Abstract
Gathering elemental data from rock material using X-ray florescence (XRF)-techniques is a relatively common practice in the Delaware Basin. As such, operators often amass very large datasets comprising thousands of sample points that superficially appear ideal for “big data” projects. However, varying sampling strategies between core and cuttings but also over the lifetime of an analytical program means that not all data can be directly or meaningfully compared.
In this paper we discuss the pros and cons of different sampling approaches when attempting to resolve the questions in the following areas: (a) regional or field wide correlation, (b) characterization of landing zones and (c) characterization of depositional environments. Additionally, we will also show how data can be successfully integrated from high resolution core analysis (2-12 inch vertical resolution) to low resolution (30ft-50ft) vertical cuttings.
Typically, XRF datasets from cores are gathered at a high resolution over a relatively thin interval to provide detailed facies and depositional environment information. However, as these datasets can show such small-scale variability, it often becomes difficult to integrate this data into more regional and broader scale findings. Conversely, cuttings can be sampled from a far higher number of wells and as such cover a much wider stratigraphic and geographic area, with sample density controlled by sample collection. Datasets gathered from cuttings are commonly collected for either more regional characterization or for landing zone identification. Due to the composite nature of cuttings, however, high resolution facies variability in sequences can be lost at a 20 or 30ft interval, making it tough to meaningfully define landing zones and integrate data from lateral wells using vertical cuttings data alone.
Using a series of Delaware Basin case studies, we firstly show how relative changes in elements and element ratios, from widely spaced cuttings material in vertical wells, are used to provide robust regional correlation frameworks that complement and refine stratigraphic tops picked from wireline log data. We will also highlight some of the difficulties in tying vertical cutting data with high resolution core data and strategies to resolve these issues. Finally, we will show how data acquired from core can provide detailed insight into landing zone characterization and insights into the rapidly changing depositional environments of the Delaware Basin, through Wolfcamp and Bone Spring time. This type of analysis can be easily integrated with data from lateral wells in order to understand and ultimately predict the type of lateral facies variation expected from different landing zones.
By systematically working through XRF datasets at different sampling resolutions we are able to utilize and integrate these datasets more efficiently. Ultimately, we can start to understand the optimal sampling resolution needed to solve different characterization or stratigraphic problems in different Delaware Basin formations and design more focused and “fit for purpose” analytical programs in the future.
