Research Of Variable-Viscosity Acid Fracturing Technique Evaluation In Jingbian Gas Field

Currently, reserves of low-permeability gas and oil reservoirs which have being placed on production have made up more than one third of the total producing reserves of China. Most of these reservoirs are still in a state of low produce and low effect. Moreover, in unproduced reserves, reserves of low-permeability gas and oil reservoirs accounted for an even larger proportion. Therefore, acid fracturing techniques have become one of the main measures to make these low-permeability reservoirs put into production, increase production and even produce stably. The Lower Paleozoic carbonate reservoir of Jingbian Gas Field displayed the characteristics of lower permeability, lower pressure, higher heterogeneity and more difficult exploitation. It becomes difficult to satisfy the highly developing and economical requirement through conventional fracturing and acidizing methods after the wide development in the year of 2000, which consequently leads to the laboratory study and field testing of variable-viscosity acid targetted on improving the single well produivity in the year of 2000 to 2003. Based on the variable-viscosity acid fracturing technique, 14 wells had been constructed in the early stage, the result of which indicated that wells with a good physical property in the first and second type of reservoirs presented an obvious reconstruction effect; for wells with a bad physical property, if there was an enough gas sources and good connectivity, the effect was also relatively obvious. But, there were also some wells whose reconstruction effect was poor because of the improper acid compoundings. Hence, for the 9 wells tested in the later period, the liquid quality and construction displacement must meet the required design. According to the data & result analysis of the 23 wells'site testing, variable-viscosity acid showed a high quality of filtration control and reducing acid-rock reaction, which realized the initial goal, with the effective rate and the average open flow capacity reaching 91.3% and 39.7×104m3/d, respectively. In this paper, in order to analyse the main influencing factors and influencing degrees of all kinds of factors to deliverability after variable-viscosity acid fracturing, the grey correlation analytical method was applied, which showed that construction displacement, electrical resistivity, effective thickness, acid volume and porosity are the main influencing factors, which can provide an effective guidance for the later well and layer selection, fracturing design. Also in this paper, a production estimating model was established for variable-viscosity acid fracturing operation complying with the support vector machine(SVM). Verifying with prodution data, accurate performance on estimating was indicated by this model after proper organizing influence factors. Excellent ecnomical performance was demonstrated by computing the economic indexs such as payback period, internal rate of return and financial net present value.