Overburden stress and pore pressure prediction for the North Rumaila oilfield, Iraq

The aim of this study is to give an estimation of the pore pressure in all formations starting from surface to the main reservoir (Zubair Formation) in North Rumaila oilfield. Pore pressure estimation is fundamental in minimizing the nonproductive time (NPT) caused by wellbore instability or mud losses. Two methods were used to predict pore pressure: first, direct measurements of by RFT tool where almost all measurements indicated low pore pressure within reservoirs intervals (Zubair, Nahr Umr and Mishrif Formations) as a result of hydrocarbon production. Second, the indirect prediction, this technique relied on the disparity of the petrophysical characteristics of normally and abnormally compacted formations determined by the compressional transit time data (∆t). This method showed that most of the formations in Rumaila field are equal or less than the normal compaction trend line (NCTL) except the Shale layers in Tanuma, Ahmadi and Zubair Formations as these layers exhibit low permeability and subjected to under-compaction which occurs in rapidly subsiding basins.