Reservoir geochemistry: methods, applications and opportunities

Abstract

Petroleum reservoirs often contain compositionally heterogeneous petroleum, water and sometimes gas columns which can be interpreted in geologically useful ways. Kilometre-scale lateral compositional heterogeneities in fluid columns suggest petroleum emplacement directions, directions of water flow in biodegraded oilfields and the presence of major barriers to fluid flow within reservoirs. Vertical fluid column heterogeneities on a 10 m scale suggest that reservoirs are vertically compartmentalized. These data can be used as a tool in reservoir description and are thus relevant to many aspects of reservoir appraisal and development. The data supplement those generated by reservoir geologists and engineers, and can be obtained immediately after drilling, at reasonable cost. Much recent work has focused on polar nitrogen (N) and oxygen (O) containing compounds such as quinolines, carbazoles and phenols. These compounds interact relatively strongly with water, rock minerals and each other, and may significantly influence the viscosity and pressure-volume-temperature (PVT) properties of petroleum, and also reservoir wettability. There are obvious links here between reservoir geochemistry and the more traditional disciplines of petroleum and reservoir engineering which we expect to be exploited in the coming years. In the absence of phase changes during migration, the composition of reservoired oil reflects the expelled oil plus changes induced by adsorption, especially of polar compounds, onto solid phases or by partitioning into porewaters along secondary migration pathways. The extent of change, as measured by the relative abundances of selected compounds in reservoired oil and associated water, is potentially a direct measure of migration volume and thus of the relative amounts of water, oil and rock on a migration pathway. We present a simplified, equilibrium model which may allow one to assess migration volumes, and use n -hexane/benzene ratios of some North Sea oils to suggest that these oils have contacted fewer than one hundred volumes of water on their migration pathways. Future work should aim to quantify the interactions of migrating and reservoired petroleum with rock and water, and should yield a more quantitative assessment of both migration volumes and the controls of reservoir wettability.

The source kitchen of the Niger Delta oils: case study on Nembe Creek E1.0 and the Kolo Creek E2.0 reservoirs

“…When hydrocarbon charges from the hydrocarbon kitchen arrive a reservoir, those gain access via a network of pores embedded in the matrix of the rocks or via fractures or faults, usually those bearing the lowest capillary entry pressure. The early arriving petroleum is usually in a series of fronts, depending on the reservoir dynamics, the arriving petroleum will occupy its position within the reservoir, later charges arriving will displace the earlier charges into reservoir (Larter and Aplin 1995). The earlier charges are generated and expelled from a less mature source rock in the kitchen, overtime as generation, expulsion and migration progresses the source rock in the kitchen undergoes subsidence and matures, hence later charges from the source rock into the reservoir are more mature than earlier charges, this results in lateral compositional variation and indeed subtle maturity differences expressed as a maturity gradient across the reservoir.…”

“…The maturity gradient increases in the direction of the kitchen. Parameters such as GORs, biomarkers (maturity markers), water flow directions (n-alkane concentrations) and compositional step changes are employed for determining directions of source kitchens in basins (Larter and Aplin 1995).…”

“…This is suggested to be the source of the petroleum charging the Kolo Creek and Nembe Creek reservoirs. The Nembe Creek reservoir is situated much more seaward than the Kolo Creek reservoir and the Nembe Creek reservoir bears more mature petroleum, the lateral maturity concept holds that the more mature petroleum which are the later charging fronts are always closer to the petroleum source kitchen (Larter and Aplin 1995). It can be suggested that the source kitchen of the Niger Delta petroleum is in the distal delta front, which consists the prodelta Akata marine shales.…”

A Rapid Method of Crude Oil Analysis Using FT-IR Spectroscopy

“…Since its recognition as a scientific discipline in 1959 (Hunt et al, 2002), petroleum geochemistry has developed into an established science that improves exploration and production efficiency (Peter and Fowler, 2002) and it is also used in solves other reservoir related problems (Larter and Aplin, 1995). The mainspring for this dynamism and diversification has been due to improvements/combination of already existing geochemical techniques (Larter and Aplin, 1995;Hunt, et al, 2002), or the discovery of entirely new techniques/applications in the petroleum industries (Larter and Aplin, 1995).…”

“…The mainspring for this dynamism and diversification has been due to improvements/combination of already existing geochemical techniques (Larter and Aplin, 1995;Hunt, et al, 2002), or the discovery of entirely new techniques/applications in the petroleum industries (Larter and Aplin, 1995). This, itself, has been driven by the need in the techniques for increased sensitivity, specificity and sophistication on one hand (Hunt et al, 2002) and the need for simplicity and rapid response on the other (Larter and Aplin, 1995), since it is common to have up to 500 core extracts waiting to be screened (Larter and Aplin, 1995) Prior to the advent of combined gas chromatography/mass spectroscopy (GCMS), sample characterization (Crude oil), had been carried out using liquid chromatography (LC), thin layer chromatography (TLC) and gas chromatography (GC) (Larter and Aplin, 1995). However, these techniques are lengthy, tediousand laborious, as well as expensive to run on a routine basis (Aske, 2001).…”