Petroleum geochemical analysis of oil and oil seepage samples from the Salin Basin, Central Burma Depression, Myanmar

The present report summarizes petroleum geochemical analyses carried out of a set of oil samples collected from producing fields or oil seepages in the Central Burma Depression of Myanmar. The petroleum geology of onshore Myanmar is excellently summarised by Ridd & Racey (2015), to which paper reference is made for further information. All samples were collected from oil-wells or seepages in the Salin Basin, which is one of at least seven subbasins found within the large (approximately 2000 km long) downwarp known as the Central Burma Depression, developed along the Indo-Burman ranges that border the depression to the west. (fig. 1.).

The Central Burma Depression hosts an up to 15 kilometres thick succession of Albian to recent sediments, including both marine and terrestrial deposits. Within the Central Burma Depression, extensive folding and faulting is common, giving rise to a variety of structural traps that in several subbasins hold petroleum accumulations. Among the petroliferous basins, the Salin Basin is the more important, with an exploration history extending approximately 130 years back in time. The thick sedimentary succession can be studied along the margins of the depression, first and foremost to the West (generally known as “The Western Outcrops”), but to the North, in the Chindwin Basin, outcrops are accessible on both sides of the depression. Data from outcrops combined with well-information make it clear that a large number of both potential reservoir units and source units are present within the depression (Fig. 2).

Compositional data on oils and source rocks of Myanmar are very sparse, but an important study was published by Curiale et al. (1994), who investigated a series of oils (31 samples) from the Salin Basin plus two rock samples (a “resin” accumulation embedded in shale and an Eocene age coal). The study is highly commendable. It is comprehensive and thorough and constitute unrivalled the most important source of information pertaining to petroleum composition in Myanmar/Burma. The overall petroleum composition is generally very uniform, pointing to a predominantly terrestrial source, and the authors conclude that all oils belong to a single family, where the differences observed may essentially be attributed to differences in the level of biodegradation. Moreover, the authors suggest a deep Palaeogene (presumably Eocene) terrestrial source for the oils, and propose an exploration model where deeper and older traps were filled first with shallower and younger traps being filled be later by more mature charges bypassing previously filled deeper/older traps, causing shallower/younger traps to host oils showing higher maturity than deeper/older traps. The investigations and analyses, carried out at GEUS in Denmark, aim to demonstrate if further detail can be added to the conclusions made by Curiale et al. (1994) by analysing samples from the same study area by present day techniques.

Pending a positive outcome and procurement of necessary funding, it is the intention of GEUS, in collaboration with the M.O.G.E. to expand the study to cover larger parts of Myanmar by analysing samples from other petroliferous basins, as well as from areas outside the Central Burma Depression, as for instance seepage areas in the Rakhine Province along the western coast of Myanmar, offshore which petroleum exploration is presently taking place.

A comprehensive and integrated overview of petroleum and source rock characteristics in Myanmar will be of great value to both the national petroleum administration for better understanding the hydrocarbon potential of the country and to the industry responsible for carrying out active exploration.