- Let's continue with our series on petroleum geochemistry applications. Today the topic is on applications of petroleum geochemistry to appraisal. Today's topic is as follows: We'll discuss the role of geochemistry in the exploration-production lifecycle and during appraisal. We'll also discuss the main sample types for geochemistry studies, as well as geochemistry analytical programs during appraisal. We'll talk about the main questions addressed by geochemistry during appraisal and the main controls on oil quality, source rock type and maturity indicators from oil and gas geochemistry, and secondary in-reservoir processes affecting fluid quality of the accumulation. We discussed this figure on the role of geochemistry in the exploration-production lifecycle in more detail in Part 1 of our series. The lifecycle stages through which our conversional plate goes through are exploration appraisal, development, and production. At the end there is an abandonment environmental remediation stage that is not covered in this series of lectures. During exploration and appraisal, the focus is on the search and discovery of a commercial hydrocarbon accumulation, evaluating the size of the accumulation, type of fluids: oil vs gas, as well as fluid properties, which define the quality and price of the fluid and are used in the economic evaluation and appraisal. During these stages petroleum system analysis has a very important role and incorporates a continuous interaction between building the geologic model basin model, and using exploration geochemistry to evaluate the main components of the petroleum system such as source rock, charge, migration, and accumulation. Drilling an exploration well, which results in hydrocarbon discovery, usually marks the transition to appraisal stage. The appraisal stage involves drilling of additional appraisal wells, to evaluate the extent and value of the discovery. During the appraisal stage, reservoir geochemistry may be utilized to evaluate presence of additional reservoir accumulations, fluid properties, in-reservoir processes like biodegradation, water washing, and others that could alter fluid properties and reservoir compartmentalization. We'll discuss some of these topics in more detail in the following section. So let's discuss briefly the role of geochemistry during appraisal. During appraisal, geochemistry results are used to calibrate and improve the existing basin model with newly acquired well data and for integration with reservoir fluid properties from PVT analysis and reservoir characterization. Appraisal is also the stage when a lot of very important new information is acquired from the appraisal wells. The information gathered at this stage is of paramount importance because it provides data for the static conditions of the system. For example, reservoir pressure, reservoir temperature, and fluid properties, which will start to change once production from multiple wells begins later on.