致密砂岩气藏钻井完井液滤液自吸损害计算机模拟

COMPUTER SIMULATION OF DRILL-IN FLUIDS FILTRATE IMBIBITION DAMAGE TO TIGHT SANDSTONE GAS RESERVOIR

致密砂岩气层孔喉细小,毛细管自吸引起的钻井完井液滤液自吸损害近井带或裂缝面严重影响致密砂岩气藏的及时发现、准确评价和经济开发。文章选取鄂尔多斯盆地北部大牛地致密砂岩气藏岩心,进行了毛细管自吸实验,根据毛细管自吸实验,引入标定毛细管自吸的Cil方程,建立了综合利用地质参数和工程参数的滤液侵入量的数学模型,综合该模型和逆流自吸的数学模型,利用有限差分法求解并模拟出了近井带液相饱和度分布,借助岩电参数正演出滤液自吸损害后气层近井带电阻率剖面。模拟指出,盒2+3段气层比其它气层更易发生水相圈闭损害,采用保护气层的屏蔽暂堵技术和压裂改造技术,发现盒2+3段高产气层。

Tight gas reservoirs have small pore throat. Drilling and completion fluids filtrate invasion induced by spontaneous capillary imbibition into the immediate vicinity of borehole and fracture face has affected badly the discovery in time, evaluation and economic exploitation of tight gas reservoirs. This paper takes Daniudi tight gas reservoir in Ordos Basin for example, spontaneous capillary imbibition experiments were performed. Based on the experimental results, Cil’s model scaling spontaneous imbibition experiment was inducted to establish a new filtrate invasion rate model by using geologic and engineering parameters. Combined with this new filtrate invasion rate model and the mathematic model of counter-current imbibition, the saturation distribution after filtrate invasion was simulated by adopting the finite difference method, the resistivity profiles varying with time around the wellbore was also simulated on basis of the results of rock electricity property experiments. The simulation results also showed that the P1x2+3 gas reservoir is prone to be damaged by water trapping. According to actual situation in Daniudi gas field, and after the application of temporary plugging techniques and fracturing techniques, gas responses in well test data and well logging data improve, which prompts P1x2+3 gas reservoir to be detected and to become the major pay formation.