Study On Scale Mechanism And Descaling Process Of Weixinan Oilfield

The Wei Southwest WZ oilfield has developed its major reservoirs, mainly mid-porosity and middle or low permeability reservoirs. With bad reservoir characteristics, there exists strong sensitivity and significant inorganic scale. It’s easily damaged during drilling, well completion, production and workover procedures, causing many wells can’t reach the proration production requirement and strongly limiting the high efficiency development of oilfield. But considering the uncertainty in scale damage and pollution mechanism, there remains no effective control measurements. For solving the low efficiency well control problem of WZ oilfield effectively, extending the steady production period of oilfield and also offering experience and technique for other oilfield development, this paper has used mechanism analysis, laboratory experiments and mathematic simulation as main research measurements, deeply studied the scale mechanism, scale degree and scope, descale mechanism and technique. The main conclusions are as follows.(1) Based on the actual production operation of WZ Wei southwest oilfield, fully using X-ray diffraction, SEM set scanning, energy spectrum analysis and indoor dynamic displacement and other modern advanced experimental analysis method, deeply analyzing the scale type, scaling mechanism of WZ oilfield. The results show that the injection production procedure get scaled easily, mainly contain barium sulfate scale, with a certain amount of calcium carbonate scale. During the workover operation process, the fast leaking off speed of workover fluid results in more serious scale degree.(2)For workover leakage flow characteristics, consider interactions between scale ions as well as convention and diffusion among materials, and establish the mathematic model of barium sulfate scale damage in workover operation. Combining indoor experimental basic parameters for model establishment can effectively realize the prediction for barium sulfate scale damage degree and range. The saturation index method and ScaleChem software have been adopted in the prediction of barium sulfate scaling trend. The results show that the barium sulfate scale is mainly within wellbore radius of1.2m, and under the reservoir circumstances, calcium carbonate scaling trend is obvious after the mixing of formation water and seawater.(3) For WZ oilfield scale characteristics, considering the characteristics of descaling agent, use the combination of corrosion descaling method and particle size analysis, screen out one efficient barium sulfate scale remover with both the function of chelation and dispersion, and apply indoor dynamic experiments to assess the comprehensive descaling effect of scale remover-acid system. The results show that the dissolver-acid system synergy has good descaling effect.(4) According to the previous indoor experiments and simulation results, a set of descaling technology for Wei southwest WZ oilfield has been designed, and the WZ-J2well is selected for field test. After the broken down operation, the well production has been improved, which indicates the reliability of this formula and process. The completed the research content and research results in this paper have provided strong technical support for the effective management of WZ oilfield inorganic scaling damage and single well productivity improvement, and also have offered reference for technical train of thought for solving similar oilfield reproduction.