Mathematical Modeling Of The Reservoir Sandstone Matrix Acidizing Injury

Fracturing and acidizing are important stimulation and commision treatments of well, which have been extensively applied in petroleum industry. however, these treatments may cause new damage to the reservior that would result in some treatments of fracturing and acidizing inefficiency and short period of validity, this problem especially outstanding in the sandstone reservoir matrix acidization treatment.Therefor, it makes great senses to study the reservior damage of sandstone acidizing. At present, this study are mainly based on laboratory investigation, but from the experiment, we just gain a qualificative or semiquantitative conclusion.According to the current limitations of sandstone acidizing damage research, Based on predecessors'research and analysis of the reservior damage mechanism of sandstone acidizing, the types and gradation of reservior damage were studied by mathematical simulation based on the analysis of reservior damage mechanism in sandstone acidizing treatment systematically, the five main contents are as fllows:(1) From the internal and external cause, the damage mechanism of the compatibility of acid and fluid, compatibility of acid and rock, the improper implement were relatively comprehensively studied.(2) This paper proposed a new method of reservior damage quantitive diagnosis in the sandstone acidizing treatment based on the knowledge of fluid mechanics in porous medium, chemical reaction engineering and others. By mathematical simulation, the primary damage factors were studied, obtaining some mathematical models and relevant solutions, for example, the secondary precipitate damage forecast model, hydrate expansion damage forecast model, fine particle migration damage forecast model, inorganic scale damage forecast model and exotic solid damage forecast model.(3) The quantitative forcasting programme of reservior damage in the sandstone acidizing treatments was established, the affecting factors of main damage types were quantitatively studied.(4) On the basis of the examples, the reservior damage types and degrees that might exist in the sandstone matrix acidizing were diagnosed.(5) According to the primary damage factors and degrees in the sandstone acidizing, this paper proposed some prevention and harnessing measures of the reservior damage in the sandstone acidizing treatments in view of the acidizing fluid, implement parameters, flowback after acidizing.Based on these studies, the main results obtained were as follows:(1) Considering the impact of a variety of the secondary precipitate damage, this paper established a sandstone acidizing geochemistry model, by which the volume of secondary precipitation was calculated and the reservior damage was forecasted; the five designed damage model could forecast the damage types and degrees in the sandstone acidizing treatments.(2) The quantitative analysis showed that the silica gel depositing was inevitable, when the acid concentration was high, a fluosilicate sediment would form.The three precipitates of aluminum fluoride, potassium fluosilicate and silica gel would form at low displacement, while the aluminum fluoride and silica gel precipitates at high displacement. Sediments of the reservoir and the extent of the harm arising directly proportional to the concentration of sediments.(3) The analysis of examples indicated that the main reservior damage were secondary precipitate blockage, the subsequent were hydrate expansion, fine particle migration, the damage of inorganic scale and exotic solid was relatively less.The results of this paper will supply theoretical foundation considering the reservior protection to the design of matrix acidization, and promote the efficiency of sandstone reservoir matrix acidization treatment and its period of validity.