Reconstruction of Water Encroachment History in 4D in a Brown-field Using Time Lapse Pulsed Neutron Capture Log - A Case Study

Pulsed neutron capture logs are excellent in picking up the oil-water contact in a sandstone reservoir if the porosity is reasonably good and formation water salinity is high. PNC logs have been used in this study done in a sector of a large Middle Cretaceous clastic reservoir in Kuwait having a long production history of more than 60 years. The wells have rich collection of time lapse PNC logs recorded at regular intervals. The oil water contact obtained from these logs were integrated and interpolated to track the movement of the oil water interface of the reservoir through time. Seven time planes, 1992, 2002, 2004, 2006, 2008, 2010 and 2012, were identified for this study. Initially the data points were picked up in those time planes where there were PNC logs indicating exact position of the contact. There were 131 actual log based data points having high confidence level. In the next phase those contacts were interpolated in other wells by correlation taking into account the geology in consideration. 233 data points were thus estimated. The exercise resulted in reconstruction of the water encroachment history in 4D. It was useful in locating the remaining oil to be targeted in future.