مطالعه شبیه سازی عددی سورفاکتانت سیل برای نفوذپذیری کم نفتی در شرایط فشار آستانه

Based on the non-Darcy flow characteristics of surfactant flooding in the low permeability oilfield, considering the changes of threshold pressure and influence of surfactant on convection, diffusion, adsorption and retention, a mathematical model is established for a three-dimensional, two-phase, three-component surfactant flooding. A new treatment for the changes of threshold pressure and a novel correction method for the relative permeability curve in the process of surfactant flooding are derived, which enhances the matching degree between the mathematical model and field practice. The mathematical model was used to perform the numerical simulation study for a pilot test of surfactant flooding in Chao 45 Block of Daqing Oilfield, a proper injection plan was optimized. After the optimized plan was carried out in oilfield, the desirable effects, like pressure-reducing, injection rate increase, and the increase of oil recovery, were achieved. The average oil increase for single well reaches 37%, the ratio of cost to revenue is above 1:4, so the economic effect of scale is promising.

The laboratory experiments show that the surfactant flooding can reduce oil-water interfacial tension[1], increase the dispersion of oil in water, make oil droplets more deformable and so easier to pass pore throat[2-4], lower the threshold pressure and reduce residual oil saturation[5,6]. The reflection is the moving-up and right shift of oil phase’s relative permeability curve, and the increase of end-point value of water phase’s relative permeability curve.The concrete phenomena in oilfield production are that the amount of water injection increases and the recovery efficiency is enhanced as the injection pressure decreases[7]. Several pilot tests of surfactant flooding were carried out in Daqing’s low permeability oilfields, such as Yushulin Oilfield and Chaoyanggou Oilfield, the objectives of pilot tests are to reduce the injection pressure, to increase the injection rate and to enhance the oil recovery. Because the cost of surfactant is comparatively high, before the surfactant flooding is applied in oilfield, the reservoir numerical simulation study is first used to determine the optimal concentration of surfactant, proper amount of surfactant injected, and injection mode to obtain the maximum economic benefit. At present, the main commercial surfactant flooding softwares are UTCHEM and GRANDTM.Both softwares do not consider a threshold pressure[8],and are primarily used for medium-high permeability reservoir[9]. For the low permeability oilfield, the most obvious strength of surfactant flooding is thereduction of threshold pressure, the increase of production rate and enhanced oil recovery efficiency.Therefore, the current commercial simulation software cannot simulate the above mechanisms. In this article, a new mathematical model of surfactant flooding, based on a compositional model, is established. A new treatment method for the changes of threshold pressure and a novel correction method for the relative permeability curve in the process of surfactant flooding are included in the model. This model was used to optimize the injection plan for pilot test of surfactant flooding in Chaoyanggou Oilfield of Daqing, in order to provide a theoretical support for the decision on the development of oilfield

(1) A mathematical model has been established for the three-dimensional, two-phase, threecomponent surfactant flooding, which includes the variance of threshold pressure in the process of surfactant flooding in the low permeability oilfield. (2) A new treatment method for the changes of threshold pressure and a novel correction method for the relative permeability curve in the process of surfactant flooding are presented, which enhances the matching between the mathematical model and field practice. The error of main development indexes are within 5%.(3) This model can simulate the variance of number of displaced oil layers due to the lowering of threshold pressure before and after surfactant flooding in the low permeability oilfield.(4) The pilot test shows that surfactant flooding can decrease water injection pressure, increase the water injectivity in low permeable layers, and increase the number of displaced oil layers, increase the oil production. The extent of increase reaches 37% while the ratio of cost to revenue is above