Study On Reservoir Characteristics And Damage Mechanism Of The Kepingtage Formation Of The Silurian In The Well 11 Of Tazhong

With the rapid development of modern petroleum industry and the increasing demand for oil resources,the low permeability reservoirs have gradually become the key battleground of oil exploration and development.However,it tends to be polluted and damaged during drilling,completing and producing as well since the low permeability reservoir has serious heterogeneity,tight properties,high mud content as well as tiny pore throat radius,furthermore,the economic benefits could be only gained by virtue of acidification and fracturing.Therefore,comprehensively conducting research on the feature and damage mechanism of low permeability reservoir plays the important role of developing low permeability reservoir and lay foundation for reservoir protection.The low permeability sandstone formation in TZ11 Silurian has presently exposed many problems,such as the lower production and less effective production stimulation due to not well understanding of the geological characteristics,accordingly,it is necessary to deeply study the feature and to evaluate the reservoir damage mechanism and damage type during drilling,fracturing and acidizing treatment.This paper targets at the TZ11 Silurian Kepingtage formation,based on systematically analyzing of the formation geological feature,and carries out many dynamic adaptability evaluation experiments between different working fluid(i.e.drilling fluid,acidizing fluid,fracturing fluid),to optimize the acidizing,fracturing formula as well as acidizing parameters,moreover,the main damage mechanism,types and degree also to be diagnosised and proposes specific protecting measures to provide the basis for scientific and effective reservoir development and effectively implement the increasing of reserves and production in combination with a variety of micro analysis methods,such as XRD,scanning electron microscopy,the casting thin sections,ion concentration ICP analysis,nuclear magnetic resonance(NMR)and so forth.The research methods regarding the reservoir damage mechanism owe to drilling,acidizing and fracturing are developed could offer some reference to exploit the same oil reservoir in this thesis.The research results from this paper show that,(1)The Kepingtage SII group of 3 sub segment is the main reservoir that of low permeability TZ11 Silurian oilfield,the reservoir referred to as tidal flat sedimentary system.The lithology is mainly middle-fine grain lithic sandstone and the main interstitial material of reservoir consist of clay minerals,carbonate and silica.The pore types mainly include residual inter-granular pores and inter-granular dissolved pores.(2)The results from the indoor simulated underbalanced drilling experiment show that the damage degree caused by the oil-base drilling fluid system is below 20%,furthermore,we found the key damage mechanism is poor mud cake that does not form effective filter cake,oil-water emulsion,wettability reversal damage and intrusion by solid and liquid phase because of unstable underbalance state.(3)Take acidification as the stimulation,the results from the low intensity and high strength acidizing experiments with the optimized mud acid system show that the reservoir core permeability could be improved by 30%-40%and 60%-90%,respectively.However,it will lead to secondary sediment and produce the particle migration damage on account of improper controlling of flow-back speed ratio and time.It shows that the mud acid system could effectively remove the near wellbore damage and the formation seepage ability is significantly be improved when the optimized acidizing formula and parameters is applied to the actual production,acidating transformation acheved 100%successful rate.(4)Take fracturing as the stimulation,studies show that the 0.3%guanidine gum fracturing fluid system may reduce the damage level to that of the reservoir can support,and the damages from the fracturing fluid system include the adsorption and retention of fracturing fluid polymers,the pores and throats blocked by fracturing fluid residue,the particle migration as well as oil/water emulsion so forth.It shows that the transforming efficiency could be up to 89%and the significant increasing of production is gained when the optimized fracturing fluid system is applied to the actual production.(5)In order to reach the purpose of reservoir protecting,we recommend adopting the whole process of underbalanced drilling technology and cooperating with the corresponding technology including temporary plugging acidizing,the retarded acid system,as well as the water-based fracturing fluid system that have low residue or polymer and so on.