In order to determine the genesis and the factors that control the low-porosity and low- permeability sandstone reservoirs in the eastern Sulige Gas Field in the Ordos Basin, systematic studies on the sedimentary faci...In order to determine the genesis and the factors that control the low-porosity and low- permeability sandstone reservoirs in the eastern Sulige Gas Field in the Ordos Basin, systematic studies on the sedimentary facies and diagenesis were conducted by means of analysis of cores, thin sections, fluid inclusions, X-ray diffraction, cathode luminescence and scanning electron microscope. It was found that the sand bodies of the major gas reservoirs in the Shan1 section （P1S1） and the He8 section （P2H8） were formed during the Permian as sedimentary facies such as braided-channel bars, braided-river channels and point bars of a meandering river. Four types of diagenetic facies developed subsequently： in order from the best to the poorest properties these are type A （weak compaction, early calcite cement-chlorite film facies）, type B （moderate compaction, quartz overgrowth-feldspar corrosion-kaolinite filling facies）, type C （strong compaction, late calcite cement-quartz corrosion facies） and type D （matrix filling and strong compaction facies）. This diagenesis is undoubtedly the main reason for the poor reservoir properties of sandstone reservoirs, but the sedimentary facies are the underlying factors that greatly affect the diagenesis and thus the reservoir performance. Favorable diagenetic facies developed mainly in relatively small lithofacies such as braided-river channels, channel bars and point bars. The vertical distribution of the physical properties and the diagenetic facies of the reservoirs are related to the stratigraphic succession. Most of the sandstones between mudstones and thin beds of sandstone are unfavorable diagenetic facies. Analyses indicate that siliceous cementation can hardly be stopped by hydrocarbon filling. Authigenic chlorite could hardly protect the primary porosity. It not only occupies pore space, but also blocks pathways through sandstone reservoirs, so that it has significant influence on the permeability. Authigenic chlorite cannot be used as a marker for a specific sedimentary facies because it can be formed in different sedimentary facies, but it indicates high hydrodynamic conditions and presence of favorable reservoirs.展开更多
Comparisons have been made among lithology, diagenesis, and reservoir characteristics of gas-bearing and non-gas-bearing ones in the Sulige gas field of the Ordos Basin based on the laboratory analysis of thin section...Comparisons have been made among lithology, diagenesis, and reservoir characteristics of gas-bearing and non-gas-bearing ones in the Sulige gas field of the Ordos Basin based on the laboratory analysis of thin sections, scanning electron microscope, and liquid inclusion of the reservoirs. The reservoirs of the Sulige gas field are now in the middle stage of diagenesis and have undergone compaction, cementation and dissolution. The secondary pore of the reservoir originated from the dissolution of the feldspar and tuff because of the organic acid action from the source rocks during the diagenetic middle stage. Gas-bearing reservoirs are common in soluble pore diagenetic facies of coarse detritus quartzose sandstone, whereas non-gas-bearing ones are common in tense compaction diagenetic facies of mud-bearing medium-fine detritus quartzose sandstone and residual intergranular pore diagenetic facies of mud-bearing medium-coarse detritus quartzose sandstone. The secondary pore is developed in gas-bearing reservoirs of the Sulige gas-field as the medium-coarse grain reservoirs formed in a powerful sedimentary environment and experienced strong dissolution. However, the sediments of fine grain size form the non-gas-bearing reservoirs because of less residual primary pore and secondary pore.展开更多
To accurately measure and evaluate reserves is critical for ensuring successful production of unconventional oil and gas. This work proposes a volumetric model to evaluate the tight sandstone gas reserves of the Permi...To accurately measure and evaluate reserves is critical for ensuring successful production of unconventional oil and gas. This work proposes a volumetric model to evaluate the tight sandstone gas reserves of the Permian Sulige gas field in the Ordos Basin. The reserves can be determined by four major parameters of reservoir cutoffs, net pay, gas-bearing area and compression factor Z, which are controlled by reservoir characteristics and sedimentation. Well logging, seismic analysis, core analysis and gas testing, as well as thin section identification and SEM analysis were used to analyze the pore evolution and pore-throat structure. The porosity and permeability cutoffs are determined by distribution function curve,empirical statistics and intersection plot. Net pay and gas-bearing area are determined based on the cutoffs, gas testing and sand body distribution, and the compression factor Z is obtained by gas component. The results demonstrate that the reservoir in the Sulige gas field is characterized by ultralow porosity and permeability, and the cutoffs of porosity and permeability are 5% and 0.15×10^(–3) μm^2, respectively. The net pay and gas-bearing area are mainly affected by the sedimentary facies, sand body types and distribution. The gas component is dominated by methane which accounts for more than 90%, and the compression factor Z of H_8(P_2h_8) and S_1(P_1s_1) are 0.98 and 0.985, respectively. The distributary channels stacked and overlapped, forming a wide and thick sand body with good developed intergranular pores and intercrystalline pores. The upper part of channel sand with good porosity and permeability can be sweet spot for gas exploration. The complete set of calculation systems proposed for tight gas reserve calculation has proved to be effective based on application and feedback. This model provides a new concept and consideration for reserve prediction and calculation in other areas.展开更多
Given sustaining exploration, the eastern zone of the Sulige gas field may soon become a key area of exploitation. In order to explore its genesis, types and distribution of the reservoir sandstones in the eastern zon...Given sustaining exploration, the eastern zone of the Sulige gas field may soon become a key area of exploitation. In order to explore its genesis, types and distribution of the reservoir sandstones in the eastern zone of this gas field, we focused in our study on the provenance and detailed sedimentary facies of sandstone of the He8 （the eighth part of the Shihezi formation, Permian system） and Shanxil （the first part of the Shanxi formation, Permian system） members, based on core observations, analyses in petrography, granularity and logging. The results show that： 1） the sandstone provenance of Shanxil and He8 in the eastern zone of the Sulige gas field is from the north of the Ordos Basin, characterized by dual directions from the north and northeast. 2） The He8 and Shanxil members were deposited in a fluvial-delta sedimentary system. The He8 was mainly deposited in braided rivers, in- cluding braided channels, channel bars, levee and floodplain sub-environments, whereas the Shanxil Member was deposited in braided rivers and deltas, including braided channels, channel bars, floodplains, tributaries and inter-tributary sub-environments. 3） Sedimentary facies bands migrated in drastic fashion towards the basin from the Shanxil to the He8 Member. Base levels of sedi- mentation generally present a trend of small increases in-amplitude, large decreasing amplitudes and slow and gradual Increases. 4） The continuity of the reservoir sandbodies along the source direction is better than that perpendicular to the direction. Compared with Shanxil, both dimensions and continuity of the sandbodies in He8 are better from which we conclude that it is the most fa- vorable part of the reservoir.展开更多
Based on the analysis of influencing factors of tight gas recovery and reservoir geological characteristics, the types of remaining tight gas reserves in the Sulige gas field are summarized from the perspective of res...Based on the analysis of influencing factors of tight gas recovery and reservoir geological characteristics, the types of remaining tight gas reserves in the Sulige gas field are summarized from the perspective of residual gas genesis to estimate residual gas reserves of different types and provide corresponding technical strategies for enhancing gas recovery. The residual gas reserves in the Sulige gas field can be divided into four types: well pattern uncontrollable, horizontal well missing, imperfect perforation, blocking zone in composite sandbodies. Among them, the uncontrolled remaining gas of well pattern and blocking zone in composite sandbodies are the main body for tapping potential and improving recovery factor, and well pattern infilling adjustment is the main means. Taking into account reservoir geological characteristics, production dynamic response and economic benefit requirements, four methods for infilling vertical well pattern, i.e., quantitative geological model method, dynamic controlled range of gas well method, production interference method and economic and technical index evaluation method, as well as a design method of combined vertical well pattern with horizontal well pattern are established. Under certain economic and technological conditions, the reasonable well pattern density of enrichment zone of gas field is proved to be 4 wells per square kilometers, which can increase the recovery rate of the gas field from 32% to about 50%. Meanwhile, five matching techniques for enhancing gas recovery aimed at interlayer undeveloped residual gas have been formed, including tapping potential of old wells, technological technology optimizing of new wells, rational production system optimizing, drainage and gas producing, and reducing waste production, which could increase the recovery rate for 5% based on well pattern infilling. The research results provide effective support for the long-term stable production of 230×108 m3/a of the Sulige gas field and production growth in the Changqing gas area.展开更多
To further ascertain the origin of the Ordovician Majiagou Formation reservoirs in the Ordos Basin,the M54-M51 sub-members of the Ordovician Majiagou Formation in the eastern Sulige gasfield of Ordos Basin were taken ...To further ascertain the origin of the Ordovician Majiagou Formation reservoirs in the Ordos Basin,the M54-M51 sub-members of the Ordovician Majiagou Formation in the eastern Sulige gasfield of Ordos Basin were taken as examples to analyze the vertical development characteristics of eogenetic karst and to discover the dissolution mechanism and its control on reservoirs through observation of a large number of cores and thin sections.According to detailed analysis of petrologic characteristics,the reservoir rock types include micritic dolomite,grain dolomite and microbialite which have mainly moldic pore,intergranular(dissolved)pore,and(dissolved)residual framework pore as main reservoir space respectively.The study area developed upward-shallowing sequences,with an exposure surface at the top of a single upward-shallowing sequence.The karst systems under the exposure surface had typical exposure characteristics of early dissolution and filling,indicating these reservoirs were related to the facies-controlled eogenetic karstification.With the increase of karstification intensity,the reservoirs became worse in physical properties.展开更多
Gas expansion caused by significant exhumation in the Sulige gas field in the Ordos Basin since Late Cretaceous and its effects on hydrocarbon accumulation have been investigated systematically based on comprehensive ...Gas expansion caused by significant exhumation in the Sulige gas field in the Ordos Basin since Late Cretaceous and its effects on hydrocarbon accumulation have been investigated systematically based on comprehensive analysis of geochemical,fluid inclusion and production data.The results indicate that gas volume expansion since the Late Cretaceous was the driving force for adjustment and secondary charging of tight sandstone gas reservoirs in the Sulige gas field of the Ordos Basin.The gas retained in the source rocks expanded in volume,resulting in gas re-expulsion,migration and secondary charging into reservoirs,while the gas volume expansion in the tight reservoirs caused the increase of gas saturation,gas-bearing area and gas column height,which worked together to increase the gas content of the reservoir and bring about large-scale gas accumulation events.The Sulige gas field had experienced a two-stage accumulation process,burial before the end of Early Cretaceous and uplifting since the Late Cretaceous.In the burial stage,natural gas was driven by hydrocarbon generation overpressure to migrate and accumulate,while in the uplifting stage,the gas volume expansion drove internal adjustment inside gas reservoirs and secondary charging to form new reservoirs.On the whole,the gas reservoir adjustment and secondary charging during uplifting stage is more significant in the eastern gas field than that in the west,which is favorable for forming gas-rich area.展开更多
To seek effective ways of lowering development cost and tapping inter-well remaining reserves, sidetracking horizontal wells from old wells in Su10 and Su53 Block were conducted. The engineering and geological problem...To seek effective ways of lowering development cost and tapping inter-well remaining reserves, sidetracking horizontal wells from old wells in Su10 and Su53 Block were conducted. The engineering and geological problems such as leakage, collapse and sticking in slim-hole sidetracking, and difficult evaluation of remaining gas were gradually overcome, and a set of drilling and completion technology, well deployment optimization technology and geo-steering technology suitable for sidetracking horizontal wells in tight sandstone gas reservoirs have been worked out. By making full use of the old well, sidetracking horizontal wells can greatly reduce development costs, enhance the producing degree of inter-well remaining reserves, and get production 3-5 times of that of adjacent vertical wells.Its production effect is influenced by encountered sandstone length, the position of the horizontal segment in the reservoir, produced effective reservoir thickness, gas saturation, controlled reserves and fracturing effect, etc. Up to now, in Block Su10 and Su53, 12 sidetracking horizontal wells have been drilled, which have an average drilling cycle of 49 days, average horizontal section length of 689 m,average effective drilling ratio of 61.5%, average well-head pressure of 16.2 MPa, and daily output of 4.7×10~4 m^3 at the initial stage after production. By the end of 2017, the average yield increment was more than 1 000×10~4 m^3 with good effect. With the increase of low yield old wells, wells in the enrichment regions tend to be saturated and the rest gas-bearing areas are lower in grade, therefore, sidetracking horizontal well can be used for optimization of well pattern, well deployment mode and exploitation of remaining oil areas.展开更多
With the grade of hydrocarbon resources becoming poorer,tight sandstone gas reservoirs may serve as the key to the enhancement of both reserves and productivity.Accordingly,high efficient and sustainable development o...With the grade of hydrocarbon resources becoming poorer,tight sandstone gas reservoirs may serve as the key to the enhancement of both reserves and productivity.Accordingly,high efficient and sustainable development of the large and over-large tight sandstone reservoirs is very important.However,currently,there is no effective method available for macro-analysis.Based on the latest research findings from the Sulige Gasfield,the largest onshore tight sandstone gas reservoir in China,studies were conducted in five aspects,i.e.reserve scale,development scale,dynamic reserve evaluation,rules in production declines of gasfields and undeveloped resource evaluation,to identify challenges to the production stabilization of gas reservoirs.In addition,key evidences and constraints for the solutions to the difficulties in production stabilization were proposed to provide necessary technical supports for high-efficient development in later stages.Research results show that the major challenges to production stabilization include seven aspects,such as low development induced by improper allocation of well patterns,uneven declines in productivity induced by specific features of reservoir formations and fluids,difficulties in the development of some reserves due to complex gas/water correlation,and differences in production performances by using different production techniques.Finally,guided by the development principles of“promoting productivity by using innovative technologies in different spaces and time”,13 key technologies,such as comprehensive optimization of development well patterns,multi-dimensional matrix for gas well management and“positive”water discharging and gas production technologies,were proposed to further prolong peak production time and enhance the recovery rates of tight gas reservoirs.展开更多
The Sulige tight sandstone gas reservoir is marked by low permeability,intricate pore structures,and notable lateral heterogeneity,making it difficult to predict the productivity of fractured horizontal wells in the r...The Sulige tight sandstone gas reservoir is marked by low permeability,intricate pore structures,and notable lateral heterogeneity,making it difficult to predict the productivity of fractured horizontal wells in the reservoir.In this study,a productivity prediction model for fractured horizontal wells is developed based on the characteristics of the Sulige gas reservoir,including its high start-up pressure gradient,strong stress sensitivity,obvious non-Darcy flow,and typical slippage and diffusion effects.This new model fully accounts for each hydraulic fracture in the horizontal wells based on the superposition principle and Green's function.This model facilitates efficient productivity calculations and enables rapid quantitative analysis of the influencing factors specific to horizontal wells with hydraulic fractures,fully integrating the specific characteristics of the Sulige gas field.The accuracy of this model is tested against field data from Wells LX1 and LX2 in the Sulige field,indicating good agreement between the predicted values and field data.Well LX2 is used as a case study to analyze the influences of geological and engineering factors on well productivity.The following conclusions are drawn:1)Well productivity is notably influenced by the start-up pressure gradient and stress sensitivity,with a minor impact from non-Darcy effects.2)Productivity linearly decreases with increased hydraulic fracture spacing.3)Productivity increases,and the increment rate gradually decreases,with increases in the length and conductivity of the hydraulic fractures.This model provides valuable guidance on predicting productivity in tight sandstone gas reservoirs,such as that of the Sulige gas field.展开更多
Shut-in after fracturing has become an important supporting technology for volume fracturing in unconventional oil and gas wells, which is helpful for gas and water imbibition replacement to increase single well produ...Shut-in after fracturing has become an important supporting technology for volume fracturing in unconventional oil and gas wells, which is helpful for gas and water imbibition replacement to increase single well production. In this paper, the hydraulic pressure, capillary pressure and osmotic pressure, the three main forces that affect well production, are calculated and compared in the Sulige tight sandstone gas field and Fuling shale gas field. The results show that the total forces affecting well production in the Sulige gas field are similar to those in the Fuling shale gas field, and it has the potential to exhibit shut-in after fracturing. For the characteristics of “low pressure” and “water blocking risk” in Sulige gas field, it is suggested that:(1)injecting N_(2) or CO_(2) during hydraulic fracturing and reasonably controlling the shut-in time after fracturing, such as shut-in for approximately 30 h, can ensure effective natural fluid flowback while replenishing energy to the formation and reduce the damage caused by water blocking and (2)the waterproof lock slickwater is used in the test wells, and the result shows that slickwater can reduce the reservoir damage and increase well production when compared with guanidine gum fracturing fluid. This research can provide some basis and reference for the field test of shut-in after fracturing in the Sulige tight sandstone gas field.展开更多
The origin and distribution of Upper Paleozoic reservoirs pressure in mid-northem Ordos Basin has attracted widespread attention in recent years.The reservoir pressure of Sulige area shows characteristics of basically...The origin and distribution of Upper Paleozoic reservoirs pressure in mid-northem Ordos Basin has attracted widespread attention in recent years.The reservoir pressure of Sulige area shows characteristics of basically subnormal pressure,and the reservoir pressure of Yulin area shows characteristics of basically normal hydrostatic pressure.展开更多
By virtue of unique technical and economical advantages,horizontal well development has become a key technology in the high-efficiency development of tight gas reservoirs,however,this has worked unsatisfactorily in un...By virtue of unique technical and economical advantages,horizontal well development has become a key technology in the high-efficiency development of tight gas reservoirs,however,this has worked unsatisfactorily in unstratified gas reservoirs.In this paper,the orientation and coverage of gas-bearing sand bodies(in isolated distribution)of Member 8 of Permian Lower Shihezi Fm in the Sulige Gasfield were analyzed by means of outcrop analogy,geostatistical analysis and pilot tests of dense well patterns.Then,four gas-bearing sand distribution patterns suitable for the deployment of horizontal wells in Member 8 were proposed according to the precise geological anatomy results of dense well patterns.These patterns include thick massive isolated pattern,vertically superimposed pattern with physical interlayers,vertically superimposed pattern with argillaceous interlayers and lateral sugar-coated haw string pattern.Based on the statistics on gas-bearing sand bodies drilled by horizontal well drilling,the drilled gas-bearing sand bodies are 670-1300 m long.Based on production data correction,numerical simulation and economic evaluation,the length of rational horizontal sections were optimized by performing a case study of the vertically superimposed reservoirs with physical interlayers in the typical well group SuX-18-36 of Su-X Block.It is indicated that the rational horizontal well length within 1200 m in the Sulige Gasfield under current economic and technical conditions.This paper provides a technical support for the highefficiency development of the Sulige Gasfield in the future.展开更多
Centralized and group well deployment and factory-like fracturing techniques are adopted for low-permeability tight sandstone reservoirs in the Sulige Gasfield,Ordos Basin,so as to realize its efficient and economic d...Centralized and group well deployment and factory-like fracturing techniques are adopted for low-permeability tight sandstone reservoirs in the Sulige Gasfield,Ordos Basin,so as to realize its efficient and economic development.However,environmental protection is faced with grim situations because fluid delivery rises abruptly on site in a short time due to centralized fracturing of the well group.Based on the characteristics of gas testing after fracturing in this gas field,a fracturing flowback fluid recovery and treatment method suitable for the Sulige Gasfield has been developed with the landform features of this area taken into account.Firstly,a high-efficiency well-to-well fracturing flowback fluid recovery and reutilization technique was developed with multi-effect surfactant polymer recoverable fracturing fluid system as the core,and in virtue of this technique,the treatment efficiency of conventional guar gum fracturing fluid system is increased.Secondly,for recovering and treating the end fluids on the well sites,a fine fracturing flowback fluid recovery and treatment technique has been worked out with“coagulation and precipitation,filtration and disinfection,and sludge dewatering”as the main part.Owing to the application of this method,the on-site water resource utilization ratio has been increased and environmental protection pressure concerned with fracturing operation has been relieved.In 2014,field tests were performed in 62 wells of 10 well groups,with 32980 m3 cumulative treated flowback fluid,17160 m3 reutilization volume and reutilization ratio over 70%.Obviously,remarkable social and economical benefits are thus realized.展开更多
Based on the exploration and development achievements of the Sulige Gasfield in the Ordos Basin,tight sandstone gas yield has been increased essentially in China.Recovery enhancement is always the core subject in rese...Based on the exploration and development achievements of the Sulige Gasfield in the Ordos Basin,tight sandstone gas yield has been increased essentially in China.Recovery enhancement is always the core subject in researches.In this paper,the development history of the Sulige Gasfield was reviewed focusing on the technological progress in single well production enhancement.Then,the technical ideas on and countermeasures for transforming the traditional development modes and increasing recovery factor were discussed.It is shown that the development technologies in the evaluation and the production enhancement and stabilization of giant tight sandstone gas reservoirs are changed progressively.The fast increase of gas production in this field is made possible by well location arrangement technology based on sweep spot screening,horizontal well development technology,well type and well pattern optimization technology,fast drilling technology,reservoir stimulation technology,drainage gas recovery technology and integrated construction mode.And finally,the technical ideas of recovery enhancement during the 13th Five-Year Plan were proposed in nine aspects,including gas field development,planning and evaluation technology based on single-well life cycle analysis;dynamic evaluation and infilling technology for mixed well patterns targeting recovery enhancement;one-shot recovery enhancement technology for a new areal pattern area with integrated multiple well patterns and multiple series of strata;reserve evaluation model based on risk and benefit evaluation;gas-well precise management technology with multi-dimensional matrix;potential tapping technology for low production and low efficiency wells;novel wellsite environmental protection technology;surface process based on integrated equipments;and C_(3)^(+)mixed hydrocarbon recovery technology.It provides technically reliable support for the development of tight sandstone gas reservoirs in the Sulige Gasfield during the 13th Five-Year Plan.展开更多
An outstanding issue in the oil and gas industry is how to evaluate quantitatively the influences of water production on production per-formance of gas wells.Based on gasewater flow theories,therefore,a new method was...An outstanding issue in the oil and gas industry is how to evaluate quantitatively the influences of water production on production per-formance of gas wells.Based on gasewater flow theories,therefore,a new method was proposed in this paper to evaluate quantitatively the production performance of water-producing gas wells by using gas&water relative permeability curves after a comparative study was conducted thoroughly.In this way,quantitative evaluation was performed on production capacity,gas production,ultimate cumulative gas production and recovery factor of water-producing gas wells.Then,a case study was carried out of the tight sandstone gas reservoirs with strong heterogeneity in the Sulige gas field,Ordos Basin.This method was verified in terms of practicability and reliability through a large amount of calculation based on the actual production performance data of various gas wells with different volumes of water produced.Finally,empirical formula and charts were established for water-producing gas wells in this field to quantitatively evaluate their production capacity,gas production,ultimate cumulative gas production and recovery factor in the conditions of different wateregas ratios.These formula and charts provide technical support for the field application and dissemination of the method.Study results show that water production is serious in the west of this field with wateregas ratio varying in a large range.If the average wateregas ratio is 1.0(or 2.0)m^(3)/10^(4) m^(3),production capacity,cumulative gas pro-duction and recovery factor of gas wells will be respectively 24.4%(or 40.2%),24.4%(or 40.2%)and 17.4%(or 33.2%).展开更多
As a typical tight sandstone gasfield with strong heterogeneity,the Sulige Gas Field in the Ordos Basin faces major challenges in its development because the reservoirs in the gasfield are small in effective sand scal...As a typical tight sandstone gasfield with strong heterogeneity,the Sulige Gas Field in the Ordos Basin faces major challenges in its development because the reservoirs in the gasfield are small in effective sand scale,rapid in lithologic change,strong in plane heterogeneity,and poor in connectivity.How to scientifically deploy development wells to improve the recovery is the most important issue for the successful development of this kind of gasfields.Therefore,a well inference analysis was conducted tofigure out the impact of well pattern density on the recovery based on the research of many years in gasfield development methods and the summary of practical effect.In this paper,we put forward for thefirst time the concept of inter-well interference probability,and present the relationship between the probability of inter-well interference and well pattern density of the Sulige Gas Field.Then we established a mathematical model for the optimization of development well pattern by combiningfine sand anatomy,reservoir engineering,numerical simulation and economic evaluation,and obtained a quantitative relationship between recovery and well pattern density.Furthermore,on the basis of comprehensive analysis,a reasonable development well pattern was designed for the Sulige Gas Field:this well pattern is parallelogram in shape,with a density of 3.1 wells/km2,well spacing of 500 m,and row spacing of 650 m.Development practices have confirmed that this scheme is capable of achieving better economic benefits,producing geological reserves as far as possible and improving the ultimate recovery of such gasfields.展开更多
The Sulige Gas Field in the Ordos Basin is the largest tight gasfield in China,with proved reserves exceeding 2×10^(12)m^(3).As the main contributor to gas production in PetroChina Changqing Oilfield Company,The ...The Sulige Gas Field in the Ordos Basin is the largest tight gasfield in China,with proved reserves exceeding 2×10^(12)m^(3).As the main contributor to gas production in PetroChina Changqing Oilfield Company,The Sulige Gas Field is in the stage of stable production.Maximizing the stable production period is a focus and challenge for the gasfield now.To address a series of problems influencing the efficient development of Sulige gasfield,such as large-scale remaining gas reserves between wells/layers and low ratio of employed reserves,the main technologies for enhanced gas recovery(EGR)of tight gas reservoirs were developed by multidisciplinary research with respect to development geology,reservoir engineering,drilling and production process,and surface gathering and transportation.Experiments were conducted on reservoir description and remaining gas characterization,well pattern thickening optimization,vertical well separate-layer fracturing,horizontal-well multi-stage multi-cluster volume fracturing for their improvement and upgrading.The orientation of EGR for tight gas reservoirs is pro-posed.The following results are obtained.First,well pattern thickening optimization is the most important EGR method,which can increase the recovery rate by more than 6%.Second,based on continuous upgrading and promotion,either of reservoir stimulation technology and drainage gas recovery technology can increase the recovery rate by more than 2%.The gathering and transportation technology which further reduces the wellhead pressure can increase the recovery rate by about 1.5%.Third,the EGR technology should be oriented to maximize the quantity of employed reserves,especially by way of new technologies such asfine remaining gas characterization,well pattern/type optimization,cross-layer fracturing of a multi-thin-layer reservoir by horizontal wells,intelligent drainage gas recovery,and multi-stage pressurization.It is concluded that the development of key EGR technologies will help increase the recovery rate of The Sulige Gas Field by 10%e15%,and will provide an effective support for The Sulige Gas Field to maintain the production at 300108 m^(3)/a for a long term and for the Changqing gas province to increase the production to 500×10^(8)m^(3)/a,which will ultimately ensure the national energy security.展开更多
The characteristics of diagenetic minerals and their effects on reservoir quality of the tight sandstones of the Permian in Sulige gas field of the Ordos Basin were studied through observations on thin sections,scanni...The characteristics of diagenetic minerals and their effects on reservoir quality of the tight sandstones of the Permian in Sulige gas field of the Ordos Basin were studied through observations on thin sections,scanning electron microscopy,energy dispersive spectroscopy analysis and electron microprobe analysis.Diagenetic minerals in the Permian sandstones consist of illite,kaolinite,chlorite,siliceous and calcite cements.Large amounts of intercrystalline pores between kaolinite and illite provide channels for acidic fluids flow and thereby were conducive to the formation of clastic solution pores,intergranular solution pores and composite pores.Authigenic chlorite occurs in the form of three morphotypes as grain-coating,pore-lining and pore-filling.Grain-coating and pore-lining chlorite with different crystal shapes occur as coatings on the framework grains.Pore-filling chlorite precipitated as discrete flaky plates in pore spaces.Quartz microcrystals developed but quartz overgrowth did not develop because of the occurrence of porelining chlorite.This,in turn,led to the preservation of primary pores by occupying potential nucleation sites for quartz overgrowth and thereby preventing quartz microcrystals from merging into quartz overgrowth.This process is regarded as the most important for influencing the quality of the lithophysical properties.Calcite cement was mainly precipitated during a late diagenetic stage and has a negative effect on the reservoir quality.This study provides important insights into analyzing the relationship between diagenetic minerals and reservoir quality and the results are directly applicable to the exploration and development of tight sandstone reservoirs all over the world.展开更多
Up to now,the Sulige area in Ordos Basin has the favorable exploration area of 55×10^(3) km^(2),the total reserve of natural gas of nearly 6×10^(12) m^(3) and the proven reserve(including basic proven reserv...Up to now,the Sulige area in Ordos Basin has the favorable exploration area of 55×10^(3) km^(2),the total reserve of natural gas of nearly 6×10^(12) m^(3) and the proven reserve(including basic proven reserve)of 4.77×10^(12) m^(3),where the annual production of natural gas reaches 23×10^(9) m^(3),and the Sulige gasfield is the largest onshore natural gas field in China.The pay zone of the Sulige gasfield mainly is Member 8 of Shihezi Formation and Member 1 of Shanxi Formation of Permian which belong to the typical tight sandstone gas reservoir.The coal measure strata in Carboniferous Benxi Formation,Permian Taiyuan Formation and Shanxi Formation provide abundant gas sources for the Gulige gas reservoirs.An open-flow sedimentary model of lacustrine delta is developed,the gentle bottom,sand supply from multisource,strong hydrodynamic force and multi-period superposition control the distribution of largearea reservoir sand body.Lithology of the reservoir is the sandstone of the fluvial-delta facies,the physical property is poor and the heterogeneity is strong,the average porosity ranges from 4%to 12%and the average permeability varies from 0.01 to 1 mD.The gas reservoir is characterized by wide hydrocarbon generation,pervasive hydrocarbon charging,short-range migration and massive accumulation.The pressure coefficient of the gas reservoir ranges from 0.62 to 0.90,indicating the low-pressure gas reservoir,and the single-well yield is low.Full digital seismic technique in the desert area,nonlongitudinal seismic technique in the loess plateau,accurate logging evaluation technique,tight sand reservoir stimulation technology and horizontal well development technology are key technologies for exploration and development of Sulige gasfield.展开更多
基金supported by the major national special projects for technology:Enrichment Regularity and Distribution Prediction for Hydrocarbon of Key Clastic Rocks in Central and Western Regions (Approval No.: 2011ZX05002-006)National Natural Science Foundation of China (Approval No.: 41372135 and 41402120)Research and Innovation Team Plan Fund of Shandong University of Science and Technology (Approval No.: 2010KYTD103)
文摘In order to determine the genesis and the factors that control the low-porosity and low- permeability sandstone reservoirs in the eastern Sulige Gas Field in the Ordos Basin, systematic studies on the sedimentary facies and diagenesis were conducted by means of analysis of cores, thin sections, fluid inclusions, X-ray diffraction, cathode luminescence and scanning electron microscope. It was found that the sand bodies of the major gas reservoirs in the Shan1 section （P1S1） and the He8 section （P2H8） were formed during the Permian as sedimentary facies such as braided-channel bars, braided-river channels and point bars of a meandering river. Four types of diagenetic facies developed subsequently： in order from the best to the poorest properties these are type A （weak compaction, early calcite cement-chlorite film facies）, type B （moderate compaction, quartz overgrowth-feldspar corrosion-kaolinite filling facies）, type C （strong compaction, late calcite cement-quartz corrosion facies） and type D （matrix filling and strong compaction facies）. This diagenesis is undoubtedly the main reason for the poor reservoir properties of sandstone reservoirs, but the sedimentary facies are the underlying factors that greatly affect the diagenesis and thus the reservoir performance. Favorable diagenetic facies developed mainly in relatively small lithofacies such as braided-river channels, channel bars and point bars. The vertical distribution of the physical properties and the diagenetic facies of the reservoirs are related to the stratigraphic succession. Most of the sandstones between mudstones and thin beds of sandstone are unfavorable diagenetic facies. Analyses indicate that siliceous cementation can hardly be stopped by hydrocarbon filling. Authigenic chlorite could hardly protect the primary porosity. It not only occupies pore space, but also blocks pathways through sandstone reservoirs, so that it has significant influence on the permeability. Authigenic chlorite cannot be used as a marker for a specific sedimentary facies because it can be formed in different sedimentary facies, but it indicates high hydrodynamic conditions and presence of favorable reservoirs.
基金financed by the National Key Basic Program (National 973 project,2001CB209100,2006CB202306)
文摘Comparisons have been made among lithology, diagenesis, and reservoir characteristics of gas-bearing and non-gas-bearing ones in the Sulige gas field of the Ordos Basin based on the laboratory analysis of thin sections, scanning electron microscope, and liquid inclusion of the reservoirs. The reservoirs of the Sulige gas field are now in the middle stage of diagenesis and have undergone compaction, cementation and dissolution. The secondary pore of the reservoir originated from the dissolution of the feldspar and tuff because of the organic acid action from the source rocks during the diagenetic middle stage. Gas-bearing reservoirs are common in soluble pore diagenetic facies of coarse detritus quartzose sandstone, whereas non-gas-bearing ones are common in tense compaction diagenetic facies of mud-bearing medium-fine detritus quartzose sandstone and residual intergranular pore diagenetic facies of mud-bearing medium-coarse detritus quartzose sandstone. The secondary pore is developed in gas-bearing reservoirs of the Sulige gas-field as the medium-coarse grain reservoirs formed in a powerful sedimentary environment and experienced strong dissolution. However, the sediments of fine grain size form the non-gas-bearing reservoirs because of less residual primary pore and secondary pore.
基金funded by the Geological Survey Project of the China Geological Survey (grants No. DD20189614, DD20160173)the National Science Foundation of China (grants No. 41702204, 41402120)
文摘To accurately measure and evaluate reserves is critical for ensuring successful production of unconventional oil and gas. This work proposes a volumetric model to evaluate the tight sandstone gas reserves of the Permian Sulige gas field in the Ordos Basin. The reserves can be determined by four major parameters of reservoir cutoffs, net pay, gas-bearing area and compression factor Z, which are controlled by reservoir characteristics and sedimentation. Well logging, seismic analysis, core analysis and gas testing, as well as thin section identification and SEM analysis were used to analyze the pore evolution and pore-throat structure. The porosity and permeability cutoffs are determined by distribution function curve,empirical statistics and intersection plot. Net pay and gas-bearing area are determined based on the cutoffs, gas testing and sand body distribution, and the compression factor Z is obtained by gas component. The results demonstrate that the reservoir in the Sulige gas field is characterized by ultralow porosity and permeability, and the cutoffs of porosity and permeability are 5% and 0.15×10^(–3) μm^2, respectively. The net pay and gas-bearing area are mainly affected by the sedimentary facies, sand body types and distribution. The gas component is dominated by methane which accounts for more than 90%, and the compression factor Z of H_8(P_2h_8) and S_1(P_1s_1) are 0.98 and 0.985, respectively. The distributary channels stacked and overlapped, forming a wide and thick sand body with good developed intergranular pores and intercrystalline pores. The upper part of channel sand with good porosity and permeability can be sweet spot for gas exploration. The complete set of calculation systems proposed for tight gas reserve calculation has proved to be effective based on application and feedback. This model provides a new concept and consideration for reserve prediction and calculation in other areas.
基金supported by the National Basic Re-search Program of China (No2003CB214603)
文摘Given sustaining exploration, the eastern zone of the Sulige gas field may soon become a key area of exploitation. In order to explore its genesis, types and distribution of the reservoir sandstones in the eastern zone of this gas field, we focused in our study on the provenance and detailed sedimentary facies of sandstone of the He8 （the eighth part of the Shihezi formation, Permian system） and Shanxil （the first part of the Shanxi formation, Permian system） members, based on core observations, analyses in petrography, granularity and logging. The results show that： 1） the sandstone provenance of Shanxil and He8 in the eastern zone of the Sulige gas field is from the north of the Ordos Basin, characterized by dual directions from the north and northeast. 2） The He8 and Shanxil members were deposited in a fluvial-delta sedimentary system. The He8 was mainly deposited in braided rivers, in- cluding braided channels, channel bars, levee and floodplain sub-environments, whereas the Shanxil Member was deposited in braided rivers and deltas, including braided channels, channel bars, floodplains, tributaries and inter-tributary sub-environments. 3） Sedimentary facies bands migrated in drastic fashion towards the basin from the Shanxil to the He8 Member. Base levels of sedi- mentation generally present a trend of small increases in-amplitude, large decreasing amplitudes and slow and gradual Increases. 4） The continuity of the reservoir sandbodies along the source direction is better than that perpendicular to the direction. Compared with Shanxil, both dimensions and continuity of the sandbodies in He8 are better from which we conclude that it is the most fa- vorable part of the reservoir.
基金Supported by the China National Science and Technology Major Project(2016ZX05047)
文摘Based on the analysis of influencing factors of tight gas recovery and reservoir geological characteristics, the types of remaining tight gas reserves in the Sulige gas field are summarized from the perspective of residual gas genesis to estimate residual gas reserves of different types and provide corresponding technical strategies for enhancing gas recovery. The residual gas reserves in the Sulige gas field can be divided into four types: well pattern uncontrollable, horizontal well missing, imperfect perforation, blocking zone in composite sandbodies. Among them, the uncontrolled remaining gas of well pattern and blocking zone in composite sandbodies are the main body for tapping potential and improving recovery factor, and well pattern infilling adjustment is the main means. Taking into account reservoir geological characteristics, production dynamic response and economic benefit requirements, four methods for infilling vertical well pattern, i.e., quantitative geological model method, dynamic controlled range of gas well method, production interference method and economic and technical index evaluation method, as well as a design method of combined vertical well pattern with horizontal well pattern are established. Under certain economic and technological conditions, the reasonable well pattern density of enrichment zone of gas field is proved to be 4 wells per square kilometers, which can increase the recovery rate of the gas field from 32% to about 50%. Meanwhile, five matching techniques for enhancing gas recovery aimed at interlayer undeveloped residual gas have been formed, including tapping potential of old wells, technological technology optimizing of new wells, rational production system optimizing, drainage and gas producing, and reducing waste production, which could increase the recovery rate for 5% based on well pattern infilling. The research results provide effective support for the long-term stable production of 230×108 m3/a of the Sulige gas field and production growth in the Changqing gas area.
基金Supported by the China National Science and Technology Major Project(2016ZX05004006-001-002)CNPC-Southwest Petroleum University Innovation Consortium Technology Cooperation Project
文摘To further ascertain the origin of the Ordovician Majiagou Formation reservoirs in the Ordos Basin,the M54-M51 sub-members of the Ordovician Majiagou Formation in the eastern Sulige gasfield of Ordos Basin were taken as examples to analyze the vertical development characteristics of eogenetic karst and to discover the dissolution mechanism and its control on reservoirs through observation of a large number of cores and thin sections.According to detailed analysis of petrologic characteristics,the reservoir rock types include micritic dolomite,grain dolomite and microbialite which have mainly moldic pore,intergranular(dissolved)pore,and(dissolved)residual framework pore as main reservoir space respectively.The study area developed upward-shallowing sequences,with an exposure surface at the top of a single upward-shallowing sequence.The karst systems under the exposure surface had typical exposure characteristics of early dissolution and filling,indicating these reservoirs were related to the facies-controlled eogenetic karstification.With the increase of karstification intensity,the reservoirs became worse in physical properties.
基金Supported by the National Natural Science Foundation of China(41502132)China National Demonstration Project(2016ZX05050).
文摘Gas expansion caused by significant exhumation in the Sulige gas field in the Ordos Basin since Late Cretaceous and its effects on hydrocarbon accumulation have been investigated systematically based on comprehensive analysis of geochemical,fluid inclusion and production data.The results indicate that gas volume expansion since the Late Cretaceous was the driving force for adjustment and secondary charging of tight sandstone gas reservoirs in the Sulige gas field of the Ordos Basin.The gas retained in the source rocks expanded in volume,resulting in gas re-expulsion,migration and secondary charging into reservoirs,while the gas volume expansion in the tight reservoirs caused the increase of gas saturation,gas-bearing area and gas column height,which worked together to increase the gas content of the reservoir and bring about large-scale gas accumulation events.The Sulige gas field had experienced a two-stage accumulation process,burial before the end of Early Cretaceous and uplifting since the Late Cretaceous.In the burial stage,natural gas was driven by hydrocarbon generation overpressure to migrate and accumulate,while in the uplifting stage,the gas volume expansion drove internal adjustment inside gas reservoirs and secondary charging to form new reservoirs.On the whole,the gas reservoir adjustment and secondary charging during uplifting stage is more significant in the eastern gas field than that in the west,which is favorable for forming gas-rich area.
基金Supported by the Project of Great Wall Drilling Company in CNPC(2015A25-2(2012))
文摘To seek effective ways of lowering development cost and tapping inter-well remaining reserves, sidetracking horizontal wells from old wells in Su10 and Su53 Block were conducted. The engineering and geological problems such as leakage, collapse and sticking in slim-hole sidetracking, and difficult evaluation of remaining gas were gradually overcome, and a set of drilling and completion technology, well deployment optimization technology and geo-steering technology suitable for sidetracking horizontal wells in tight sandstone gas reservoirs have been worked out. By making full use of the old well, sidetracking horizontal wells can greatly reduce development costs, enhance the producing degree of inter-well remaining reserves, and get production 3-5 times of that of adjacent vertical wells.Its production effect is influenced by encountered sandstone length, the position of the horizontal segment in the reservoir, produced effective reservoir thickness, gas saturation, controlled reserves and fracturing effect, etc. Up to now, in Block Su10 and Su53, 12 sidetracking horizontal wells have been drilled, which have an average drilling cycle of 49 days, average horizontal section length of 689 m,average effective drilling ratio of 61.5%, average well-head pressure of 16.2 MPa, and daily output of 4.7×10~4 m^3 at the initial stage after production. By the end of 2017, the average yield increment was more than 1 000×10~4 m^3 with good effect. With the increase of low yield old wells, wells in the enrichment regions tend to be saturated and the rest gas-bearing areas are lower in grade, therefore, sidetracking horizontal well can be used for optimization of well pattern, well deployment mode and exploitation of remaining oil areas.
基金National Science and Technology Major Project“Demonstration Project of Development of Large-Scale Low-Permeability Lithologic and Stratigraphic Reservoirs in the Ordos Basin”(No.2011ZX05044)Scientific Research and Technical Development Project of CNPC(No.2012E-1306).
文摘With the grade of hydrocarbon resources becoming poorer,tight sandstone gas reservoirs may serve as the key to the enhancement of both reserves and productivity.Accordingly,high efficient and sustainable development of the large and over-large tight sandstone reservoirs is very important.However,currently,there is no effective method available for macro-analysis.Based on the latest research findings from the Sulige Gasfield,the largest onshore tight sandstone gas reservoir in China,studies were conducted in five aspects,i.e.reserve scale,development scale,dynamic reserve evaluation,rules in production declines of gasfields and undeveloped resource evaluation,to identify challenges to the production stabilization of gas reservoirs.In addition,key evidences and constraints for the solutions to the difficulties in production stabilization were proposed to provide necessary technical supports for high-efficient development in later stages.Research results show that the major challenges to production stabilization include seven aspects,such as low development induced by improper allocation of well patterns,uneven declines in productivity induced by specific features of reservoir formations and fluids,difficulties in the development of some reserves due to complex gas/water correlation,and differences in production performances by using different production techniques.Finally,guided by the development principles of“promoting productivity by using innovative technologies in different spaces and time”,13 key technologies,such as comprehensive optimization of development well patterns,multi-dimensional matrix for gas well management and“positive”water discharging and gas production technologies,were proposed to further prolong peak production time and enhance the recovery rates of tight gas reservoirs.
基金support from the Natural Science Foundation of Sichuan Province(Grant Nos.2022NSFSC0185 and 2023NSFSC0938)the National Natural Science Foundation of China(Grant No.42172313)are appreciated.
文摘The Sulige tight sandstone gas reservoir is marked by low permeability,intricate pore structures,and notable lateral heterogeneity,making it difficult to predict the productivity of fractured horizontal wells in the reservoir.In this study,a productivity prediction model for fractured horizontal wells is developed based on the characteristics of the Sulige gas reservoir,including its high start-up pressure gradient,strong stress sensitivity,obvious non-Darcy flow,and typical slippage and diffusion effects.This new model fully accounts for each hydraulic fracture in the horizontal wells based on the superposition principle and Green's function.This model facilitates efficient productivity calculations and enables rapid quantitative analysis of the influencing factors specific to horizontal wells with hydraulic fractures,fully integrating the specific characteristics of the Sulige gas field.The accuracy of this model is tested against field data from Wells LX1 and LX2 in the Sulige field,indicating good agreement between the predicted values and field data.Well LX2 is used as a case study to analyze the influences of geological and engineering factors on well productivity.The following conclusions are drawn:1)Well productivity is notably influenced by the start-up pressure gradient and stress sensitivity,with a minor impact from non-Darcy effects.2)Productivity linearly decreases with increased hydraulic fracture spacing.3)Productivity increases,and the increment rate gradually decreases,with increases in the length and conductivity of the hydraulic fractures.This model provides valuable guidance on predicting productivity in tight sandstone gas reservoirs,such as that of the Sulige gas field.
基金China National Science and Technology Major Projects (2016ZX05050) “Large-scale low-permeability core formation oil and gas reservoir development demonstration project in Ordos Basin”.
文摘Shut-in after fracturing has become an important supporting technology for volume fracturing in unconventional oil and gas wells, which is helpful for gas and water imbibition replacement to increase single well production. In this paper, the hydraulic pressure, capillary pressure and osmotic pressure, the three main forces that affect well production, are calculated and compared in the Sulige tight sandstone gas field and Fuling shale gas field. The results show that the total forces affecting well production in the Sulige gas field are similar to those in the Fuling shale gas field, and it has the potential to exhibit shut-in after fracturing. For the characteristics of “low pressure” and “water blocking risk” in Sulige gas field, it is suggested that:(1)injecting N_(2) or CO_(2) during hydraulic fracturing and reasonably controlling the shut-in time after fracturing, such as shut-in for approximately 30 h, can ensure effective natural fluid flowback while replenishing energy to the formation and reduce the damage caused by water blocking and (2)the waterproof lock slickwater is used in the test wells, and the result shows that slickwater can reduce the reservoir damage and increase well production when compared with guanidine gum fracturing fluid. This research can provide some basis and reference for the field test of shut-in after fracturing in the Sulige tight sandstone gas field.
文摘The origin and distribution of Upper Paleozoic reservoirs pressure in mid-northem Ordos Basin has attracted widespread attention in recent years.The reservoir pressure of Sulige area shows characteristics of basically subnormal pressure,and the reservoir pressure of Yulin area shows characteristics of basically normal hydrostatic pressure.
基金Project supported by the National Major Scientific and Technological Project,“Key Development Technologies for Natural Gas”(Grant No.2011ZX05015).
文摘By virtue of unique technical and economical advantages,horizontal well development has become a key technology in the high-efficiency development of tight gas reservoirs,however,this has worked unsatisfactorily in unstratified gas reservoirs.In this paper,the orientation and coverage of gas-bearing sand bodies(in isolated distribution)of Member 8 of Permian Lower Shihezi Fm in the Sulige Gasfield were analyzed by means of outcrop analogy,geostatistical analysis and pilot tests of dense well patterns.Then,four gas-bearing sand distribution patterns suitable for the deployment of horizontal wells in Member 8 were proposed according to the precise geological anatomy results of dense well patterns.These patterns include thick massive isolated pattern,vertically superimposed pattern with physical interlayers,vertically superimposed pattern with argillaceous interlayers and lateral sugar-coated haw string pattern.Based on the statistics on gas-bearing sand bodies drilled by horizontal well drilling,the drilled gas-bearing sand bodies are 670-1300 m long.Based on production data correction,numerical simulation and economic evaluation,the length of rational horizontal sections were optimized by performing a case study of the vertically superimposed reservoirs with physical interlayers in the typical well group SuX-18-36 of Su-X Block.It is indicated that the rational horizontal well length within 1200 m in the Sulige Gasfield under current economic and technical conditions.This paper provides a technical support for the highefficiency development of the Sulige Gasfield in the future.
文摘Centralized and group well deployment and factory-like fracturing techniques are adopted for low-permeability tight sandstone reservoirs in the Sulige Gasfield,Ordos Basin,so as to realize its efficient and economic development.However,environmental protection is faced with grim situations because fluid delivery rises abruptly on site in a short time due to centralized fracturing of the well group.Based on the characteristics of gas testing after fracturing in this gas field,a fracturing flowback fluid recovery and treatment method suitable for the Sulige Gasfield has been developed with the landform features of this area taken into account.Firstly,a high-efficiency well-to-well fracturing flowback fluid recovery and reutilization technique was developed with multi-effect surfactant polymer recoverable fracturing fluid system as the core,and in virtue of this technique,the treatment efficiency of conventional guar gum fracturing fluid system is increased.Secondly,for recovering and treating the end fluids on the well sites,a fine fracturing flowback fluid recovery and treatment technique has been worked out with“coagulation and precipitation,filtration and disinfection,and sludge dewatering”as the main part.Owing to the application of this method,the on-site water resource utilization ratio has been increased and environmental protection pressure concerned with fracturing operation has been relieved.In 2014,field tests were performed in 62 wells of 10 well groups,with 32980 m3 cumulative treated flowback fluid,17160 m3 reutilization volume and reutilization ratio over 70%.Obviously,remarkable social and economical benefits are thus realized.
基金Project supported by the National Major Scientific and Technological Project,“Demonstration Project of Large Low-permeability Lithologic-stratigraphic Oil and Gas Reservoirs in Ordos Basin”(Grant No.2011ZX05044)the CNPC Scientific Research and Technical Development Project,“Major Engineering Technologies for Development of Tight Gas Reservoirs”(Grant No.2012E-1306).
文摘Based on the exploration and development achievements of the Sulige Gasfield in the Ordos Basin,tight sandstone gas yield has been increased essentially in China.Recovery enhancement is always the core subject in researches.In this paper,the development history of the Sulige Gasfield was reviewed focusing on the technological progress in single well production enhancement.Then,the technical ideas on and countermeasures for transforming the traditional development modes and increasing recovery factor were discussed.It is shown that the development technologies in the evaluation and the production enhancement and stabilization of giant tight sandstone gas reservoirs are changed progressively.The fast increase of gas production in this field is made possible by well location arrangement technology based on sweep spot screening,horizontal well development technology,well type and well pattern optimization technology,fast drilling technology,reservoir stimulation technology,drainage gas recovery technology and integrated construction mode.And finally,the technical ideas of recovery enhancement during the 13th Five-Year Plan were proposed in nine aspects,including gas field development,planning and evaluation technology based on single-well life cycle analysis;dynamic evaluation and infilling technology for mixed well patterns targeting recovery enhancement;one-shot recovery enhancement technology for a new areal pattern area with integrated multiple well patterns and multiple series of strata;reserve evaluation model based on risk and benefit evaluation;gas-well precise management technology with multi-dimensional matrix;potential tapping technology for low production and low efficiency wells;novel wellsite environmental protection technology;surface process based on integrated equipments;and C_(3)^(+)mixed hydrocarbon recovery technology.It provides technically reliable support for the development of tight sandstone gas reservoirs in the Sulige Gasfield during the 13th Five-Year Plan.
基金Project supported by National Major Science and Technology Project“Effective techniques for commercial production of low-permeability low-abundance sandstone gas reservoirs”(Grant No.2011ZX05015-001).
文摘An outstanding issue in the oil and gas industry is how to evaluate quantitatively the influences of water production on production per-formance of gas wells.Based on gasewater flow theories,therefore,a new method was proposed in this paper to evaluate quantitatively the production performance of water-producing gas wells by using gas&water relative permeability curves after a comparative study was conducted thoroughly.In this way,quantitative evaluation was performed on production capacity,gas production,ultimate cumulative gas production and recovery factor of water-producing gas wells.Then,a case study was carried out of the tight sandstone gas reservoirs with strong heterogeneity in the Sulige gas field,Ordos Basin.This method was verified in terms of practicability and reliability through a large amount of calculation based on the actual production performance data of various gas wells with different volumes of water produced.Finally,empirical formula and charts were established for water-producing gas wells in this field to quantitatively evaluate their production capacity,gas production,ultimate cumulative gas production and recovery factor in the conditions of different wateregas ratios.These formula and charts provide technical support for the field application and dissemination of the method.Study results show that water production is serious in the west of this field with wateregas ratio varying in a large range.If the average wateregas ratio is 1.0(or 2.0)m^(3)/10^(4) m^(3),production capacity,cumulative gas pro-duction and recovery factor of gas wells will be respectively 24.4%(or 40.2%),24.4%(or 40.2%)and 17.4%(or 33.2%).
文摘As a typical tight sandstone gasfield with strong heterogeneity,the Sulige Gas Field in the Ordos Basin faces major challenges in its development because the reservoirs in the gasfield are small in effective sand scale,rapid in lithologic change,strong in plane heterogeneity,and poor in connectivity.How to scientifically deploy development wells to improve the recovery is the most important issue for the successful development of this kind of gasfields.Therefore,a well inference analysis was conducted tofigure out the impact of well pattern density on the recovery based on the research of many years in gasfield development methods and the summary of practical effect.In this paper,we put forward for thefirst time the concept of inter-well interference probability,and present the relationship between the probability of inter-well interference and well pattern density of the Sulige Gas Field.Then we established a mathematical model for the optimization of development well pattern by combiningfine sand anatomy,reservoir engineering,numerical simulation and economic evaluation,and obtained a quantitative relationship between recovery and well pattern density.Furthermore,on the basis of comprehensive analysis,a reasonable development well pattern was designed for the Sulige Gas Field:this well pattern is parallelogram in shape,with a density of 3.1 wells/km2,well spacing of 500 m,and row spacing of 650 m.Development practices have confirmed that this scheme is capable of achieving better economic benefits,producing geological reserves as far as possible and improving the ultimate recovery of such gasfields.
基金supported by CNPC Scientific Research and Tech-nology Development Project"Enhanced gas Recovery Method Research and Pilot Test for Developed Gas Fields"(No.:2022KT0901).
文摘The Sulige Gas Field in the Ordos Basin is the largest tight gasfield in China,with proved reserves exceeding 2×10^(12)m^(3).As the main contributor to gas production in PetroChina Changqing Oilfield Company,The Sulige Gas Field is in the stage of stable production.Maximizing the stable production period is a focus and challenge for the gasfield now.To address a series of problems influencing the efficient development of Sulige gasfield,such as large-scale remaining gas reserves between wells/layers and low ratio of employed reserves,the main technologies for enhanced gas recovery(EGR)of tight gas reservoirs were developed by multidisciplinary research with respect to development geology,reservoir engineering,drilling and production process,and surface gathering and transportation.Experiments were conducted on reservoir description and remaining gas characterization,well pattern thickening optimization,vertical well separate-layer fracturing,horizontal-well multi-stage multi-cluster volume fracturing for their improvement and upgrading.The orientation of EGR for tight gas reservoirs is pro-posed.The following results are obtained.First,well pattern thickening optimization is the most important EGR method,which can increase the recovery rate by more than 6%.Second,based on continuous upgrading and promotion,either of reservoir stimulation technology and drainage gas recovery technology can increase the recovery rate by more than 2%.The gathering and transportation technology which further reduces the wellhead pressure can increase the recovery rate by about 1.5%.Third,the EGR technology should be oriented to maximize the quantity of employed reserves,especially by way of new technologies such asfine remaining gas characterization,well pattern/type optimization,cross-layer fracturing of a multi-thin-layer reservoir by horizontal wells,intelligent drainage gas recovery,and multi-stage pressurization.It is concluded that the development of key EGR technologies will help increase the recovery rate of The Sulige Gas Field by 10%e15%,and will provide an effective support for The Sulige Gas Field to maintain the production at 300108 m^(3)/a for a long term and for the Changqing gas province to increase the production to 500×10^(8)m^(3)/a,which will ultimately ensure the national energy security.
基金supported by the National Natural Science Foundation of China(grant No.42172167)China-ASEAN(Association of Southeast Asian Nations)Maritime Cooperation Fund Project(grant No.12120100500017001)。
文摘The characteristics of diagenetic minerals and their effects on reservoir quality of the tight sandstones of the Permian in Sulige gas field of the Ordos Basin were studied through observations on thin sections,scanning electron microscopy,energy dispersive spectroscopy analysis and electron microprobe analysis.Diagenetic minerals in the Permian sandstones consist of illite,kaolinite,chlorite,siliceous and calcite cements.Large amounts of intercrystalline pores between kaolinite and illite provide channels for acidic fluids flow and thereby were conducive to the formation of clastic solution pores,intergranular solution pores and composite pores.Authigenic chlorite occurs in the form of three morphotypes as grain-coating,pore-lining and pore-filling.Grain-coating and pore-lining chlorite with different crystal shapes occur as coatings on the framework grains.Pore-filling chlorite precipitated as discrete flaky plates in pore spaces.Quartz microcrystals developed but quartz overgrowth did not develop because of the occurrence of porelining chlorite.This,in turn,led to the preservation of primary pores by occupying potential nucleation sites for quartz overgrowth and thereby preventing quartz microcrystals from merging into quartz overgrowth.This process is regarded as the most important for influencing the quality of the lithophysical properties.Calcite cement was mainly precipitated during a late diagenetic stage and has a negative effect on the reservoir quality.This study provides important insights into analyzing the relationship between diagenetic minerals and reservoir quality and the results are directly applicable to the exploration and development of tight sandstone reservoirs all over the world.
基金The work was supported by the Science and Technology Major Project of PetroChina(No.2016E-05)Preliminary Project of PetroChina Exploration&Production Company(No.135YQZP-2017-KT11).
文摘Up to now,the Sulige area in Ordos Basin has the favorable exploration area of 55×10^(3) km^(2),the total reserve of natural gas of nearly 6×10^(12) m^(3) and the proven reserve(including basic proven reserve)of 4.77×10^(12) m^(3),where the annual production of natural gas reaches 23×10^(9) m^(3),and the Sulige gasfield is the largest onshore natural gas field in China.The pay zone of the Sulige gasfield mainly is Member 8 of Shihezi Formation and Member 1 of Shanxi Formation of Permian which belong to the typical tight sandstone gas reservoir.The coal measure strata in Carboniferous Benxi Formation,Permian Taiyuan Formation and Shanxi Formation provide abundant gas sources for the Gulige gas reservoirs.An open-flow sedimentary model of lacustrine delta is developed,the gentle bottom,sand supply from multisource,strong hydrodynamic force and multi-period superposition control the distribution of largearea reservoir sand body.Lithology of the reservoir is the sandstone of the fluvial-delta facies,the physical property is poor and the heterogeneity is strong,the average porosity ranges from 4%to 12%and the average permeability varies from 0.01 to 1 mD.The gas reservoir is characterized by wide hydrocarbon generation,pervasive hydrocarbon charging,short-range migration and massive accumulation.The pressure coefficient of the gas reservoir ranges from 0.62 to 0.90,indicating the low-pressure gas reservoir,and the single-well yield is low.Full digital seismic technique in the desert area,nonlongitudinal seismic technique in the loess plateau,accurate logging evaluation technique,tight sand reservoir stimulation technology and horizontal well development technology are key technologies for exploration and development of Sulige gasfield.
