南沙中业群礁地区中生代残留盆地GPU重力异常三维反演

3D inversion of gravity anomaly with GPU in the Mesozoic residual basins of Nansha Thitu Island and reefs area

近年来,三维重力反演方法成为位场反演研究的热点。反演过程由大量的正演计算组成,随剖分单元增加,传统中央处理器(central processing unit,CPU)串行算法的耗时呈指数递增。本文利用图形处理器(graphic processing unit,GPU)并行处理技术提出一种新的反演计算方法,即把每个地面观测点的重力异常计算分配到GPU并行线程中,充分发挥GPU计算数量级的加速性能,因此,反演效率得到极大的提升。作者将该方法应用到南沙靶区三维重力异常遗传算法反演中。研究结果表明,在遗传600代的情况下,使用GPU并行方法可以将反演耗时从超过17天降至7小时,大大减少计算时间。靶区重力异常反演结果和实际观测结果进一步说明了该方法的有效性。通过计算确定三维密度分布,并给出了NH973-1测线上的密度剖面,分析认为地震剖面乱反射区密度在2.24—2.53g·cm-3,可能是中生代沉积地层。最后通过提取地层界面深度及厚度,发现靶区部分区域中生代沉积地层埋深在1.5km以内、厚度大于2.5km,具有较高的油气前景和勘探价值。

The three-dimensional （3D） gravity inversion based on the properties model is very popular in recent years. The inversion is composed of numerous forward calculations. With the increasing magnitude of target mesh, the time of the regular CPU （central processing unit） serial algorithm will exponentially increase. In this study, the authors use the GPU （graphic processing unit） parallel processing technology and put forward a new computing method of inversion to distribute the calculations of every observed point’s gravity anomaly among the GPU parallel threads. The new method takes full advantage of GPU’s operational capability and greatly accelerates the inversion. The authors applied this new method in the 3D inversion of gravity anomaly of Nansha’s target area by the genetic algorithm method. The results show that using the GPU parallel algorithm can reduce the time of inversion from more than 17 days to 7 hours in 600 generations. The inversion and observation of target’s gravity anomaly show the method is efficient. Then, the authors obtained the 3D density distribution of the target and made a density profile of the NH973-1 survey line. Through the analysis, the authors found the density range of the area with random reflection in the seismic profile is 2.24？2.53 g·cm？3 and believed this area might be a Mesozoic deposit layer. At last, by locating some parameters the authors found some of the target area has a high level of oil and gas prospects due to their shallow depth （less than 1.5 km） and large thickness （more than 2.5 km） of Mesozoic deposit layer.