Deep oil and gas exploration and exploitation have made a series of significant breakthroughs in recent years.However，the progress，challenges and development trend of exploration and development of onshore deep oil and gas resources in China have not been systematically analyzed.This article summarized five fundamental characters of deep petroleum resources：(1)More gas and less oil，with complicated phase state；(2)Universally high temperature and high pressure，but great differences existing in different basins or strata；(3)Multi hydrocarbon accommodation，multi hydrocarbon sources；(4)Relatively dense reservoir，but having large scale efficient reservoirs；(5)Complicated accumulation and multi period reconstructions.Based on the exploration and development history of deep oil and gas，it is regarded that the exploration and development of deep petroleum in China is at the “large-scale discovery stage”，and great achievements have been obtained in the carbonate/clastic/volcanic reservoirs，but four challenges still exist：(1)complex hydrocarbon generation，reservoir evolution and accumulation restrict the exploration orientation and targets；(2)the long period and high cost of well drilling restrict the petroleum discovery and efficient development；(3)immature high temperature & high pressure slim hole logging technology restricts accurate identification of hydrocarbon reservoir;(4)unadapted petroleum recovery technique and equipment restrict effective development and large scale utilization.On the basis of comprehensive analysis，it is concluded that deep petroleum resources mainly exist in three areas of six basins in onshore China，with great exploration potential，which is strategic replacement.It is suggested that petroleum companies，universities research institute should be gathered to overcome problems in limited time，integrate innovative achievements，and develop deep oil & gas exploration and development theories and technical system to support deep oil & gas rapid development.
In recent years，China’s deep oil & gas exploration and exploitation has developed rapidly.Technological development has played an important role in rapid exploration and high efficiency development.Aimed at the complex engineering geological environment of deep oil & gas in China，this paper has combed the four technological systems that have made great progress，mainly including:(1)seismic imaging and reservoir prediction techniques for deep complex structures，“2W1S” technique (wide-band，wide azimuth and small bin)，RTM (Reverse Time Migration)，integrated modeling technology for belt，and variable velocity mapping technique，improving structural interpretation accuracy，ensuring high precision imaging and prediction of deep geological bodies；(2)deep speed raising and efficiency drilling technology series，which greatly improved the drilling speed，reduced drilling cost and drilling risk；(3)development of deep high temperature and high pressure logging technology series，which provided a guarantee for the accurate identification of reservoir properties and fluid properties；(4)the deep and efficient development technology，especially the deep reservoir，which improved the development and maturity of the reconstruction volume technology， the production of single well and the benefit of deep oil and gas development.Based on the analysis of the current development of the four major technological systems，focused on the challenges of deep oil and gas exploration and development，this paper further points out the development direction of the four major technology series of deep oil and gas exploration and development，pointing out that the development of technical system of applicability and economy is the key to realize high efficiency and low cost exploration and development of deep oil and gas.
Deep dolomite in craton basin is an important field for future natural gas exploration in China.Through statistical analysis，it is clear that the main types of deep dolomite are granular dolomite，microbial dolomite and crystalline dolomite，the pore types are mainly fractured fissure cavity and fractured pore type.It is pointed out that favorable sedimentary microfacies are the material basis for pore formation，early dissolution is a necessary condition for pore formation，dolomitization is beneficial to preservation of early pores，epigenetic karstification and structural fracture improve reservoir property.Definite，the deep quality dolomite reservoirs are still facies controlled，the deep dolomite reservoir is more inherited than transformed，the vertical distribution is not controlled by depth，but controlled by early sedimentary cycles，the lateral distribution is not controlled by karstification，but controlled by high-energy sedimentary facies belts.It is considered that the exploration of deep quality dolomite reservoirs in the future will be mainly “both sides of the inner rift of platform” and carbonate ramps.
The dolostone of Cambrian Longwangmiao Formation has been significant gas exploration area in Sichuan Basin.In Gaoshiti-Moxi regions,giant gas pool with thousands of billion cubic meters’ reserve has been discovered.But the origin of reservoir and the distribution patterns were still in dispute,which has constrained the dolostone exploration of Longwangmiao Formation.Based on the outcrop geological survey,cores and thin-sections observation,reservoir geochemical characteristics study and reservoir simulation experiments,this paper focuses on the characteristics,origin and distribution patterns of the dolostone reservoir in Longwangmiao Formation.Two achievements were acquired:①The Longwangmiao Formation of Cambrian could be divided into upper part and lower part in Sichuan Basin.Based on the two parts of Longwangmiao Formation,two ligthofacies paleogeographic maps were accomplished and the carbonate ramp sedimentary models were established.The grainstone shoals are mainly distributed in the shallow ramp of the upper part in Longwangmiao Formation.②The grainstone shoals are the developing basis of dolostone reservoir in Longwangmiao Formation and the contemporaneous dissolution was the key factors of the development of grainstone shoal reservoir in Longwangmiao Formation.Controlled by the exposure surface,the dissolution vugs are not only extensively distributed,but also successionally developed along the contemporaneous pore zones.The distribution patterns could be predicted.The geological understandings of the origin of dolostone reservoir in Longwangmiao Formation show that the reservoir distributed in the areas of karstification in Gaoshiti-Moxi regions,and the widespread grainstone shoals in the whole basin are the potential exploration targets.
In the Sinian Dengsi period,the Gaoshiti-Moxi structure located in east side of Mianzhu-Changning intracratonic rift.There is a platform edge with microfacies of algal plaster mound,psammitic beach and dolomitic flat.With the exposure and erosion of Tongwan Ⅱ episode of tectonic uplift in the Late Sinian,it became Karst weathering crust formation.The Dengsi member was corrosion vuggy dolomite reservoir with main reservoir space of vug,pore and fracture.On the basis of the quantitative analysis with core description,imaging-log and conventional log,the reservoir space can be divided into six types,such as cavernous,vuggy,pore,fracture-vuggy,fracture-pore,and fracture.In the vertical,according to the type of reservoir space and its combination characteristics,there are five combination patterns,such as cave-vuggy,fracture-vuggy,vuggy,fracture-pore and fracture.The cave-vuggy type and fracture-vuggy type are the best reservoir combination pattern which has long-term high production and steady produce of gas. The vuggy type is long-term middle production and steady produce of gas,while fracture-pore type and fracture type are high gas production and short stable period.
Based on regional geology,core description and thin section observation,the petrology and reservoir properties of the microbial carbonates of Upper Sinian Dengying Formation (Z2dn) in eastern Gaoshiti area in the Sichuan Basin are investigated in detail.The origin of the microbial dolostone is analyzed briefly.Dolostones dominate in microbial carbonate rocks of Dengying Formation and the lithology include stromatolite,spherulite,thrombolite and spongy layered dolomite.Microbial dolostone reservoirs are mainly developed in both the upper & lower parts of Z2dn4,and in Z2dn2.The reservoir space is composed of fenestral pores,skeleton cavities,inter-particle dissolution pores,inter-crystal dissolution pores and moldic pores.The good reservoirs mostly have a porosity range of 1% to 6% and permeability of less than 1×10-3μm2.The formation and distribution of the microbial dolomite reservoirs are jointly controlled by the original rock type and digenesis.Different microbial textures in the originally deposited rocks determined the types of reservoir space and pore structure.Diagenesis is a key factor for development of microbial reservoirs.The constructive diagenesis for forming good reservoirs are early microbial dolomitization,karst,and burial dissolution;while the destructive diagenesis are over-dolomitization and intense silicification.
The massive collapsed-paleocave systems in Sinian carbonate strata in central Sichuan Basin are found based on 3D high resolution seismic data and coherence seismic attribute.Collapsed-paleocave systems are distributed near the strike-slip faults and the fault intersect spots;on the profile,they occur as seismic events push-down,lenticularity,and accompany with multi-phase concentric circular faults,the vertical extension of the collapsed-paleocave systems can reach the Pre-Sinian basement.The inherited faults are widely developed in the research area,especially the tensional faults which are generated by the Xingkai Taphrogeny,providing channel for water migration and hydrothermal migration.As the extension acted more vigorous,the hydrothermal channel would be more developed,and the size of collapsed-paleocave system would get larger.Based on the core and geochemical data,it is assumed that the formation of collapsed-paleocave system is mainly affected by the structured-hydrothermal karstification.Pore and fracture in the collapsed-paleocave systems gradually form intracrystalline pores and hydrothermal karstificated pores through late hydrothermalism,by which the petrophysical properties of the collapsed-paleocave systems are further improved.The collapsed-paleocave systems are probably the favorable targets for gas exploration.
Natural gas was found mainly stored in corroded pores and caves in the Lower Cambrian Longwangmiao Formation dolomite gas reservoirs in the Moxi block of Sichuan Basin.Because of the diversity of combination of pores and holes and fractures,different reservoir physical property and different gas well deliverability are found in different position of the grain beach with strong heterogeneity.So,it is difficult for the connectivity evaluation on this.Based on the reservoir characteristics,the combination of dynamic and static analysis method of gas well connectivity was built.Firstly,based on static data,comparative analysis methods of geological characteristics,formation pressure,and fluid property are used to evaluate gas reservoir (well) connectivity.Secondly,based on dynamic data,comparative analysis methods are used to evaluate gas reservoir (well) connectivity,which include pressure build-up test,pseudo-interference well test,and production performance analysis.Finally,based on pseudo-steady seepage theory,i.e.gas rate is proportional to the dynamic reserve controlled by the well.Gas well connectivity was comprehensively evaluated by the combination of dynamic and static analysis method.In a case study from the well block of Moxi 9,gas reservoir (well) connectivity is good in the main body of grain beach.For example,the fluid property is similar for all wells,and the formational pressures synchronously decline between new wells and old wells.No boundary features are found in Log well test curves,and inter-well interference phenomenon is found in the curve of normalized rate and metrical balance pseudo time,and gas rate is proportional to the dynamic reserve controlled by the well.When Well Moxi 009-X6 was put into production,its formation pressure was higher than that of Well Moxi 009-X1 at the same time,which is 1.5 kilometers away from Well Moxi 009-X6.Further,it is not connected to all but a certain direction.
Carbonate stratigraphy developed in the Sinian,Qigebulake Formation,Tarim Basin,which is mainly composed of carbonate ancient stratum,formed the old geological times.Core observation,thin section analysis and outcrop measurement showed that the petrological type of Qigebulake Formation contains microbial dolomite,grain dolostone,crystalline grain dolostone and hybrid sedimentary rock.The statistics data of 150 thin sections show that microbial dolomite accounted for about 30%,grain dolostone for 25%,crystalline dolostone for 30%,and peperite accounted for 15%.The reservoir space type of Qigebulake Formation contains inter-crystalline pore,inter-granular pore,microbial lattice,solution cavity,and fracture.By collecting and testing porosity and permeability data,it is proposed that microbial dolomite porosity distributed between 2.5% and 3.5%.The grain crystalline dolostone porosity value distributed between 2%-4%,and the biggest can be close to 9%.The bigger the grain size,the greater the permeability and porosity.Tgrain dolostone porosity ranges from 2% to 3.5%,partly up to 7% which is related to inter-granular corrosion cavity reservoir space.On this basis of carbon and oxygen isotope and inclusion data analysis,combined with the sedimentary microfacies,atmospheric fresh water dissolution is the main contributor of reservoir.Burial dissolution and tectonic hydrothermal process for reservoir preservation and transformation also play an important role in reservoir formation.
The Lower Permian is one of the important strata of natural gas exploration and development in Sichuan Basin.There are strong heterogeneity,well logging evaluation,prestack processing and reservoir prediction of fracture cave type reservoirs.Therefore,to carry out research of geophysical technology and the formation of supporting technology,mainly include: first,through in-depth analysis of logging,conventional logging and electric imaging and stone wave logging data,establish reservoir logging response characteristics,grasp the fractured vertical distribution;Second,on the basis of this,put forward the amplitude preserving processing technology in in terms of static correction,SNR,consistency and improve the resolution of seismic data,the high accuracy;through the forward model,establish Maokou reservoir seismic response model,guide the optimization of seismic attributes to carry out cave of prediction;through the prestack stochastic inversion,predict quantitative reservoir.The carbonate fracture cave unit used 3D visualization technology of space carving in the depiction;Cave Automatic Tracking Based on the discrete model for fractured vuggy connectivity is analyzed.The prediction results proved consistence with the actual drilling well,which provide a basis for well deployment,and put forward “go out looking for karst structure”,shallow deep to find out the new ideas.It has important guiding significance to deepen the exploration and development of new exploration field expansion of Maokou Formation of complex carbonate gas reservoir.
Identification of gas and water is a key problem in gas reservoir logging evaluation,and a method for identifying gas water by using T2 spectral center location difference under different observation modes is proposed.Theoretical analysis shows that the change of the T2 spectrum center position can be changed by changing measurement mode,and the natural gas is more sensitive than the formation water.Based on the theory,gas-water recognition software is developed,and tested in Sichuan Basin.The result is confirmed by the oil testing conclusion,and the validation of the method is demonstrated.The method is applied in several wells,and results show that the method has good recognition effect.And we also found that recognition accuracy of different echo interval mode is higher than that of different waiting time mode.
The traditional Archie model has certain inapplicability in carbonate reservoirs,due to the complex pore structure and strong heterogeneity.For example,the variable values of cement index (m) and saturation index (n) often lead to a great deal of difficulties in saturation estimation.Based on the rock physics volume model,the saturation index (n) is assumed to be constant and redefine cementation exponent (m) as a pore structure index.It is used to replace the effect of the original Archie cementation exponent and saturation index on water saturation calculation.Rock physical experiment is hard to be applied to the rocks from the complex reservoir.For the carbonate sample with fracture and dissolution vuggy,we can’t obtain the cores easily.Therefore,the effects of the law of aspect ratio,porosity,clay content on the formation factor F and pore structure index of carbonate reservoir rocks are studied by numerical simulation.A new saturation model with variable index of pore structure is developed after the compositions of pore structure are employed in our research.The field logging data from one well in Sichuan Oilfield is processed using the new saturation model,and the applications of the new saturation model suggest that saturation precision has been improved.
Longwangmiao Formation gas reservoir in the Gaoshiti-Moxi area is currently the focus of petroleum exploration and development in Sichuan Provence.The reservoir has dissolved pores and contains asphalt.In usual experiment,plenty of dissolved pores which developed around core’s surface can’t be saturated by salt water and thus can’t be detected by NMR.What’s more,we found NMR signal in dry core samples.After quantities of comparison experiments of pure asphalt and mixture of asphalt and sand,we confirm the NMR signal in dry core sample comes from asphalt.We develop a calibration method of dissolved pores around surface and asphalt NMR signal in dry core sample.The result shows that after calibration,the NMR porosity has better agreement with helium porosity and NMR bound water saturation has better agreement with weighing method.T2 cutoff value can’t be influenced by dissolved pores around surface but must be through asphalt NMR signal calibration.The data through calibration can characterize the fluid’s and pore’s information of the reservoir more precisely.
Liner slot completion is one of the main horizontal well completion types,which has remarkable advantages,such as huge discharge area,and low cost.Uniform acid arrangement is the key to stimulation of horizontal well with liner slot completion.It is hard to implement acid arrangement in horizontal well with liner slot completion,through the annulus space between liner slot and wellbore is not sealed successfully,routine sectional stimulation technologies are limited.A new acid arrangement technology in horizontal well with liner slot completion was generated,via theoretical and experimental research.It can define formation damage characteristics of different well intervals through predicting initial skin factor profile of horizontal well intervals.Mathematical model of acid flowing in horizontal well was established,and diversion pressure of different intervals was simulated.Optimizing the liner cutting parameters,and different diversion pressures were obtained by changing quantity of diversion dosage.The acid wormhole shape was characterized by numerical method,which is able to optimize acid system.It was applied to 8 wells in Anyue Gasfield.The average of stimulation multiple proportion was 1.95,and the average testing production of individual well increased about 67.3×104m3/d,compared with perforation completion,single well completion saving cost 9 million yuan.Therefore,the economic benefit is remarkable,which serves as a reference for other gas reservoir.
In the stimulation process of carbonate gas reservoirs in the Gaoshiti-Moxi area of Sichuan Basin,problems like the difficulty in reasonable acid placement due to long construction intervals and strong reservoir heterogeneity exist in those highly deviated. In order to provide a solution,laboratory research and pilot tests were conducted,and a new diversion (multistage temporary plugging) technology applicable to gas wells was developed. Based on the laboratory experiment,the soluble ball has a high degradation rate,fully meeting the field construction requirements of natural gas wells. The application in typical wells shows that,the production increase of wells adopting this technology is tremendously higher than other wells adopting other acid placement technologies. This technology provides a brand new acid placement solution for natural gas wells as well as a new technical approach to the acidizing frac treatment of long construction intervals and heterogeneous reservoirs,so it is of large-scale popularization and application values.
In this study the nanoparticles of suitable size and hydrophobic degree were introduced in the liquid as solid foam stabilizer to solve the problem of unloading of deep gas well with high gas temperature (110-150℃) and salinity.The nanoparticles can adsorb onto the gas/water interface to form a solid film which will prevent the coalescence and coarsening of bubbles,therefore the foaming ability and foam stabilizing ability of liquid foam unloading agent were greatly improved.In order to provide guidance for use in gas well,the foaming properties of different concentration of nanoparticles stabilized foam unloading agent was tested in real-time using high temperature and high pressure foam evaluation instrument.Meanwhile,the external factors such as salinity,temperature and pressure on the properties of nanoparticles stabilized foaming agent were also examined.The results show that its initial bubble volume V0 and half-life t1/2 reached as large as 2 160mL and 765s respectively under 250 000mg/L salinity.Besides,its initial bubble volume V0 and half-life t1/2 reached as high as 1 925mL and 700s at 150℃.These data proved that the nanoparticles have strong ability to stabilize the foams.The field application results show that the nanoparticles foam unloading agent performs well.
The effect of reservoir stimulation is not ideal for ultra-deep fractured reservoir of Tarim Oilfield Company,so the main factors affecting the reservoir stimulation and influence law of these factors were studied,and the efficient stimulation measures were proposed.Geomechanical studies have shown that the main factors affecting natural fractures opening including natural fracture occurrence,reservoir stress,pore pressure increment caused by the stimulation,the angle between maximum principal stress direction and natural fracture orientation,cohesion and so on.High angle natural fractures are prone to shear failure; the greater the pore pressure increment during stimulation,the greater the stress difference between the maximum and minimum horizontal stress,natural fractures are more easily open by shear failure.The smaller the angle between natural fracture strike and the maximum principal stress direction,the more easily the natural fractures shear failure occurs.Cohesion has a greater impact on natural fractures opening rate,and lower cohesion can greatly increase the natural fractures opening rate.Cohesion drops from 14MPa to 0MPa,natural fractures open rate increases from 11.5% to 71.2%,the crack opening rate increases by 59.7%.Reservoir simulation studies have shown that to improve the longitudinal producing degree is better than lateral producing degree to improve well productivity.By temporarily blocking natural fractures,the higher pump injection to increase bottom hole pressure,and pre-acidification to reduce crack cohesion,the crack opening rate increases,reservoir producing degree and the effect of stimulation are improved greatly.The reservoir stimulation countermeasures are an efficient way to yield higher production in ultra-deep fractured reservoir.
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