The Effect Of Sulfate Scale On Oil Production Index

Waterflooding in oil development is a common and mature method for enhancing oil re-covery in fields, reservoir environment factors variation during injection and the incompati-bility between the injected water and formation water will probably cause scaling in the hy-drocarbon reservoirs, well bores and gathering pipelines. Among common scales, barium sul-fate is notorious for its low solubility, which increases investment to remove it and as a result, highly interrupt the normal production operation and makes severe economic losses. Hence, it is meaningful to develop dynamic scaling prediction model and to study on the influence of oil production index based on the characteristics of barium sulfate scaling process. This paper studied the following aspects:Firstly, based on a great deal of literatures, the inorganic scaling mechanisms related to barium sulfate were elaborated. Key factors of barium sulfate scaling were analyzed, upon which barium sulfate scaling prediction model was fully analyzed and discussed.Secondly, ion concentration distribution model and one dimensional scaling prediction model with diffusion terms were thoroughly studied. The related parameters were modified, and the experimental method of obtaining model parameters were optimized, which was proved to be reasonable.Then, this paper explores the barium sulfate scaling, scaling amount distribution and maximum amount of scale effect on productivity index, and forecasts it.Specific results are as follows:(1) Applied Image method to solve concentration distribution model and its inverse problem to obtain dynamic coefficient and reservoir damage coefficient. The concentration distribution of the scale in the core is simulated.(2) Introducing diffusion term, the asymptotic expansion method is used to solve the model. Combined with experimental data of the core diffusion tests and core steady dis-placement tests, dimensionless diffusion coefficient and dimensionless kinetic coefficients were obtained.(3) Based on the model of one dimensional scaling prediction model of core with diffu-sion, the change of scale and scale distribution of barium sulfate scale in the process of dis-placement experiment was discussed. Analysis of the dimensionless diffusion coefficient and dimensionless kinetic constants, the displacement time and the influence of injection ion con-centration ratio on the prediction results;(4) A one-dimensional scaling prediction model for the formation of the near well zone was revised, and the effect of the amount of the barium sulfate, the distribution of the scale and the amount of the largest scale on the oil recovery index were studied.