Qaidam basin,which is the seventh-largest petroliferous basins in China,is rich in oil and gas resources.Therefore,the basin possesses the conditions to be a large-scale oil and gas field.However,the strong Cenozoic Himalayan orogeny resulted in the complex structure of Qaidam basin.The source-reservoir-cap assemblage of the oil and gas field has been reformed intensively.And later reformations make the exploration become more difficult.For the petroleum enterprise,once faced a harsher circumstance to increase reserve and production.However,in recent years with the great support of the joint-stock company leadership,Qinghai Oilfield Company continues to emancipate the mind.In terms of carefully and systematic analysis of the structure,deposition and petroleum geological conditions of Qaidam basin,explorationists changing the old exploration thoughts positively,and the exploration work obtains continuous breakthroughs.Two oil fields with 100 million ton reserves (Kunbei,Yingdong) and three oil fields with 50 million ton reserves (Hongliuquan,Wunan and Mabei) were sequentially discovered by Qinghai Oilfield Company.Natural gas risk exploration in deep zone of Eboliang Ⅲ and Tainan reserves fields has also gains a major breakthrough progress.According to summarize the successful experience,we can sum up five guiding ideologies and four working principles.These ideas and principles play very important roles in making exploration work get breakthrough progress and successfully increasing reserves and production of Qaidam basin
Petroleum exploration is increasingly extending to middle-deep strata worldwide.In the northwestern Qaidam basin,to provide references for finding new regional exploration field and similar studies worldwide,this article analyzed reservoir characteristics and its genesis based on a case study in the middle-deep strata of the Jianshan structure.The basic reservoir characteristics were obtained by combined methods including detailed microscope observation,reservoir space characterization and physical property analyses.The results show that the lithology is mainly composed of mudstone and argillaceous and calcareous siltstone.The basic type of reservoir space includes fracture and secondary dissolution pore.Residual intergranular pore was also observed.The physical property is of relatively low-quality with porosity and permeability being approximately 5% and less than 1×10-3μm,respectively.This indicates that the reservoir belongs to the type of low porosity and especially low permeability.Combined with geological setting,the reservoir genesis was summarized and concluded as an integrated influence of sedimentary and diagenetic processes.The sedimentary process is the basis for the development of low-permeability reservoir,compaction and cementation is key for the densification of reservoir,while fracture and dissolution is necessary condition for the reservoir formation.
In this study,rock assemblage were interpreted credibly in various aspects,including lithological association,sedimentary facies,well logging and geophysical prospecting,on the basis of outcrops,core drilling and seismic data.The results of Paleogene study in Qaidam basin indicate that the coarse clastic sediments in the lower segment of Lulehe Formation have a nearby source and make typical alluvial fans under the oxidation environment.The Mesozoic strata or Paleozoic rocks are defined by an angular unconformity which is overlain by the segment of Lulehe Formation.Basin comprehensive analysis shows Qaidam basin experienced a large-scale intense tectonic movement at the turn of the Cretaceous and the Paleogene.And the sediment records of Lulehe Formation is the response of the collision between India and Eurasian plates.
Stratigraphic correlation is difficult in the west segment,north edge of Qaidam basin due to the lack of marker beds,and the traditional method of sedimentary cycle division is highly dependent on researchers.Researchers have tried single spectrum method to solve the above problems,but the results need to be improved.In this paper,we analyze and determine the division of Paleogene-Neogene sedimentary cycles in the west segment,north edge of Qaidam basin with mathematical method of combining frequency spectral analysis,moving average and wavelet analysis.Also we analyze research meaning of division about sedimentary cycles in layer division and analysis of sedimentary environment.Results show that it is complementary,interactive and effective to apply three methods synthetically for sedimentary cycle analyses,and division of sedimentary cycles is an effective assistant method to stratigraphic correlation.Partitioning results of sedimentary cycles are very useful to analyze amplitude of variation and frequency characteristic of sediment-size and deepen the understanding of the variance in sediment environment.
Based on outcrop observation,core description,well logging and analysis assay data,the sedimentary features and sequence of lower Ganchaigou Formation in Mabei area, western segment of northern margin of Qaidam basin is analyzed.The results indicate that it develops braided deposition.And a detailed description of the sedimentary microfacies characteristic of braided deposit is given.Conglomerates,sandstones,mudstones are the main lithology type,and the percentage of conglomerates is low.And it is a normal grading change from coarse to thin.Based on this conclusion,sedimentary features and sequence of braided river are established.With the deep research on sedimentary sequence and the physical properties characteristics,the sedimentary microfacies are the main controlling factors of reservoir.
This article based on the drilling in Hongshan sag and the systemic analysis of middle Jurassic hydrocarbon source rocks surrounding outcrop profile,the abundance of organic matter and types,the composition of the hydrocarbons and evolutional stages of alkylation were comprehensive analsed and evaluated,the analysis shows that the major type of middle Jurassic hydrocarbon source rock is mudstone and oil shale in Hongshan sag,the organic matter deposits in fresh water environment,there into oil shale is Ⅱ,shale,carbonaceous mudstone and coal are mostly Ⅲ1-Ⅲ2.The most of middle Jurassic hydrocarbon source rocks in the surface profile of Hongshan sag belong to unbaked to low maturity,the underground middle Jurassic hydrocarbon source rocks also mainly belong to unbaked to low maturity,and a little of the organic matter belongs to maturity.Overall middle Jurassic of Hongshan sag has certain resource potential,which is an appreciable exploration area.
According to 3D seismic data in southwestern Qaidam basin,it can be find that there are 4 secondary depression:Hongshi,Zhahaquan,Alaer and Qiekelike.Through research on structure evolution and hydrocarbon generation of the depression,we get a viewpoint that Hongshi,Zhahaquan and eastern Qiekelike depression are early sustained sedimentation,the source rocks in Tertiary System have a characteristics of multi-bed,great thickness and superior quality,and Zhahaquan and eastern Qikelike is an entire hydrocarbon generation depression in early time.Combined with oil source comparison and oil-gas,it can be indicated that there are two hydrocarbon generation center in Hongshi and Zhahaquan-Qiekelike with a figure of partly generating hydrocarbon in big depression and oil-gas accumulate near-source and around the depression.While,the two source center contain 8.86 hundred million tons oil and gas.Provided hydrocarbon by the two oil source center,Qigequan-Shaxi,Yuejin,Wunan,and Kunbei,which develop several delta frontal zones and beach bar sand zone,become a favorable area for lithologic hydrocarbon reservoir.
Nanbaxian oil-gas field belongs to complex fault block oil-gas field.The N1—N22 hydrocarbon reservoirs controlled by tectonic,faults,lithology,etc.have complex fluid properties,several sets of oil-gas-water systems,and no united oil-gas-water separating surface.The oil and gas field development efficiency has been seriously affected by the difficulties in reservoir identification through logging data,developing orientation and modes.Through the comprehensive application of reservoir fluid properties test and analysis,high pressure property,natural gas composition analysis,and production output data,it is concluded that N1—N22 reservoir is dominated by gas and gas condensate reservoirs with small amount of gas condensate reservoirs with oil rings.Feasibility of development of the natural energy failure,gas injection,water injection has been analysed to provide basis for improving development beneficial result.
The hydrocarbon concentration of Nanbaxian oil-gas field which is complex fault block reservoirs are controlled by many factors such as structure,fault,lithology,and so on.The oil-gas field has a variety of reservoiring schema,while the deep E13 strata composed a native high-pressure gas reservoir and the middle-shallow N1-N22 strata composed a secondary normal-pressure oil-gas reservoir.Based on the latest exploration results and dynamic exploitation data this paper analyzed the reservoir accumulation pattern of “oil in upper strata and gas in lower strata” and reached following conclusions:The E13 gas reservoir,which was formed by the second period of injection,is an abnormally high-pressure protogene reservoir with good trapping conditions;The protogene E23 reservoir was destroyed by Xianbei fault formed during later period,which allowed the migration of hydrocarbon to upper strata;The N1-N22reservoir was the result from effects of faults and lithology,which was a normal-pressure secondary oil-gas reservoir and formed by the first period of injection.The conclusions have directive significances to the exploitation of Nanbaxian oil-gas field.
Based on the abundant drilling and logging data,full application of deposition theory,analyses of the sedimentary facies of the lower Ganchaigou Formation in the Gasikule oilfield，4 types of sedimentary facies have been identified in the study area,including delta,coastal lake,shallow lake and semi-deep lake.Frequent seiches of lake in the upper member of the lower Ganchaigou Formation in the region are studied through single well facies and profile facies analyses.It formed 5 fourth class sequences during the process of small-scale lake transgression to lake regression,which determined the vertical evolution and superimposed texture of sedimentary microfacies in the study area.Through the study of sedimentary facies,sedimentary microfacies have been divided,which provide significant guidance to the future research and the exploration and development of the studied formation.
Recently a new type of natural gas was found in the Neogene of Yiliping region,Qaidam basin.The paper evaluated the conditions of the natural gas source rock,established the accumulation model of this natural gas,calculated the amount of the natural gas resources preliminary and analyzed the favorable exploration zones.The authors believe that the gas in Neogene System is the thermogenic gas,the main types of organic matter are Ⅲ and Ⅱ2,there is a huge amount of natural gas resources,the westen tectonic belt of Yiliping depression is the favorable zone of next exploration because it is not only shallow burial,but also formed earlier.The article studied the accumulation conditions and exploration potential of Yiliping gas system,enhanced the understanding of the geology of this area,this will guide further research and deployment.
Yishen-1 well has obtained commercial gas flow in the Neogene Shizigou Formation.Results show that the Sanhu area of the Neogene Shizigou Formation has biogenic gas,but the study of the Neogene in Sanhu area is very poor and lack of drilling targets.In order to make a breakthrough of the situation to find biogenic gas in the Quaternary and widen the biogenic gas exploration field,this paper combined drilling/logging,seismic and Milankovitch cycles to study the high resolution sequence stratigraphy of the Neogene in Sanhu depression,Qaidam basin.Results show that Shizigou Formation equals to a Ⅲ sequence (long-term datum plane cycles).Six sequence boundaries can be further identified and divided into five Ⅳ sequence (medium-term datum plane cycles) in Shizigou Formation.Each sequence can be further divided into half cycle of increasing and half cycle of descending.The delta front sandstone thinning out and sand lens trap which develop in half cycle of increasing period of Sequence III (sq3) are favorable target for further exploration.
Nanyishan shallow oil pool lies in the northern part of western Qaidamu basin,which is one of the important low permeability and low porosity reservoirs of Qinghai Oilfield Company.It is a synsedimentary anticline,which is clamped by syngenetic faults on north and south wings.The researches of lithotype and sedimentation mode are necessary for its efficient exploitation.Based on the previous research and through microscopic observations of plenty of rock slices and carbonate analyses,the paper proves that the lithology of the Nanyishan shallow oil pool formations is interlaced with pelytic and arenaceous laminae deposited in semi-deep lacustrine environment.Due to the particularity of its lithology,the paper recommended a naming system based on rock composition.
Sedimentation and changes of sediments under different diagenetic conditions is key to the reservoir research and evaluation. Through systematic analyses of core slices,cast thin sections,clay mineral X-ray diffraction and scanning electron microscopy,it is summarized that diagenesis of the lower Youshashan Formation in the Wunan oilfield includes mechanical compaction,cementation,dissolution and metasomatism. Dissolution is a favorable factor for the improvement of reservoir properties,while compaction,cementation and metasomatism are unfavorable to the reservoirs. Studies on diagenetic sequence demonstrate that reservoir sandstones of the lower Youshashan Formation in the Wunan oil field are during the early diagenetic B substage. Researches on diagenesis are beneficial to the reservoir classification and evaluation of the lower Youshashan Formation in the Wunan oil field,as well as prediction of favorable reservoirs.
Huatugou oilfield is located in the western Qaidam basin,and N22 reservoir is the research area in the upper part of an oil bearing intervals,the current trial mining development.Therefore,understanding the types and characteristics of the sedimentary microfacies,sedimentary microfacies plane,vertical distribution,exploration of the relationship between the sedimentary microfacies and oiliness has guiding significance to the exploration and development.Comprehensive analyses of the core,grain size,lithology,well logging reveal that the reservoir section of the delta plain subfacies is subdivided into 3 types of sedimentary microfacies including distributary channel,floodplain and river flood plain.Analysis of sedimentary microfacies of plane and longitudinal distribution has been performed.Based on the coring oily and oil testing,test mining information on the foundation,relationship between the three sedimentary microfacies and oil-bearing property are explored.Our results show that reservoir branch channel and floodplain depositional microfacies have certain industrial oil flow,which is the main objective for further exploration.
With a combination of core,logging,testing and seismic data,based on the microfacies research under the isochronous high resolution sequence stratigraphic framework,with the application of seismic attributes,frequency,waveform classification and the amplitude of the visualization perspective,wave impedance inversion technology,comprehensive sediment and reservoir study on the lower Ganchaigou Formation in the Hongliuquan structure in western Qaidam has been carried out.Results have shown that such methods combining well shock with logging analysis can effectively solve the problem of lithology reservoir prediction,and has an important reference to the development of lithologic reservoirs in other areas.
The authors have analyzed geophysical data,such as Bouguer gravity,aero-magnetism,geological profile,and structural patterns from the Qaidam basin and adjacent regions.The first-order structure of the basin is a broad Cenozoic synclinorium,which is the mirror reflection of the mantle.The development of the synclinorium was coupled with the deformation of the upper-crust,lower-crust flow,and the upper mantle,suggesting that Cenozoic structural evolution of the Qaidam basin resulted directly from the uplift of the mantle.Qaidam basin is naturally a synclinorium depression,accommodating by upper-crust winding and lower-crust flowing.
After years of development,the Sebei 1 gas field has accumulated a wealth of experience,but also encountered problems such as sand,water,great changes in dynamic reserves,etc.To date recovery percent of this gas field is over 10%,reaching the lower limit for dynamic reserve evaluation.In this paper,material balance-pressure drop method was used to calculate the dynamic reserves,and influencing factors of dynamic reserves were analysed for this gas field.Based on a comprehensive analyses of permeability,water,pressure and other factors on the well test interpretation,it is pointed out that permeability is the dominated influencing factor,which provide a reference to the application of the Sebei gas field reserves and development of the gas field.
Due to special sedimentary environment,Sebei No.1 gas field formed vertical distribution with frequent alternative deposition of sand and shale.As a Quaternary unconsolidated sand gas field,it widely distributed mud sandwich，which has certain thickness and permeability.Based on the analysis of lithology,distribution and permeability of Sebei gas field interlayer,the author believes that mudstone barrier is well developed,with some water content.Water channeling of claystone barrier is the main source of water breakthrough in accordance with the status of water production.Therefore as to water control and precaution it is very important that the author researches the characteristic of interlayer and its operation on water breakthrough.
Reservoir formations of Sebei gasfield are unconsolidated and are prone to sand production.Accurate sand-production predictions are necessary for consequent selections of sand-control methods.This paper analysed and verified the vertical and lateral sand-production laws of reservoir formations through four different empirical prediction models，including compressional wave slowness,sanding index,combined modulus and Schlumberger ratio.Meanwhile,this paper predicted critical sand-production pressure differential through empirical,BP and Arco models,and obtained that the Arco model is more proper through comparison with field test data.Finally,a sand-production prediction model built in laboratories was demonstrated in this contribution,whose deviation is within 15% through correlation with real sand-production statistical data.
Sebei gas field in the Qaidam basin is a Quaternary unconsolidated sandstone gas field with gentle field structure,loose reservoir lithology,low gas saturation and complex gas/water relationship.The effluent mode of Sebei gas field includes edge water invasion,water channeling in the muddy compartment,water channeling in the water layer and transfer of reservoir bound water into free water.Among them,the reservoir bound water into free water is a new mode.During the development of gas field,with the continuous gas recovery,formation pressure decreases gradually.Hence,reservoirs become compressed under the overlying strata leading to the decrease of porosity and increase of formation water saturation.When the reservoir pressure drops to a certain extent,part of the bound water gradually was converted into free water,affecting the gas production.Based on the geological characteristics of reservoirs,combined with effluent rules,the effluent origin and types were analyzed for the Sebei gas field.Based on the development experiments and analytical data,a prediction chart of reservoir bound water into free water was obtained.The chart has different intersection point for the reservoir water saturation curves and bound water saturation curves.The intersection point pressure is the critical effluent pressure for the bound water in the gas reservoirs.Studies have shown that with the decrease of gas reservoir pressure,it is possible for gas reservoir bound water converting into free water.
Gasikule oilfield E13 reservior belongs to low permeability reservoir and is hard to be developed due to strong heterogeneities.Every oil layer has its own ultimate production-injection well spacing due to the existence of starting pressure gradient and different properties.Determination of rational production-injection well spacing is significant for economic and effective exploitation.This paper established the relationship between degree of water flooding reserves and production-injection well spacing considering vertical heterogeneity of the E13 reservoir,analyzing the controlling factors effecting degree of water flooding reserves,putting forward the method of determination rational production-injection well spacing.
Horizontal well geosteering is the key technique for the success of horizontal well. According to the technical problems such as the great changes in reservoir lithology and formation dips, and poor rock debris representative of cuttings of the Gasikule oilfieldN1-N12 reservoir, starting with the optimization of well deployment, with in-depth analysis of reservoir structural feature, strengthening of stratigraphic correlation, combination of comprehensive logging data, a set of horizontal well geosteering technology which is applicable for this reservoir has been established. Good application has been achieved during the drilling of horizontal wells.
Gasikule oil field is one of the main oil reservoirs in the current development in Qaidam basin.As a favorable area of effectively producing newly geological reserves and achieving the goal of productivity construction,it presents some difficulties in reservoir development in the footwall south part of GasikuleN1—N12 oil reservoir for its long distribution of well sections,poor plane discontinuity of oil sand and oil-water relationship controlled by lithology.For many years,combined with drilling data and production test data,oil-water relationship has been further clarified through old well review by some scientific methods to develop comprehensive study on reservoir geological characterization,such as geological method and logging method,so that better profit is taken during the progressive development practice based on the strategy of pre-drilling evaluation,process tracking and understanding deepening.It is also instructive to improve the development effect of the study region and complex lithology reservoir.
In the oil-field development,the output constitution includes three parts：the old well natural output,the measure output,and the new well output,among which measure output has the biggest influence from the artificial controlling factor.This article through affects the oil well measure benefit many factor generalized analysis,the quotation measure increases the oil mass △Q=f(Cc,Po) the function relationship,increased the oil mass and measure expense these two targets under the different oil price with the measure,the utilization economic evaluation theory-profit and loss principle of detailed balance,the research proposed under the different oil price the measure was lowest increases the oil boundary formula and the measure well is lowest increases the oil boundary benefit dynamic evaluation criteria molded relief map version.Carries on the forecast by this to the measure benefit with latter to appraise,achieved the optimal measure,avoids investing invalid,enhances the measure economical effectiveness,the improvement oil-field development economic efficiency goal.This article take Yaaz Kuller the E13 oil deposit in 2010 the work 16 well inferior compression fracture measure well as an example,has proven this method to the measure optimal pre-appraisal effect.Meanwhile in 2010 whole year the measure work as regularly proved this standard drawing version take this oil deposit to appraise after the measure the mine feasibility,the usability.This method is simple,is direct-viewing,is one scientific management.The benefit forecast can the effective optimal measure,avoid investing invalid,saves the expense,enhances the economic efficiency,after the benefit the appraisal can explicitly the measure effect,the quantification benefit,provides the reliable reference for later measure direction.
甘公网安备 62010202000678号
