Characteristics And Quantitative Prediction Of Fractures In Ultra-Deep Tight Sandstone Reservoirs,Bozi-Dabei Zone,Kuqa Depression

With the increase of energy desire in the world,unconventional oil and gas resources indicate great potential.Tight sandstone gas resources are abundant in the Bozi-Dabei area,which is the primary exploration and development area of the Kuqa Depression.The area is impacted by multi-period tectonic activity,and natural fractures are forming in the reservoir.Natural fractures play a key role in the transportation and storage of tight sandstone gas and can significantly enhance the pore-permeability structure of tight reservoirs.There is an urgent need to undertake quantitative studies on cracks in the Bozi-Dabei ultra-deep thick sandstone reservoir in order to facilitate effective exploration and development.This thesis quantitatively characterizes the parameters of fractures in dense sandstone reservoirs in the study area and reveals fracture development characteristics using various methods such as field outcrop observation,core description,cast thin section analysis,and imaging log decoding;R/S analysis was utilized to evaluate single-well fracture development using preferred fracture-sensitive logging curves;establish a three-dimensional fracture model of the target layer in the study area to quantitatively predict the spatial distribution of natural fractures.The results show that:(1)The natural fracture types in the study area are primarily shear fractures,followed by tension-shear fractures and the least tension fractures;the angles are primarily high-angle oblique intersections and vertical fractures,with lowangle oblique intersections and horizontal fractures being rare;the directions are primarily NNW-SSE,NW-SE,NE-SW,and E-W;the apparent fracture openness is primarily concentrated between 0-0.5 mm;the fractures good.The tiny fractures are mostly tectonic penetration fractures,with only a few grain edge fractures and intragrain fractures.(2)The fracture development index Q was developed using the R/S analysis approach to quantitatively estimate the fracture development distribution of single wells.The results show that the degree of fracture development varies greatly from well area to well area,and the degree of fracture development within the same well area varies greatly at different depth sections;lithology and layer thickness are the main factors influencing each well’s fracture development;and various factors such as fracture production,filling condition,and detection range of conventional logging curve may lead to errors between prediction results and actual results.(3)To identify the spatial variation of rock mechanical parameters,a three-dimensional geological model of the target layer in the study area was constructed,with the modulus of elasticity primarily ranging from 38-60 GPa,Poisson’s ratio primarily ranging from0.29-0.32,and its spatial spread in a striped pattern,with spatial differences in lithological assemblages being the main influencing factors.(4)In order to quantitatively predict the distribution of natural fracture development in the target layer in the study area,a three-dimensional fracture model is established using deterministic and stochastic fracture modeling techniques.The results show that the fracture development varies significantly between different blocks,with the fracture development in the eastern part of the study area being higher,and the prediction results are in excellent agreement with the actual results.(5)Many factors influence the distribution of fracture development: the formation of fractures in the area is determined by the overall paleotectonic stress field;the density of fractures increases with distance from the fault;there are differences in the degree of fracture development among various lithologies,indicating that fine sandstone is superior to siltstone and far superior to mudstone;the thinner the stratum,the more fractures are produced.In this thesis,there are 58 figures,15 tables and 131 references.