Study On Quantitative Prediction Of Rock Fracture In Oil And Gas Reservoirs

Rock fractures of oil and gas reservoir are not only the important reservoir space for oil and gas,but also a channel for oil and gas migration.Crack prediction of reservoir rocks can be used to understand the permeability of reservoirs and provide scientific basis for dividing stratigraphic sequence and layout of well pattern.At present,although many kinds of methods on the prediction of rock fractures are developed,there are many deficiencies,such as methods using to predict rock fractures are single,the main factors affecting the reservoir fractures are not completely considered.So in this paper,based on the previous research results,elastic mechanics,mesoscopic damage mechanics,rock fracture mechanics and finite element theory,combined with indoor rock mechanics experiment,micro infrared spectroscopy experiment,digital image processing technology and numerical simulation technology,taking the Yumishan formation reservoirs carbonate rocks in Ren No.11 district of Renqiu Oilfield as an example,considering the influence of seepage,stress and other factors on reservoir rock fractures,the quantitative prediction of reservoir rock fractures of oil and gas reservoir are carried out from the microscopic and macroscopic scales.Finally,the following conclusions are obtained:(1)Based on the analysis of geological data,logging data and core data,it is concluded that the reservoir rocks are various types of dolomite.The minerals mainly include brittle minerals such as MgO and CaO.The rock fractures of study area are consisted with tensile cracks,shear cracks,and the dissolved holes.(2)The infrared spectroscopy experiment of rock sample was carried out.The experimental results show that the sample medium is mainly dolomite,and the mesoscopic structure of the rock sample is characterized by the microscopic infrared spectroscopy.Combined with the digital image processing technology,the characterized results are imported to finite element software.(3)Based on the theory of microscopic damage mechanics of rock,the process of mesoscale fracturing of carbonate rocks was simulated.The results indicate that,the microcracks first appear in the interface areas between pore and transition zone,and then microcracks go to the transition zone,and then extended to the dolomite medium area,and finally cracks form fracture and result in rock damage.Under the vertical stress,the rock cracks are extended along the vertical direction,the resulting cracks are tensile cracks and the rock is destroyed by tensile stress.Under the combined action of horizontal and vertical stress,when the stress in both directions are same value,the cracks are shear crack and extend in all directions.When the horizontal stress is different from the vertical stress,the rock cracks mainly extend along the stress,and the cracks are mainly tensile cracks.(4)Combined with the rock fracture criterion,the fractures of the carbonate reservoir were studied in two cases: the stress field alone effect and the stress and seepage together effect.The results indicate that the shear fractures are more developed than tensile fractures in the reservoir.The interaction between seepage and stress causes the fracture parameter value to be larger than the stress alone action.