Geoscience Australia Marine Survey GA0332 (SS05/2011): Natural hydrocarbon seepage survey of the offshore northern Perth Basin - Phosphorus fractions in seabed sediments.

In September and October of 2011 Geoscience Australia surveyed part of the offshore northern Perth Basin in order to map potential sites of natural hydrocarbon seepage. The primary objectives of the survey were to map the spatial distribution of seepage sites and characterise the nature of the seepage at these sites (gas vs oil, macroseepage vs microseepage; palaeo vs modern day seepage) on the basis of: acoustic signatures in the water column, shallow subsurface and on the seabed; geochemical signatures in rock and sediment samples and the water column; and biological signatures on the seabed. Areas of potential natural hydrocarbon seepage that were surveyed included proven (drilled) oil and gas accumulations, a breached structure, undrilled hydrocarbon prospects, and areas with potential signatures of fluid seepage identified in seismic, satellite remote sensing and multibeam bathymetry data. Within each of these areas the survey acquired: water column measurements with the CTD; acoustic data with single- and multi-beam echosounders, sidescan sonar and sub-bottom profiler (sidescan not acquired in Area F as it was too deep in places); and sediment and biological samples with the Smith-McIntyre Grab. In addition, data were collected with a remotely operated vehicle (ROV), integrated hydrocarbon sensor array, and CO2 sensor in selected areas. Sampling with the gravity corer had limited success in many of the more shallow areas (A-E) due to the coarse sandy nature of the seabed sediments. This dataset comprise phosphorus (P) fractions (adsorbed/oxide-associated-P; authigenic-P; detrital-P; and organic-P) in the upper ~2cm of seabed sediment.

2011年9月至10月，澳大利亚地质调查局（Geoscience Australia）针对珀斯盆地北部近海部分区域开展勘测作业，以绘制天然烃类渗漏（natural hydrocarbon seepage）潜在点位的空间分布图。本次勘测的核心目标为：基于水体、浅表层地层及海底的声学信号特征（acoustic signatures），岩石、沉积物样品与水体中的地球化学信号特征（geochemical signatures），以及海底生物信号特征（biological signatures）三类依据，明确渗漏点位的空间分布，并刻画各点位的渗漏性质——区分天然气与原油渗漏、宏观渗漏（macroseepage）与微观渗漏（microseepage），以及古渗漏与现代渗漏。本次勘测覆盖的潜在天然烃类渗漏区域包括：经钻井验证的已探明油气藏（proven (drilled) oil and gas accumulations）、一处遭破坏的构造（breached structure）、未进行钻探的油气远景区块（undrilled hydrocarbon prospects），以及通过地震、卫星遥感与多波束水深数据（multibeam bathymetry data）识别出具有流体渗漏潜在信号的区域。在上述各区域内，勘测团队获取了如下数据与样品：采用CTD（温盐深仪）开展水体参数测量；使用单波束与多波束回声测深仪（single- and multi-beam echosounders）、侧扫声呐（sidescan sonar）及浅地层剖面仪（sub-bottom profiler）采集声学数据（F区域因局部水深过深，未获取侧扫声呐数据）；采用史密斯-麦金太尔采泥器（Smith-McIntyre Grab）采集沉积物与生物样品。此外，在选定区域内，还通过遥控水下机器人（ROV）、集成烃类传感器阵列（integrated hydrocarbon sensor array）及二氧化碳传感器（CO2 sensor）完成了相关数据采集。由于海底沉积物以粗砂质为主，重力岩芯取样器（gravity corer）在A至E等多数浅水区的实施效果有限。本数据集涵盖海底表层约2厘米沉积物中的磷（P）组分数据，具体包含吸附态/氧化物结合态磷（adsorbed/oxide-associated-P）、自生磷（authigenic-P）、碎屑磷（detrital-P）及有机磷（organic-P）四类组分。