Recovery is a crucial index for evaluating the development effectiveness of gas reservoirs, and improving recovery is an eternal goal in gas reservoir development. However, numerous factors affect gas reservoir recovery, making it challenging to identify key factors and quantify their influence effect. By introducing dynamic reserves, the recovery of gas reservoirs is divided into two parts: reserve utilization degree and dynamic reserve recovery, establishing a binary quantitative evaluation method for gas reservoir recovery. By analyzing reserve utilization degree and dynamic reserve recovery from the reservoir to the block and then to individual wells, key factors affecting recovery can be effectively identified, and the impact of each factor can be quantified. The study of the Shuangjiaba Carboniferous gas reservoir shows that the reserve utilization degree is 77.3

The characteristics of low porosity, low permeability, and small pore radius of the shale oil reservoir in the Lucaogou Formation make it difficult to develop and result in low production.CO2 huff and n-puff can effectively improve the recovery rate of shale oil in the Lucaogou Formation.In this study, high-pressure mercury injection technology was used to characterize the pore distribution of the core samples.Combined with nuclear magnetic resonance technology, the recovery of different pores during CO2 huff and n-puff were studied, and the effects of injection pressure and soaking time on core recovery were analyzed.Parallel CO2 huff and puff experiment were conducted to investigate the influence of reservoir heterogeneity on the recovery of CO2 huff and n-puff.The results showed that the pores in the Lucaogou Formation shale oil reservoir were mainly nano-pores, and small pores with a pore radius between 2nm and 50nm accounted for more than 70% of the total pores.The content of large pores in the core samples increased with the increase of core permeability.CO2 huff and n-puff can effectively extract shale oil from the Lucaogou Formation.When the injection pressure is higher than the minimum miscibility pressure, increasing the injection pressure can increase the oil recovery efficiency of large pores in the core samples.The higher the content of large pores, the greater the oil recovery rate of the core samples.When the soaking time is increased from 5h to 10h, the dissolution and diffusion of CO2 in small pores are enhanced, and the recovery rate of small pores increases by about 10%.However, the recovery rate of small pores no longer increases when the soaking time exceeds 10h.The presence of fractures can effectively enhance the recovery of small pores around the fractures.However, the presence of fractures increases the heterogeneity of the reservoir, and the greater the difference in core permeability, the lower the recovery rate of small pores.The recovery rate of small pores in the matrix core samples is only 12.17%.

Ultradeep carbonate gas reservoirs have typical characteristics such as diverse storage media,strong heterogeneity,high temperature,and high pressure.They are generally developed using deviated wells,which complicates the evaluation of gas well productivity.Considering factors such as multiple storage media,stress sensitivity,nonlinear percolation,threshold pressure ef-fect,and well deviation angle,a trinomial productivity prediction model was established based on the Forchheimer's gas-phase dif-ferential equation,stress sensitivity and physical simulation experimental data of gas-phase flow.The gas well productivity of differ-ent types of carbonate reservoirs in different regions was predicted,and the effects of the above factors on gas productivity were ana-lyzed.The results indicate that pore-type and low-permeability cavity-type reservoirs are affected by threshold pressure effects,while fracture-cavity type and high-permeability cavity-type reservoirs are influenced by nonlinear flow.Therefore,the trinomial productivity prediction model is more suitable for ultradeep carbonate gas reservoirs with diverse reservoir types.Different types of reservoirs exhibit different degrees of stress sensitivity and nonlinear flow characteristics.Physical simulation experiments on the cores from various reservoirs are necessary to determine the parameters required for the productivity equation.The well deviation angle creates a negative skin factor affecting gas well productivity.When the well deviation angle is greater than 55°,the gas well productivity of all types of reservoirs starts to increase rapidly,especially for fracture-cavity type reservoirs.The threshold pressure effect has a significant negative impact on productivity at low pressure differentials,whereas stress sensitivity and nonlinear flow mainly impact at high pressure differentials.Starting pressure gradient and nonlinear flow significantly inhibit gas well productivity when their coefficients are 0.01-0.048 MPa/m and 109-1012 m-1,respectively.In contrast,the productivity loss caused by stress sen-sitivity is relatively stable.The dominant factors affecting well productivity are the skin coefficient and formation coefficient.During the development stage,the impact of the nonlinear flow effect on high-permeability reservoirs and the threshold pressure effect on low-permeability reservoirs is also significant.

The tight gas reservoir of the second member of Xujiahe formation in HechuanX gas field is rich in reserve and has a great prospect of exploration and development. However, after being explored for over 10 years, the recovery degree of technical recoverable reserve is still low. How to enhance recovery has become the core of the gas reservoir, and the calculation of single-well dynamic reserve is the basis for further evaluation of development potential and enhancement of gas recovery. Therefore, through data sorting and rechecking, the geological features are re-recognized, and the development position of effective reservoir and the distribution of gas and water are clarified by combining dynamic and static data. Meanwhile, this paper discusses and analyzes the characteristics and adaptability of six kinds of dynamic reserve calculation methods. Aiming at the problems of poor data quality and inaccurate bottomhole pressure after production splitting caused by centralized measurement of well group in HechuanX gas field, a set of dynamic reserve calculation process is established based on four methods: Material balance method, Arps declining method, Power law exponential decline method and Analogy method. Besides each step of calculation is analyzed in detail. Finally, based on the re-recognition of geological characteristics and the calculation results of single-well dynamic reserve, three recovery countermeasures including new well infilling, tapping potential of old wells and drainage gas recovery are formed. The research results provide effective support for enhancing gas recovery and effective development of HechuanX gas field and similar gas reservoirs.

Paleo-karst controls reservoirs in the fourth member of the Sinian Dengying formation in the Sichuan Basin. It is crucial to characterize the paleo-karst zone architecture to understand better the distribution of reservoirs controlled by the multi-stage ancient water tables. We divide vertical paleo-karst zones using cores and formation micro-scanner images based on the groundwater movement and development of pores and fractures. Then we analyze positions and variations of paleo-karst water tables according to the characteristics of different paleo-karst zones. Besides, we illustrate the distribution of underflow subzones and the development of reservoirs in each subzone. This paper reveals the relationship between paleo-karst landform relative elevation, paleo-karst zone thickness and reservoir thickness. Thus, we build the paleo-karst evolutionary pattern in the study area. Research suggests that vadose, underflow, and slow flow zones develop in the intended interval. We identify four underflow subzones in response to four paleo-karst water tables. Compared with the vadose zone, the underflow zone is thicker and holds more reservoirs, mainly distributed in the upper part of the single underflow subzone. Higher paleo-karst landform can possess a thicker vadose zone and thinner underflow zone. Besides, an excellent positive linear correlation exists between reservoir thickness and paleo-karst zone thickness. The thickness of the subzone constrains the development of reservoirs in it. The second and third underflow subzones are the most favorable intervals, owning more reservoirs.

The Damaoping-Gaofengchang area is located at the southeastern end of the Huankaijiang-Liangping Trough in eastern Sichuan, which is controlled by the double tectonic action of northwest and northeast. The Changxing Formation reefs and the Feixianguan Formation shoal facies reservoirs are well developed. Only 4 wells in the main area of Damaoping have good production results, while the other wells have relatively poor production and test results. Based on the existing data of drilling, logging, seismic and development performance, the subdivision of sublayers and the redefinition of reef period are carried out with wavelet transform and sequence stratigraphy. The development model and distribution character of reef are established, combining with seismic forward and inversion characteristics, and reservoir distribution characteristics are evaluated with experimental analysis, development performance, logging interpretation and geological model establishment. The Changxing Formation is divided into 2 sequences and 5 sublayers. The reefs are mainly developed in Sequence II which has three stages. The first stage develops in the flooded system tract of Sequence II, and the second and third stages develop in the high-water system tract of Sequence II. In the seismic profile, the reef is characterized by increased uplift of Changxing top formation, weak amplitude and discontinuous internal weak amplitude of Changxing formation. The three phases of reef are all developed in the main area of Damaoping, which are superposed on the plane to form an unclosed ring feature. It is characterized by three rows of reefs in Damaoping xi area which showed the characteristics of near east-west migration. The reef was formed into a fracture-porous dolomite reservoir through early freshwater dolomization. The fractures improve the seepage capacity of the reservoir, and the production capacity is well. This paper puts forward the method of reef sequence division and fine characterization, which provides a certain research basis for the exploration and development of the Changxing organic reef in the Huankaijiang-Liangping trough, and will promote the further effective development of the organic reef and similar fractured pore type dolomite.

Both complete and uncompleted radiolarian siliceous shells were developed at Wufeng-Longmaxi radiolarian siliceous shale laminae in Sichuan Basin. Micro- and ultra-micropetrological observation suggests that they were successively filled by calcite, pyrite and organic–silicon complex, where pyrite and organic–silicon complex filled dissolved pores associated with calcite during sedimentation. Calcite was derived from calcium carbonate produced by microbial activities at the seawater surface. The environment of radiolarian siliceous shell cavities, which was suitable for sulfate reducing bacterial growth or dissolved hydrogen sulfide reducing Fe3+, contributed positively to pyrite development. Organic–silicon complex development was related to microorganism metabolism that was an important silica source. Honeycomb-like organic pores were developed in cavities with complete shells, but were not developed in cavities with uncompleted shells. This is because the latter could not withstand overburden pressure compared with the former. The only approach to figure out organic pore carriers and understand sequences and development processes of minerals and organic matter is to select weakly compacted radiolarian siliceous shale laminae to carry out micro- and ultra-micropetrological observation and geochemical testing via various technologies.

Most of gas reservoirs are affected by water invasion during production. When gas production is affected by water invasion, some of the natural gas will be blocked inside the gas reservoir, which will lead to the decrease of gas well productivity and the loss of dynamic reserves, and ultimately affect the recovery and development effect of gas reservoir. IN order to evaluate the dynamic reserves of water invasion gas reservoir in the whole life cycle, taking Carboniferous gas reservoir in East Sichuan as an example, this paper conduct an in-depth study on the dynamic reserves evaluation of water invasion gas reservoir at different development stages. Based on the static bottom-hole pressure data, cumulative gas production data of gas reservoir and daily production data of gas wells, the static material balance and fluid mass balance method are used to evaluate the dynamic reserves of water invasion gas reservoirs in different stages. A continuous curve is used to characterize the varying dynamic reserves of gas reservoirs in the whole development cycle, which breaks through the traditional idea of regarding it as a constant value. It can be used to evaluate and predict the dynamic reserves in the whole development cycle of gas reservoir, and quantitatively evaluate the impact of water invasion on the dynamic reserves of gas reservoirs in different stages. It is important for the decision-making of water control in early development stage and potential tapping in middle and late development stage.

针对四川盆地磨溪区块震旦系顶面古岩溶"微地貌"单元划分不系统、研究较为缺乏的问题,综合分析磨溪区块的三维地震资料和钻井资料,论证并选取下寒武统沧浪铺组内部海泛面作为震旦系灯影组的上覆标志面,采用印模法恢复了震旦系顶面的古岩溶地貌.在此基础上,借鉴地貌学的经典坡位分类,结合磨溪区块震旦系顶面古岩溶地貌的发育特征,建立了磨溪区块震旦系顶面古岩溶微地貌的发育模式.优选坡度、剖面曲率、相对高程和长宽比4个参数,厘定各参数定量表征的标准,结合沟谷提取的分析结果,将磨溪区块划分为8类古岩溶微地貌单元,明确了磨溪区块震旦系顶面不同微地貌单元的发育特征,分析了不同微地貌单元中垂向岩溶风化带及溶蚀孔洞层发育程度的差异.研究表明,磨溪区块可划分为陡坡、坡肩、坡脚、残丘、坡顶、坡底、洼地和沟谷8类古岩溶微地貌单元.其中,残丘、洼地、坡顶和坡底在平面上呈低长宽比的似圆状、不规则状;坡肩、陡坡、坡脚和沟谷呈条带状.从坡肩、坡脚到坡底,各微地貌单元中的地表岩溶带和垂直渗流带厚度明显减小,水平潜流带厚度增大.溶蚀孔洞层在水平潜流带中的发育程度大于地表岩溶带和垂直渗流带中的发育程度,且水平潜流带厚度越大的部位其溶蚀孔洞层的累计厚度越大.坡底是有利于溶蚀孔洞层发育的微地貌单元.

Reasonable production of gas wells is the key to achieve efficient and sustainable development of gas reservoirs. Most of the developed gas reservoirs produced formation water. Water invasion leads to the decline of gas well productivity and gas reservoir recovery, the increase of production management and environmental protection risk, and the reduction of gas field development benefits. It is difficult to eliminate the negative impact of water invasion in the later stage of gas reservoir development. Therefore, in the early stage of gas reservoir development, it is necessary to consider the water control factors to determine the reasonable production rate of gas wells. Taking the Carboniferous gas reservoirs in eastern Sichuan Basin as an example, this paper analyses the water production performance, flow conditions of different types of formation water and their influences on the development of gas reservoir. A method is established to determine the reasonable producing pressure drop for controlling pore water invasion and edge-water invasion, which can guide the reasonable production proration of gas wells. Typical gas reservoirs show that the water invasion performance is not only related to the geological factors, but also to the production factors. When the producing pressure drop of gas wells meets the requirements of water invasion control, the recovery of gas reservoir can be increased by 10%–20%.

In order to reduce the cost of wellheads, the production rate of the gas wells in the Hechuan Gas Field are mostly measured in groups, which raises a stringent barrier for industries to determine the production rate of each single well. The technique for determining the production of a single well from the production of the well-group can be called the production splitting method (PSM). In this work, we proposed a novel PSM for the multi-well-monitor system (MWMS) on the basis of the Beggs and Brill (BB) correlation. This proposed method can account for the multi-phase flow together with the features of the pipelines. Specifically, we discretize the pipeline into small segments and recognize the flow pattern in each segment. The pressure drop along the pipeline is calculated with the Beggs and Brill correlation, and the production of each well is subsequently determined with a trial method. We also applied this proposed method to a field case, and the calculated results show that the results from this work undergo an excellent agreement with the field data.

四川盆地磨溪区块灯影组四段气藏储集空间多样,储层非均质性强,流体渗流规律复杂.气藏开发过程表现为以下3个特征:①气井产能差异大,以中高产井为主;②气井稳产能力差异大,大多数井稳产能力较强;③分段酸压工艺和特殊工艺井可大幅度提高气井产能.为弄清气井产能分布特征,采用气藏工程研究与综合地质研究相结合,分析气井产能在平面上的分布特征.研究结果表明:气井产能在平面上具有明显的分区分带特征.气井产能在平面上主要分布在4个区域:Ⅰ区,上覆灰岩厚度为0m区域;Ⅱ区,上覆灰岩厚度介于0～5m之间区域;Ⅲ区,上覆灰岩厚度介于5～20 m之间区域;Ⅳ区,上覆灰岩厚度介于20～40 m之间区域,同时建立了不同区域内气井产能与上覆灰岩厚度的拟合公式.气井产能在平面上主要分布在台缘带、台内带和坡折带3个带,气井产能由台缘带、台内带到坡折带依次减小.研究成果可有效支撑气藏开发建产区筛选、井位部署和气井产能评价.

Different from conventional gas reservoirs, ultra-deep fractured tight sandstone gas reservoirs have the characteristics of abnormal high pressure, tight matrix, and natural fractures developed in heterogeneity, and strong stress sensitivity. Taking Keshen2 gas reservoir in Tarim basin as example, based on routine core analysis, overburden core analysis, well logging and production data, the stress sensitivity of reservoir rocks and its influence on gas reserves estimation are evaluated. The results show that for this kind of gas reservoir, not only the permeability is strong stress sensitive, but also the porosity is strong sensitive. If the stress sensitivity of porosity is neglected, on the one hand, the geological reserves evaluated by volume method will be overestimated by 30

The Sinian Dengying Formation carbonate reservoir dominated by matrix pores and vugs in the Gaoshiti-Moxi area is characterized by strong heterogeneity. Such reservoirs with their tight matrix is identified as low-porosity and low-permeability, and yet with naturally-occurring fractures and dissolution vugs. To improve the reservoir exploitation, optimal production parameters specific to each type of gas wells are required. This paper summarized the geological and production indexes of this reservoir, classified the gas well into varied types based on the pressure build-up well testing, modern production decline analysis and reservoir geological data analysis, and also concluded the identification method of the gas well type. The gas wells in this reservoir were divided into four types, which respectively present the fluid flow characteristics of drilling through the large fracture-vug system, drilling through the fracture-vug with connectivity to the surrounding, drilling through the isolated fracture-vug and at last drilling through the reservoir matrix. The dynamic reserves of different types of gas wells vary considerably, while a positive correlation is seen between the dynamic reserves and effective reservoir thickness in terms a specific type of gas wells. This research carried out classification of the gas well, and correspondingly proposed the identification method, on the basis of the analysis on the geological and production data of the gas reservoir, which lays down the foundation for further production parameter optimization for the production well in the Sinian gas reservoir of this area and accelerates the production capacity building progress of the reservoir in a scientific manner.

Ultra-deep naturally fractured tight sandstone gas reservoirs have the characteristics of tight matrix, natural fractures development, strong heterogeneity and complex gas-water relations. There is strong uncertainty of gas reserves estimation in the early stage for such reservoirs, which brings big challenge to the development design of gas fields. Taking Keshen gas field in Tarim basin as example, during the early development stage, the dynamic reserves were much less than those of proven geologic reserves. As results, the actual production performances are obviously different from those of conceptual design. What are the reasons? How to adjust the development program of gas field? Based on special core analysis, production performance analysis, gas reservoir engineering method, and numerical simulations, influencing factors on evaluation of dynamic reserves for ultra-deep fractured tight sanstone gas reservoirs are analyzed. The results show that rock pore compressibility, recovery percent of gas reserves, gas supply capacity of matrix rock, water invasion are the major factors affecting the evaluation of dynamic reserves. On the basis of above analysis, some suggestions are given for the evaluation of dynamic reserves in Ultra-deep fractured tight sandstone gas reservoirs. For this kind of reservoirs, it is reasonable to determine the gas production scale based on dynamic reserves instead of proven geological reserves.