At present, natural gas accounts for a low proportion in China's primary energy consumption structure and is highly dependent on foreign sources. Changqing gas province of the Ordos Basin where PetroChina Changqing Oilfield Company (referred to as Changqing Oilfield) is located is one of China's four major natural gas production bases. It bears the important responsibility for ensuring people's livelihood and promoting the healthy development of society economy. In recent years, Changqing Oilfield actively implements national instructive spirit on vigorously promoting domestic oil and gas exploration and development strength and formulates the secondary acceleration development strategies. Its annual natural gas production in 2020 reaches 448.5 × 108 m3 and oil and gas equivalent exceeds 6000 × 104 t, tamping its important position of “Western Daqing” in this industry. In order to further promote the continuous stable production and realize the goal of quality and efficiency improvement in Changqing gas province, this paper analyzes the situations and challenges of natural gas development in this gas province, prepares the development technological countermeasures and forecast the natural gas development prospect. And the following research results are obtained. First, the natural gas exploration and development in Changqing gas province is divided into four stages and the main technologies for the development of low-permeability carbonate gas reservoir, low-permeability sandstone gas reservoir and tight sandstone gas reservoir are formed. Second, the natural gas development in Changqing gas province faces six challenges, such as low reserve production degree, sharp decline of production rates and complex distribution of remaining undeveloped reserves of developed gas fields. And twenty-six development technological countermeasures are put forward correspondingly, such as well pattern thickening, extension and reserve increase, secondary production layer potential tapping and fine gas well management. Third, the development direction and goal of natural gas development in Changqing gas province is to pay equal attention to the stable production of old gas fields and the production increase of new areas and carry out conventional gas and unconventional gas research simultaneously. In conclusion, the annual natural gas production of Changqing gas province will maintain a sound momentum of steady growth and will exceed 500 × 108 m3 at the end of the 14th Five-Year Plan and maintain at a stable level for a long term, which is conducive to the optimization of domestic energy consumption structure and realization of “carbon peak and carbon neutrality”.

The old well sidetracking technology is an effective means to stabilize production and increase recovery in later stage of gas field development. Based on economical and reservoir geologic parameters of Sulige low-permeability gas field in China, method and procedure of old well sidetracking selection standards are established, which can effectively improve the sidetracking effect and adequately develop remaining gas. Comprehensively considering corresponding economic parameters including sidetracking drilling cost, operating cost, management cost, gas production rate and gas price, recoverable reserve standard of sidetracking well is determined first. According to gas recovery, gas-bearing area, porosity and gas saturation, standards of remaining geological reserve, reserve abundance and gas pay thickness of sidetracking well are obtained. According to extension direction and distribution characteristics of the sand body in research area, numerical simulation conceptual model of typical sidetracking horizontal well is established, and then standards of old gas well production rate and gas cumulative production rate for sidetracking are obtained. According to the standards, well Su 36-6-9CH is selected to be sidetracked as a horizontal well and its development effect is good. The method has important value of popularization and application in similar low-permeability gas reservoir.

Braided river reservoirs occupy a large proportion in domestic tight sandstone gas reservoirs, which were represented by the tight gas reservoir of sulige gas field in ordos basin, and the reservoirs are heterogeneous. The establishment of braided river reservoir geological knowledge data-base is very important for reservoir prediction between Wells. Under the guidance of braided river sedimentary prototype model based on outcrop anatomy and Google Earth satellite image analysis of modern sedimentary, by analyzing the logging data of horizontal Wells, and studying the relationship between the horizontal well trajectory and the sand cap/bottom structure, the lithology, GR and gas measurement comparison methods of parameters in the geological knowledge database of tight reservoirs were established, which can be used to quantitative anatomy of underground geological knowledge data-base. The results show that the four sand drilling modes of the horizontal section are established. And the effective drilling effect of the horizontal section can be effectively improved by relying on tracking the structural fluctuation of the sand cap/bottom based on the four sand drilling modes. Using actual lateral horizontal well anatomy to establish reservoir geological knowledge database can effectively reflect the braided river dense sandstone reservoir heterogeneity, and the prediction of reservoir “sweet spot” between Wells is realized. In this way, the establishment and application method of reservoir underground geological knowledge database on horizontal wells are proposed, and the inter-well reservoir prediction and the three-dimensional spatial simulation characterization from the five-stage channel to the three-stage internal configuration of diara are realized, which is of great significance for horizontal well deployment and geological guidance.

为落实苏里格气田强非均质致密砂岩气藏储量规模和动用程度、评价稳产潜力,基于储层地质知识库,通过细分计算单元采用"容积法"完成储量复算;结合储层静态参数、气井生产指标及内部收益率建立了储量分类评价标准,将储量分为富集区、致密区和富水区三类;优选"单井控制面积法"评价已动用储量和剩余未动用储量.评价结果表明,苏里格气田储量基础落实,各区块储量动用程度差异大,储量综合动用程度为40.1％,剩余未动用储量规模大,稳产潜力较好.目前经济技术条件下,气田稳产主要通过井网加密、侧钻水平井及查层补孔的方式来提高富集区和致密区储量动用程度,富水区剩余储量的有效动用仍须进一步攻关.

The origin of grain dolomite in M55 Member of Ordovician Majiagou Formation in northwestern Ordos Basin was studied by geochemical and petrological tests on core samples. Observation of cores, thin sections and casting thin sections, analysis of cathodoluminescence, X-ray diffraction, microscopic sampling of trace elements, laser sampling δ18O and δ13C, and fluid inclusion homogenization temperature were conducted. The results show that the dolomite is the product of recrystallization of micritic to crystal powder dolomite rather than the product of dolomitization of grain limestone. In the spherical grains are residual gypsum and halite pseudo crystals identical with those in the host micritic dolomite. The spherical particles of dolomite has similar trace elements and δ18O and δ13C characteristics to micritic dolomite. Furthermore, Mn/Sr ratio of the fine—medium dolomite between the dolomite grains is about 5-8, while Mn/Sr ratios of calcite in limestone, micritic dolostone in micritic dolomite, and micritic and powdery dolomite are about 0-2, indicating that the dolomite experienced strong diagenesis. Homogenization temperature of inclusions of fine—medium dolomite is about 148. 19 °C, higher than that of inclusions in micritic to crystal powder dolomite (about 122.60 °C), which also supports the conclusion that the grain dolomite experienced burial diagenesis and negative shift of δ18O and δ13C. The δ18O, δ13C values of micritic to crystal powder dolomite match with the negative migration, but those of calcite in limestone don't. It is of great significance to elucidate the genesis of "dolomite recrystallization" for the prediction of such dolomite reservoirs.

In view of the 2D section geo-steering technology based on the start well and the end well, the relationship between adjacent wells cannot be fully reflected, and the reservoir prediction effect is poor. Using data measurement of 10 modern braided rivers, architecture dissection of three encryption areas, and analysis of 50 horizontal well data, this paper establishes the single-layer microfacies geological database of braided river reservoir. As a constraint, taking advantage of the adaptive channel facies modeling method by the control of the body curve and 20 × 20 × 0.2 m fine grid design, the 3D facies model of multi-period stacked channels is set up, and then, after the analysis and classification of the quality-controlled models, probability prediction models is built according to different geological conditions, in order to guide horizontal well geo-steering. The results show that this method achieves better effect compared with the traditional methods, the success rate reaches 90.9%, the sandstone drilling rate is increased by 8% points, and the test yield and the production capacity are improved significantly. This method provides strong technical support for the highly economic and effective development of strong heterogeneity and tight sandstone gas reservoirs.

苏里格气田属于典型的致密砂岩气藏,针对其纵向上多层系含气、横向上砂体连续性差的地质特征,形成多层系大井组混合井网立体开发技术.通过复合砂体垂向分期,单期河道砂体平面划界,明确有效砂体孤立型、切割叠置型、堆积叠置型和横向局部连通型4种叠置方式.利用现场干扰试验、气藏工程论证等方法优化井网,针对不同砂体叠置方式和储集层特征,形成混合井网.考虑水平井、直井和定向井的开发优势,形成针对古生界多层系的大井组混合井网立体开发技术.该技术实现了山1段和盒8段河流相砂岩储集层、马家沟组五段海相碳酸盐岩储集层立体开发,整体储量一次动用,有效提高储量动用程度,降低开发成本,保障气田经济有效开发.

下奥陶统马家沟组马五1-5段是苏里格气田东区主要产层段,其勘探潜力巨大.基于岩心观察、铸体薄片及分析化验等资料,对马五段进行储层特征及控制因素分析.研究表明,苏里格东区在马五5期为局限台地相带的潮坪亚相沉积.马五1-4为含膏云坪亚相,马五5为颗粒滩相;发育含膏细-粉晶白云岩和中-粗晶白云岩.苏里格气田东区马五1-5段储集空间包括孔隙和裂缝2大类,其中孔隙主要为溶蚀孔、膏模孔、晶间孔、晶间溶孔和裂缝包括溶蚀缝、微裂缝和构造缝等.储层发育和分布主要受控于:沉积环境决定了多类型储层发育;马五1-4层段准同生白云石化和渗透回流白云石化及马五5段埋藏白云石化作用是碳酸盐岩储层发育的决定条件,白云石化作用改善了储集性能;苏里格气田马五1-5层段碳酸盐岩储层经历了不同阶段溶蚀作用(同生、表生、埋藏)而形成有利的溶孔、溶缝储层,提高了储层储集性能.

When studying the production decline law of gas reservoir at present, the Arps decline model and the grey GM (1, 1) model are mainly used. The application of grey GM (2, 1) model is less. Arps decline model is difficult to correctly judge the decline type at one time, and the calculation process is complex. When calculating the hyperbolic decline equation, due to the different starting point of the algorithm and the different mathematical approaches, you may get different results. The essence of the grey GM (1, 1) model is the index form, when it is used to study the other type of the production decline law of gas reservoir, the error is much bigger. Therefore, the grey GM (2, 1) model is introduced. The calculation results show that the grey model method is simple and practical, with high precision and reliable results. The grey model can be used on the production decline rule of gas reservoir.

The reservoir of the block A in Sulige gas field was a typically low porosity and low permeability reservoir with fluvial phase deposition, in which the lower layer He 8 is braided river deposits. Because of the incompleteness of seismic data and the low resolution of analysis in the small layer, the plane distribution of the sedimentary phases of layers and the small-scale layers obtained from seismic inversion are often not ideal enough. Lithology thickness ratio and logging phases are the main methods for understanding the distribution of sedimentary phases. Taking the lower layer He 8 of block A in Sulige gas field as an example, through combining the thickness ratio with logging phases together. The principle of determining the plane boundary of sedimentary phases was established, and a more systematic method for determining the plane distribution of braided river phases was formed. By means of this method, the sedimentary phase distribution in the lower layer He 8 in dense well pattern of block A was studied. The plane distribution parameters of the geological bodies such as the channel, the heart and the beach are obtained. Compared with the related geological bodies of modern rivers, it was proved that this method is more reasonable for the prediction of fluvial phase braided river deposits.

基于国内外研究成果建立了辫状河构型模式,并利用测井、野外露头及气井动态资料,对鄂尔多斯盆地中—东部下石盒子组八段(盒八段)辫状河储层进行构型解剖.在野外露头中识别出河道带,心滩与河道充填,单元坝与心滩内水道,大型倾斜层与中型交错层,中型平行层与小型交错层共5级构型单元.运用所测量交错层系厚度资料推算露头剖面中心滩长为1 163～1 592 m,宽为282～390 m,该推算值与实际测量值相符合.对野外露头和苏里格气田密井网区盒八段储层构型解剖表明:河道带砂体、心滩砂体之间发育多成因的、连续的渗流屏障,连通性较差;心滩内部渗流屏障规模较小,因此可将心滩视为独立的储渗单元.运用成像测井资料推算出苏里格气田盒八段辫状河心滩长为602～1 243 m,宽为143～302 m,大部分心滩规模小于目前气田的井距和排距;气井动态资料也证明目前的井网密度下,有效储层井间连通性较差,因此苏里格气田具备加大井网密度的潜力.

针对现有辫状河储层构型单元定量表征方法关键参数获取困难且可靠性存疑的问题,以储层构型理论为指导,基于现代辫状河沉积、钻井岩心、录井和测井等资料,提出了基于单一辫状河道宽度的构型单元定量表征方法.首先,根据单井构型单元解释结果,确定同期辫状河道平面分布;其次,根据连井对比剖面,确定连井剖面内单一辫状河道间的界线位置;再次,根据现代辫状河单一辫状河道宽度与构型单元关系定量模型,限定辫状水道宽度、复合心滩长度及宽度等4级构型单元规模;最后,在单一辫状河道内确定4级构型单元平面分布,进而在密集井网区对复合心滩进行解剖,确定单个心滩位置和几何形态.采用该方法对苏××提高采收率试验区盒8下1-3单层辫状河致密砂岩气藏进行了分析,结果表明:该单层砂岩气藏发育5条单一辫状河道,其宽度为1 050～1 890 m;辫状水道宽度为234～435 m;复合心滩长度和宽度分别为1 931～3 569 m、685～1 242 m;单个心滩长度和宽度分别为660～1 880 m、310～1 030m.

苏里格气田是典型的强非均质性致密砂岩气藏,目前已进入稳产阶段,储量资源基础需要重新落实.随开发程度提高,不同储层储量动用程度大有不同,后期部署产能建设井位、确保气田长期稳产的难度日益增大.开展已动用地质储量评价,明确气田剩余未动用地质储量,是气田技术挖潜和稳产的基础.针对此问题,以苏里格气田苏14区块盒8、山1段为研究对象,采用容积法对目的层进行储量复算,结合现有井网情况,针对不同井网控制程度,采用不同方法计算不同井网情况下的已动用地质储量,落实了已动用地质储量的规模及分布.结果显示,该区块目前已动用地质储量占复算储量基础的39.54％,实现区块长期稳产具有可行性.该研究对苏14区块后续井位部署和稳产技术政策研究有重要作用,对苏里格气田其他各区块及同类型气田的有效开发有借鉴意义.

Sandstone formations in braided river reservoir of H8x in the Sulige Gasfield are characterized by poor continuity and connectivity, and high heterogeneity.To enhance efficiency of gasfield development, reservoir architecture theories have been used in the Well Su×× within the study area to identify underground braided channel and diara, and to determine their internal structures accurately.Eventually, patterns for distribution of effective sandstone formations can be determined.Research results show diaras have gas-bearing properties significantly better than those of braided channels.On the other hand, internal structures, regional lithologic features and different physical properties of braided channel and diara may jointly control distribution of effective sandstone formations;Effective sandstone formations in braided channels distributed predominantly in rough-sized sediments in lower parts;Except interlayers, surfaces toward flows in diara conatin effective sandstone formation.Core sections of diara are dominated by effective sandstone formations, with non-effective sandstone formation distributed regionally.Surfaces opposite to flow in the diara have poor gas-bearing properties in general with effective sandstone formations distributed in middle and lower parts with rough particles.Generally speaking, surface against flows, cores and lower parts of braided channel in the diara shall be considered as major target sandstone formations for fine development in the Sulige Gasfield in future.Relevant researches may provide reliable geologic foundations for horizontal well optimization design and for high-efficiency development of the Sulige Gasfield.

The 3D geological relation between adjacent wells cannot be fully characterized by the 2D-secton geosteering technology,which usually leads to poor reservoir prediction.A geology database for the monolayer sedimentar,microfacies of braided river reservoir is established according to the modern braided river sedimentation,outcrop,structure analysis of infilling region and horizontal well data.As a constraint,a target-based Adaptive Channel sedimentary facies modeling method is used to establish a 3D sedimentary microfacies rnodel with multi-stage stacking channels and prediction models with different probabilities to guide the horizontal-well geo-steering.The corresponding horizontal-well geo-steering success rate has reached 90.9％.Comparing with that of traditional methods,the sandbody drilling rate is increased by about 8percentage points and the gas reservoir drilling rate is increased by about 5％,which results in significant test gas production and productivity.This research could provide certain technical reference for the efficient development of tight sandstone gas reservoirs with strong reservoir heterogeneity.

The phenomenon of "low-resistivity" gas reservoir and "high-resistivity" water reservoir exist side by side, rapid changes of longitudinal resistivity of the water reservoir and gas and water mixed reservoir in the Su 54 area of Sugeli gas field which caused gas-water identification difficulty. First, the genesis of low-resistivity gas reservoir in tight sand had been analysed. And then, the crossplot acoustic-resistivity method, multiple discriminant analysis method and support vector machine method had been used on gas-water identification method in research. Finaly, the gas testing and production dynamic data had been used to verify. The study results show that: the additional conductivity of clay minerals in tight sand reservoir and mud invasion is the main reason for the low-resistivity gas reservoir. And the three gas-water identification methods based on gas testing and production dynamic data made a better recognition effect in practical application; especially the gas-water recognition precision of support vector machine method reaches 93%. This study provides a new thought for the gas-water identification of tight sand gas reservoir.

苏里格气田是典型的低渗、低压、低丰度的强非均质性致密岩性气田.水平井开发对于提高单井产量作用显著,然而水平井随钻地质导向难度大是制约其高效开发的瓶颈.针对地质导向过程中微幅构造难判断、井底岩性难识别以及易钻遇泥岩隔夹层等问题,在水平井部署与设计的基础上,通过分析水平段钻遇泥岩时的具体情况,并结合砂体垂向叠置关系及储层内部构型分析,总结了一套适合苏里格气田盒8段气藏的水平段导向调整措施,并以AH井实钻为例加以说明.多年的水平井开发实践表明,采用水平井随钻地质导向技术进行水平井开发,平均砂岩钻遇率达85.7％,平均有效储层钻遇率达62.5％,水平井单井产量是直井的3～5倍.

The opinions to the sedimentary facies in the western Sulige gas field were so different that they lead to the big difficulty to forecast the sandbody distribution in exploration and development .We studied the sedimentary facies through adopting the techniques and methods of stone characteristics analysis ,sedimentary structure description ,and fossil observation ;revealed sedimentary sequences of outcrop from Chengjiazhuang based on the facies logging and seismic reflection related to fluvial facies researched by predecessors in the Lower He8 Member .The research results show that the braided river deposition is the main facies type of the Lower He 8 Member in Western Sulige Gas Field .In our opinion , the frequent climate change from dry to humid is the controlling factor ,which resulted in the large thickness of sandbody ,strong heterogeneity ,and lateral variation of reservoir .

By researching the channel sandbody in the He-8 Member of Lower Shihezi Formation of Permian System in Sulige large gas field in Ordos Basin,the genetic types and distribution patterns of channel sandbody in He-8 Member has been established.Through analyzing detailed core observation and symbols of sedimentary facies,it was concluded that the sedimentary environment in the area is braid river deposit in the lower section of the He-8 Member,while it is mandering river deposit in the upper section of the He-8 Member.It is anastomosed river deposit in some local area.The lithology and lithofacies of the sandbody are closely related to its gas-bearing property,and the gas-bearing sandbody have good correspondence with the coarse lithofacies units.The coarse lithofacies were mainly developed both in high-energy braid channel and its central bar and the lower part of point bar of the meandering river.According to the study of the channel sandbody distribution pattern,we have found that there are the high-energy braid channels and low-energy braid channels in the lower section of the He-8 Member,and the anastomosed river in the north and mandering river in the south in the upper section of the He-8 Member.

Hydro-upgrading and jet fuel refining combined process was adopted in a 20,000 bpd middle pressure hydro-upgrading unit of Jinxi Petrochemical Co to produce the qualified jet fuel and optimum diesel distillate with setting point < 0°C under the conditions of feedstock final boiling point (bp) 391°C without distilled tail oil. Commercial application showed that #3 jet fuel with the smoke point < 20 mm and #0 diesel were directly produced without further refining, the feedstock with final bp 363°C. Refining/upgrading flexible hydrogenation scheme could be realized through the reaction temperature adjustment.