海上少井条件下低渗薄礁滩灰岩储层甜点定量解释——以珠江口盆地A油田为例

珠江口盆地A油田礁滩灰岩储层超薄、横向变化快、储层非均质性强及孔、渗关系复杂,加之海上钻井资料少、地震资料的纵、横向分辨率低,导致低渗储层甜点评价难度大。为此,建立了物探-测井-地质一体化定量解释薄层灰岩低渗储层甜点的技术对策。针对灰岩速度异常、厚度小、横向变化快等复杂油气藏,结合全波形反演的浅中层速度建模和网格层析中深层速度建模方法,利用反射波和折射波能量更新速度模型,减少速度误差,有效改善了成像质量,从而确保相带划分精度。基于孔隙形态因子校正技术优化复杂灰岩孔、渗关系,直接使用稳定的地震反演弹性参数解释渗透率,从而将渗透率解释模型向三维空间扩展。对于薄层、少井条件的地震资料反演,首次运用综合一维测井岩相和二维平面相联合嵌套约束的分级相控叠前高分辨率地震反演技术,定量表征了礁滩灰岩油藏低渗储层甜点。结合地震数据及反演结果精细解释了礁滩体层位,将灰岩层段分为致密碳酸盐岩台地、生物滩、下部生物礁以及上部生物礁共四个研究单元;认为灰岩低渗储层甜点局部发育,主要分布在1井以北、2井以南的礁滩主体部位。

Quantitative interpretation of sweet spots in low-permeability limestone reservoirs in thin reef beach with few offshore wells:A case study of A oilfield in Pearl River Mouth Basin

The reef-beach limestone reservoir in A oilfield in Pearl River Mouth Basin has an ultra-thin thickness, rapid lateral change, strong heterogeneity, and complex porosity-permeability relationship. In addition, limited offshore drilling data and low vertical and lateral resolution of seismic data make it difficult to evaluate sweet spots in low-permeability reservoirs. Therefore, we propose a technical strategy for quantitatively interpreting sweet spots in low-permeability limestone reservoirs with thin layers by integrating geophysical prospecting, logging, and geology. For complex oil and gas reservoirs with abnormal velocity in limestone, small thickness, and rapid lateral change, we combine the shallow-middle layer velocity modeling method of full waveform inversion and the middle-deep layer velocity modeling method of grid tomography and use the energy of reflected and refracted waves to update the velocity model, so as to reduce the velocity error, improve the imaging quality effectively, and ensure facies division accuracy. The porosity-permeability relationship of complex limestones is optimized based on pore-morphology factor correction technology, and the stable elastic parameters of seismic inversion are directly used to interpret the permeability, which thus expands the permeability interpretation model to the three-dimensional space. For seismic inversion with thin layers and few wells, the multi-stage facies-controlled pre-stack seismic inversion technique with high resolution, which combines comprehensive nesting constraints of one-dimensional logging lithofacies and two-dimensional planar facies, is used for the first time to quantitatively characterize the sweet spots in low-permeability limestone reservoirs in the reef beach. According to the seismic data and inversion results, the strata of the reef beach are explained in detail, and the limestone strata are divided into four research units:tight carbonate rock platform, organic bank, lower organic reef, and upper organic reef. The sweet spots in low-permeability limestone reservoirs are locally developed and are mainly distributed in the main reef beach part in the north of Well 1 and south of Well 2.