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In order to make prudent decisions regarding crude purchases, it is important to have access to up-to-date, accurate crude assays. Using old assays may result in an inaccurate picture of the value of the crude; crude quality is continually changing as the wells mature and as crude from different wells are blended. For example, the API of Forties drifted from an average of about 40° in 1996 to about 44.5° in 2006. Therefore, recent crude assays must be used in order to obtain the most accurate picture of the value of the crude. Sometimes, even the variation between different cargoes within a short time span can be significant. For example, assays of Forties Blend have revealed that API variations of up to 3° can occur just from one cargo to another.
While one option is to run complete crude assays on every batch of crude, this method is impractical as it can be quite costly and time consuming; the necessary testing can take up to a few weeks and cost over $20K. Another option is to use crude assay software that can estimate complete crude assays from limited information. This is the premise behind some commercial programs. Crude assays are determined based on trends observed in large databases of actual crude assays. The actual assays are correlated to more readily available factors such as API gravity, sulfur content, origin, and maturity. This allows the processing characteristics for additional crudes with similar characteristics and origin to be predicted even when only a limited number of parameters are known. Of course, the advancement of crude assay software does not mean that running actual crude assays is not necessary, but the software tools do help users fill in the gaps between assays or provide useful information when actual assays are not available.
The followings are some of vendors' software programs capable of predicting or updating crude assays.
It characterizes potential crude blends from the standpoint of corrosion, desalting, fouling, and product quality. The predictive model comprises two parts: (1) a database of refinery configurations and operating experiences with specific crudes and crude blends (Knowledge Base), and (2) a Predictive Engine that uses the database to estimate the risks to specific equipment that are associated with processing a particular crude or crude blend. The database is first scanned for examples that are most like the crude blend under investigation and an algorithm is then used to forecast the performance of the new crude blend. If similar examples are not found, mathematical models are used to predict possible impacts.
It is a web-based application that is capable of quickly identifying crudes matching user-defined criteria from a large collection of crude data. Additionally, the program allows access to the Crude Information Management System (CIMS) run by PetroTech Intel. CIMS supplies updated information regarding changes to existing crude grades and notices of new crude discoveries. A second program, Crude Assay Management System (H/CAMS), uses detailed crude assay information to predict the yields and properties of cuts leaving the CDU for a specific crude or specified crude blends. The yield predictions can help users determine the appropriate crude or crude blend to use in order to obtain the desired crude unit cuts.
It assists refiners with crude selection and blending by determining the optimal crude blend based on simulations that identify the qualities of the splits leaving the CDU. The program compares which crude blend produces streams leaving the CDU that meet the preset targets (e.g., composition, yield, etc.).
It allows users to quickly compare crude choices, look for synergies in crude blends, and identify which crude oils are most appropriate for the user's refinery. When analyzing crude blends, the program allows users to input criteria such as API gravity requirements, maximum sulfur content, acidity restrictions, as well as specify requirements for specific crude fractions such as the 500-600°F (260-315°C) cut. The program then analyzes the crude blend based on a collection of crude assays and reveals which constraints the blend meets. The user also specifies whether each constraint is an absolute requirement, in which case any blend falling outside the specified parameter is rejected, or whether the constraint is somewhat flexible in which case the blend is presented with a warning when it falls outside of the specified parameter.
Source: Opportunity Crude Report II: Technologies & Strategies for Meeting Evolving Market & Environmental Challenges, published by Hydrocarbon Publishing Company