| Baolang oilfield is situated in Yanqi,the Hui nationality autonomous county of BayingolMonglian autonomous state,Xinjiang Vygur Autonomous Region.It is also situated on theBaolang-Sumu structural zone,north of Bohu depression,Yanqi basin.The main productionformation is Sangonghe formation of Baolang oilfield,Northwest China.The facies are,underwater distributary channel of braided delta front in upper section,and distributary channel ofbraided delta plain in lower section.Main lithologies are Gravel,Pebbled Sandstone,Coarsesandstone,Siltstone and fine sandstone,etc.The maturities of rock content and rock structure arelow.The reservoir is a coarse grain and low permeability reservoir (LPR) developed frombraided delta.The sand thickness varies from lm to 6m,with distinct multi-interlayer.Thechannel path change frequently,which caused the high heterogeneity reservoir.The averageporosity ranges from 12% to 14%,and average permeability ranges from 2.97 mD to 27.3 mD,ofdifferent oil groups,within Sangonghe formation.Distribution of reservoir properties and fluidare complex.The thickness is large,average thickness ofⅢ1-oilgroup is about 20 meters.Alsothe structure is unique with the growth of many fractures.The reservoir is a representative ofunconventional reservoirs,low density,low porosity,low permeability,coarse grain,high claycontent,fractures and complex structure.After 13 years' production,some geological related problems still affects the efficientexploration of the reservoir.First is the 3D sand structure and flow unit distribution,second is fracture characterization and how it affects the fluid flow.third are the controlling factors thatcause increasing water production.All these problems need to be studied to enhance the oilproduction of this area.This thesis brings forward a systematic and efficient method to construct an integratedmodel for fractured low permeability reservoir,and evaluate the fluid flow performance withindifferent orientation fracture and different flow units reservoirs by using statistics,geostatistics,stochastic modeling,and large and small scale numerical simulation methods.The main contents of this thesis include five parts:First,divide the FU type based on layers correlation,core analysis,core test,reservoircharacter parameters,petrophysical facies,etc.by clustering method.Then build the FUprediction model by multi regression method.At last,figure out and analysis the FU distributionin section and plane,integrated with the distribution of sandstone.Second,make an integrated characterization for the fractures,include measure the fractureline density,dip,and azimuth,and construct the identifying and predicting model for low anglefracture and high angle fracture by log and structural curvature,respectively.At last,plot thecontour map of fracture density.Third,compare the fracture modeling results which is constructed by different stochasticmodeling parameters and methodsFourth,build 3D discrete fracture modeling for low angle fracture and high angle fracture,based on digitize and convert the fracture line density into fracture area density.And,construct ageo-model for the low permeability matrix,controlled by multi-surface and flow units.Fifth,make comparisons of the fluid flow performance for models with different flow unitsand different fracture character by large- and small-scale simulation models.Also,make a casenumerical simulation for the III1 oil layer group,and analyze the oil distribution character basedon well history lnatch.The main results as follows:1.The FU are divided into 5 types,FU-A,FU-B,FU-C,FU-D,and FU-E,by FZI=4μm,FZI=2.72μm,FZI=1.85μm and FZI=1.36μm,respectively.The correlation coefficientbetween predicted permeability,controlled by FUs,and core measured permeability ishigher than 0.7.The predicted permeability can meet the demand for fine reservoircharacterization.2.The fractures in the studied area can be divided into two types,tectonic and complex(include tectonic and sedimentary) formation.Complex formation fracture is frequentlyobserved,fault-related fracture is second.Complex formation fractures account for 60%,while tectonic fracture account for 40%.Ahnost,the fractures are divided into two types,low angle fracture and high angle fracture by the fracture dip.The azimuth of HAF,has three directions,NE,SW,and SE,with average of 156°.Dip angles are varied from15-85°,most of them between 40-75°,and the average is 54.2°.It is varied in differentsections of the anticline,NW higher than SE.Dip of LAF ranges from 0°to 20°,havingno constant trend direction.They growth like"thin biscuit",some fracture space is smallthan 5cm.3.Tri-porosity can be used to predict the fracture intensity (FI) of LAF.The critical valueis 0.3.Multiple regression method was used to construct the fracture intensity calculationmodel by software SPSSTM.The correlation coefficient between predict FI and cored FIis 0.716.With this model,VB programs were written and used to calculate the FI ofmost wells except some wells which having no logs of CNL,AC,and DEN.Then thecontour maps of predicted fracture density distributions were plotted.HAF distribution ispredicted by calculating and comparing the fracture growth index with the cored fractureintensity.4.The FU grouped core-scale simulation results show that it got the highest recovery witheach FU produced individually,and it got an equivalent recovery with grouping FU-Aand FU-B and separating FU-C.Other group-models got lower recovery.Pilot studyresults show that there are no big changes of the total oil recovery for different wellspacing model when the relative pore volume injection speed is equivalent;but there arebigger differences for different injection speed models with same well spacing.5.Four simulation results,each with a different orientation fracture,show that when watercut increased up to 98%,the relationship of oil recovery is,fracture oriented 135°againstdisplacing direction＜45°＜0°＜90°＜Non-fracture model,with FU-A,FU-B and FU-Cmatrix.6.Compared with non-fracture model,when water cut increasing up to 98%,the water cutof FU-A and FU-B decrease,but that of FU-C increase.The recovery of FU-A increase,of FU-B and FU-C decrease,and the total recovery decrease,since the cross flowthrough fracture.7.The simulation results for discrete fracture with equivalent method show that the impactis bigger by fracture equivalent grid size when the permeability of matrix is lower;whenthe cell size in vertical equal the reservoir thickness,the decrease of water cut more than20 %;the suitable grid size in vertical is proportionally with matrix permeability.8.The multi-surfaces and FU controlled modeling method can simulate the sandstoneaccurately.Also the distribution of properties can be simulated properly.The biggestmajor range of Mud,FU-A,FU-B,FU-C,FU-D and FU-E are 635m,429m,520m,558m,556m,and 783m,respectively.The maximum major range of porosity in FU-B,FU-C,FU-D and FU-E are 483m,676m,516m and 628m,respectively.The minimumMinor range of FU-B,FU-C,FU-D and FU-E are 248m,200m,264m and 232m,respectively.The transformations of permeability versus FU-A,FU-B,FU-C,FU-D and FU-E are 52.5 to 162.6,18.3 to 97,6.6 to 51.6,2.5 to 17.8 and 1.4 to 16.8,respectively.Several properties models have been generated.9.Discrete fracture models with different fracture parameters were constructed andcompared.It shows that when fracture area density are 0.05m2/m3,0.1m2/m3,0.5m2/m3,1 m2/m3,2m2/m3,and 10m2/m3,the average porosity are 0.0000,0.0002,0.0019,0.0028,0.0087 and 0.0461,respectively;the average sigma are 3984m-2,371m-2,1476m-2,3x106m-2,8x105m-2,and 1x105m-2,respectively;the average permeability are lmD,10mD,79mD,119mD,369mD,1260mD and 1941mD,respectively.The upscaledporosity and permeability of the fracture model have linear relationship with fracturearea density.10.The simulation results,using above models,show that there are no linear relationshipbetween oil recovery and cumulative oil production and fracture area density.Theinflexions of the oil recovery trend for FU-A,FU-B and FU-C are 2m2/m3,2m2/m3 and1 m2/m3,respectively.Cumulative oil production decrease when fracture area density lessthan 0.5m2/m3,and increase when it bigger than 0.5m2/m3.When the production andinjection well situated in fracture azimuth (Parallel model),the oil recovery andcumulative oil production both less than that when they situated perpendicular withfracture azimuth (Perpendicular model).The time,when water cut up to 98%,ofperpendicular models is later than parallel model when matrix is FU-A,andperpendicular model is earlier than that of parallel model when matrix is FU-B andFU-C.11.DFN model of HAF and LAF have been generated with stochastic modeling methodrespectively.And then the DFN model was upscaled for porosity,permeability,sigmawith Oda method.The average porosity of total model is 0.4%.The average permeabilityin I-,J-,and K-direction,of total model are l lmD,22mD and 13mD,respectively.Themean of fracture space in I-,J-,K-direction are 2.78m,4.19m,and 0.58m respectively.The average sigma of total model is 18836 m-2.The residual oil is controlled by,inefficient network between production and injection,the little fault,sandstonedistribution and the heterogeneity properties of FU.
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