| Water injection is an effective method of replacing reservoir depletion, increasing formation pressure and improving recovery ratio. The re-inject of production water not only avoid environmental pollution, but also achieving the purpose of holding pressure. But in the injection process, the injected water is contact with reservoir rock and fluid, and various physical chemical reaction, which can damage the formation.In addition, the disqualification water will rise the collection system and borehole to corrupt, which significantly reduced the effect of water.So it’s very important to study the compatibility between injected water and formation in the oilfield development and discuss the root of the above phenomenon. For Jidong Gao shangpu field which is a reservoir with sensitivity of the clay minerals, the low injected water salinity can cause clay mineral inflation, a lot of injected water will directly cause permeability drop, reservoir damage.In addition, in the treatment process of sewage,the water quality will directly influence the oilfield development effect, for example if the injected water contains suspended particles, and oil, and bacteria, and are injected back into reservoir will result in filtration end plug, injectivity decline, injection pressure increase,and enlarge the reservoir heterogeneity, makes the oil reservoir energy shortage, oil well production decline. At the same time, injected water dissolving oxygen, carbon dioxide gas will cause corrosion on the ground engineering equipment, shorten the water flooding equipment and the service life of the pipelines. The corrosion products in the injected water can also pollute reservoir. If We don’t consider injected water quality and water sensitivity of formation, then substandard injected water in the reservoir can cause porepassage plugs and permeability drop, and lead to the decline of oil and gas water injectivity coefficient, if have damaged it will be difficult to get recovery, thus seriously affect oil field development efficiency.From Jidong oilfield present development situation, although after a long period of water flooding there forms many throats, some of the water injection well still occurs plugging phenomenon, making water injection pressure increases, thus can’t complete injection allocation, weakens the waterflooding effect. For current production situation, the urgent researches on jidong oilfield reservoir damage mechanism are needed,researches on the compatibility between injected water and reservoir shuou be taken, so as to solve the present problems such as the water pressure increases, water injectivity index declines and poor flood effectiveness.Based on the analysis of the characteristics of Jidong Gao shangpu reservoir and the current water injection situation, this paper makes the use of oil reservoir rock cores,simulate oilfield water injection conditions, and proceed reservoir sensitivity evaluation experiments,determine the characteristics of reservoir sensitivity damage; It studied the experimental evaluation adaptation of the injected water, including water scaling prediction、the experimental research about static compatibility of injected water and fluid in reservoir and the experimental research about dynamic compatibility of injected water, clear compatibility characteristics between injected water and fluid in the reservoir; It studied experiment and the impact on formation damage of injected water,analyzed the damage factors during water injection in Jidong Gao shangpu reservoir; It studied the sensitivity and scaling prediction methods, compiled "reservoir damage prediction software"by using VB language,can predict speed-sensitivity、water sensitivity、salinity sensitivity、acid sensitivity and Alkali sensitivity,quickly predict scaling trend of surface water and underground water and the largest scale amount and gave the calcium carbonate scale scaling degree description; Automatically generate sensitivity and scaling prediction results report and output results in form of Word document;compare results from the"reservoir damage prediction software"and those from experiments,verified the validity and practicability of the software.1.The results from sensitivity expermiments are as follow:The critical flow velocity range of Gao shangpu reservoir is0.3～0.5ml/min,Gaoshennan block belongs to medium to strong-weak speed sensitivity reservoir,Gaozhongshenbei block belongs to medium to weak-no speed sensitivity reservoir.Speed sensitivity results from particle migration deposition and plugging in kaolinite. Gao shangpu reservoir belongs to strong water sensitivity oilfield. Gaoshennan block belongs to medium to strong water sensitivity reservoir, Gaozhongshenbei block belongs to medium to strong-strong water sensitivity, critical salinities of both blocks are equal to or greater than6000mg/L. Water salinity of this reservoir is1499.34mg/L, which is far lower than the critical salinity, in a clay expansion is easily happened in the process of water injection.2.The adaptive resarch results of injected water and results of formation damage expermiments of injected water are as follws:There is no soild substance and no emulsion fluid after mixing injiected water and formation crude,which show good compatibility between injected water and formation curde; injected water in Gao shangpu reservoir show bad compatibility with formation water,scaling prediction indicates that there is a trend of CaCO3after mixing injected water and formation crude;but according to indoor Static and dynamic evaluation experiments,formation damange from scaling is not serious,so scaling is not the main reason of formation damage;the damage degree of permeability is more than25%when inject fine filtered water,whch shows water sensitivity is the main reason that causes injection well jams; injection water suspended solids content is2mg/L, particle size median diameter is8.145μm because of low permeability, if part of the small particles were brought into the oil reservoir they form internal filter cake near the well and the larger particles form block in the wall, volumetric flow experimental and single factor analysis of experimental results show solid particles plugging is the main reason leading to formation damage.3.The main results of formation damage predicting research are as follows:Through a comparative study to get a accurate prediction model of forecasting reservoir sensitivity and a accurate method of scaling prediction.The model can predict speed-sensitivity、water sensivity、salinity sensitivity、acid sensitivity and Alkali sensitivity on the basis of content of clay amount、kaolinite、illite and illite/smectite and data of average porosity and average air permeability; the method can quickly predict scaling trend of surface water and underground water and the largest scale amount and give the calcium carbonate scale scaling degree description on the basis of data of formation water and injected water and formation pressure temperature and PH; Compile "reservoir damage prediction softwaro"by using VB language which can automatically generate sensitivity and scaling prediction results report and output results in form of Word document;Compare results from the"reservoir damage prediction software"and those from experiments,and have verified the validity and practicability of the software. |
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