is usually divided into five secondary structural units, including the Sikeshu sag, Qigu fault–fold belt, Huomatu anticlinal zone, Huan anticlinal zone, and Fukang fault zone B）。天山北皮埃蒙特推力带是多相叠加和继承构造带，通常分为五个次级构造单元，包括四州凹陷、齐固断裂褶皱带、火马图背斜带、桓斜带、阜康断裂带[50].。 SJB表面的主要部分被第四纪地层覆盖。SJB地区的地层从旧到新是二叠纪，三叠纪，侏罗纪和古新世（图1C)C）。其中，八道湾组和西山窑组是研究区的主要含煤地层，广泛分布在SJB（图1C)C）。西山尧组的含煤地层形成于湖相-三角洲沉积系统[，]。西山尧组地层在今霍尔果斯河和四公河之间有多个煤堆积中心，厚大于40 m，受构造和沉积条件的控制[]。

3. Paragenetic Sequence of Coal Measure Sandstone Diagenesis煤测量砂岩成岩成岩的副成因序列

3.1. Determination of Diagenetic Stage成岩阶段的测定

成岩阶段的澄清应基于古温（The clarification of diagenetic stages should be based on paleo-temperature (T), vitrinite reflectance (Ro), maximum pyrolysis peak temperature (Tmax), and smectite mixed layer ratio (S%) of I/S, spatial and temporal assemblages of authigenic minerals and the contact relationships between particles ）、镜质体反射率（Ro）、最大热解峰温度（Tmax）和I/S的蒙脱石混合层比（S%）、自生矿物的空间和时间组合以及颗粒之间的接触关系[5，22，67]. The 。研究区西山尧组煤测页岩Ro of coal measure shale in the Xishanyao formation in the study area ranges from 0.63–0.89%. The clay minerals of the coal measure sandstone are dominated by I/S, kaolinite and illite, with the mixed layer ratio (S%) of I/S ranging from 10–30% (avg on 18%). The compaction strongly influences the coal measure sandstone, with contact relationships composed of line contact, concave-convex contact, and suture contact. The reconstructed thermal history of the Jurassic strata, which is conducted by Wang et al.为0.63~0.89%。煤测量砂岩的粘土矿物以I/S、高岭石和伊利石为主，I/S的混合层比（S%）为10-30%（平均为18%）。压实对煤测量砂岩有很大影响，其接触关系由线接触、凹凸接触和缝合接触组成。Wang等人[68]进行的侏罗纪地层热学重建[68], found that the maximum burial depth of the Xishanyao formation exceeded 发现，西山瑶组的最大埋藏深度超过3000 m and the paleotemperature exceeded 100 °C. According to the diagenetic stage classification standard of clastic rocks (China’s oil and gas industry standard 米，古温度超过100°C。 根据碎屑岩成岩阶段分类标准（我国油气行业标准SY/T5477-2003), it can be comprehensively determined that the diagenetic stage of the Xishanyao formation coal measure sandstone is in the mesodiagenesis A1 and A2 stage (Figure 2).），可以综合确定西山尧组煤测砂岩成岩阶段处于介生系A1和A2阶段（图8）。

3.2. Diagenetic Sequences of Coal Measure Sandstone煤测量砂岩的成岩序列

结合SJB的热学和埋藏史，参考我国油气行业标准SY/T5477-2003中碎屑岩成岩阶段的划分，总结了该区西山尧组煤测量砂岩的成岩演化情况如下：

Combining with the thermal and burial history of the SJB, referring to the division of diagenetic stages in clastic rocks of China’s oil and gas industry standard SY/T5477-2003, the diagenetic evolution of the Xishanyao formation coal measure sandstone in the area is summarized as follows:

• Syndiagenesis同源

In this stage, the diagenetic environment has not been completely disconnected from the overlying water. The organic matter deposited in the peat swamp generates CO

在这个阶段，成岩环境尚未与上覆水完全断开。沉积在泥炭沼泽中的有机物产生一氧化碳

₂ under the action of microorganisms and dissolves in water, making the diagenetic environment weakly acidic. Due to the acidic nature of the sedimentary water, the surface of the detrital particles is rarely coated by a chlorite clay film. Due to the strong hydrodynamic environment during the sedimentary period, the coal measure sandstone contains a certain amount of plastic micrite carbonate and carbonaceous fragments will be blended into the sandstone.

在微生物的作用下溶解在水中，使成岩环境呈弱酸性。由于沉积水的酸性，碎屑颗粒的表面很少被亚氯酸盐粘土膜覆盖。由于沉积期水动力环境较强，煤测砂岩中含有一定量的碳酸盐塑性硅矿，碳质碎片会掺入砂岩中。

• Eodiagenesis (at the depth （在深度< 2 km, temperature < 70 °C, and Ro < 0.5%)2公里，温度<70°C，Ro<0.5%）

The type and degree of diagenesis in the eodiagenesis stage will affect the type of diagenesis and the physical properties of the reservoir in the later diagenetic stage 发育阶段成岩作用的类型和程度将影响成岩作用的类型和后期成岩期储集层的物理性质[22]. At this stage, the diagenetic environment is weakly acidic, and the diagenesis types include mechanical compaction, cementation (mainly argillaceous cementation) and dissolution, and the diagenetic environment gradually changes to a closed system. The compaction significantly reduces primary porosity 。在这个阶段，成岩环境是弱酸性的，成岩类型包括机械压实，胶结（主要是泥质胶结）和溶解，成岩环境逐渐转变为封闭系统。压实显著降低了初级孔隙率[69，70], due to the shallow burial depth and the high subsidence rate. The rock is in a weakly consolidated and semi-consolidated state, and the contact relationships of the clastic particles change from point contact to point-line contact. Pore types of the coal measure sandstone in this stage are mainly primary pores, and a small amount of micrite carbonate cement fills the pores.，这是由于埋藏深度较浅且沉降率高。岩石处于弱固结和半固结状态，碎屑颗粒的接触关系从点接触到点线接触发生变化。该阶段测煤砂岩的孔隙类型主要是初级孔隙，少量的硅藻土碳酸盐水泥填充孔隙。 With the increase in temperature, the coal seams and dark shale gradually released organic acid and CO随着气温的升高，煤层和深色页岩逐渐释放出有机酸和一氧化碳。₂  [[64], which makes the diagenetic environment gradually change to a weak acid. The feldspar and detrital grains began to dissolve slightly and form dissolution pores (Figure 2).，这使得成岩环境逐渐转变为弱酸。长石和碎屑颗粒开始轻微溶解并形成溶解孔（图9）。

• Mesodiagenesis (at the depth > 2 km, temperature > 70 °C, and Ro > 0.5%)

The effect of compaction in the mesodiagenesis A stage was extremely strong, and the compaction type gradually shifted from mechanical compaction to chemical compaction. The contact relationships change from point contact and line contact to line contact, concave–convex contact and suture contact during this stage, along with a large proportion of brittle minerals broken up. The dissolution pores formed in the eodiagenesis stage are damaged under the compaction, and the damage of compaction to the quality of the reservoir is further strengthened. The mesodiagenesis A stage can be further divided into two substages, A1 and A2, according to temperature and Ro. These two substages have certain differences in diagenetic environment and diagenetic reaction: In the mesodiagenesis A1 stage, the temperature was 70–90 °C, and the Ro was 0.5–0.7%, in an acidic diagenetic environment. The amount of organic acid generated in coal measures reaches the highest level at this temperature [71], the diagenetic environment is acidic, and the tensity of dissolution reached the highest level (Figure 29). The massive dissolution of feldspar, aluminosilicate lithic fragments and early micrite carbonate cement formed a large number of dissolution pores and mould pores. Because of the relatively closed diagenetic system, the dissolution products cannot be discharged. This has led to the kaolinite filling pores and quartz overgrowth (part of the SiO₂ comes from the chemical compaction). In the Mesodiagenesis A2 stage, the temperature was 90–130 °C, and the Ro was 0.7–1.3%. The acidic diagenetic environment is gradually weakened due to the decomposition of organic acids. The effect of dissolution decreases gradually, while the cementation is gradually increases. The quartz overgrowth gradually decreases, which is manifested as second level quartz cementation. Late period carbonate cementation (dolomite and ankerite) gradually filled the pore space (Figure 29). The clay minerals appear abundantly and fill the pores, further reducing the porosity.

4. Diagenetic Control of Coal Measure Reservoir Quality

Reservoir quality is influenced by diagenetic activities, such as compaction, cementation, dissolution, recrystallization, and metasomatism [20,72]. For the Xishanyao formation coal measure sandstone, compaction, dissolution and cementation are the main diagenetic controlling factors for reservoir quality.

4.1. The Influence of Compaction on Reservoir Quality

CThe compaction is one of the main factors that cause the reduction of intergranular pore volume [73] and the densification of coal measure sandstone reservoirs. Plastic particles in the sandstone have a weak compaction resistance, while the rigid particles have a high compaction resistance ability [61,74]. The coal measure sandstones of the Xishanyao formation contain a high content of plastic grains, such as volcanic lithic fragments, muddy gravel and carbonaceous fragments, which makes its compaction resistance ability weak. The coal measure sandstone reservoirs are strongly affected by mechanical compaction, which is characteristic of the close contacted clastic particles, the ruptured rigid particles, and the deformed plastic particles. Chemical compaction commonly happens in SJB due to the high intensity of compaction, which may lead to particle suture contact and reduced interparticle space. The intense mechanical and chemical compaction has a great negative effect on the physical properties of the sandstone reservoir.

4.2. The Influence of Cementation on Reservoir Quality

The coal measure sandstone of the Xishanyao formation in the SJB is mainly clay mineral cement, followed by quartz cement and carbonate cement. The development of these cementations is one of the main factors leading to the significant decline in reservoir quality [74,75,76,77]. The closed diagenetic system of coal measure sandstone prevents the dissolution products from being discharged in time, which also leads to the development of authigenic kaolinite cementation and quartz cementation. The developed kaolinite cement fills the pore space in large quantities, but its loose inter-crystalline structure contains inter-crystalline pores that can resist compaction [78]. In addition, illite and I/S mainly fill intergranular pores and pore throats, thereby reducing the reservoir quality of the sandstone [65,79,80]. In summary, different types of clay minerals occur widely and fill or divide the pore space, resulting in tortuous pore throats, reducing pore connectivity, and weakening seepage capacity [13,37,65,79,80]. The content of volcanic lithic fragments in coal measure sandstone is relatively high, which may inhibit the quartz overgrowth to some extent [77]. It can be observed that the overgrowth level of the coal measure sandstone is shown in the second stage (Figure 5A,C). The quartz overgrowth in the eodiagenesis stage can help the sandstone better resist compaction. In the mesodiagenesis, pressure solution, feldspar dissolution and clay mineral transformation produced many SiO₂  (aq), which developed into the quartz cement [13,81,82]. The carbonate cement is locally developed in coal measure sandstones. In the eodiagenesis stage, several micrite carbonate particles blended in the coal measure sandstone, which blocked and filled the intergranular pores. In the mesodiagenesis A2 stage, the late period dolomite and ankerite cements appeared in the sandstone, which blocked the intergranular pores of the sandstone and reduced the reservoir quality (Figure 5A,H,I).

4.3. The Influence of Dissolution on Reservoir Quality

The dissolution in diagenesis has a positive effect on reservoir physical properties [13]. The coal seam and dark shale begin to produce organic acids through the decomposition of plant residues during the eodiagenesis stage [71] and reaching a peak in the mesodiagenesis stage (temperature range from 80 °C to 140 °C, [37,83]). The amount of organic acid generated in the coal measure is much higher than in other source rocks [5,7,84]. The sedimentary environment makes the sandstone have good primary physical properties and pore connectivity, and the weak dissolution in the eodiagenesis stage provides a seepage channel for the migration of acidic fluids in the mesodiagenesis stage. The large proportion of aluminosilicate minerals, such as feldspar and volcanic in coal measure sandstone provides a good material basis for the dissolution [5]. Dissolution is most intense in mesodiagenesis. During this period, the thermal evolution of organic matter releases a large number of organic acids into the diagenetic system of the sandstone, causing the soluble minerals to selectively dissolve and form a large number of intragranular dissolved pores and intergranular dissolution pores [35]. Overall, the diagenetic stage of the coal measure sandstone in this area is mainly in the A1 and A2 stages of the mesodiagenesis, which happens to be the most intense stage of organic acid dissolution. The dissolution has brought a great positive effect on the physical properties of the reservoir.