USGS National and Global Oil and Gas Assessment Project - North-Central Montana and Williston Basin Provinces, Heath Formation Assessment Unit Boundaries

The Assessment Unit is the fundamental unit used in the National Assessment Project for the assessment of undiscovered oil and gas resources. The Assessment Unit is defined within the context of the higher-level Total Petroleum System. The Assessment Unit is shown herein as a geographic boundary interpreted, defined, and mapped by the geologist responsible for the province and incorporates a set of known or postulated oil and (or) gas accumulations sharing similar geologic, geographic, and temporal properties within the Total Petroleum System, such as source rock, timing, migration pathways, trapping mechanism, and hydrocarbon type. The Assessment Unit boundary is defined geologically as the limits of the geologic elements that define the Assessment Unit, such as limits of reservoir rock, geologic structures, source rock, and seal lithologies. The only exceptions to this are Assessment Units that border the Federal-State water boundary. In these cases, the Federal-State water boundary forms part of the Assessment Unit boundary.

评价单元（Assessment Unit）是国家未发现油气资源评价项目中用于评估未发现油气资源的基本单元。该评价单元是在更高级别的含油气系统（Total Petroleum System）框架内完成定义的。本文所呈现的评价单元，由负责该油气省的地质学家通过解释、界定并圈绘地理边界来框定，其包含一组已知或假定的油气藏——这些油气藏在含油气系统内具备相似的地质、地理与时间属性，涵盖烃源岩、成藏时序、运移路径、圈闭机制以及烃类类型等要素。评价单元的边界在地质层面被定义为构成该评价单元的各类地质要素的范围，例如储集岩分布范围、地质构造、烃源岩以及盖层岩性的边界。唯一的例外为毗邻联邦-州域水域边界的评价单元，在此类情形下，联邦-州域水域边界将作为评价单元边界的组成部分。