The Lower Silurian Longmaxi Formation is a major horizon for shale gas development in the Changning block in Sichuan Basin.In this study,the fracture features in the Longmaxi Formation in the Changning block were inve...The Lower Silurian Longmaxi Formation is a major horizon for shale gas development in the Changning block in Sichuan Basin.In this study,the fracture features in the Longmaxi Formation in the Changning block were investigated through outcrop observation,core description,inclusion testing,and Fullbore Formation MicroImage logging.The results showed that tectogenetic shear fractures dominated the Longmaxi Formation,with maximum principal stress in the SSW,NW,and NE directions.According to fracture features and stress analysis,three phases of faults were generated by tectonic movements after the buried depth reached a maximum in the study area:phase 1 nearly EW-trending faults formed in the middle-late Yanshanian,phase 2 NE-trending faults formed from the end of the Yanshanian to the early Himalayan,and phase 3 NW-trending faults formed from the middle Himalayan to the present.According to the regression analysis of the tested shale gas production and faults,the faults with a throw of>200 m could have a great effect on gas production,and high-yield wells were generally located over 1 km away from faults.Based on the dissection of tectonic styles and typical wells drilled in the Changning block,three shale gas accumulation models were established:wide gentle syncline+internal smalxl fault,subdued anticline+large fault,and slope+internal fault.The study reveals the mechanism of fault influence on shale gas accumulation in the Longmaxi Formation in the Changning block and provides a reference for efficient shale gas production in the Sichuan Basin.展开更多
The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep wate...The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep water sedimentation , representing the main branch of the Palaeo - Tethys polyisland ocean in the Hercynian - Indo-sinian stage .This belt could be further subdivided into three tectono - lithofacies zones . In the east zone , terrigenous elastics , argillaceous ,marl-argillaceous and silicate sedi-ments lie on the metamorphosed Early Palaeozoic base ment in concealed unconformity , representing deep water sediments on a passive continental margin . The central zone , although the basement rocks are absent from outcropping here , includes a contemporary complex of various sedimentary types , among them one type is of deep ocean sediments represented by radiolarian bedded chert , appearing from at least early Early Devonian to the Middle Triassic . Another type includes pure carbonates of the Early Carboniferous to the Late Permian , a type of shallow water carbonate platform on seamount or oceanic plateau within an ocean basin . In the west zone , the Permo - Carboniferous terrigenous elastics , argillaceous and silicate sediments appear again -representing the passive continental slope sedimentation in the east of the Baoshan - Gengma massif .As the Permo-Carboniferous rock types,sedimentary environments and palaeontological characters of the east and west zones are quite similar , we hold that these two zones were originally formed all on the eastern continental slope of the Baoshan - Gengma massif , and were separated due to eastward thrust later in the Indosinian orogeny . Intense thrust compacting also resulted in tectonic melange in the central zone , which is displayed by shallow water carbonates overlapping on or embedded in deep water volcanics . In the Lancangjiang belt , the Permo - Carboniferous are very complicated in sedimentary types which include island arc volcanics , deep water turbidites, silicolites and shallow water carbonates , representing the active continental margin in the west of the Simao massif. Whether there existed by Early Permi an, a Lincang magma tic arc still awaits further evidence . From the Late Permian,both the Changning-Meng-lian belt and the Lancangjiang belt experienced important sedimentary and volanic events which took place contemporaneously or penecontemporaneously but with different characters . Evidence for the Lincang magmatic arc began to be apparent , and the turbidite deep water basin in the Lancangjiang belt closed . Nevertheless , the Palaeo - Tethys oceanic basin , represented by the Changning - Menglian suture zone , existed until the Mid-dle Triassic . In the Late Triassic . massifs of Baoshan -Gengma ,Simao - Lincang ,collided and aggregated ,resulting in the disappearance of the Palaeo - Tethys ocean .展开更多
Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A ser...Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A series of earthquakes with magnitudes up to 5.6 occurred during a short period after the mainshock,and we thus refer to these earthquakes as the Changning M6 earthquake sequence(or swarm).The mainshock was located very close to a salt mine,into which for^3 decades fresh water had been extensively injected through several wells at a depth of 2.7–3 km.It was also near(within^15 km)the epicenter of the 18 December 2018 M5.7 Xingwen earthquake,which is thought to have been induced by shale gas hydraulic fracturing(HF),prompting questions about the possible involvement of industrial activities in the M6 sequence.Following previous studies,this paper focuses on the relationship between injection and seismicity in the Shuanghe salt field and its adjacent Shangluo shale gas block.Except for a period of serious water loss after the start of cross-well injection in 2005–2006,the frequency of earthquakes shows a slightly increasing tendency.Overall,there is a good correlation between the event rate in the Shuanghe area and the loss of injected water.More than 400 M≥3 earthquakes,including 40 M≥4 and 5 M≥5 events,had been observed by the end of August 2019.Meanwhile,in the Shangluo area,seismicity has increased during drilling and HF operations(mostly in vertical wells)since about 2009,and dramatically since the end of 2014,coincident with the start of systematic HF in the area.The event rate shows a progressively increasing background with some fluctuations,paralleling the increase in HF operations.More than 700 M≥3 earthquakes,including 10 M≥4 and 3 M≥5 in spatially and temporally clustered seismic events,are correlated closely with active fracturing platforms.Well-resolved centroid moment tensor results for M≥4 earthquakes were shown to occur at very shallow depths around shale formations with active HF,in agreement with some of the clusters,which occurred within the coverage area of temporary or new permanent monitoring stations and thus have been precisely located.After the Xingwen M5.7 earthquake,seismic activity in the salt well area increased significantly.The Xingwen earthquake may have created a unidirectional rupture to the NNW,with an end point close to the NW-trending fault of the Shuanghe earthquake.Thus,a fault in the Changning anticline might have terminated the fault rupture of the Xingwen earthquake,possibly giving the Xingwen earthquake a role in promoting the Changning M6 event.展开更多
A continuous Ordovician-Silurian boundary section from the upper Wufeng Formation through the Kuanyinchiao Formation to the lower Lungmachi Formation has been carefully measured and collected at Shuanghe of Changning,...A continuous Ordovician-Silurian boundary section from the upper Wufeng Formation through the Kuanyinchiao Formation to the lower Lungmachi Formation has been carefully measured and collected at Shuanghe of Changning, southern Sichuan Province. For the first time, the temporal changes of α- and β-diversities of the Hirnantia fauna have been discussed in great detail. The general trend of brachiopod diversity change, increasing upward, is consistent with the regional trend of the Yangtze Platform, which had been controlled by both intrinsic and extrinsic factors. However, the sudden drop of diversity for a short period in the upper Kuanyinchiao Formation might have been controlled by environmental factors rather than normal faunal turnover. Synecological analysis using numerical methods recognizes two brachiopod-dominated associations of the Hirnantia fauna, the Dalmanella-Kinnella Association and the Mirorthis Association, both living in an offshore, deeper water environment corresponding to BA3-upper BA4, particularly lower BA3.展开更多
Hydraulic fracturing is a key technology in shale gas extraction,whether hydraulic fracturing induces earthquakes has become a hot topic in the public and the focus of scholars’research.The urgency of shale gas minin...Hydraulic fracturing is a key technology in shale gas extraction,whether hydraulic fracturing induces earthquakes has become a hot topic in the public and the focus of scholars’research.The urgency of shale gas mining and the catastrophic nature of earthquakes highlight the urgent need to study this issue.The Changning anticline at the southern margin of the Sichuan Basin is a key area for shale gas exploitation.Taking this as an example,this paper applies the velocity model of the study area to reposition the M5.7 magnitude earthquake on December 16,2018 and the M5.3 magnitude earthquake on January 03,2019 and their aftershock sequence in this area.Using shale gas exploration drilling and reflection seismic data to carry out structural analysis,and recovering the tectonic geological setting of earthquake occurrence by restoring the formation process of the Changning anticline,to further explore the seismic mechanism.Our results show that the Changning anticline is a large basement fault-bend fold,and the displacement of the fault forming the anticline is 18 km,and the Changning anticline absorbs 33%of the fault slip.The Silurian Longmaxi Formation of the Changning anticline experienced larger-parallel shearing along underlying basement faults,forming a micro-fracture system.The footwall ramp of the basement fault is reactivated at present,earthquakes in this area mostly occur along the footwall ramp of the basement fault and above and below it.The anticlinal and synclinal hinge zones are also the earthquake concentration areas,but the earthquake magnitude decreases upwards along the kink-band,and small earthquakes below M2.0 occur in the Silurian Longmaxi Formation.So far,the earthquake in the Changning anticline mainly occurred in the southern limb of the anticline,which is a natural earthquake formed along the footwall ramp of the basement fault.The earthquakes in the Changning area are possible related to the geo-tectonic setting for the southeast outward compression of the Qinghai-Tibet Plateau at present,the moderate or large-scale earthquakes in the southwest Sichuan Basin are mainly due to the reactivation during late Quaternary of the earlier formed faults.It is suggested to carry out scientific monitoring of seismic activities in shale gas development zones.展开更多
After several years of exploration practices in the Changning-Weiyuan national shale gas pilot zone,the industrial production has been achieved in a number of vertical and horizontal wells completed by SRV fracturing,...After several years of exploration practices in the Changning-Weiyuan national shale gas pilot zone,the industrial production has been achieved in a number of vertical and horizontal wells completed by SRV fracturing,and a series of independent shale gas reservoir stimulation technologies have come into being.Next,it is necessary to consider how to enhance the efficiency of fracturing by a factory-mode operation.This paper presents the deployment of Changning Well Pad A,the first cluster horizontal shale gas well group,and proposes the optimal design for the factory operation mode of this Pad according to the requirements of wellpad fracturing stimulation technologies and the mountainous landform in the Sichuan Basin.Accordingly,a zipper-fracturing mode was firstly adopted in the factory fracturing on wellpad.With the application of standardized field process,zipper operation,assembly line work,staggered placement of downhole fractures,and microseismic monitoring in real time,the speed of fracturing reached 3.16 stages a day on average,and the stimulated reservoir volume was maximized,which has fully revealed how the factory operation mode contributes to the large-scale SRV fracturing of horizontal shale gas cluster wells on wellpads in the aspect of speed and efficiency.Moreover,the fracturing process,operation mode,surface facilities and post-fracturing preliminary evaluation of the zipper-fracturing in the well group were examined comprehensively.It is concluded from the practice that the zipper-fracturing in the two wells enhanced the efficiency by 78%and stimulated reservoir volume by 50%compared with the single-well fracturing at the preliminary stage in this area.展开更多
In this study,we aim to clarify the structural characteristics and deformation process of the Changning anticline.We carefully interpret 38 two-dimensional(2D)seismic profiles in the study area and establish three-dim...In this study,we aim to clarify the structural characteristics and deformation process of the Changning anticline.We carefully interpret 38 two-dimensional(2D)seismic profiles in the study area and establish three-dimensional(3D)geometric and quantitative kinematic models of the Changning anticline.This study shows that the basement fault controls the formation of the Changning anticline.The fault slope of the main fault in the basement shows’steep in the upper and gentle in the lower’structural characteristics vertically,possessing obvious segmentary characteristics transversely and presents the overall characteristics of’steep in the east and gentle in the west’.Further analysis shows that the Changning anticline proceeds west and terminates at the boundary defined by current surface features but gradually disappears westward across the Mt.Huaying fault zone.Furthermore,we identified that deformation of the Changning anticline began during the early Yanshanian movement period.Under compressional stress from the southeast,the anticline slid forward along the basement fault until the end of the Yanshanian movement period,when the dominant WNW-ESE structure gradually emerged.Since the Himalayan movement period,a series of NE-trending structures have been formed in the anticline,owing to multi-directional compressive stress.展开更多
According to information from on-the-spot investigations, the tectonics of salt mining areas and digital seismic records, we studied the activity of earthquakes induced by water pumping in and out of the salt mines in...According to information from on-the-spot investigations, the tectonics of salt mining areas and digital seismic records, we studied the activity of earthquakes induced by water pumping in and out of the salt mines in Shuanghe town, Changning county, Sichuan Province. The study found that the rates of water injection and extraction in the Shuanghe salt mining region were evenly matched before April 2006 and earthquake activity was stable. On the other hand, shallow small and moderate earthquake numbers increased sharply after the water injection rate became much larger than the water extraction rate. Large injection over a long time may causes the permeation of water through pre-existing small fractures and micro-cracks in the Changning anticlinal and accelerate the rupture of micro tectonic formations in nearby regions, inducing small earthquake swarm activity. The Q value calculated by using digital earthquake records indicates a relatively inhomogeneous medium in this area. The results of the accurate location of small earthquakes show that sources are relatively shallow and are concentrated at a depth of 2km to 3km. Focal mechanism solutions reveal a normal dip-slip character of shallow earthquakes. All of these show certain characteristics of earthquake activity induced by water injection.展开更多
Identification of sweet spot is of great significance in confirming shale gas prospects to realize large-scale economic shale gas development.In this paper,geological characteristics of shale gas reservoirs were compa...Identification of sweet spot is of great significance in confirming shale gas prospects to realize large-scale economic shale gas development.In this paper,geological characteristics of shale gas reservoirs were compared and analyzed based on abundant data of domestic and foreign shale gas reservoirs.Key elements of sweet spots were illustrated,including net thickness of gas shale,total organic carbon(TOC)content,types and maturity(Ro)of organic matters,rock matrix and its physical properties(porosity and permeability),and development characteristics of natural fractures.After the data in Changning and Weiyuan blocks,the Sichuan Basin,were analyzed,the geologic laws of shale gas enrichment were summarized based on the economic exploitation characteristics of shale gas and the correlation between the elements.The elements of favorable“sweet spots”of marine shale gas reservoirs in the Changning block and their distribution characteristics were confirmed.Firstly,the quality of gas source rocks is ensured with the continuous thickness of effective gas shale larger than 30 m,TOC>2.0% and R_(o)=2.4-3.5%.Secondly,the quality of reservoir is ensured with the brittle minerals content being 30-69%,the clay mineral content lower than 30% and a single lamination thickness being 0.1-1.0 m.And thirdly,the porosity is higher than 2.0%,the permeability is larger than 50 nD,gas content is higher than 1.45 m^(3)/t,and formation is under normal pressure-overpressure system,which ensures the production modes and capacities.Finally,the primary and secondary elements that control the“sweet spots”of shale gas reservoirs were further analyzed and their restrictive relationships with each other were also discussed.展开更多
In recent years,great progress has been made in geologic evaluation,engineering test and development optimization of the Lower Cambrian Wufeng FmeLower Silurian Longmaxi Fm shale gas in the Sichuan Basin,and the main ...In recent years,great progress has been made in geologic evaluation,engineering test and development optimization of the Lower Cambrian Wufeng FmeLower Silurian Longmaxi Fm shale gas in the Sichuan Basin,and the main shale gas exploitation technologies have been un-derstood preliminarily.In addition,scale productivity construction has been completed in Jiaoshiba,Changning and Weiyuan blocks.In this paper,the Wufeng FmeLongmaxi Fm shale gas wells in Changning Block were taken as the study object to provide technical reference for the development design of similar shale-gas horizontal wells.The technology combining geology with engineering,dynamic with static,and statistical analysis with simulation prediction was applied to quantify the main factors controlling shale-gas well productivity,develop the shale-gas well production prediction model,and optimize the key technical parameters of geologic target of shale-gas horizontal wells in the block(e.g.roadway orientation,location and spacing,horizontal section length and gas well production index).In order to realize high productivity of shale gas wells,it is necessary to maximize the included angle between the horizontal section orientation and the maximum major stress and fracture development direction,deploy horizontal-well roadway in top-quality shale layers,and drill the horizontal section in type I reservoirs over 1000 m long.It is concluded that high productivity of shale gas wells is guaranteed by the horizontal-well wellbore integrity and the optimized low-viscosity slickwater and ceramsite fracturing technology for complex fracture creation.Based on the research results,the technical policies for shale gas development of Changning Block are prepared and a guidance and reference are provided for the shale gas development and productivity construction in the block and the development design of similar shale-gas horizontal wells.展开更多
The Changning region,located in the southern Sichuan Basin,has historically been regarded as tectonically stable.However,in recent years,seismicity has increased significantly alongside the expansion of large-scale in...The Changning region,located in the southern Sichuan Basin,has historically been regarded as tectonically stable.However,in recent years,seismicity has increased significantly alongside the expansion of large-scale industrial activities.The successive occurrences of the Xingwen MS5.7 and Changning MS6.0 earthquakes within a short interval have attracted considerable attention from both the seismological community and the public.To better understand the relationship between industrial activities and subsurface velocity structures,as well as their influence on seismicity,this study first selects a large number of high-quality P-and S-wave first arrival times from a dense array of temporary broadband seismic stations,and then conducts local earthquake traveltime tomography to invert for high-resolution P-and S-wave velocity models in the shallow crust beneath the Changning hydraulic fracturing zone.The results reveal that velocity heterogeneities are generally correlated well with stratigraphic age,while localized velocity anomalies near industrial extraction layers are associated with injection pressure variations.Moreover,a low P-wave velocity anomaly forms a continuous belt linking the Xingwen and Changning seismic zones,indicative of a deep subsurface fluid migration channel.Although alternative seismogenic mechanisms cannot be ruled out,this finding preferentially supports a hypothesis in which fluid migration along a long-distance channel activated by the Xingwen earthquake contributes to the initiation of the Changning earthquake.展开更多
The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely asso...The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely associated with induced seismic events.The present study was conducted to examine the role of halite in frictional properties.To this end,laboratory measurements were taken for simulated fault gouge composed of halite.Slide-hold-slide(SHS)shear experiments were performed on gouges with grain size<106 mm at constant normal stress from 5 MPa to 30 MPa and constant shear velocity in the range of 1-10 mm/s.Halite gouge shows higher frictional strength and frictional healing rate than most minerals.The results reveal that the fault within halite can potentially generate intense seismic events and more significant aftershocks.An increase in normal stress leads to a reduction in frictional healing,with frictional strength initially increasing and then decreasing.The elevated shear velocity following fault activation facilitates fault dilation,diminishes the frictional strength of the fault,and contributes to fault healing during the inter-seismic period.The aforementioned findings will contribute to a comprehensive understanding of the potential for the healing property of induced seismicity on faults containing halite,particularly in the Changning region of China.展开更多
In this paper,the Lower Silurian Longmaxi shale samples and the backflow fracturing fluid in the Changning Block of the Sichuan Basin were selected to investigate the damage mechanism of retained fracturing fluid to f...In this paper,the Lower Silurian Longmaxi shale samples and the backflow fracturing fluid in the Changning Block of the Sichuan Basin were selected to investigate the damage mechanism of retained fracturing fluid to fractures in shale gas reservoirs.Thus,experiments were conducted on fracturing fluid backflow and gas-driving fracturing fluids.The changes of liquid permeability of shale samples,solid particle size distribution and turbidity of the backflow fracturing fluid were monitored.The gas permeability before and after fracturing fluid gas drive was compared,and the damage degree and mechanism of the backflow fracturing fluid to the fractures in shale samples were analyzed.And the following research results were obtained.First,the damage rate of shale permeability after the fracturing fluid backflow is between 53.1%and 97.6%,and the range of the solid particle size of the flowback fluid is significantly reduced.The main reservoir damage modes include phase trapping damage caused by liquid phase retention,blockage caused by the solid phase residue,particle migration induced by gas-carrying liquid and salt precipitation.Second,in the stage of gas phase flow,the damage rate of permeability drops to 23.1-80.2%,and the damage caused by liquid phase retention is relieved,but the damage caused by the blockage of solid phase residue and the salt precipitation of flowback on the facture surface is inevitable.Third,based on the damage mechanism of fracturing fluid backflow in shale gas wells to fractures,considering the treatment difficulty of the flowback and its damage to reservoir fractures,it is recommended to give a full play to the fracturing capacity of fracturing fluid and optimize the properties and dosages of fracturing fluid so as to reduce the flowback of fracturing fluid as much as possible.展开更多
Studies on the origin of shale brittleness are of great significance to understanding shale gas accumulation laws.The current studies,however,mostly focus on the improvement of shale brittleness by biological quartz e...Studies on the origin of shale brittleness are of great significance to understanding shale gas accumulation laws.The current studies,however,mostly focus on the improvement of shale brittleness by biological quartz enrichment,but rarely on the recrystallization of quartz in the process of diagenetic evolution.In this paper,a series of researches were carried out on the Lower Silurian Longmaxi Fm marine shale in the Changning block of the Sichuan Basin.Firstly,shale pore,mineral component and bedding characteristics were observed by means of cathodoluminescence(CL),scanning electron microscope(SEM)and so on.Then,the control effects of quartz origin,overpressure environment and diagenetic evolution on shale brittleness were investigated by analyzing the mineral composition and siliceous composition of shale microscopically.Finally,the authigenic embrittlement model of marine shale was put forward and the geological significance of authigenic microcrystalline quartz to the improvement of shale brittleness in the process of diagenesis was illustrated.The following results were obtained.First,during the sedimentation,burial and diagenetic evolution,shale experiences diagenetic changes which help increase quartz content and form concealed fracture networks,thus benefiting the formation of complex flow pathways in later stimulation.Second,organic matters play a positive role in improving shale brittleness in the process of geological evolution.It promotes the formation of authigenic microcrystalline quartz and improves the brittleness of shale.In conclusion,due to the authigenic embrittlement of shale in the process of diagenesis,rock structure is changed,rock strength is enhanced and shale porosity is preserved.Consequently,reservoir space in shale is improved and the enrichment state of shale gas is modified.Therefore,the preservation condition under the control of tectonic movement factors is vital to geological evaluation on shale gas.In addition,marine shale is certainly well brittle after authigenic embrittlement in the process of diagenesis as long as its organic matter content is abundant.展开更多
In order to provide technical support for the shale gas exploration and development in the Lower Silurian Longmaxi Formation of the Sichuan Basin,this paper takes the Longmaxi Formation in the Changning and Fuling Sha...In order to provide technical support for the shale gas exploration and development in the Lower Silurian Longmaxi Formation of the Sichuan Basin,this paper takes the Longmaxi Formation in the Changning and Fuling Shale Gas Fields as the research object to quantitatively characterize the development characteristics of natural fractures in the Longmaxi Formation shale by means of helium pycnometry,X-ray diffraction(XRD),true density testing and other methods,with the aid of the modified petrophysical model.Then,the development types and genetic mechanisms of natural fractures and their influences on shale gas development are discussed.The following research results are obtained.First,the modified petrophysical model can accurately describe the pore system in the Changning shale with a fitting rate of 0.74.Second,the development of natural fractures in shale is different in various regions.The natural fractures in the Changning Shale Gas Field,controlled by basement thrust faults,decollement layers and internal folds,are locally developed and filled with calcareous,and the average fracture porosity is 0.15%.In the Fuling Shale Gas Field,however,natural fractures,mainly controlled by reverse faults and slippage effect,are commonly more developed and unfilled or semi-filled with siliceous,and the average fracture porosity is 1.30%.Third,under the formation conditions,the opening of natural fractures is different.The natural fractures in the Changning Shale Gas Field are basically closed with weaker flowing ability,while those in the Fuling Shale Gas Field are relatively open with stronger flowing ability.Fourth,the occurrence mode of shale gas is influenced by natural fractures,and it is internally dominated by free gas.The initial gas production of shale gas wells is higher.In conclusion,(1)the regression coefficient is introduced to calculate the actual total organic matter content,which promotes the modified petrophysical model to describe matrix pores and fracture pores more accurately;(2)the development of natural fractures in the shale producing pay of the Sichuan Basin is relatively beneficial to shale gas enrichment and exploitation,but the flowing ability of the natural fractures will be weakened under the original formation conditions.展开更多
So far,large-scale development of shale gas wells above 3500 m in the Changning Block of the Sichuan Basin has been realized by means of the large-scale hydraulic fracturing technology.As the main process parameters a...So far,large-scale development of shale gas wells above 3500 m in the Changning Block of the Sichuan Basin has been realized by means of the large-scale hydraulic fracturing technology.As the main process parameters arefinally set,however,the improvement rate of its stimulation effect tends to slow down,while in North America,single-well production has increased significantly by shortening cluster spacing and increasing proppant volumes.In order to provide a reliable practice basis for optimizing the parameters of shale gas fracturing process,this paper analyzes the productivity increasing mechanism of the new fracturing technology of intensive stageþhigh-intensity proppant injection by virtue of the model for calculating induced stress and multi-stage and multi-cluster productivity of horizontal wells.And accordingly,the main en-gineering factors of fracturing stimulation technology were ascertained.Then,after the pilot test scheme on this new fracturing technology was formulated according to the geological parameters of this block,the pilot test was carried out.Finally,the fracturing process parameters were optimized based on actual production effects and experimental results.And the following research results were obtained.First,shortening the spacing between main fractures,increasing the interference degree of induced stress and improving the stimulation degree of hydraulic fractures to shale reservoirs are the technical keys to the intense stage,and increasing the proppant volume,reducing the influence degree of proppant embedding and breaking on the attenuation of fracture conductivity and ensuring the long-term conductivity of propped fractures are the internal causes of significant production increase through high-intensity proppant injection.Second,the optimized implementation parameters of this new process in the Changning Block are as follows.The cluster spacing is in the range of 15e20 m,the proppant injection intensity is 2.0e2.5 t/m,and the liquid consuming intensity is 30e35 m3/m.It is concluded that this new process increases the single-well production of shale gas wells and the development benefit of the Changning Block and provides technical support for improving the comprehensive development benefit of shale gas wells in this block.展开更多
Horizontal shale gas well fracturing is mostly carried out by pumping bridge plugs.In the case of casing deformation,the bridge plug can not be pumped down to the designated position,so the hole sections below the def...Horizontal shale gas well fracturing is mostly carried out by pumping bridge plugs.In the case of casing deformation,the bridge plug can not be pumped down to the designated position,so the hole sections below the deformation could not be stimulated according to the design program.About 30%of horizontal shale gas wells in the Changning and Weiyuan Blocks,Sichuan Basin,suffer various casing deformation after fracturing.Previously,the hole sections which could not be stimulated due to casing deformation were generally abandoned.As a result,the resources controlled by shale gas wells weren't exploited effectively and the fracturing effect was impacted greatly.There are a lot of difficulties in investigating casing deformation,such as complex mechanisms,various influencing factors and unpredictable deformation time.Therefore,it is especially important to seek a staged fracturing technology suitable for the casing deformation sections.In this paper,the staged fracturing technology with sand plugs inside fractures and the staged fracturing technology with temporary plugging balls were tested in casing deformation wells.The staged fracturing technology with sand plugs inside fractures was carried out in the mode of single-stage perforation and single-stage fracturing.The staged fracturing technology with temporary plugging balls was conducted in the mode of single perforation,continuous fracturing and staged ball dropping.Then,two kinds of technologies were compared in terms of their advantages and disadvantages.Finally,they were tested on site.According to the pressure response,the pressure monitoring of the adjacent wells and the microseismic monitoring in the process of actual fracturing,both technologies are effective in the stimulation of the casing deformation sections,realizing well control reserves efficiently and guaranteeing fracturing effects.展开更多
As shale gas development is advancing continuously and rapidly,how to deeply analyze the production performance of shale gas wells and evaluate their production characteristics has become an urgent problem in the eval...As shale gas development is advancing continuously and rapidly,how to deeply analyze the production performance of shale gas wells and evaluate their production characteristics has become an urgent problem in the evaluation of shale gas productivity construction zone,the formulation of new area development scheme and the preparation of planning program.Some scholars have applied the Logical Growth Model(LGM)in the production decline analysis of unconventional gas wells,but the influences of shale gas reservoir and development characteristics are not taken into consideration.Therefore,this method still has some space of further development and improvement.In this paper,a Logistic Growth Model considering shale gas reservoirs and development characteristics(RB-LGM)was established based on the previous research results.Then,it was applied to the shale gas development wells in the Changning Block of the Sichuan Basin to analyze their production performance,and the analysis results were compared with thefitting and prediction results provided by the Arps hyperbolic decline model.Finally,the optimal well spacing of horizontal wells was determined using RB-LGM.And the following research results were obtained.First,shale gas is produced by deploying horizontal wells in the clustered pattern in a large number,so on the basis of LGM,RB-LGM takes shale gas reservoir parameters(thickness,shale density,gas content)and development parameters(horizontal section length,well spacing and recovery factor)as the logic control factors of horizontal-well gas productionfitting,so that the production prediction result of gas well is more reasonable.Second,RB-LGM can not only wellfit the early production data of gas well,but ensure the convergence of the later prediction results under the control of logical conditions.Third,RB-LGM takes into account the influence of shale gas reservoir and development characteristics so as to optimize the horizontal well pattern and analyze the change trend of reservoir parameters in the development area through data inversion.展开更多
The dual-level bar counter,Braille floor plan on the wall and sign language board collectively define the compact pub hidden in Shanghai's Changning District-a space created for people including those with disabil...The dual-level bar counter,Braille floor plan on the wall and sign language board collectively define the compact pub hidden in Shanghai's Changning District-a space created for people including those with disabilities.展开更多
基金supported by The Science and Technology Project of CNPC,China(Grant No.2023ZZ21)Research Project of PetroChina Southwest Oil&Gas Field Company,China(Grant No.20220304-19)Research Project of PetroChina Southwest Oil&Gas Field Company,China(Grant No.20220304-08).
文摘The Lower Silurian Longmaxi Formation is a major horizon for shale gas development in the Changning block in Sichuan Basin.In this study,the fracture features in the Longmaxi Formation in the Changning block were investigated through outcrop observation,core description,inclusion testing,and Fullbore Formation MicroImage logging.The results showed that tectogenetic shear fractures dominated the Longmaxi Formation,with maximum principal stress in the SSW,NW,and NE directions.According to fracture features and stress analysis,three phases of faults were generated by tectonic movements after the buried depth reached a maximum in the study area:phase 1 nearly EW-trending faults formed in the middle-late Yanshanian,phase 2 NE-trending faults formed from the end of the Yanshanian to the early Himalayan,and phase 3 NW-trending faults formed from the middle Himalayan to the present.According to the regression analysis of the tested shale gas production and faults,the faults with a throw of>200 m could have a great effect on gas production,and high-yield wells were generally located over 1 km away from faults.Based on the dissection of tectonic styles and typical wells drilled in the Changning block,three shale gas accumulation models were established:wide gentle syncline+internal smalxl fault,subdued anticline+large fault,and slope+internal fault.The study reveals the mechanism of fault influence on shale gas accumulation in the Longmaxi Formation in the Changning block and provides a reference for efficient shale gas production in the Sichuan Basin.
文摘The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep water sedimentation , representing the main branch of the Palaeo - Tethys polyisland ocean in the Hercynian - Indo-sinian stage .This belt could be further subdivided into three tectono - lithofacies zones . In the east zone , terrigenous elastics , argillaceous ,marl-argillaceous and silicate sedi-ments lie on the metamorphosed Early Palaeozoic base ment in concealed unconformity , representing deep water sediments on a passive continental margin . The central zone , although the basement rocks are absent from outcropping here , includes a contemporary complex of various sedimentary types , among them one type is of deep ocean sediments represented by radiolarian bedded chert , appearing from at least early Early Devonian to the Middle Triassic . Another type includes pure carbonates of the Early Carboniferous to the Late Permian , a type of shallow water carbonate platform on seamount or oceanic plateau within an ocean basin . In the west zone , the Permo - Carboniferous terrigenous elastics , argillaceous and silicate sediments appear again -representing the passive continental slope sedimentation in the east of the Baoshan - Gengma massif .As the Permo-Carboniferous rock types,sedimentary environments and palaeontological characters of the east and west zones are quite similar , we hold that these two zones were originally formed all on the eastern continental slope of the Baoshan - Gengma massif , and were separated due to eastward thrust later in the Indosinian orogeny . Intense thrust compacting also resulted in tectonic melange in the central zone , which is displayed by shallow water carbonates overlapping on or embedded in deep water volcanics . In the Lancangjiang belt , the Permo - Carboniferous are very complicated in sedimentary types which include island arc volcanics , deep water turbidites, silicolites and shallow water carbonates , representing the active continental margin in the west of the Simao massif. Whether there existed by Early Permi an, a Lincang magma tic arc still awaits further evidence . From the Late Permian,both the Changning-Meng-lian belt and the Lancangjiang belt experienced important sedimentary and volanic events which took place contemporaneously or penecontemporaneously but with different characters . Evidence for the Lincang magmatic arc began to be apparent , and the turbidite deep water basin in the Lancangjiang belt closed . Nevertheless , the Palaeo - Tethys oceanic basin , represented by the Changning - Menglian suture zone , existed until the Mid-dle Triassic . In the Late Triassic . massifs of Baoshan -Gengma ,Simao - Lincang ,collided and aggregated ,resulting in the disappearance of the Palaeo - Tethys ocean .
基金the State Scholarship Fund of China (No. 201804190004)
文摘Late at night on 17 June 2019,a magnitude 6.0 earthquake struck Shuanghe Town and its surrounding area in Changning County,Sichuan,China,becoming the largest earthquake recorded within the southern Sichuan Basin.A series of earthquakes with magnitudes up to 5.6 occurred during a short period after the mainshock,and we thus refer to these earthquakes as the Changning M6 earthquake sequence(or swarm).The mainshock was located very close to a salt mine,into which for^3 decades fresh water had been extensively injected through several wells at a depth of 2.7–3 km.It was also near(within^15 km)the epicenter of the 18 December 2018 M5.7 Xingwen earthquake,which is thought to have been induced by shale gas hydraulic fracturing(HF),prompting questions about the possible involvement of industrial activities in the M6 sequence.Following previous studies,this paper focuses on the relationship between injection and seismicity in the Shuanghe salt field and its adjacent Shangluo shale gas block.Except for a period of serious water loss after the start of cross-well injection in 2005–2006,the frequency of earthquakes shows a slightly increasing tendency.Overall,there is a good correlation between the event rate in the Shuanghe area and the loss of injected water.More than 400 M≥3 earthquakes,including 40 M≥4 and 5 M≥5 events,had been observed by the end of August 2019.Meanwhile,in the Shangluo area,seismicity has increased during drilling and HF operations(mostly in vertical wells)since about 2009,and dramatically since the end of 2014,coincident with the start of systematic HF in the area.The event rate shows a progressively increasing background with some fluctuations,paralleling the increase in HF operations.More than 700 M≥3 earthquakes,including 10 M≥4 and 3 M≥5 in spatially and temporally clustered seismic events,are correlated closely with active fracturing platforms.Well-resolved centroid moment tensor results for M≥4 earthquakes were shown to occur at very shallow depths around shale formations with active HF,in agreement with some of the clusters,which occurred within the coverage area of temporary or new permanent monitoring stations and thus have been precisely located.After the Xingwen M5.7 earthquake,seismic activity in the salt well area increased significantly.The Xingwen earthquake may have created a unidirectional rupture to the NNW,with an end point close to the NW-trending fault of the Shuanghe earthquake.Thus,a fault in the Changning anticline might have terminated the fault rupture of the Xingwen earthquake,possibly giving the Xingwen earthquake a role in promoting the Changning M6 event.
基金supported by the Chinese Academy of Sciences (KZCX2-YW-Q05-01)the Ministry of Science and Technology of China (2006FY120300-5)the National Natural Science Foundation of China (40825006, 40972020), and the State Key Laboratory of Palaeobiology and Stratigraphy of NIGPAS
文摘A continuous Ordovician-Silurian boundary section from the upper Wufeng Formation through the Kuanyinchiao Formation to the lower Lungmachi Formation has been carefully measured and collected at Shuanghe of Changning, southern Sichuan Province. For the first time, the temporal changes of α- and β-diversities of the Hirnantia fauna have been discussed in great detail. The general trend of brachiopod diversity change, increasing upward, is consistent with the regional trend of the Yangtze Platform, which had been controlled by both intrinsic and extrinsic factors. However, the sudden drop of diversity for a short period in the upper Kuanyinchiao Formation might have been controlled by environmental factors rather than normal faunal turnover. Synecological analysis using numerical methods recognizes two brachiopod-dominated associations of the Hirnantia fauna, the Dalmanella-Kinnella Association and the Mirorthis Association, both living in an offshore, deeper water environment corresponding to BA3-upper BA4, particularly lower BA3.
基金Supported by the National Natural Science Foundation of China(41430316,40739906,41272237).
文摘Hydraulic fracturing is a key technology in shale gas extraction,whether hydraulic fracturing induces earthquakes has become a hot topic in the public and the focus of scholars’research.The urgency of shale gas mining and the catastrophic nature of earthquakes highlight the urgent need to study this issue.The Changning anticline at the southern margin of the Sichuan Basin is a key area for shale gas exploitation.Taking this as an example,this paper applies the velocity model of the study area to reposition the M5.7 magnitude earthquake on December 16,2018 and the M5.3 magnitude earthquake on January 03,2019 and their aftershock sequence in this area.Using shale gas exploration drilling and reflection seismic data to carry out structural analysis,and recovering the tectonic geological setting of earthquake occurrence by restoring the formation process of the Changning anticline,to further explore the seismic mechanism.Our results show that the Changning anticline is a large basement fault-bend fold,and the displacement of the fault forming the anticline is 18 km,and the Changning anticline absorbs 33%of the fault slip.The Silurian Longmaxi Formation of the Changning anticline experienced larger-parallel shearing along underlying basement faults,forming a micro-fracture system.The footwall ramp of the basement fault is reactivated at present,earthquakes in this area mostly occur along the footwall ramp of the basement fault and above and below it.The anticlinal and synclinal hinge zones are also the earthquake concentration areas,but the earthquake magnitude decreases upwards along the kink-band,and small earthquakes below M2.0 occur in the Silurian Longmaxi Formation.So far,the earthquake in the Changning anticline mainly occurred in the southern limb of the anticline,which is a natural earthquake formed along the footwall ramp of the basement fault.The earthquakes in the Changning area are possible related to the geo-tectonic setting for the southeast outward compression of the Qinghai-Tibet Plateau at present,the moderate or large-scale earthquakes in the southwest Sichuan Basin are mainly due to the reactivation during late Quaternary of the earlier formed faults.It is suggested to carry out scientific monitoring of seismic activities in shale gas development zones.
文摘After several years of exploration practices in the Changning-Weiyuan national shale gas pilot zone,the industrial production has been achieved in a number of vertical and horizontal wells completed by SRV fracturing,and a series of independent shale gas reservoir stimulation technologies have come into being.Next,it is necessary to consider how to enhance the efficiency of fracturing by a factory-mode operation.This paper presents the deployment of Changning Well Pad A,the first cluster horizontal shale gas well group,and proposes the optimal design for the factory operation mode of this Pad according to the requirements of wellpad fracturing stimulation technologies and the mountainous landform in the Sichuan Basin.Accordingly,a zipper-fracturing mode was firstly adopted in the factory fracturing on wellpad.With the application of standardized field process,zipper operation,assembly line work,staggered placement of downhole fractures,and microseismic monitoring in real time,the speed of fracturing reached 3.16 stages a day on average,and the stimulated reservoir volume was maximized,which has fully revealed how the factory operation mode contributes to the large-scale SRV fracturing of horizontal shale gas cluster wells on wellpads in the aspect of speed and efficiency.Moreover,the fracturing process,operation mode,surface facilities and post-fracturing preliminary evaluation of the zipper-fracturing in the well group were examined comprehensively.It is concluded from the practice that the zipper-fracturing in the two wells enhanced the efficiency by 78%and stimulated reservoir volume by 50%compared with the single-well fracturing at the preliminary stage in this area.
基金supported by the National Natural Science Foundation of China(Grant No.U19B6003-01)。
文摘In this study,we aim to clarify the structural characteristics and deformation process of the Changning anticline.We carefully interpret 38 two-dimensional(2D)seismic profiles in the study area and establish three-dimensional(3D)geometric and quantitative kinematic models of the Changning anticline.This study shows that the basement fault controls the formation of the Changning anticline.The fault slope of the main fault in the basement shows’steep in the upper and gentle in the lower’structural characteristics vertically,possessing obvious segmentary characteristics transversely and presents the overall characteristics of’steep in the east and gentle in the west’.Further analysis shows that the Changning anticline proceeds west and terminates at the boundary defined by current surface features but gradually disappears westward across the Mt.Huaying fault zone.Furthermore,we identified that deformation of the Changning anticline began during the early Yanshanian movement period.Under compressional stress from the southeast,the anticline slid forward along the basement fault until the end of the Yanshanian movement period,when the dominant WNW-ESE structure gradually emerged.Since the Himalayan movement period,a series of NE-trending structures have been formed in the anticline,owing to multi-directional compressive stress.
基金Key Project in the National Science and Technology Pillar Program in the Eleventh"Five-year Plan" Period (2006BA01B02-01-01)Project in the National Science and Technology Pillar Program(2006BAC01B04),China
文摘According to information from on-the-spot investigations, the tectonics of salt mining areas and digital seismic records, we studied the activity of earthquakes induced by water pumping in and out of the salt mines in Shuanghe town, Changning county, Sichuan Province. The study found that the rates of water injection and extraction in the Shuanghe salt mining region were evenly matched before April 2006 and earthquake activity was stable. On the other hand, shallow small and moderate earthquake numbers increased sharply after the water injection rate became much larger than the water extraction rate. Large injection over a long time may causes the permeation of water through pre-existing small fractures and micro-cracks in the Changning anticlinal and accelerate the rupture of micro tectonic formations in nearby regions, inducing small earthquake swarm activity. The Q value calculated by using digital earthquake records indicates a relatively inhomogeneous medium in this area. The results of the accurate location of small earthquakes show that sources are relatively shallow and are concentrated at a depth of 2km to 3km. Focal mechanism solutions reveal a normal dip-slip character of shallow earthquakes. All of these show certain characteristics of earthquake activity induced by water injection.
基金Project supported by the National Natural Science Foundation of China,“Comparative Study on Elements of Sweet Spots of Shale Oil and Shale Gas”(Grant No.41472123).
文摘Identification of sweet spot is of great significance in confirming shale gas prospects to realize large-scale economic shale gas development.In this paper,geological characteristics of shale gas reservoirs were compared and analyzed based on abundant data of domestic and foreign shale gas reservoirs.Key elements of sweet spots were illustrated,including net thickness of gas shale,total organic carbon(TOC)content,types and maturity(Ro)of organic matters,rock matrix and its physical properties(porosity and permeability),and development characteristics of natural fractures.After the data in Changning and Weiyuan blocks,the Sichuan Basin,were analyzed,the geologic laws of shale gas enrichment were summarized based on the economic exploitation characteristics of shale gas and the correlation between the elements.The elements of favorable“sweet spots”of marine shale gas reservoirs in the Changning block and their distribution characteristics were confirmed.Firstly,the quality of gas source rocks is ensured with the continuous thickness of effective gas shale larger than 30 m,TOC>2.0% and R_(o)=2.4-3.5%.Secondly,the quality of reservoir is ensured with the brittle minerals content being 30-69%,the clay mineral content lower than 30% and a single lamination thickness being 0.1-1.0 m.And thirdly,the porosity is higher than 2.0%,the permeability is larger than 50 nD,gas content is higher than 1.45 m^(3)/t,and formation is under normal pressure-overpressure system,which ensures the production modes and capacities.Finally,the primary and secondary elements that control the“sweet spots”of shale gas reservoirs were further analyzed and their restrictive relationships with each other were also discussed.
文摘In recent years,great progress has been made in geologic evaluation,engineering test and development optimization of the Lower Cambrian Wufeng FmeLower Silurian Longmaxi Fm shale gas in the Sichuan Basin,and the main shale gas exploitation technologies have been un-derstood preliminarily.In addition,scale productivity construction has been completed in Jiaoshiba,Changning and Weiyuan blocks.In this paper,the Wufeng FmeLongmaxi Fm shale gas wells in Changning Block were taken as the study object to provide technical reference for the development design of similar shale-gas horizontal wells.The technology combining geology with engineering,dynamic with static,and statistical analysis with simulation prediction was applied to quantify the main factors controlling shale-gas well productivity,develop the shale-gas well production prediction model,and optimize the key technical parameters of geologic target of shale-gas horizontal wells in the block(e.g.roadway orientation,location and spacing,horizontal section length and gas well production index).In order to realize high productivity of shale gas wells,it is necessary to maximize the included angle between the horizontal section orientation and the maximum major stress and fracture development direction,deploy horizontal-well roadway in top-quality shale layers,and drill the horizontal section in type I reservoirs over 1000 m long.It is concluded that high productivity of shale gas wells is guaranteed by the horizontal-well wellbore integrity and the optimized low-viscosity slickwater and ceramsite fracturing technology for complex fracture creation.Based on the research results,the technical policies for shale gas development of Changning Block are prepared and a guidance and reference are provided for the shale gas development and productivity construction in the block and the development design of similar shale-gas horizontal wells.
基金supported by the National Key Research and Development Program of China(Grant No.2020YFA0710600)the National Natural Science Foundation of China(Grant No.U23A2029)。
文摘The Changning region,located in the southern Sichuan Basin,has historically been regarded as tectonically stable.However,in recent years,seismicity has increased significantly alongside the expansion of large-scale industrial activities.The successive occurrences of the Xingwen MS5.7 and Changning MS6.0 earthquakes within a short interval have attracted considerable attention from both the seismological community and the public.To better understand the relationship between industrial activities and subsurface velocity structures,as well as their influence on seismicity,this study first selects a large number of high-quality P-and S-wave first arrival times from a dense array of temporary broadband seismic stations,and then conducts local earthquake traveltime tomography to invert for high-resolution P-and S-wave velocity models in the shallow crust beneath the Changning hydraulic fracturing zone.The results reveal that velocity heterogeneities are generally correlated well with stratigraphic age,while localized velocity anomalies near industrial extraction layers are associated with injection pressure variations.Moreover,a low P-wave velocity anomaly forms a continuous belt linking the Xingwen and Changning seismic zones,indicative of a deep subsurface fluid migration channel.Although alternative seismogenic mechanisms cannot be ruled out,this finding preferentially supports a hypothesis in which fluid migration along a long-distance channel activated by the Xingwen earthquake contributes to the initiation of the Changning earthquake.
基金supported by the National Key Research and Development Project(Grant No.2023YFE0110900)the National Natural Science Foundation of China(Grant Nos.42320104003 and 42077247).
文摘The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely associated with induced seismic events.The present study was conducted to examine the role of halite in frictional properties.To this end,laboratory measurements were taken for simulated fault gouge composed of halite.Slide-hold-slide(SHS)shear experiments were performed on gouges with grain size<106 mm at constant normal stress from 5 MPa to 30 MPa and constant shear velocity in the range of 1-10 mm/s.Halite gouge shows higher frictional strength and frictional healing rate than most minerals.The results reveal that the fault within halite can potentially generate intense seismic events and more significant aftershocks.An increase in normal stress leads to a reduction in frictional healing,with frictional strength initially increasing and then decreasing.The elevated shear velocity following fault activation facilitates fault dilation,diminishes the frictional strength of the fault,and contributes to fault healing during the inter-seismic period.The aforementioned findings will contribute to a comprehensive understanding of the potential for the healing property of induced seismicity on faults containing halite,particularly in the Changning region of China.
基金supported by General Program of National Natural Science Foundation of China"Study on the gas transmission mechanism for permeability improvement and acceleration through oxidation-assisted cracking in organic matter-enriched shale"(No.:51674209)Major Breeding Project of Sichuan Provincial Colleges,Universities for Conversion of Scientific&Technological Achievements"Method of improving gas recovery of organic matter-enriched shale gas reservoirs"(No.:17CZ0040)2017 Science&Technology Project of PetroChina Southwest Oil&Gasfield Company"Study on the interaction mechanism of shale and fracturing fluids and flowback rules in the Changning Block"(No.20170302-03).
文摘In this paper,the Lower Silurian Longmaxi shale samples and the backflow fracturing fluid in the Changning Block of the Sichuan Basin were selected to investigate the damage mechanism of retained fracturing fluid to fractures in shale gas reservoirs.Thus,experiments were conducted on fracturing fluid backflow and gas-driving fracturing fluids.The changes of liquid permeability of shale samples,solid particle size distribution and turbidity of the backflow fracturing fluid were monitored.The gas permeability before and after fracturing fluid gas drive was compared,and the damage degree and mechanism of the backflow fracturing fluid to the fractures in shale samples were analyzed.And the following research results were obtained.First,the damage rate of shale permeability after the fracturing fluid backflow is between 53.1%and 97.6%,and the range of the solid particle size of the flowback fluid is significantly reduced.The main reservoir damage modes include phase trapping damage caused by liquid phase retention,blockage caused by the solid phase residue,particle migration induced by gas-carrying liquid and salt precipitation.Second,in the stage of gas phase flow,the damage rate of permeability drops to 23.1-80.2%,and the damage caused by liquid phase retention is relieved,but the damage caused by the blockage of solid phase residue and the salt precipitation of flowback on the facture surface is inevitable.Third,based on the damage mechanism of fracturing fluid backflow in shale gas wells to fractures,considering the treatment difficulty of the flowback and its damage to reservoir fractures,it is recommended to give a full play to the fracturing capacity of fracturing fluid and optimize the properties and dosages of fracturing fluid so as to reduce the flowback of fracturing fluid as much as possible.
基金supported by the National Major Science and Technology Project“Shale gas enrichment conditions and play evaluation technologies and their application in the Sichuan Basin and its periphery”(No.:2017ZX05035).
文摘Studies on the origin of shale brittleness are of great significance to understanding shale gas accumulation laws.The current studies,however,mostly focus on the improvement of shale brittleness by biological quartz enrichment,but rarely on the recrystallization of quartz in the process of diagenetic evolution.In this paper,a series of researches were carried out on the Lower Silurian Longmaxi Fm marine shale in the Changning block of the Sichuan Basin.Firstly,shale pore,mineral component and bedding characteristics were observed by means of cathodoluminescence(CL),scanning electron microscope(SEM)and so on.Then,the control effects of quartz origin,overpressure environment and diagenetic evolution on shale brittleness were investigated by analyzing the mineral composition and siliceous composition of shale microscopically.Finally,the authigenic embrittlement model of marine shale was put forward and the geological significance of authigenic microcrystalline quartz to the improvement of shale brittleness in the process of diagenesis was illustrated.The following results were obtained.First,during the sedimentation,burial and diagenetic evolution,shale experiences diagenetic changes which help increase quartz content and form concealed fracture networks,thus benefiting the formation of complex flow pathways in later stimulation.Second,organic matters play a positive role in improving shale brittleness in the process of geological evolution.It promotes the formation of authigenic microcrystalline quartz and improves the brittleness of shale.In conclusion,due to the authigenic embrittlement of shale in the process of diagenesis,rock structure is changed,rock strength is enhanced and shale porosity is preserved.Consequently,reservoir space in shale is improved and the enrichment state of shale gas is modified.Therefore,the preservation condition under the control of tectonic movement factors is vital to geological evaluation on shale gas.In addition,marine shale is certainly well brittle after authigenic embrittlement in the process of diagenesis as long as its organic matter content is abundant.
基金Project supported by the National Major Science and Technology Project“Formation and Enrichment Conditions of Shale Gas in the Sichuan Basin and Its Surrounding Areas,Technologies for Selecting Regions,Evaluation and Applications”(No.:2017ZX05035)。
文摘In order to provide technical support for the shale gas exploration and development in the Lower Silurian Longmaxi Formation of the Sichuan Basin,this paper takes the Longmaxi Formation in the Changning and Fuling Shale Gas Fields as the research object to quantitatively characterize the development characteristics of natural fractures in the Longmaxi Formation shale by means of helium pycnometry,X-ray diffraction(XRD),true density testing and other methods,with the aid of the modified petrophysical model.Then,the development types and genetic mechanisms of natural fractures and their influences on shale gas development are discussed.The following research results are obtained.First,the modified petrophysical model can accurately describe the pore system in the Changning shale with a fitting rate of 0.74.Second,the development of natural fractures in shale is different in various regions.The natural fractures in the Changning Shale Gas Field,controlled by basement thrust faults,decollement layers and internal folds,are locally developed and filled with calcareous,and the average fracture porosity is 0.15%.In the Fuling Shale Gas Field,however,natural fractures,mainly controlled by reverse faults and slippage effect,are commonly more developed and unfilled or semi-filled with siliceous,and the average fracture porosity is 1.30%.Third,under the formation conditions,the opening of natural fractures is different.The natural fractures in the Changning Shale Gas Field are basically closed with weaker flowing ability,while those in the Fuling Shale Gas Field are relatively open with stronger flowing ability.Fourth,the occurrence mode of shale gas is influenced by natural fractures,and it is internally dominated by free gas.The initial gas production of shale gas wells is higher.In conclusion,(1)the regression coefficient is introduced to calculate the actual total organic matter content,which promotes the modified petrophysical model to describe matrix pores and fracture pores more accurately;(2)the development of natural fractures in the shale producing pay of the Sichuan Basin is relatively beneficial to shale gas enrichment and exploitation,but the flowing ability of the natural fractures will be weakened under the original formation conditions.
基金supported by the National Major Science and Technology Project"Changning-Weiyuan Shale Gas Development Demonstration Project"(No.:2016ZX05062)PetroChina Major Science and Technology Project"Research and Application of Key Technologies in Gas Production of 30 billion cubic meters in Southwest Oil&Gas Field Company"(No.:2016E-0612).
文摘So far,large-scale development of shale gas wells above 3500 m in the Changning Block of the Sichuan Basin has been realized by means of the large-scale hydraulic fracturing technology.As the main process parameters arefinally set,however,the improvement rate of its stimulation effect tends to slow down,while in North America,single-well production has increased significantly by shortening cluster spacing and increasing proppant volumes.In order to provide a reliable practice basis for optimizing the parameters of shale gas fracturing process,this paper analyzes the productivity increasing mechanism of the new fracturing technology of intensive stageþhigh-intensity proppant injection by virtue of the model for calculating induced stress and multi-stage and multi-cluster productivity of horizontal wells.And accordingly,the main en-gineering factors of fracturing stimulation technology were ascertained.Then,after the pilot test scheme on this new fracturing technology was formulated according to the geological parameters of this block,the pilot test was carried out.Finally,the fracturing process parameters were optimized based on actual production effects and experimental results.And the following research results were obtained.First,shortening the spacing between main fractures,increasing the interference degree of induced stress and improving the stimulation degree of hydraulic fractures to shale reservoirs are the technical keys to the intense stage,and increasing the proppant volume,reducing the influence degree of proppant embedding and breaking on the attenuation of fracture conductivity and ensuring the long-term conductivity of propped fractures are the internal causes of significant production increase through high-intensity proppant injection.Second,the optimized implementation parameters of this new process in the Changning Block are as follows.The cluster spacing is in the range of 15e20 m,the proppant injection intensity is 2.0e2.5 t/m,and the liquid consuming intensity is 30e35 m3/m.It is concluded that this new process increases the single-well production of shale gas wells and the development benefit of the Changning Block and provides technical support for improving the comprehensive development benefit of shale gas wells in this block.
基金Project supported by the National Key Basic Research and Development Program(973 Program)“Theory and Technology Adaptability of Shale Gas Development in Typical Marine Blocks in South China”(No.2013CB228006).
文摘Horizontal shale gas well fracturing is mostly carried out by pumping bridge plugs.In the case of casing deformation,the bridge plug can not be pumped down to the designated position,so the hole sections below the deformation could not be stimulated according to the design program.About 30%of horizontal shale gas wells in the Changning and Weiyuan Blocks,Sichuan Basin,suffer various casing deformation after fracturing.Previously,the hole sections which could not be stimulated due to casing deformation were generally abandoned.As a result,the resources controlled by shale gas wells weren't exploited effectively and the fracturing effect was impacted greatly.There are a lot of difficulties in investigating casing deformation,such as complex mechanisms,various influencing factors and unpredictable deformation time.Therefore,it is especially important to seek a staged fracturing technology suitable for the casing deformation sections.In this paper,the staged fracturing technology with sand plugs inside fractures and the staged fracturing technology with temporary plugging balls were tested in casing deformation wells.The staged fracturing technology with sand plugs inside fractures was carried out in the mode of single-stage perforation and single-stage fracturing.The staged fracturing technology with temporary plugging balls was conducted in the mode of single perforation,continuous fracturing and staged ball dropping.Then,two kinds of technologies were compared in terms of their advantages and disadvantages.Finally,they were tested on site.According to the pressure response,the pressure monitoring of the adjacent wells and the microseismic monitoring in the process of actual fracturing,both technologies are effective in the stimulation of the casing deformation sections,realizing well control reserves efficiently and guaranteeing fracturing effects.
基金Project supported by the National Major Science and Technology Project“Evaluation of industrial shale gas productivity construction zone and research on main factors controlling high yield”(No.2017ZX05035-004)。
文摘As shale gas development is advancing continuously and rapidly,how to deeply analyze the production performance of shale gas wells and evaluate their production characteristics has become an urgent problem in the evaluation of shale gas productivity construction zone,the formulation of new area development scheme and the preparation of planning program.Some scholars have applied the Logical Growth Model(LGM)in the production decline analysis of unconventional gas wells,but the influences of shale gas reservoir and development characteristics are not taken into consideration.Therefore,this method still has some space of further development and improvement.In this paper,a Logistic Growth Model considering shale gas reservoirs and development characteristics(RB-LGM)was established based on the previous research results.Then,it was applied to the shale gas development wells in the Changning Block of the Sichuan Basin to analyze their production performance,and the analysis results were compared with thefitting and prediction results provided by the Arps hyperbolic decline model.Finally,the optimal well spacing of horizontal wells was determined using RB-LGM.And the following research results were obtained.First,shale gas is produced by deploying horizontal wells in the clustered pattern in a large number,so on the basis of LGM,RB-LGM takes shale gas reservoir parameters(thickness,shale density,gas content)and development parameters(horizontal section length,well spacing and recovery factor)as the logic control factors of horizontal-well gas productionfitting,so that the production prediction result of gas well is more reasonable.Second,RB-LGM can not only wellfit the early production data of gas well,but ensure the convergence of the later prediction results under the control of logical conditions.Third,RB-LGM takes into account the influence of shale gas reservoir and development characteristics so as to optimize the horizontal well pattern and analyze the change trend of reservoir parameters in the development area through data inversion.
文摘The dual-level bar counter,Braille floor plan on the wall and sign language board collectively define the compact pub hidden in Shanghai's Changning District-a space created for people including those with disabilities.
