Theoretical Progress and Key Technologies of Onshore Ultra-Deep Oil/Gas Exploration

Oil/gas exploration around the world has extended into deep and ultra-deep strata because it is increasingly difficult to find new large-scale oil/gas reservoirs in shallow–middle buried strata. In recent years, China has made remarkable achievements in oil/gas exploration in ultra-deep areas including carbonate and clastic reservoirs. Some (ultra) large-scale oil and gas fields have been discovered. The oil/gas accumulation mechanisms and key technologies of oil/gas reservoir exploration and development are summarized in this study in order to share China’s experiences. Ultra-deep oil/gas originates from numerous sources of hydrocarbons and multiphase charging. Liquid hydrocarbons can form in ultradeep layers due to low geothermal gradients or overpressures, and the natural gas composition in ultra-deep areas is complicated by the reactions between deep hydrocarbons, water, and rock or by the addition of mantle- or crust-sourced gases. These oils/gases are mainly stored in the original highenergy reef/shoal complexes or in sand body sediments. They usually have high original porosity. Secondary pores are often developed by dissolution, dolomitization, and fracturing in the late stage. The early pores have been preserved by retentive diageneses such as the early charging of hydrocarbons. Oil/gas accumulation in ultra-deep areas generally has the characteristics of near-source accumulation and sustained preservation. The effective exploration and development of ultra-deep oil/gas reservoirs depend on the support of key technologies. Use of the latest technologies such as seismic signal acquisition and processing, low porosity and permeability zone prediction, and gas–water identification has enabled the discovery of ultra-deep oil/gas resources. In addition, advanced technologies for drilling, completion, and oil/gas testing have ensured the effective development of these fields.

Pressure control method and device innovative design for deep oil in-situ exploration and coring

Deep oil exploration coring technology cannot accurately maintain the in-situ pressure and temperature of samples, which leads to a distortion of deep oil and gas resource reserve evaluations based on conventional cores and cannot guide the development of deep oil and gas resources on Earth. The fundamental reason is the lack of temperature and pressure control in in-situ coring environments. In this paper, a pressure control method of a coring device is studied. The theory and method of deep intelligent temperature-pressure coupling control are innovatively proposed, and a multifield coupling dynamic sealing model is established. The optimal cardinality three term PID (Proportional-Integral-Differential) intelligent control algorithm of pressure system is developed. The temperature-pressure characteristic of the gas-liquid two-phase cavity is analyzed, and the pressure intelligent control is carried out based on three term PID control algorithms. An in-situ condition-preserved coring (ICP-Coring) device is developed, and an intelligent control system for the temperature and pressure of the coring device is designed and verified by experiments. The results show that the temperature-pressure coupling control system can effectively realize stable sealing under temperature-pressure fields of 140 MPa and 150 °C. The temperature-pressure coupling control method can accurately realize a constant pressure inside the coring device. The maximum working pressure is 140 MPa, and the effective pressure compensation range is 20 MPa. The numerical simulation experiment of pressure system control algorithm is carried out, and the optimal cardinality and three term coefficients are obtained. The pressure steady-state error is less than 0.01%. The method of temperature-pressure coupling control has guiding significance for coring device research, and is also the basis for temperature-pressure decoupling control in ICP-Coring.

Crude oil cracking in deep reservoirs:A review of the controlling factors and estimation methods

The natural cracking of crude oils in deep reservoirs has gained great interest due to continuously increasing depth of petroleum exploration and exploitation.Complex oil compositions and surroundings as well as complicated geological evolutions make oil cracking in nature much more complex than industrial pyrolysis.So far,numerous studies,focused on this topic,have made considerable progress although there still exist some drawbacks.However,a comprehensive review on crude oil cracking is yet to be conducted.This article systematically reviews the controlling factors of oil cracking from six aspects,namely,oil compositions,temperature and time,pressure,water,minerals and solid organic matter.We compare previous experimental and modelling results and present new field cases.In the following,we evaluate the prevailing estimation methods for the extent of oil cracking,and elucidate other factors that may interfere with the application of these estimation methods.This review will be helpful for further investigations of crude oil cracking and provides a guide for estimation of the cracking extent of crude oils.

Origin and accumulation of high-maturity oil and gas in deep parts of the Baxian Depression, Bohai Bay Basin, China

Great quantities of light oil and gas are produced from deep buried hill reservoirs at depths of 5,641 m to 6,027 m and 190 ℃ to 201 ℃ in the Niudong-1 Well, representing the deepest and hottest commercial hydrocarbons discovered in the Bohai Bay Basin in eastern China. This discovery suggests favorable exploration prospects for the deep parts of the basin. However, the discovery raises questions regarding the genesis and accumulation of hydrocarbons in deep reservoirs. Based on the geochemical features of the hydrocarbons and characteristics of the source rocks as well as thermal simulation experiments of hydrocarbon generation, we conclude that the oil and gas were generated from the highly mature Sha-4 Member （Es4） source rocks instead of thermal cracking of crude oils in earlier accumulations. The source kitchen with abnormal pressures and karsted carbonate reservoirs control the formation of high-maturity hydrocarbon accumulations in the buried hills （i.e., Niudong-1） in conjunction with several structural-lithologic traps in the ES4 reservoirs since the deposition of the upper Minghuazhen Formation. This means the oil and gas exploration potential in the deep parts of the Baxian Depression is probably high.

Enrichment characteristics and exploration directions of deep shale gas of Ordovician-Silurian in the Sichuan Basin and its surrounding areas,China

The enrichment characteristics of deep shale gas in the Ordovician Wufeng-Silurian Longmaxi formations in the Sichuan Basin and its surrounding areas are investigated through experiments under high temperature and high pressure,including petrophysical properties analyses,triaxial stress test and isothermal adsorption of methane experiment.(1)The deep shale reservoirs drop significantly in porosity and permeability compared with shallower shale reservoirs,and contain mainly free gas.(2)With higher deviatoric stress and axial strain,the deep shale reservoirs have higher difficulty fracturing.(3)Affected by structural location and morphology,fracture characteristics,geofluid activity stages and intensity,deep shale gas reservoirs have more complicated preservation conditions.(4)To achieve the commercial development of deep shale gas reservoirs,deepening geological understanding is the basis,and exploring reservoir simulation technology befitting the geological features is the key.(5)The siliceous shale and limestone-bearing siliceous shale in the Metabolograptus persculptus-Parakidograptus acuminatus zones(LM1-LM3 graptolite zones)are the high-production intervals for deep shale gas and the most favorable landing targets for horizontal drilling.Deeps water areas such as Jiaoshiba,Wulong,Luzhou and Changning with deep shale reservoirs over 10 m thickness are the most favorable areas for deep shale gas enrichment.It is recommended to carry out exploration and development practice in deep-water shale gas areas deposited deep with burial depth no more than 5000 m where the geological structure is simple and the shale thickness in the LM1-LM3 graptolite zone is greater than 10 m.It is better to increase the lateral length of horizontal wells,and apply techniques including high intensity of perforations,large volume of proppant,far-field and near-wellbore diversions to maximize the stimulated deep reservoir volume.

Enrichment Mechanism and Prospects of Deep Oil and Gas

With the deepening of oil and gas exploration,the importance of depth is increasingly highlighted.The risk of preservation of storage space in deep reservoirs is greater than that in shallow and medium layers.Deep layers mean older strata,more complex structural evolution and more complex hydrocarbon accumulation processes,and even adjustment and transformation of oil and gas reservoirs.This paper systematically investigates the current status and research progress of deep oil and gas exploration around the world and looks forward to the future research focus of deep oil and gas.In the deep,especially the ultra-deep layers,carbonate reservoirs play a more important role than clastic rocks.Karst,fault-karst and dolomite reservoirs are the main types of deep and ultra-deep reservoirs.The common feature of most deep large and medium-sized oil and gas reservoirs is that they formed in the early with shallow depth.Fault activity and evolution of trap highs are the main ways to cause physical adjustment of oil and gas reservoirs.Crude oil cracking and thermochemical sulfate reduction(TSR)are the main chemical modification effects in the reservoir.Large-scale high-quality dolomite reservoirs is the main direction of deep oil and gas exploration.Accurate identification of oil and gas charging,adjustment and reformation processes is the key to understanding deep oil and gas distribution.High-precision detection technology and high-precision dating technology are an important guarantee for deep oil and gas research.

Deepwater and Deep Layers： the Strategic Choices for China＇s Oil and Gas Resources Development

On December 2,2017,the 2^(nd) Seminaron the Development Strategy of China‘s Oil and Gas Resources was held in Beijing.This seminar was hosted by the Strategic Research Center for Oil and Gas Resources,Ministry of Land(MLR)and Resources and sponsored by both the CNOOC Exploration Department and the School of Ocean and Earth Sciences of Tongji University.With the theme of"deepwater and deep-layer oil and gas resources and development strategy",the

Driving forces and their relative contributions to hydrocarbon expulsion from deep source rocks: A case of the Cambrian source rocks in the Tarim Basin

To thoroughly understand the dynamic mechanism of hydrocarbon expulsion from deep source rocks,in this study,five types of hydrocarbon expulsion dynamics(thermal expansion,hydrocarbon diffusion,compaction,product volume expansion,and capillary pressure difference(CPD))are studied.A model is proposed herein to evaluate the relative contribution of different dynamics for hydrocarbon expulsion using the principle of mass balance,and the model has been applied to the Cambrian source rocks in the Tarim Basin.The evaluation results show that during hydrocarbon expulsion from the source rocks,the relative contribution of CPD is the largest(>50%),followed by compaction(10%-40%),product volume expansion(5%-30%),and thermal expansion(2%-20%).The relative contribution of diffusion to hydrocarbon expulsion is minimal(<10%).These results demonstrate that CPD plays an important role in the hydrocarbon expulsion process of deep source rocks.The hydrocarbon expulsion process of source rocks can be categorized into three stages based on the contribution of different dynamics to the process:the first stage is dominated by compaction and diffusion to expel hydrocarbons,the second stage is dominated by product volume expansion and CPD,and the third stage is dominated by product volume expansion and CPD.This research offers new insights into hydrocarbon exploration in tight oil and gas reservoirs.

The construction of technical standard system for ultra deep and high sour gas fields in Northeast Sichuan

To deal with the exploitation difficulties of gas fields in Northeast Sichuan with deep marine strata, after researching the relative standards domestic and abroad extensively, summarizing and promoting the successful experiences and failure lessons of project construction technology application scientifically, Sinopec has established an integrated technical standard system for the exploration and development of ultra deep and high sour gas fields. The system consists of 51 enterprise standards and covers 7 professions including geophysical prospecting, drilling, drilling log, well logging, gas formation test and production, sour gas gathering and transferring system, and HSE (health,safety,environment). It guides and guarantees the safe, high-quality and high-efficiency project construction effectively by means of enhancing the engineering design criterion, recommending the data processing and interpretation methods, identifying the requirements of operation and field inspection and standardizing the application of technical equipments.

Analysis of the world oil and gas exploration situation in 2021

The global exploration investment, new oil and gas discoveries, exploration business adjustment strategies of oil companies in 2021, and future favorable exploration domains are systematically analyzed using commercial databases such as IHS and public information of oil companies. It has been found that the world oil and gas exploration situation in 2021 has continued the downturn since the outbreak of COVID-19. The investment and drilling workload decreased slightly, but the success rate of exploration wells, especially deepwater exploration wells, increased significantly, and the newly discovered reserves increased slightly compared with last year. Deep waters of the passive continental margin basins are still the leading sites for discovering conventional large and medium-sized oil and gas fields. The conventional oil and gas exploration in deep formations of onshore petroliferous basins has been keeping a good state, with tight/shale oil and gas discoveries made in Saudi Arabia, Russia, and other countries. While strengthening the exploration and development of local resources, national, international, and independent oil companies have been focusing on major overseas frontiers using their advantages, including risk exploration in deep waters and natural gas. Future favorable exploration directions in the three major frontiers, the global deep waters, deep onshore formations, and unconventional resources, have been clarified. Four suggestions are put forward for the global exploration business of Chinese oil companies: first, a farm in global deepwater frontier basins in advance through bidding at a low cost and adopt the “dual exploration model” after making large-scale discoveries;second, enter new blocks of emerging hot basins in the world through farm-in and other ways, to find large oil and gas fields quickly;third, cooperate with national oil companies of the resource host countries in the form of joint research and actively participate exploration of deep onshore formations of petroliferous basins;fourth, track tight/shale oil and gas cooperation opportunities in a few countries such as Saudi Arabia and Russia, and take advantage of mature domestic theories and technologies to farm in at an appropriate time.

Regional gravity survey and application in oil and gas exploration in China

Ground gravity survey for regional structure unit delineation and oil and gas exploration in China is addressed in this paper with examples. Gravity survey scales, coverage, technical regulations and achievements at the national level are introduced, including data processing and anomaly interpretation techniques. Bouguer anomalies of terrestrial territories of China and classification of anomalous feature zones are also described;they are well correlated with lithotectonical boundaries, fault zones, and unexposed igneous plutons. Recent study results of petroliferous sedimentary basins are presented as well, including concealed boundaries and major structures of large basins. It is concluded that gravity survey is the most effective and economic method in unveiling unexposed and deep-seated structures, targeting and delineating oil and gas-bearing sedimentary basins, and locating main trap structures within prolific basins in early stage of exploration in China. Suggestions for improving exploration of both conventional and unconventional oil and gas reservoirs in China are also given in the paper.

Hydrate Prevention Strategies and the Associated Cost in the Gulf of Mexico

With the petroleum industry endeavoring to develop promising oil and gas in deeper water, gas hydrates prevention is a serious concern for oil and gas producing companies producing at conditions in the hydrate region. This paper details lessons learned from the successful field deployment of AA LDHI and proper implementation strategies used for 3 different practical fields as case studies in the Gulf of Mexico. From the 3 field experiences, the AA LDHI has been used to replace the conventional thermodynamic hydrate inhibitor due to its numerous benefits during steady state operations and transition operations where AA LDHI is injected prior to extended shut in and restart for fields producing at low water cut. However, the strategy to develop a cost effective chemical management of hydrates for fields producing at high water cut is by pumping methanol or diesel to push down the wellbore fluid below the mud line during planned and unplanned shut-ins to delay water production, it also secures the riser with non hydrate fluids. This illustrates how the AA LDHIs are used in conjunction with more conventional hydrate management approaches to reach an optimal cost effective field hydrate management solution. However, this shows that the key to overall success of hydrate prevention is a full integration of a good front end design, a comprehensive deployment and an effective down hole monitoring system.

Geologic-Geophysical Indicators of the Deep Structure of Zones of Geothermal Anomalies for Allocation of Channels of the Deep Heat and Mass Transfer

On the basis of the analysis of field thermogeochemical data along abnormal zones of a thermal stream in the Bukhara-Khiva, oil-and-gas region of the Turan (Tegermen, Chagakul, Shimoly Alat, Beshtepa) was succeeded to obtain important data on a deep structure of sites. Data of gas-chemical and geothermal observations show about confinedness of abnormal concentration of methane to zones of the increased values of the temperature field the measured values of temperatures (Tegermen Square and others). On geoelectric section mines 2-D of inversion of the MT-field depth of 4000 m are lower, among very high-resistance the chemogenic and carbonate deposits of the Paleozoic is traced the subvertical carrying-out abnormal zone. This zone is identified as the channel of a deep heat and mass transfer with which hydrocarbon (HC) deposits are connected. It is shown that electro-investigation when using a geophysical complex can and has to become “advancing” at exploration by oil and gas.

Deep structural research of the South China Sea: Progresses and directions

The South China Sea(SCS)is the hotspot of geological scientific research and nature resource exploration and development due to the potential for enormous hydrocarbon resource development and a complex formation and evolution process.The SCS has experienced complex geological processes including continental lithospheric breakup,seafloor spreading and oceanic crust subduction,which leads debates for decades.However,there are still no clear answers regarding to the following aspects:the crustal and Moho structure,the structure of the continent-ocean transition zone,the formation and evolution process and geodynamic mechanism,and deep processes and their coupling relationships with the petroliferous basins in the SCS.Under the guidance of the“Deep-Earth”science and technology innovation strategy of the Ministry of Natural Resources,deep structural and comprehensive geological research are carried out in the SCS.Geophysical investigations such as long array-large volume deep reflection seismic,gravity,magnetism and ocean bottom seismometer are carried out.The authors proposed that joint gravitymagnetic-seismic inversion should be used to obtain deep crustal information in the SCS and construct high resolution deep structural sections in different regions of the SCS.This paper systematically interpreted the formation and evolution of the SCS and explored the coupling relationship between deep structure and evolution of Mesozoic-Cenozoic basins in the SCS.It is of great significance for promoting the geosystem scientific research and resource exploration of the SCS.

Diagenetic evolution and effects on reservoir development of the Dengying and Longwangmiao formations,Central Sichuan Basin,Southwestern China

The deeply buried Lower Cambrian Longwangmiao Formation and Upper Ediacaran Dengying Formation from the Sichuan Basin,China,have a total natural gas reserve up to 3×10^(12)m^(3).The complex diagenetic evolution and their impacts on the present-day reservoir quality have not been systematically elucidated,hampering the current exploration.Crucially,the integration and comparation diagenetic study on these two formations,which may be able to shed new lights on reservoir formation mechanism,are yet to be systemically evaluated.By compiling geochemistry data,including carbonate U-Pb ages and petrophysics data,coupled with new petrology,trace elements,and strontium isotope data,of various types of diagenetic carbonates,this study aims to decipher the potential links between diagenesis and reservoir development of both formations.Intriguingly,similar diagenetic sequence,which contains five distinctive dolomite phases,is established in both formations.The matrix dolomite(D1)and early dolomite cement(D2)were likely formed by reflux dolomitization,as inferred by their nearly syn-depositional U-Pb ages and elevatedδ^(18)O caused by seawater evaporation.The subsequent moderate burial dolomite cement(D3)was most plausibly the product of burial compaction as indicated by its lighterδ^(18)O and slightly younger U-Pb ages compared with D1 and D2.Whereas deep burial dolomite cements(D4 and D5)yield markedly depletedδ^(18)O,elevated ^(87)Sr/^(86)Sr,along with much younger U-Pb ages and higher precipitation temperatures,suggesting that they were likely linked to hydrothermal fluids.Despite the wide occurrence of meteoric and organic acids leaching and thermochemical sulfate reduction,they may have only played a subsidiary role on these reservoirs development.Instead,superior reservoir quality is tightly linked to tectonics as inferred by higher reservoir quality closely related to the well-developed fractures and faults filled with abundant hydrothermal minerals.Notably,good reservoirs in both formations are mainly attributed to high permeability caused by tectonics.Hence,this new contribution emphasizes the crucial role of tectonics on spatially explicit reservoir prediction of deep to ultra-deep(up to>8000 m)carbonates in the Sichuan Basin,as well as other sedimentary basin analogues in China.

Synthesis and mechanism of environmentally friendly high temperature and high salt resistant lubricants

With the exploration and development of deep and ultra-deep oil and gas,high torque and high friction during the drilling of deep and ultra-deep wells become one of the key issues affecting drilling safety and drilling speed.Meanwhile,the high temperature and high salt problem in deep formations is prominent,which poses a major challenge to the lubricity of drilling fluids under high temperature and high salt.This paper reports an organic borate ester SOP as an environmentally friendly drilling fluid lubricant.The performance evaluation results show that when 1%lubricant SOP is added to the fresh water-based mud,the lubrication coefficient decreases from 0.631 to 0.046,and the reduction rate of lubrication coefficient is 92.7%.Under the conditions of 210℃ and 30%NaCl,the reduction rate of lubricating coefficient of the base slurry with 1%SOP was still remain 81.5%.After adding 1%SOP,the wear volume decreased by 94.11%compared with the base slurry.The contact resistance experiment during the friction process shows that SOP can form a thick adsorption film on the friction surface under high temperature and high salt conditions,thus effectively reducing the friction resistance.Molecular dynamics simulation shows that lubricant SOP can be physically adsorbed on the surface of drilling tool and borehole wall through hydrogen bond and van der Waals force.XPS analysis further shows that SOP adsorbs on the friction surface and reacts with metal atoms on the friction surface to form a chemically reactive film.Therefore,under high temperature and high salt conditions,the synergistic effect of physical adsorption film and chemical reaction film effectively reduces the frictional resistance and wear of the friction surface.In addition,SOP is non-toxic and easy to degrade.Therefore,SOP is a highly effective and environmentally friendly lubricant in high temperature and high salt drilling fluid.

Geochemical Characteristics and Migration Pathways of Ordovician Carbonate Oil Reservoirs in the Tuoputai Area,Tarim Basin,Northwestern China

Exploration potential is huge and the oil resources are rich in the Ordovician reservoirs of the Tarim Basin.However,the mechanism of hydrocarbon accumulation is complex and not yet fully understood.In the Tuoputai area,the hydrocarbon migration pathways and characteristics of deep hydrocarbon accumulation are revealed through analyses of the physical data of rich oil and gas,the geochemical parameters of oil,and fluid inclusions.The results show that the Ordovician oils in the Tuoputai area have the same geochemical characteristics as the mixed oil from the Lower Cambrian source rock and the Middle–Upper Ordovician source rock.The Ordovician reservoirs have been charged three times:in the late Caledonian,late Hercynian,and Himalayan stages.Oil charging occurred in the Hercynian stage,in particular,as it is the main filling period of hydrocarbon.The north-northeast(NNE)-trending TP12 CX major fault,active in in these times and is dominant migration channel of hydrocarbon,but there is segmentation affected by the difference of activities.Oil maturity is higher in the south than in the north and is abnormally high near the major fault.Parameters related to migration indicate that oil migrated northeastward along the NNE-trending TP12 CX major fault and adjusted laterally along the secondary faults and weathering crust,forming the present characteristics of oil and gas distribution.

Predicting gas-bearing distribution using DNN based on multi-component seismic data: Quality evaluation using structural and fracture factors

The tight-fractured gas reservoir of the Upper Triassic Xujiahe Formation in the Western Sichuan Depression has low porosity and permeability. This study presents a DNN-based method for identifying gas-bearing strata in tight sandstone. First, multi-component composite seismic attributes are obtained.The strong nonlinear relationships between multi-component composite attributes and gas-bearing reservoirs can be constrained through a DNN. Therefore, we identify and predict the gas-bearing strata using a DNN. Then, sample data are fed into the DNN for training and testing. After optimized network parameters are determined by the performance curves and empirical formulas, the best deep learning gas-bearing prediction model is determined. The composite seismic attributes can then be fed into the model to extrapolate the hydrocarbon-bearing characteristics from known drilling areas to the entire region for predicting the gas reservoir distribution. Finally, we assess the proposed method in terms of the structure and fracture characteristics and predict favorable exploration areas for identifying gas reservoirs.

Prediction of wax precipitation region in wellbore during deep water oil well testing

During deep water oil well testing, the low temperature environment is easy to cause wax precipitation, which affects the normal operation of the test and increases operating costs and risks. Therefore, a numerical method for predicting the wax precipitation region in oil strings was proposed based on the temperature and pressure fields of deep water test string and the wax precipitation calculation model. And the factors affecting the wax precipitation region were analyzed. The results show that: the wax precipitation region decreases with the increase of production rate, and increases with the decrease of geothermal gradient, increase of water depth and drop of water-cut of produced fluid, and increases slightly with the increase of formation pressure. Due to the effect of temperature and pressure fields, wax precipitation region is large in test strings at the beginning of well production. Wax precipitation region gradually increases with the increase of shut-in time. These conclusions can guide wax prevention during the testing of deep water oil well, to ensure the success of the test.

Discovery and theoretical and technical innovations of Yuanba gas field in Sichuan Basin, SW China

To solve the difficulties in exploration and development in Yuanba ultra-deep gas field in Sichuan Basin,SW China,the article studies the mechanism of quality reef reservoirs development and gas accumulation and innovates techniques in ultra-deep seismic exploration,drilling,completion and testing.Through the reconstruction of dynamic depositional evolution process and regional depositional framework of homoclinal ramp-rimmed platform in Upper Permian,three theories are put forward:first,"early beach-late reef,multiple stacking,arrangement in rows and belts"is the sedimentary mode for the reservoirs in the Changxing Formation of Yuanba area;second,"dissolution in early exposure stage and dolomitization during shallow burial giving rise to the pores in matrix,overpressure caused by cracking of liquid hydrocarbon during deep burial inducing fractures"is the reservoirs development mechanisms;third,"coupling of pores and fractures"controls the development of high quality reservoirs in deep formations.From correlation of oil and source rock,it is concluded that the Wujiaping Formation and Dalong Formation of deep-water continental shelf are the major source rocks in the Permian of northern Sichuan Basin.The hydrocarbon accumulation mode in ultra-deep formations of low-deformation zones is characterized by"three-micro(micro-fault,micro-fracture interbed crack)migration,near-source enrichment,and persistent preservation".Through seismic inversion using the pore structure parameters of pore-fracture diadactic structure model,the high production gas enrichment area in Yuanba gas field is 98.5 km^2.Moreover,special well structure and unconventional well structure were used to deal with multiple pressure systems and sealing of complex formations.A kind of integral,high pressure resistant FF-level gas wellhead and ground safety linkage device was developed to accomplish safe and environmentally friendly gas production.