Climate Stratigraphy In Subsurface: \nApplication To Clastic Reservoirs Of Resak Field

Field: Earth and Planetary Sciences (Physical Sciences)

This study was carried out to test and evaluate the applicability of climate \nstratigraphy, in improving and refining subsurface correlation of Miocene reservoirs \n(Groups H, I and J) of the Resak Field, Malay Basin, Malaysia. Climate stratigraphy is a \nnewly emerging stratigraphy concept that uses cyclicity in climate. It is defined as a \nstratigraphic succession of climatic changes through geologic time. This research focuses \non an entirely new methodology for the stratigraphic interpretation based on spectral \n(frequency) analysis of facies-sensitive wireline-logs using CycloLog® methods and \nclimate stratigraphy approach. \nClimate stratigraphy depends on the importance of orbitally- forced climate \nchange as a major control on vertical lithofacies succession. Orbitally driven \n(Milankovitch) climate change takes place at timescales of 104-105 years. It is driven by \nchanges of insolation, the flux of solar energy at the Earth's surface and its distribution \nwith latitude. Climate is a major influence on every stage in the cycle of weathering, \nerosion, transport and deposition of sediments. \nThe Cyclolog® software was used in this study. The software uses spectral \nmethods to analyze the facies sensitive wireline log which in this case, the Gamma Ray \nlog was used. Prediction error filter was computed to generate the PEFA (prediction error \nfilter analysis). When numerically integrated, the PEFA curve yields a still more valuable \ncurve - the INPEF A (Integrated PEF A) curve. This curve reveals trends and other \npatterns that are not generally apparent from the original log data. From this INPEFA \ncurve, key bounding surfaces were identified for the subdivision of geological \nsuccession. New terminologies and nomenclatures were used for climate stratigraphic \nanalysis. Integrating data such as seismic, sequence stratigraphy, cores and \nbiostratigraphic have proven its importance in guiding and constraining the climate \nstratigraphic analysis and interpretation of well data. \nResult for the semi-regional scale stratigraphy framework of the Resak Field \nshows that all lower order major negative bounding surfaces (NBS) of the wells' climate \nstratigraphic framework coincided with or marked quite near to the established seismic \nhorizons. This is observed for StratPac Architecture 1000 and 2000 which are also known \nas Groups J and I respectively. However, for StratPac Architecture 3000 which is known \nas Group H, the top of this package was marked shallower than the established seismic \ntop. The top of this package however coincides with the top of the biostratigraphic top of \nGroup H where it is indicated by acme of nannofossils NN5. \nFor reservoir scale stratigraphy framework, comparison was conducted between \nthe bounding surfaces of both climate stratigraphy and sequence stratigraphy. Results \nshow that the major NBS coincides with the Sequence Boundary (SB) and the positive \nbounding surface (PBS) coincides with Flooding Surfaces (FS). Each of the sequence or \nsystems tract can be further subdivided and refined into a higher order sequences known \nas StratPac Sets (5th to 6th order) using INPEFA curves and verified by the cores. \nSince the climate stratigraphy concept is fairly new and has yet to be fully \nunderstood and evaluated, more studies are needed to establish more detailed relationship \nbetween the key surfaces of seismic and sequence stratigraphy and those revealed by \nINPEF A. Studies should also be carried out in other fields to evaluate and validate the \napplicability of the tool and climate stratigraphy concept itself.