Establishing a Petroleum System Framework in the Northern Gulf of Thailand
The establishment of a petroleum system framework helps define exploration risks, even in producing areas. Effective source rocks are often not sampled, leaving stratigraphic position uncertain. One such area is the northern Gulf of Thailand, where an active exploration program is underway. This work examines methods used to develop an integrated basin study where significant gaps existed in the dataset.
Basin model construction required refinement of the regional stratigraphic framework, adding layers and carrier beds representing interconnected but uncorrelatable sands. This synthetic stratigraphy reproduced the discovery well’s accumulations and calibration points at other fields. Although prior models exist, concerns surfaced about overestimates of crustal stretching and maturity profiles complicated by deviated well data. Sand and coal content were re-estimated, changing thermal conductivities. Vitrinite reflectance data were screened for quality, used to calibrate heat flow at key wells, and linked to other studies for confirmation of regional trends. Rifting aspects had minimal impact. Maturity trends were consistent with other geochemical indicators from oil and gas data. Interval thicknesses on opposing sides of faults suggested periods of structural movement and migration along faults. The impact of structural evolution on migration has been tied to discoveries and laddering of hydrocarbons as they move westward.
With limits placed on source presence by drilling, geochemical data provided a picture of source character and environment of deposition. Analyses of oils and gases yielded indicators of productivity, lake level, marine influence, environment of deposition, algal productivity, and plant input. Empirical oil and gas windows were derived and used to “triangulate” a stratigraphic source position. Observed hydrocarbons were consistent with an Oligocene lacustrine source rock, appearing as three distinct ‘lakes’ that occasionally coalesced. The source is predominantly Type I from a deep productive lake, but Types I/III mixed affinities occur in a shallower, perhaps swampy, lake to the south. A shallow third lake has different properties. Thermal cracking of oils is limited to the central region.
The resultant integrated basin models identified oil- or gas-prone areas as well as migration focus. These data supported the location of new platforms and the acquisition of new exploration concessions, as well as the relinquishment of acreage.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009