Sand body connected volumes,especially the sand body volumes connected to wells is important for the production of oil fields and the design of development programs.With the wide applications of the stochastic reservoir modeling techniques,the evaluation of uncertainty in reservoir characterization has great significance.However,due to many uncertainties,the conventional evaluation method requires large CPU time.In this paper,using the method designed by orthogonal experiment to quantitatively evaluate the uncertain parameters of the fluvial reservoir,it greatly improves the efficiency and accuracy of the uncertain parameters.After careful study of the literature and analyses of various parameters controlling the sand body connected volumes,and according to most of the oil fields,we have established different levels of the parameters.Using orthogonal experiment to design 18 trials of 3 levels with 6 factors,Petrel model software was used to simulate and analyze the test results.
The research on formation and evolution of abnormal formation pressure is of significant importance for understanding the known hydrocarbon accumulation process.However,there is no such quantitative research on Mesozoic formation pressure evolution in the Ordos Basin.Based on acoustic time data and physical data in the studied area,the formation pressure in the late period of Early Cretaceous with maximum burial depth in Longdong area of the Ordos Basin and formation pressure nowadays were respectively calculated by equivalent depth method and quantitative calculation formula of formation fluid pressure after stratum denudation as a result of tectonic uplift,and the formation pressure change characteristics in the two critical periods were determined.Evolution of historical formation pressure in the studied area was restored using ancient formation pressure value in different periods of geologic history obtained by pressure measurement of fluid inclusions.The results show that the residual pressure in Mesozoic strata in Longdong area is generally developed in the late period of Early Cretaceous.The residual pressure in Chang 7 subsection is the highest and can reach 14.50 MPa.After strata denudation due to tectonic uplift,subnormal pressure in Mesozoic strata is generally formed in the studied area except for Chang 7 subsection in some districts.The subnormal pressure generally ranges from -9.42 to -2.25 MPa.The development and evolution of abnormal formation pressure were divided into three stages: initial abnormally high pressure accumulation stage,abnormally high pressure expulsion stage and subnormal pressure formation stage,and this is consistent with Mesozoic burial evolution and hydrocarbon generation history in this basin.Abnormally high pressure is important dynamic force for primary and secondary migration of oil and gas.Most of the Longdong area meets dynamic condition of hydrocarbon expulsion of Chang 7 source rocks to Chang 8 reservoir.The area with lower residual pressure in Chang 8 Formation is the main directional area for oil-gas migration and accumulation.
Abundant natural gas reservoirs with burial depth >3 500 m have been found recently in the Shahejie Formation of the Qikou Depression.The natural gas reservoirs were distributed linearly along the faults and were featured by hybrid gas-oil-water relationships,which were widely recognized in unconventional hydrocarbon reservoirs.In order to understand the occurrence of natural gas in geological conditions for guiding further exploration，this paper calculated the content of gas component dissolved in the crude oil and formation water,affected by temperature,pressure,crude oil property,water salinity,and then compared with the oil production and natural gas output.Most natural gases of Shahejie reservoirs dissolved in the oil and water have been saturated to supersaturation,which formed the hybrid gas-oil-water relationship of free gas in deep transition to shallow of dissolved gas in oil reservoirs or a small amount of free gas,and those reservoirs linearly along those fault which connect with the gas source can be rich in free gas.Meanwhile,the paper discussed the pattern of the oil and gas migration and accumulation after analysis of the occurrences of the natural gas and the distribution of the gas and oil reservoirs.The areas in shallow linearly along those deep faults connecting oil and gas source are benefit to search of condensate gas reservoirs or pure gas reservoirs,in the middle-deep layers for the existence of oil-generating window with the huge quantities of crude oil being better to look for oil reservoirs or dissolved gas-oil reservoirs or light oil reservoirs,and in deep the concomitant fracture traps are easy to enrich the free gas and form the condensate gas reservoirs and the pure gas reservoirs.
The Cenozoic Qikou Sag is a typical extensional faulted basin.The faults′ character and it′s evolution played a key role in hydrocarbon accumulation.In this article we summarized the main characteristics of the faults,and demonstrated the role played by the faults on hydrocarbon conduction and seal process.We divided the Cenozoic faults into three fracture systems,and found that the faults characteristics,the structure style,the tectonic stress state coupling with hydrocarbon reservoir formation stages controlled the conducting or sealing state of the faults to the reservoir and finally formed three typical hydrocarbon reservoir formation modes.
Oil and gas resources are rich in Chengdong area of Jiyang depression.The faults here are closely related with the migration and accumulation of oil and gas.Based on the study of the fault activity,the thermal evolution of source rocks and the migration pathways of the study area,we discussed the fault conduction and hydrocarbon migration feature.The results show that Chennan fault is the sole source fault in this area and its fault activity increases from west to east and the fault active time becomes later along this direction.The Es3 source rocks of Bonan depression are the main hydrocarbon provision layers for Chengdong area and compared with the west part of the sag,the source rocks in the east part are more thermal evolved and have better hydrocarbon provision ability.The match between the fault activity of Chengnan fault and the generation and expulsion history of source rocks control their hydrocarbon migration ability.As the match becomes better,the fault migration ability,the migration amount and the migration distance all increase.The hydrocarbon has a tendency of migrating from the sag to Chenan fault terrace zone and then into Chendong uplift.There are several charging points including Chenggu12,Chenggu13,Chenggu92,etc.and they are usually distributed in the structural ridge,the fault and the structural ridge control the advantageous pathway and migration direction.
Accurate determination of the oil-charging threshold throat plays an important role in recognizing the oil accumulation process.The oil-charging threshold of throats in tight sandstone in Gongshangmiao Oilfield of Sichuan Basin has been studied by means of theoretical calculation and of the observation using environmental scanning and energy spectrum (ESEM) in this paper.Based on the fluid mechanical equilibrium,the calculated theoretical threshold near the interface between source rocks and reservoirs is 29.06 nm.Because the direct influence of the oil-generation overpressure on the fluid is not as strong as the one near the interface,the threshold in the middle of tight sand reservoirs was measured as 59.66 nm with ESEM instead of mechanical analysis.Connecting the thresholds with the mercury injection capillary pressure test (MICPT) on tight sandstone reservoirs,it is predicted that oil saturation near the interface between source rock and reservoir and the one in the middle of reservoirs are 69.5% and 60.4% respectively,which are in good accordance with the well test.Researches on thresholds in different parts of reservoirs could provide a theoretical basis for the study on tight oil charging mechanism and a practical method for tight oil saturation prediction and play assessment.
The reservoir characteristics of Dengying Formation (Sinian) in central Sichuan Basin were studied from petrology,reservoir space types and characteristics and physical property based on drilling data,macroscopic and microscopic observation.Factors affecting physical properties were also discussed from sedimentary facies,diagenesis and tectonic movement.The rock types are mainly dolomite and breccia,the reservoir spaces are secondary pores,caves and fractures,the reservoir is fracture-pore type with low porosity and low permeability and the beach subfacies have the best physical property.Compaction,cementation,filling and silicification are the destructive diagenesis.Recrystallization and dissolution are beneficial for physical properties.Fractures formed by tectonic movement greatly improve the reservoir permeability.
Recently,tight sand gas plays have been discovered in the Lower Cretaceous of Changling fault depression,southern Songliao Basin.By analyzing abundant materials,it is concluded that the dominant provenance is in the south and southwest of the depression.During the transition from a fault depression to a sag,the dominant sedimentary facies are braided river and braided river delta,with other facies such as alluvial fan,fan delta and lacustrine.In the early stage of the deposition progress,several separated depressions form.Faulted steep slope controls the distribution of fan deltas and also the distribution of depocenters.Gentle slope controls the distribution of braided rivers and braided river deltas.During the late stage of depositional progress,only one depocenter remains in the north.The abundant sediments from southern provenance prograde to the north.During the deposition of Quan I member,the only depocenter immigrates to the north.Braided rivers fill the main area of Changling Sag,and the river channels stacked in a large area.Based on the analyses of sedimentary systems,we predicted two potential reservoir belts: one is the braided river sand belts of Denglouku Formation on the south low uplift,the other one is braided river sand belts of lower Quan I member in the southern Changling sag.
As one of the most important kinds of reservoir,conglomerate reservoir has always been a key area to explorationists and developers of oilfield.It is characterized by quick changes of sedimentary facies and strong heterogeneity of reservoirs.Lithology of conglomerate and sand-conglomerate took the leading role.On the base of lithology analyses,the strata were divided into three sets.The first set is from S47—S327,and its lithology is dominated by sand-conglomerate.Sandstone,cobble conglomerate,pebble stone and fine conglomerate showed as a thin layer.The second set is from S317—S237,and its lithology is mainly of sandstone.Fine conglomerate,pebble stone and sand-conglomerate presented as thin layer.The third set is from S227 to S36,and mudstone took the leading role.Sandstone,sand-conglomerate,fine conglomerate and pebble stone appeared as thin layer.Based on these researches,the reservoir architecture were carved up into thirteen types with four degrees such as channel flow conglomerate,laminar flow conglomerate and so on.During this process,well logging data and other information were combined.At the same time,relationship between lithology and reservoir architecture were studied.One or two types of lithology of sand-conglomerate and pebble stone took the leading role in reservoir architecture of channel flow conglomerate and channel beach conglomerate,and high-permeability belt often formed at their position.Although laminar flow conglomerate extended like schistose,the types of lithology of it changed quickly.And on type of lithology took the leading role.Some mudstone of fine grain lithology developed as boundary of reservoir architecture,and they strengthened the heterogeneity of reservoir.The difficulty of reservoir development increased.Sand-conglomerate and sandstone formed main body of braided channel and braided sandstone-conglomerate dam.Lithology characteristics of them were similar with laminar flow conglomerate.The influence of lithology and reservoir architecture to reservoir physical properties and reservoir development were discussed later.
When passive continental margin extends to both sides,it is easy to form conjugate continental margin.On both sides of the Atlantic Ocean in the West Africa and South America is a typical example.Due to the conjugate evolution,continental margin usually has similar petroleum geological conditions.Based on this,East Africa continental margin,under the background of breakup of East and West Gondwana,should also be similar to the Atlantic conjugate type of continental margin.However,because of no consistent breakup time between the plates,the conjugate characteristics are not obvious and were not discussed in the past.By studying tectonic evolution in East Africa,the northern section of coastal East Africa and islands areas have features of conjugate type of continental margin.Both sides underwent the tectonic evolution of early rifting and late passive continental margin and have similar petroleum geological conditions.Exploration results have confirmed that they are the most enrichment of oil and gas regions in East Africa continental margin.However,conjugated hydrocarbon type has differences on both sides.The northern section of coastal East Africa is dominated by natural gas,while islands areas are mainly heavy oil or tar.Preliminary research suggests that the late period tectonic transformation and damage led directly to the differences among the conjugated hydrocarbon accumulation.
In view of the low permeability and difficult extraction of gas in “three soft” coal seam in western Henan,China,this paper studied the deformation characteristics of gas generation and storage layers in Ⅲ coal seam.Based on ABAQUS platform and Gaocheng coal mine,a three-dimensional nonlinear fluid-solid coupling hydraulic fracturing model was established.Then,the rheology-damage-seepage coupling behavior of target layer was described by multi-parameter coupling simulation method,and the initiation and propagation of crack was simulated by cohesive element of T-P damage evolution criterion.In addition,the response mechanism of rock mass against dynamic load and the fracturing effect under dynamic condition were discussed.The results show that when the injection pressure is 4.5MPa,and injection time in about 2 hours,the influence radius of hydraulic fracturing in bedding coal seam can basically reach an ideal data of 80-100m and it greatly improves the low permeability of “three soft” coal seam.Practice also proves that correct construction method and optimal combination of technical parameters can effectively improve the permeability and gas extraction of coal seam,which has important significance to comprehensive utilization of gas in complex mining area.
In order to reveal the effect of the ultrasound on the permeability of coal rock,the principle of permeability of coal rock is expounded,and the permeability test of coal samples under the ultrasound was carried out.The measured data without ultrasound and with the ultrasound under different power are analyzed comparatively.Meanwhile,the loading of the ultrasound promotes the seepage of CH4 in the coal rock,and increases the permeability of coal samples;moreover,as the power of the ultrasound becomes stronger,the increase rate of permeability of coal samples becomes greater.On this basis,permeability relationship model of the coal rock under different confining pressure and power is calculated and fitted according to the relationship of the power of the ultrasonic wave and the flow ratio of the gas.Through the analysis of the experimental results,the principle of the ultrasound in enhancing the permeability of coalbed methane is discussed in detail.
In order to understand the physical mechanism of coalbed methane adsorption in coal in the light of mathematical models,the measurements of the isothermal methane adsorption from three coal samples with different ranks under the air dry and dry ash-free basis were fitted by the models of Langmuir,Freundlich,Toth,Langmuir-Freundlich,Extended Langmuir,BET,D-R and D-A in which the parameters have physical meanings.The p0 was defined as the virtual saturated vapor pressure in the BET,D-R and D-A models and computed via three means.Methane adsorption behaviors of samples on two bases were compared and the microscopic mechanisms of the adsorption were discussed based on the fitted values of the parameters.The fitted effects of each model respectively for a single and all three samples were analyzed comparatively.It was suggested that the B-BET-1 and B-BET-2 models have no physical meaning for the coal samples,D-R-3 and D-A-3 models can not characterize the adsorption of the flame coal,and the mechanism of abnormally high maximum adsorption capacity form the T-BET-3 model is subjected to further discussion.Comprehensively,the T,L-F,E-L,B-BET-3,T-BET-1 and T-BET-2 models are suitable to describe the supercritical isothermal adsorption of methane in coal.
Synthetically application of CBM geology,higher coal chemistry,coal petrology and petroleum engineering,new principle of coal reservoir stimulation was discussed.From the perspective of conventional reservoir acidification reconstruction,an experiment of acidization alteration of CO2 and mud acid was designed and made.Based on the results of conventional permeability,mercury injection,X-ray diffraction and SEM,the effect of acid treatment for the alteration of reservoirs was positive and productive.The minerals that coal reservoir contained were dissolved.The pore structures,seepage channels and the permeability of the coal samples after acidification were improved obviously.The main factors influencing the acidification of coal samples were the basic characteristics of porosity and permeability of coal samples before treated such as the minerals component and content,and the control of drainage after acidization alteration.
Reservoirs with low permeability always exhibit strong stress-sensitivity.According to the regression of extensive experimental data,power function is suitable for describing the stress sensitivity of reservoir permeability.However,the related reported on productivity of reservoirs with low permeability using power function of permeability is rare.This paper established a novel productivity equation for abnormally high pressure and low permeability reservoirs with consideration of threshold pressure gradient,turbulent effect as well as stress-sensitivity using the power function equation.The inflow performance relationships (IPR) were also plotted under different combination of relevant parameters.These parameters have significant effects on the productivity of low permeability gas wells,which should be taken into account when we assess the deliverability of these reservoirs.
Great challenges exist in the development of tight oil reservoirs.In order to examine the influences of geological characteristics,the orientation of horizontal wells and fracture patterns on the horizontal well production,reservoir simulation models for the fractured horizontal well were built to investigate these influences.The influence index was used to quantify the effects of these geological parameters.It is indicated that,the conductivity of natural fractures is the crucial factor to the initial productivity,and the matrix porosity is the most important factor to the decline rate.During the early period,the conductivity of natural fractures plays an important role,so does the matrix porosity during the late period.The orientation of horizontal wells should be coordinated with the orientations of natural fractures and hydraulic fractures,so as to get the highest productivity.The reasonable fracture pattern should reach an improved development.
fractured gas reservoir has very strong heterogeneity when natural fractures with different scale exist.The traditional Dual Porosity Model and its extended models can′t explain precisely about the effect of the fracture factors on the well-test curve,because these models are too idealistic for the gas reservoir.Thus,the paper presents a discrete fracture network model for gas reservoirs which contain large-scale fractures based on Monte Carlo random fractures method and Voronoi Non-Structural grid method,then founds math model of reservoir by Controlling Volume Finite difference method,and uses the fully implicit method for solving problems.Finally,after proving the well test curve of discrete fracture network model by the real well test curve of fractured reservoir,the well-test curve effected by large-scale fracture parameters (including numbers,angles,length) are discussed.The research results suggest that:the late pressure derivative curve is affected by the fracture characteristic parameters;the more number of fractures is,the greater decline of late pressure derivative curve;the longer of the length of fracture is,the earlier of late pressure derivative curve will appear,also the greater decline of late pressure derivative curve;the angle of fracture has little effect on the late pressure derivative curve,but when the fractures′ angle is basically the same with the well radial grid direction,the pressure derivative curve decreased the earliest and had the biggest drop.
In recent years,with the development of natural gas market,China′s natural gas consumption increases rapidly.However,"gas shortage" has occurred frequently because of the lack of a perfect natural gas storage mechanism,which has highlighted the importance of constructing its natural gas storage system.In this field,the experience of U.S.and some European countries is worth learning,definitely.Firstly,this paper briefly introduced the current situation of China′s natural gas supply and demand,as well as several storage methods of natural gas.And then,it analyzed the natural gas supply & demand,together with storage situation of the U.K,France,Germany,Italy,Spain,Ukraine and the U.S.At last,based on China′s current situation of natural gas storage,the paper summarized the experience of these countries,which would enlighten us how to construct our own natural gas storage system.
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