According to national demand of petroleum resource potential understanding in the eastern mature region,the applicability and confines of evaluation methods were analyzed.These methods include genetic method,statistical method,and analogy method.In allusion to problems of petroleum resource evaluation methods at home and abroad,we choose the Niuzhuang Sag as a representative region in the continental petroliferous basin of east China to calculate the petroleum resource quantity by using the play statistical method.Firstly,the source feature and distribution regularity of proved oil reserves in the study area was investigated,and then the relationship between hydrocarbon generation and reservoir formation was defined by analyzing the migration direction and path of petroleum.Finally,in combination with structure,stratum,sediment,and temperature-pressure conditions,the boundary of total petroleum system was divided.On the basis of research results above,the evaluation unit of reservoir combination was divided and the resource quantity was calculated by statistical method in the similar evaluation unit.In contrast to conventional petroleum resource evaluation method,this method,taking advantage of various geology materials of mature exploration area,can not only avoid choice of migration and accumulation coefficient which is difficult to control in genetic method,but also compensate the shortage of geology materials in statistical method.Furthermore,it can point out the difference of remaining resources in each reservoir combination,and provide the evidence for fine exploration in mature exploration area.
Sangtamu Group in Aijiashan Stratum of Upper Ordovician in western Tazhong has obvious boundary line with the below Lianglitage Group,which is the boundary of clay stone and limestone.On the base of palaeontology stratum framework and combining the lithology,electric property,geomorphic feature and seismic reflection characteristics,lots of limestone distribute at the bottom of the Sangtamu Group in the form of banded and porphyritic shape in some area.They are the identification of palaeogeomorphology highland in Lianglitage Group depositional stage and also the high energy face belt distribution feature.It is of great instruction meaning for the study of sedimentary environment.The new method is used in this article to recognize high energy face belt distribution of Lianglitage Group in Western Z15 well.The high energy face belt can be divided into berg strand in inner stage and berg stand composite in stage edge.
There was a high hydrocarbon potential in the evaporite platform dolomite of Middle Cambrian in Tarim Basin.Based on the outcrop observation and the comprehensive analyzes of common thin section,scanning electron microscope(SEM),cathodeluminescence(CL) technique and the geochemical data,we carried out the research on the characteristics of a dolomite reservoir which had deposited in the section of X in Tarim Basin during the Middle Cambrian.The results show that the Middle Cambrian rocks in the study area are of various types,and the reservoir′s space mainly includes the dissolved pores and the collapsed caverns (the collapsed shadowing hole).We also studied the reservoir′s forming mechanism through the assay of accompanying minerals and the analyses of the pore characteristics and geochemical characteristics.It indicates that the mechanisms in the study area include the atmospheric water denudation in syngenetic stage,the collapsing rock′s stacking interaction in middle burial stage and the hydrothermal dissolution in deep burial stage.The former two mechanisms were controlled by the fluctuation of sea level,so they distributed widely.However,the distribution of the third mechanism is quite limited,because it was vertically accompanied by the faults and horizontally distributed along the formation,and it may alter the early generated dissolved pores.
According to the analyses of the seismic sections and balanced sections,subsalt structural deformation strength in the east is higher than that in the west of Qiulitage structural belt of Kuqa foreland basin.Structural shortening rate in the east part ranges from 13% to 25% and subsalt structures mainly include fault-related folds,imbricated thrust and duplex in the east.Structural shortening rate is below 10% and structural styles are a series of fault blocks in the west,such as back thrust and step thrust.Using the principle of back stripping and basin modeling technology,the result suggests subsidence rate is higher in the east than that in the west.The differences in structural deformation and subsidence rate have influence on reservoir diagenesis and physical property.In the east,structural deformation is intensive.Subsidence rate is higher and deep burial time is longer.The compaction is strong and reservoir diagenesis stage is in middle diagenesis A2-B period.Visual compaction rate ranges from 37% to 64% and reservoir physical property is bad.Intense tectonism leads to development of the fractures which greatly improve reservoir permeability.On the contrary,structural deformation is faint and subsidence rate is lower in the west.Shallow burial time is longer.Visual compaction rate is between 24% and 55%,reflecting the compaction is weaker.Reservoir diagenesis stage is in middle diagenesis A1-A2 period.Reservoir physical property is better in the west.Tectonic-diagenesis is a crucial geological factor causing the inferior physical property of the reservoir in Qiulitage structural belt of Kuqa foreland basin.
Systerm researches about types,distribution and evolution of Paleogene-Neogene slope-break belts in Southwestern Qaidam Basin have been finished to find that the short cycle sedimentary slope-break belt,propering to plateau salty lake,and the fracture slope break belt are developed.The former exists in almost formations except N1, and has a NS distribution.This kind of slope-break belts control the LST,and are the mutational boundaries of distributary channels(underwater distributary channels) between underwater distributary channels(beaches and bars or slump turbidite fans).Kunbei,Alaer,Qigequan,Hongliuquan and Alaerdong,Ⅷ Faults ,which are regulatory,have the characteristics of continuous developing.Ⅺ fault belongs to the discontinuous belt because it is relatively inactive.Inverse fault slope-break belts,which are south-dipping have a more accommodation below the belts.Nevertheless,following fault slope-break belts,north-dipping,have two increscent accommodations.The first is the small reverse fault trough over belts and the second is below belts,which are the profitable zones for sandbodies.Seven lithologic reservoirs having already been found have been analysised to suggested that they are all below the slope-break belts,which have controled the developments of lithologic traps and structure-lithologic traps.On the other hand,those two kinds of belts can make up fracture-sandbody conducting system,which has dominated the hydrocarbon migration paths.So in a word,slope-break belts have the dual functions of controling sand and accumulating oil and gas.The next key drection of lithologic reservoirs is to explore the zones nearby the slope-break belts.
Pingtai area,which is located in the Qilian Mountains,is an ancient uplift for long-term and next to the Saishiteng Depression.In this paper,we discuss the accumulation conditions of oil and gas in the Pingtai area in combination with source rocks,reservoir-cap rock assemblages,trap,and migration pathway.Results show that the oil and gas accumulation in the Pingtai salient was happened outside of source rocks,oil and gas generated from the Jurassic source rocks in the Saishiteng Depression was migrated and gathered into the Tertiary sandstone reservoirs though faults and unconformity,those reservoirs always have background of ancient uplift.The exploration breakout of Ping 1 well confirmed that the ancient uplift and accumulation outside sources have good exploration potential in the piedmont zone of the Northern Margin and is main exploration direction in the Qaidam Basin.
Depended on mathematical statistics of Q type cluster,correlation analysis and ZTR indexes,we discuss the stability and non-stability of heavy minerals and their relevant assemblages in the Paleogene clastic rocks in the northern margin of Qaidam Basin,and ensure the direction of the parent sources.The content of stable minerals is more than that of non-stable one in the Paleogene heavy minerals,suggesting that the mineral had accepted a long-distance transport from the parent source.The similar characteristics of heavy mineral types,relevant assemblages and ZTR indexes occurs in interval setting of Paleogene,indicating that the inheritance sedimentation had happened in the evolutional process.Three input directions of parent sources are gotten as follows:northwestern direction from Altyn,Xiao Saishitengshan and Saishitengshan direction,and east direction from Qilian Mountain and Lüliangshan.Each source can divide into some smaller one and each of small sources is relatively independent.The fourth and fifth tectonic belts of Lenghu were commonly affected by both sources of Altyn and Xiao Saishitengshan.
Oil and gas exploration of the Qiongdongnan Basin in South China Sea have revealed that source rocks in Lower Oligocene Yacheng Formation in the deepwater area,as one of the main gas source rocks,are coal-bearing source rocks of transitional facies.Based on the controlling factors for medium-sized gas fields in deepwater basin,we carried out the whole rock pyrolysis for coal-bearing source rocks of Yacheng Formation,and conducted study on quantitative evaluation for both the upper limit of maturity for gas generation (ULMGG) or “the deadline of gas generation” and quantitative dynamic model.Linked to geological background,we tested the thermal evolution of coal-bearing source rocks under different conditions and natural gas generation.The results show that the upper limit of maturity for gas generation of the whole rock is equal to 4.38% for vitrinite reflectance (VR),where the gas generation rates change little with the increase of maturation,the ΔRO-value is 0.83% of the maximum related to VR of 4.38%Ro,and the process of gas generation from source rock nearly ends while Ro is over 4.38%.At the same time,we obtained the quantitative dynamic model for coal-bearing source rocks of Yacheng Formation under different evolution stages.By comparing to both the conclusions of pyrolysis experiments and the data of VR from the source rock of Yacheng Formation on a series of selected 8 wells in the shallow-water continental shelf basins,it indicates that the most source rocks are still far from reaching ULMGG of the whole rock for type Ⅱ kerogen.The coal-bearing source rocks of Yacheng Formation in the local areas of the deepwater basin still have preferable natural gas generation potential,especially in the areas along the central depression belt from the depocenter to both the margin and its adjacent areas.It has both theoretical and practical significance to oil and gas exploration and development in the other basins with low exploration degree in the northern South China Sea.
Northwest Africa with abundant oil and gas resources,is a hotspot of hydrocarbon exploration for worldwide oil companies,including Chinese ones.Cheliff Basin is just located in the Taylor tectonic belt of the northern Algeria as a Mesozoic petroliferous basin.Because of the multi-episodic orogeny and overprint of complex geological processes in this area,the tectonic evolution of Cheliff Basin is still unclear,which has become a major obstacle to further oil and gas exploration.Based on the tectonic geology and basin dynamics theory,as well as integrated interpretation of gravity-magnetic date,seismic data and remote sensing images,it is proposed that the Cheliff Basin is a superimposed basin after undergoing the continental margin rifting in Mesozoic and intense compressional inverse in Cenozoic.By applying the theory and methodology of petroleum system,and the seismic interpretation,the favorable zones and exploration targets are evaluated,and the eastern depression and its adjacent tectonic belts (e.g.central low uplift,Tliouanet uplift,Mostanem uplift and Ain Zeft step zone) are pointed out to be the possible target areas for oil and gas exploration.
Shwebo Basin is the back-arc basin developed and formed on the basis of Paleozoic marginal sea basin.The tectonic evolution of Shwebo Basin can be described in terms of an early stage of marginal sea basin and a later stage of back-arc basin.The primary source rocks,reservoirs and seals had formed in the second stage.Eocene source rocks generated a mass of hydrocarbon characterized mainly by gas from Oligocene to Miocene.The assemblage of self-generated and self-preserved reservoir was the most important type in the Eocene Formation,and the Oligocene reservoir can also accumulated hydrocarbon from the Eocene source through faults.There are thrust faulted traps in western basin and flower structure traps and fault anticline traps along the Sagaing strike fault in eastern basin.There are two potential exploration targets,Shwebo-1 faulted anticline traps in the Eocene and Oligocene formation in western basin,and Reef anticline traps in the Eocene and Oligocene formation in eastern basin.
The fracture developed sections are the dominant storage spaces for the reservoirs inside the buried hill.How to effectively predict the spatial distribution of the fracture section is the critical issue to explore and develop the reservoirs inside the buried hill.At present,based on core description of the fracture in the exploration and development practice of Xinglongtai buried hill in Liaohe Oilfield,great attention has been paid in order to find out the matching relationship among structural location,formation lithology,fracture characteristics,seismic response characteristics and productivity in the case of only a few exploration wells during the initial stage of exploration,and the reliability of fracture development recognition and prediction is greatly improved.Based on the above recognition,geophysical and geological statistical method has been developed originally in order to evaluate and predict fracture developed section,which integrates the borewell “hard data” with three-dimensional seismic “soft data”,establishes the correlation between the seismic reflection features,fracture development features and productivity features,and achieves the qualitative to semi-quantitative prediction of fracture developed zones.The method has effectively guided the exploration and development of the reservoirs inside the buried hill.
Thickness estimates using instantaneous phase spectrum of post-stack seismic data was explored to estimate bed thickness that is less than tuning thickness.Objective function for thickness estimates,in this method,was constructed on the basis of the instantaneous phase spectrum in the available seismic frequency band,in which magnitude and polarity of seismic reflectivity and the dominant frequency of seismic wavelet were not need to be considered.Synthetic data test showed that on the premise of seismic data without noise,bed thickness of less than and greater than tuning thickness is estimated accurately,and bed thickness estimates using the proposed method is not affected by the frequency bandwidth of seismic data and magnitude and polarity of seismic reflectivity,but thickness estimates is contaminated seriously by noise.Real seismic data examples was evaluated to demonstrate that when SNR of seismic data within the effective frequency band is very high,estimation error employing this method,compared with well logging and interpretation data,is less than 10%,providing the basis for drilling deployment of petroleum reservoir exploration and development.
With the development of seismic survey in the South China Sea,the medium and deep layer is becoming the main survey target,mainly including the Zhujiang Group and basement,and the degree of exploration of them determines the reserve volume of Eastern South China Sea.Some kinds of interference factors affect the imaging quality of the medium and deep seismic data and survey of the South China Sea.Then the most important and urgent problem is how to improve the imaging quality.Normal CMP stack theory is based on the horizontal layer.However,the premise of the dip angle common reflection surface stack method is related not with the dip angle closely,subsurface reflectors can be any angle closer to the actual geological conditions compared to the CMP stack theory.This stack method stacks the entire reflection wave in CMP and in Fresnel zone,and then forms the super-coverage and improves the S/N obviously.After the pre-theoretical research,data test and the application,this method is confirmed to improves S/N of the seismic data and fits the complex formation geological conditions and the solubility of the data can also be improved.The further application of the method could guide the survey and improve the success rate and the scale of reserves in South China Sea.
A set of Lower Jurassic source rock was found in the Xining Basin,Northwestern China.In order to investigate the potential of hydrocarbon generation and the possibility of shale gas and oil formation,the samples in the Lower Jurassic outcrop section of Dachashilang District were collected to measure the abundance,type,and maturity of the organic matters in the lacustrine and HST peat-charcoal shales.The results show that the lacustrine dark shales have the high abundance of organic matter,which are fallen into the area of general-good source rock;the carbonaceous shales have the poor organic matter,which are located within the area of poor-average source rock.Both lacustrine shales and HST carbonaceous shales are Ⅲ1 type of kerogen which is prone to gas.The vitrinite reflectance values are in range of 0.7%-0.94%,suggesting it would be mature stage for massive hydrocarbon generation.The organic geochemical feature for the Lower Jurassic share is similar with the major shale gas reservoirs in the world.Thus,we suggest that the Riyueshan Formation source rock in Xining Basin would be potential for conventional and unconventional oil and gas exploration.
The fracturing of shale reservoir belongs to the crack propagation problems of brittle material.Based on the theory of linear elastic fracture mechanics,the impact of natural fracture on hydraulic fracture is studied,and calculation model of the new crack initiation angle are constructed.On this basis,the crack propagation calculation program is developed,which is made to analyze the controlled factors of fracture network propagation pattern on the way of geology and engineer.Studies show that the natural fracture prone to shear failure and the hydraulic fracture turns to the direction of natural fracture,which is easy to form complex fracture network on the occasion of low horizontal principal stress difference and low approaching angle.The new crack initiation angle has a close relationship with natural fracture dip,horizontal stress difference and pressure in the fracture.Distribution of natural fracture (dip and distance) has an impact on the net pressure at the fracture opening and the biggest width of the fracture.Fracturing fluid with low viscosity is in favor of increasing the limit extension distance,and high construction displacement can increase the natural fracture width of the intersection and be helpful for the proppant to pass through bending section which can avoid bridge plug.The research results can provide an important theoretical reference for the fracturing design in shale reservoir.
Different from conventional gas reservoir,shale reservoir′s seepage mechanism is controlled by adsorption,diffusion,cross flow and Dracy flow,and consequently its seepage mechanism is very complicated.In this paper,desorption is taken into consideration.Considering the existence of pressure difference,except for diffusion,cross flow is introduced.In order to describe diffusion and cross flow respectively,two new parameters are introduced respectively to represent influences of the two factors.Then a comprehensive model for multi-stage fractured horizontal wells in shale gas reservoirs has been built.And on this basis,by means of the modified Lord Kelvin point source function and principle of superposition the expression of the solution has been obtained.Using Laplace inversion and Stehfest integral transformation,the bottomhole pressure of multi-stage fractured horizontal wells can be calculated,and the typical pressure curve and the contrast of the new and old mathematical model can be obtained,which can provide theoretical references for shale reservoir′s well testing and transient production evaluation.
Abundant nanopores are present in shales,and the nanopore structure plays an important role on gas adsorption and migration.Taking nitrogen molecular as probe medium,we use the nitrogen adsorption fractal analysis method to measure the pore structures and roughness in shales.The fractal dimension was obtained from the nitrogen adsorption isotherm using the Frenkel-Halsey-Hill equation.The relationship between shale composition,organic matter content,pore structure parameters and fractal dimension were plotted.The impact of fractal dimension on gas adsorption and transportation was also discussed.Results show that the pore structure in shales is fractal,and the fractal dimension is related to organic matter and micropores.The more enriched organic matter and developed micropore are associated with the much bigger fractal dimension.The degree of fractal dimension indicates the micropore development.The smaller the average pore diameter,the larger the specific surface area,and the higher the fractal dimension.Fractal dimension increases with the increasing micropores.The higher the fractal dimension,the more complicated of pore structure,which is favorable for gas adsorption rather than gas transportation.
The shale gas resources are rich in Upper Yangtze platform,especially in the Niutitang Formation.Huayuan shale gas block is located within the shale gas abundant play of Niutitang Formation in Upper Yangtze platform.Based on the stratigraphic correlation,reservoir analysis and geochemical analysis of source rock samples and in combination with previous study results,the structure,source rock and reservoirs characteristics of the Niutitang Formation in Huayuan block was systematically studied.The distribution range of the Niutitang Formation,reservoir physical property and thickness of source rocks were mapped.Furthermore,the resource volume of shale gas was calculated by using the gas content data obtained from testing in well Yuke 1 and well Cenye 1.The kerogen types of the Niutitang Formation in the Huayuan shale gas block wereⅠand Ⅱ1.With average values of TOC and R O of 3.52% and 3.58%,respectively,reflecting the source rock has entered intoover-maturity stage.The reservoirs characteristics are low porosity-ultralow permeability and high specific surface area.The recoverable resource volume of shale gas is estimated up to 3.18 billion cubic meters.The area from Minle to Longzhai,in the middle-upper of the Huayuan block can be selected for the further exploration and evaluation.
The shale gas is stored in shales mainly in adsorption and freedom states,and the former accounts for 40% to 85% of the total shale gas amount.Thus the shale adsorption capacity determines the pool scale of shale gas to some extent.In order to study the adsorption capacity and the influence factors the Jurassic shale in the northeastern Kuqa Depression,X-ray diffraction,microscopic pore structures and isothermal adsorption tests were carried out.The results indicate that the maximum amounts of adsorption (VL) range from 0.58 m3/t to 8.52m3/t,mainly lower than 2m3/t,and the Langmuir pressures are between 0.55MPa and 5.24MPa.The study shows that organic matter is the main carrier of adsorption gas and its abundance is the dominant factor influencing the adsorption capacity of the shale.When the organic matter content is low,the clay mineral is the main controlling factor for its strong adsorption capacity,and the micropore structure also significantly influences the adsorption capacity of the shale.The adsorption capacity for different types of clay minerals varies,and the illite-smectite mixed-layer has greater influence on the adsorption capacity of Jurassic shale in the northeastern Kuqa Depression for its larger adsorption property.A good positive correlation exists between the maximum amounts of adsorption gas and the specific surface area as well as total pore volume.In addition,the external conditions such as the moisture and pressure also affect the adsorption capacity to some extent.
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