Coaly facies (coals, shaly coals and coaly mudstones) are the primary source rock in several important petroleum basins in SE Asia and Australasia. Delineating these facies and quantifying their organic richness within kitchen areas are some of the key risks for petroleum exploration. To improve their delineation and characterisation using seismic data, a case study was undertaken of the coal-bearing Paleocene and Eocene intervals within the Maari 3D seismic volume area, offshore southern Taranaki Basin, New Zealand. Supporting data were acquired from well logs (including borehole image logs), existing geochemical analyses of well cuttings, and new laboratory measurements of in-situ geophysical and geochemical properties of coal samples from onshore coal mines and other outcrops. In the Paleocene–Eocene interval in the Maari 3D, coaly facies display characteristic low density (<2.5 g/cc) and velocity (<4000 m/s) and appear as bright, resistive layers in image logs. To delineate these facies in the Maari 3D volume, a post-stack seismic inversion was carried out and a P-impedance (product of density and P-wave velocity) model was prepared. Coaly facies exhibit moderate–high amplitude and moderately continuous (up to ~5 km) seismic reflectors, with low P-impedance (<9000 m/s × g/cc) character. Interval P-impedance and amplitude maps reveal temporal variation in the distribution and abundance of coaly facies within the Paleocene–Eocene coastal plain depositional environment. A logarithmic relationship between P-impedance and TOC was used to convert average P-impedance maps to proxy TOC maps for five Paleocene–Eocene time intervals. Coaly facies are most abundant in the low P-impedance areas in the southwestern and central parts of the study area where average TOC is estimated up to 30 wt.%. P-impedance-derived estimates of TOC may be less reliable in structurally high areas hosting hydrocarbon-bearing sandstones and siltstones as some of these facies show similar P-impedance character to coaly facies.

煤相（煤，泥质煤和煤质泥岩）是东南亚和大洋洲几个重要石油盆地的主要烃源岩。描绘这些相并量化它们在厨房区域内的有机丰富度是石油勘探的一些主要风险。为了使用地震数据改善它们的描述和特征，对新西兰塔拉纳基盆地南部海上Maari 3D地震体积区内含煤的古新世和始新世区间进行了案例研究。支持数据来自于测井记录（包括井眼图像测井），现有的井屑地球化学分析结果以及陆上煤矿和其他露头煤样品的原位地球物理和地球化学性质的实验室测量结果。在Maari 3D中的古新世-始新世间隔中，煤相显示出特征性的低密度（<2.5 g / cc）和速度（<4000 m / s），并且在图像测井中表现为明亮的电阻层。为了在Maari 3D体积中描述这些相，进行了叠后地震反演，并准备了P阻抗（密度和P波速度的乘积）模型。煤相表现出中等至高振幅和中等连续性（长达约5 km）的地震反射体，具有低P阻抗（<9000 m / s×g / cc）的特征。间隔的P阻抗和振幅图揭示了新世-始新世沿海平原沉积环境中煤相分布和丰度的时间变化。P阻抗和TOC之间的对数关系用于将五个古新世至始新世时间间隔的平均P阻抗图转换为代理TOC图。在研究区域的西南和中部的低P阻抗区域中，煤相最为丰富，据估计平均TOC可达30 wt。％。由P阻抗得出的TOC估计值在容纳含烃砂岩和粉砂岩的结构性较高的地区可能不那么可靠，因为其中一些相显示出与煤相相似的P阻抗特征。