Facies and Sequence Stratigraphy Analyses of Klasaman Formation in the “X Well”, Northern Salawati Basin, Papua, Indonesia

Abstract

The “X Well” is located in the Salawati Basin which is part of Western Papua. The interval of study is the Klasaman Formation that is characterized by thick sediment intercalated sandstones and shales. The movement of Sorong Fault strongly controlled the sedimentation of this formation. This study is very important to give a contribution for developing exploration prospect by predicting reservoir distribution since localized facies change may mark the distribution of sandstones. The current study aims: 1) to define the age of Klasaman Formation; 2) to define the vertical facies; 3) to define the sequence stratigraphy; and 4) to predict the lateral change of facies. Five nannofossil datum planes are found throughout the interval and cover the age Late Miocene to Early Pliocene. LO Sphenolithus abies points the age 3.65 Ma, LO Reticulofenestra pseudoumbilicus points the age 3.79 Ma, FO Pseudoemiliania lacunosa points the age 4 Ma, LO Discoaster quinqueramus and LO Discoaster berrgrenii point the age 5.59 Ma and Top of small Reticulofenestra Interval points the age 7.167 Ma. They define the NN11 up to NN16 Martini’s zonation. The age of Klasaman Formation is known as the uppermost Late Miocene to the Early Pliocene. Four facies can be identified, namely Upper Shoreface, Lower Shoreface, Offshore Transition and Offshore. The upper shoreface facies is characterized by thick and clean sandstones, about 2.41 - 20.64 meters thick, while the lower shoreface facies consists of predominantly very fine to fine-grained sandstones intercalated by siltstones and claystones. The offshore transition facies is marked by thick claystones and siltstones intercalated with thin sandstones, whilst the offshore facies is marked by thick laminated claystones. Nine Parasequences 4th order can be identified within study interval, namely Progradational Parasequence-1 to 2, Retrogradational Parasequence-3, Progradational Parasequence-4 to 6, Retrogradational Parasequence-7 to 9. They are bounded by Sequence Boundary-1 to 8. The upper shoreface sandstones of Parasequence-4 to 9 can be potential reservoir rocks in the Klasaman Formation since the sandstones are very thick and clean. The sediments of Klasaman Formation have been sourced from elevated highland in the northeast area, so the upper shoreface sandstones have changed become the offshore claystones from northeast to southwest. High sedimentation rate and rapid subsidence of the basin mark the deposition of Klasaman Formation especially during the deposition of Parasequence-6 to 9 as a result of Sorong Fault tectonics.