Software Development On Damage Diagnosis And Plugging Measures Optimization In Sandstone Reservoir

Oil and gas reservoirs are likely to be polluted in various operations such as drilling,completion,oil recovery,workover,water injection,fracture,acidification,etc.This will reduce the oil and gas production capacity and the production yield of oil and gas wells.This affects the accuracy of the interpretation.in well testing and logging.In order to protect the oil and gas reservoirs,it is necessary to fully understand the nature and characteristics of the reservoir itself and the influence of external factors on the reservoir,and the damage in oil and gas reservoirs will be identified,diagnosed,forecast and treated.Those will provide theoretical guidance and scientific basis.for increased water injection and increased production.In this paper,though the characteristics of sandstone,such as particle size of reservoir rock,mineral composition,clay composition,porosity,permeability and sensitivity,the following researches are made on the sandstone reservoir rock damage diagnosis and plugging technology:(1)The damage mechanism of sandstone reservoir is analyzed from three aspects,and these three aspects are internal factors,external factors and comprehensive effect of internal factors and external factors.Based on the field data of Xingnan Oilfield,the causes of reservoir damage are analyzed from four aspects: job construction,reservoir sensitivity,reservoir physical properties and external fluid.Based on the analysis of the damage mechanism of reservoirs,the damage factors of reservoirs are classified from two aspects respectively.On the one hand,it is the interaction between the external fluid and reservoir rock.On the other hand,it is the incompatibility between the external fluid and the fluid in the formation;(2)Through the analysis of every work link in oil and gas reservoirs,the total injures of the wellbore reservoir is decomposed into pure injures and pseudo injures.That is to say,the total skin coefficient obtained from the well test analysis is approximately equal to the total sum of the sum of the true skin coefficient of various pure injures and the sum of pseudo skin coefficient of various pseudo injures.The pure injures in the reservoir cover factors including sensitive damage(eg,speed-sensitive damage,water-sensitive injury,acid-sensitive injury,etc.),particle migration damage,clay swelling damage,inorganic scale damage,bacterial damageand solid particle damage.The mathematical models of the true skin coefficient are established for them.The main damage types are determined by the results of the skin coefficients.The damage radius is determined by the mathematical model of damage radius.The accuracy of the mathematical model is verified from the two aspects : the total skin coefficient and the coincidence rate of the mathematical models.(3)The primary and secondary damage factors are determined and the specific plugging technologies are adopted for different types of reservoir damage.The yield evaluation method of water injection wells is adopted to determine the evaluation scores of three technical indexes,including the initial growth multiple of water injection wells,the effective period and the cumulative increasement of water injection.The plugging effect of water injection wells is determined according to the evaluation criteria of the plugging effect.(4)The software on damage diagnosis and plugging measures optimization in sandstone reservoir is developed to enable automatic retrieval of network data,automatic processing of process data,automatic identification of pollution causes,quantitative description of pollution degree,intelligent judgment of governance measures,automatic evaluation of plugging effect.This software is applied to the injection wells of sandstone reservoirs and it has achieved a good effect.(5)According to the calculation and analysis of a case for a certain water injection well in Xingnan Oilfield,mathematical models of the skin coefficient are established for different types of damage in the reservoir.The main damage types and damage radius are established.The specific plugging technologies are developed and a better plugging effect has been achieved.