Sequence Stratigraphic Analysis from Well Logs of an X-Field, Niger Delta, Nigeria

Abstract

The sequence stratigraphic analysis of the area was studied using well log information in order to determine the lithostratigraphy, chronostratigraphy, possible reservoir sands, age and depositional environment of the study area for opportunities that will support exploration program. The depositional environment penetrated by the wells interpreted from log signatures gave three major facies association. The blocky and coarsening upward (funnel shape), the blocky and fining upward (bell shape) and the erratic (serrated or spiky) facies representing distributary mouth bar, distributary channel and marine mud facies respectively. The sediment deposition of the coastal deltaic and shallow marine delineated for the wells were inferred from the study. Lowstand Systems Tract (LST), Transgressive Systems Tract (TST) and Highstand Systems Tract are the depositional sequences observed. The Maximum Flooding surfaces observed from the stratigraphy analysis indicate major shale break (high shale content). The study area is dominated by altenation of sand and mudstone lithologies, which occurs in approximate ratio of 60:40. The stratigraphic column of the wells was subdivided into sequence boundary, system tracts and sedimentary cycles based on the integration of the various dataset. Some of the sequences have potential of a source rock and seals. The system tracts have the characteristics of good seal and traps. The Maximum Flooding Surfaces and sequence boundaries observed in the wells are four and five respectively. The depths at which the Maximum Flooding Surface occur are 1300, 9300, 9750 and 7050 ft while the sequence boundaries occurred at the depths of 12150, 10850, 8550, 7425 and 6875 ft respectively.