DDWC (Directional Drilling with Casing) is an effective wellbore construction technique, particularly suitable for soft marine formations. In DDWC, the casing replaces the drill pipe for sliding drilling operations, and the passability of the drill string through the casing has become one of the primary challenges in applying DDWC. This study uses ANSYS Workbench to simulate the strain and bending behavior of the casing under various geological conditions. Simulations were conducted for different wellbore trajectories, casing specifications, and materials to evaluate the feasibility of the drill string passing through the casing under different conditions. The results show that, when the dogleg severity reaches 18°/30 m and the casing’s inner diameter is 315 mm, the maximum radial strain of the casing is 4.2 mm, which cannot guarantee the successful passage of a drill string assembly with a 311 mm outer diameter. For other casing specifications, with a minimum inner diameter of 317 mm, the drill string can pass through under the maximum dogleg severity. Additionally, since the elastic modulus and Poisson’s ratio of the casing materials are identical, the strain behavior is consistent across different materials, meaning that the material does not affect the passability of the casing. Moreover, the study optimized the selection of casing specifications and materials. From the perspective of ensuring drill string passability and resource conservation, a casing with an inner diameter of 319.4 mm was chosen. To ensure the longevity of the casing and the stability of the wellbore, N80 steel was selected as the material. A sensitivity analysis was conducted on the factors affecting casing strain, and the results aligned with the simulation findings, showing that wellbore trajectory and casing specifications have a significant impact on casing strain. Verifying the passability of the drill string through the casing is critical for the development and application of DDWC technology.

Micro-pore structure affects the fluid storage and seepage in coal seams.In this paper, six samples from the Jurassic Yan'an Formation coal seam in the Shenmu area of the Ordos Basin were taken as the object of study.The pore distribution characteristics of coal seams were jointly characterized by NMR, CO2 adsorption and N2 adsorption at multiple scales, and the connectivity and homogeneity of microscopic pores were investigated by combining multi-scale joint characiterization with CT scanning.Results show that the micro-pores of coal are the main contributors to the specific surface area and pore volume, followed by meso-pores.There is a good uniformity in the pore size distribution of the micro-pores and meso-pores by combing NMR and adsorption, while considerable differences are found in the macro-pores.Displacement NMR and CT excel in reflecting the degree of connectivity, both of which are consistent in the characterization of connectivity.Parameters such as coordination number and seepage pore ratio can effectively reflect the degree of connectivity of the sample, whose patterns of connectivity is M6>M2>M12>M15>M10>M4.The saturation of bound water shows a satisfactory positive correlation with pore-throat ratio of coal samples.It can be seen that the pore structure has a great influence on the degree of fluid migration, which is the basis for studying and evaluating gas occurrence and seepage.

苏里格气田是国内致密砂岩气田的典型代表,由于储层物性差,有效砂体规模小、非均质性强,现有的水平井布井方法难以在时间、空间维度上统一多学科多尺度数据,导致设计方案与实际情况差异较大,影响了水平井的开发效果.为此,以气田二叠系下石盒子组8段、山西组1段储层为研究对象,定量分析了辫状河体系带对沉积微相展布和有效砂体分布的控制作用,分辫状河体系叠置带、过渡带形成了水平井地质目标的优选标准,进而提出了以地质模型为基础的差异化部署水平井对策.研究结果表明:①该区有效砂体厚度薄、规模小,在空间高度分散,预测难度大;②叠置带储层规模大,稳定性和连续性强,应侧重于储层厚度、储量集中程度等整体性评价,整体式部署水平井;③过渡带沉积水动力弱,储层连续性相对局限,应在优选富集区的基础上,侧重于隔夹层描述、相邻直井生产动态分析等局部"甜点"评价后再部署水平井;④可将该区水平井分为4种类型,其中Ⅰ、Ⅱ类井主要位于叠置带,Ⅲ、ⅣV类主要位于过渡带,4类井的合理配产分别为大于5×104 m3/d、(4～5)×104 m3/d、(3～4)×104 m3/d、小于3×104 m3/d.结论 认为:①根据"多层约束、分级相控"建模方法形成了高精度三维地质模型,据此部署的水平井其有效砂体钻遇率由60％提高到70％以上,能够实现水平井差异化部署;②气井开发早期应先根据地质及动态参数快速进行气井分类评价,继而按照不同井类型进行配产,以便合理利用地层能量,提高气井开发效果和最终采收率.

针对鄂尔多斯盆地东缘本溪组8#煤层方解石脉体成因不清的问题,综合运用显微岩相学、同位素地球化学和流体包裹体等方法,开展方解石脉发育期次分析以明确成脉流体来源和形成时间.研究结果表明,研究区8#煤层中发育2期方解石脉体(C1和C2),C1方解石脉的成岩流体主要为源于围岩母岩的地层卤水和富生物气有机流体,C2方解石脉的流体来源主要与有机质脱羧作用形成的液态烃类流体有关,同时C1和C2方解石脉的形成均受到早白垩世构造热事件导致的深部热液流体影响.结合研究区烃类成藏史和埋藏史分析,明确C1方解石脉的形成时间在晚三叠世—早侏罗世期间,C2脉体形成时间为晚侏罗世—早白垩世.结合研究区8#煤层勘探生产实践,方解石脉发育区域煤层气富集程度较高,具有良好的勘探开发前景.研究成果对于煤层气富集区域的勘探具有重要的参考意义.

It has been found that hydraulic fractures always exhibit complex geometry patterns by direct observation on fractured cores, geological evidence, and laboratory experiments for low permeability reservoirs. The main purpose of this chapter is to present a general fracture wing model that can be easily extended to analyze the transient pressure response of complex fracture systems. Firstly, we propose a fracture wing model and then introduce the combination method of the complex fractures using multiple wings. Secondly, three cases, including asymmetrical nonplanar fracture, multi-wing fractures connected to a vertical well and multi-wing nonplanar fractures in a horizontal well are employed to illustrate the application of the fracture wing model. Lastly, an example with synthetic data is used to illustrate the application of well test analysis of a multi-wing fractured well by the type curve match.

苏里格气田是中国致密砂岩气的典型代表,储层低渗致密,具有强非均质性,区块间差异显著,采用主体开发井网较难实现区块储量的整体有效动用,由于采收率低,故针对不同分类储量区分别进行加密调整.该研究优选气田中部苏x区块为研究区,通过分析该区块砂体分布特征等因素分析,以储量分类指数为主要依据,将研究区储量分为5类,在同时考虑技术和经济条件的前提下,对该区块进行井网加密设计.

As a typical representative of China's tight sandstone gas field,Sulige gasfield possesses the characteristics of poor reservoir property,small-scale effective sand bodies,low distribution frequency,strong heterogeneity and obvious difference between the blocks.It is difficult to realize the overall effective use of reserves by relying on the main development well pattern of 600 m × 800 m;and the recovery efficiency is only about 30％.Thus,it is necessary to conduct reserve classification and evaluation as well as implement well pattern infilling for various types of reserves.Su 14 block in central Sulige gasfield was taken as the study area.Through the fine exploration of dense drilling zones and the interference well test analysis,the reservoir development frequency and scale were clearly identified.Constrained by sedimentary facies belt,gas field reserves were divided into five types in terms of reserve abundance,reservoir superimposed style,poor gas-reservoir effect and production performance characteristics.From Type Ⅰ to Type V,reservoir thickness is re duced with the continuity worsening,the reserve grade is declining,and the yield of single well is reduced.According to the actual production data of dense well pattern,the modeling and numerical simulation results,the relationships among well pattern density,interference degree and recovery efficiency were studied for each type of reserves to demonstrate the development indexes of single well under reasonable well pattern density.Under current economic and technical conditions,the appropriate well pattern density is 2-4 wells/km2 for various types of reserve areas,and the ultimate recovery efficiency of gas field is about 50％.Moreover,the reserve configuration under complex geological conditions of tight sandstone gas field was determined through systematical study,providing a geological basis for the preparation of well pattern infilling scheme during the mid-late development stage.

Since there are many factors affecting the productivity of fractured horizontal wells, sensitivity analysis method based on conventional productivity evaluation method can not evaluate the impact of each factor comprehensively and quantitatively, a productivity prediction model was established considering interactive disturbance among fractures, skin factor of polluted fracture, fracture distribution form, finite flow in fracture and wellbore. A numerical iterative method to the model was also derived. Based on the prediction method, the sequence of the factors affecting the productivity of fractured horizontal wells was determined by orthogonal tests. The results show that the sequence of the factors affecting the productivity of fractured horizontal wells is as follows: formation permeability, pollution skin factor of fracture, net pay thickness, fracture half-length, number of fracture, fracture conductivity, effective length of horizontal wellbore, wellbore radius and fracture distribution form. It is worth pointing out that the effect of formation permeability, pollution skin of fracture and net pay thickness is significant, while the effect of wellbore radius and fracture distribution form is weaker. For a practical horizontal well, there remains precondition that formation permeability, reservoir permeability and reservoir scale are limited. Eliminating the formation damage due to stimulation and further optimizing fracture parameters based on geological data will be of great importance in improving productivity of individual well and increasing economic benefit.

室内实验是认识储层渗流规律的有效手段,低渗岩石气体渗流受到滑脱效应的影响.国内外学者在滑脱效应影响因素及受滑脱效应影响的渗透率参数测量方面进行了大量研究,但结论仍存在分歧.以鄂尔多斯盆地苏里格气田低渗砂岩气藏为研究对象,设计了新的岩心含水饱和度的建立方法,通过实验方法研究了含水饱和度、有效应力及二者耦合作用对低渗岩石气体滑脱效应的影响规律.结果表明,不同含水饱和度条件下(低于束缚水饱和度)岩心的气测渗透率与平均压力倒数仍然呈线性正相关关系,含水饱和度越高,滑脱因子越小,滑脱效应越弱;对于干岩样,围压增大气体滑脱效应变强,且滑脱因子随有效应力的增加呈线性增加的趋势,进行岩石应力敏感性实验过程中,若忽略滑脱效应的影响,未对气测渗透率做校正,实验评价结果偏低;含水饱和度比介质变形对气体滑脱效应的影响更强,对于高含水饱和度的低渗岩心,滑脱效应影响微弱,且受有效应力的影响不大.这为低渗砂岩气藏渗流机理研究提供了新思路.

While horizontal wells(HWs)development have achieved excellent performance in Sulige Gasfield,there exist practical problems including difficulty in productivity evaluation and uncertainty in determining effect factors of productivity.Based on the analyses of previous materials and data of field,this paper proposed an absolute open flow single-point equation and rapid well-controlled reserves evaluation chart for HWs and evaluated productivity of early production wells.Then main effect factors of productivity are filtered by defining productivity parameters of single fracture and unit formation thickness.Results show that it takes 100 to 600days for horizontal wells to enter the boundary controlled flow period due to poor properties and strong heterogeneity of Sulige tight gas field.The absolute open flow rate of wells concentrates between 10×104 m3/d and 50×104 m3/d with an average of 25.7×104 m3/d.The well-controlled reserves of HWs range from 4 000×104 m3 to 8 000×104 m3 with an average of 7 784×104 m3.The production capacity of horizontal well is high though it shows great difference for individual wells.Both geological and engineering factors affect HWS productivity.Specifically,the most influential geological factor is formation thickness,then,is gas saturation.The effect of porosity is slight and that of permeability is difficult to determine.Among engineering factors,effective length of horizontal wells,fracturing segments,and fracturing scale affect productivity more greatly than flowing back ratio of fracturing fluid.

Based on static geology and dynamic production data of horizontal wells in Sulige Gas Field,dynamic performance analysis was performed on old typical horizontal wells,using rate transient analysis by RTA type curve matching technique,combining with material balance equation and productivity formula of horizontal wells.A convenient evaluating chart of the horizontal wellu0027s controlled reserves was established.The chart was applied to 6horizontal wells in Suliege tight gas field.The results show that cumulative gas production per specific casing pressure drop increases with time extending and that there is a linear relationship between well controlled reserves and cumulative gas production per specific pressure drop at different production time.This correlation would become better with time extending.The established evaluating chart is simple,only requiring production data with high precision,providing a new method to evaluate well controlled reserves of horizontal wells.This chart with significant application value can also offer reference values for other evaluating methods of well controlled reserves.

Based on drift model which copes with gas-liquid phase slippage and non-uniform distribution along section of wellbore, a coupled temperature-pressure prediction model was established for varied angle gas wellbores considering momentum conservation, conservation of energy and wellbore heat transmission. The model was validated with 15 tested gas wells. The calculation showed satisfying results with average absolute error of 3?6% which meets engineering requirements.

水平井分段压裂技术是提高苏里格气田单井控制储量和采收率、实现规模有效开发的关键技术。根据一点法产能方程绘制了水平井产能图版，利用初期生产数据可快速获取水平气井的绝对无阻流量，作为气井合理产量的参考指标。通过分析63口气井的实际生产数据，回归得到平均日产气量与无阻流量之间的关系式，可用于指导气井初期配产。研究结果显示：利用水平井产能图版，仅需初期生产数据即可快速、直观地估算苏里格气田水平井的绝对无阻流量，误差范围在10%以内；水平气井的绝对无阻流量越大，其配产系数越小，二者呈负指数关系。该方法对评价压裂水平井产能、指导致密气藏产能建设有积极意义。

将气井不稳定流动阶段的产量、压力等生产数据处理为产量修正的拟压力差与拟时间,利用两者间的线性关系可以确定出裂缝长度、地层渗透率等参数,据此评价气井压裂效果、预测气井生产动态.为了准确计算拟时间值,通过引入动边界概念,将探测边界视为压力扰动的外边缘,利用积分方法求解渗流偏微分方程,得到由气井生产引起的探测边界传播规律,结合物质平衡方程获得探测范围内的平均地层压力,并借助迭代算法确定不同生产时刻对应的气体拟时间.结果表明:与拟时间相比,直接使用真实时间分析生产数据,定压生产时引起直线斜率偏小,且生产压差越大偏差程度越明显,定产生产时导致数据线性相关性变差,气井产量越高相关系数越低;在变产量生产时,利用物质平衡拟时间能够消除气体高压物性和变产量带来的非线性影响,明确生产数据间的线性关系,压裂参数的计算结果更为合理.

河流相储层平面及纵向物性变化均较快,层内非均质性严重影响了垂向水淹规律.通过建立精细数值模型,量化表征了储层内部韵律性、夹层分布特征及注采井网类型对水淹规律的影响.测试及精细数值模拟结果表明,不同储层组合形式下,水淹程度可达到15％～60％,垂向表征厚度对单井水淹规律影响较大,最高相对误差可达120％,且漏斗型储层物性夹层区域垂向表征厚度不宜大于0.4m,研究成果为油田生产井开发指标的确定及开发调整方案的编制提供了理论参考.

In fluvial reservoirs plane and vertical changes were faster.The intralayer heterogeneity characteristics of fluvial reservoir severely affected the vertical water-out rules.Based on the fine numerical model,the effect of water out characterization on rhythm,sandwich distribution and well pattern on water-out rules were quantified.The test and simulation results show that the water-out level can reach 15%~60% under different reservoir conditions.There is a big influence on water-out rules for different vertical simulation thickness with the biggest relative error of 120%,especially for reverse rhythm reservoir,the vertical simulation thickness should be smaller than 0.4min funnel sandwich region.The research result provides a theoretical reference for determining production index and production plan for oilfield development.

松辽盆地南部长岭断陷登娄库组致密砂岩地层陆续发现了新的天然气区带,显示出巨大的勘探开发前景.利用大量岩心描述及分析化验资料,对登娄库组致密砂岩储层发育的控制因素进行了研究.对比研究认为,埋藏史是控制地区间储层物性差异的主要因素;而在埋藏史相近的地区,沉积微相是控制储层发育的主要因素.沉积分异过程造成不同微相储层岩石学性质的分异,而不同岩石相在成岩作用发生不同孔隙演化过程,其机制为:粒度粗、泥质少的砂岩,在压实过程中趋向于保留更多的原生孔隙,为溶蚀过程提供流体通道,导致溶蚀孔更发育,物性最好;含泥质砂岩中,泥质杂基在压实过程中强烈形变,充填孔喉,降低了物性,特别是降低了渗透率;与泥岩接触的砂岩,极易发生早期碳酸盐胶结,大幅降低了储层孔隙度.根据以上分析认为,心滩中下部及辫状河道中部砂岩最利于形成优质储层.通过对孔隙演化过程的模拟,定量印证了以上观点.

Accumulated fluid in gas well is a key issue confronted in development design of water-producing gas pools and pro-duction management of gas wells, but at present, there are controversies on flow mechanism and water carrying prediction in gas wells. From the basic flow mechanism of two-phase flow of gas and liquid, a comprehensive prediction model was built to predict the flow pattern, temperature, pressure and water-carrying in gas wells, and this model was verified using actual well data. The result shows that the model so built can be used to predict the wellbore temperature and pressure of water-producing vertical wells, deviated wells and horizontal wells, and the prediction error is less than 5%. Under condition of annular mist flow, the fluid in the wellbore is carried out of the wellhead completely in the forms of liquid drop and membrane, so no wellbore water shall be accumulated; for conventional vertical gas wells, the wellhead data can be used to determine the accumulated fluid in gas wells; the critical value of liquid carrying in gas wells calculated by Turner model is larger than the actual value, and that calculated by Li Min model is on the small side. So it is suggested that Peng Chaoyang Model be used to calculate the liquid-carrying critical value in gas wells. For deviated wells and horizontal wells, the effects of drop deformation and hole deviation should both be considered. The liquid-carrying critical flow velocity and flowrate in horizontal section in horizontal wells is obviously smaller than that in vertical wells, while the liquid-carrying critical flow velocity and flowrate in angle buildup section first increases with the hole drift angle, but then decreases, reaching the peak when hole drift angle is between 30°and 60°, so angle buildup section is a key place for determination of accumulated fluid in gas wells.

油田开发处于高含水阶段,相同含水级别油井间剩余水驱可采储量差异较大,通过统筹分配各油井产液量,可实现相同产液量条件下产油量的最大化.结合高含水阶段单井生产特征与水驱规律的内在联系,通过水驱特征曲线与分流量方程建立了多井产液结构适时优化调整数学模型和计算模块,可计算不同时间单井最优产液量,实现不同时间阶段产油最大化.结果表明,通过产液结构的适时优化调整,在油田系统相同产液量条件下可实现有效降水增油,这种增油措施投入低收益高,且实施方便,典型油田优化年增油幅度最高可达到4％,日均含水率降低0.1％.

As for the contradictory problem of well pattern in offshore large-well-spacing and waterdrive heavy oilfields with complicated fluvial facies,BZ oilfield was used as an example to select an optimal staggered-arrangement model of well pattern in which injectors and producers are at the sides and centers of parallel channel sandbodies respectively,through the mechanism simulation and by applying a method based on the realistic sandbody distribution in oilfields.Meanwhile,the dynamic balance between injection and production and the calculation of economic well spacing density were comprehensively considered,and a mathematical model to calculate the economic numbers of oil producer and water injector was built.Finally,a chart was plotted,which can be used to select the combinations of rational producer and injector numbers for different single-well cost,injection-production ratio and water cut,providing a basis for the well pattern optimization in offshore water-drive heavy oilfields with complicated fluvial facies.