Integrated Approach to Pore Pressure and Fracture Pressure Prediction Using Well Logs: Case Study of Onshore Niger-Delta Sedimentary Basin

Abstract

This study investigated the cause of identified zones of overpressure in some selected wells in a field in the Niger Delta sedimentary basin. Two models were used each for predicting pore pressure and the corresponding fracture pressure using well log and drilling data. Shale lithology in Niger Delta is massive and characterized by high pore pressure; hence shale compaction theory is utilized in this study. The petrophysical data were evaluated using Ikon's Science Rokdoc software. The two major pore pressure prediction techniques employed are the Eaton's and Bowers' models while the Eaton's fracture pressure model and the Hubbert and Willis fracture pressure prediction models were utilized for fracture prediction. The density and sonic logs were used respectively to generate the shale trend and the shale normal compaction trend used for the prediction. The wells studied showed disequilibrium compaction of sediment to be the major mechanism that gave rise to overpressure in the Niger Delta. Clay diagenesis and fluid expansion were also observed as the secondary overpressure generation mechanism in well X-1. This secondary overpressure mechanism was observed to start approximately at depths of 10,000 ft (TVD). The top of overpressure and the pressure range in the wells studied varied from 6000 to 11,017 ft (TVD) and 1796.70 to 5297.00 psi respectively. The Eaton's model under-predicts pore pressure at the depth interval where unloading mechanism is witnessed. Since the study revealed presence of secondary overpressure generation mechanism, Bowers model was observed to be the most reliable pore pressure prediction model in the area.

Carbonate Reservoir Quality Variations in Basins with a Variable Sediment Influx: A Case Study from the Balkassar Oil Field, Potwar, Pakistan

“…In normal geologic settings, hydrostatic pressure is the normal pressure or the pressure exerted by the column of water from the formation depth to the sea level. If the pore pressure of a formation at a given depth is greater than the hydrostatic pressure, the pressure is said to be overpressure . Whereas if at any given depth, the formation pressure is lesser than the hydrostatic pressure, the formation is considered underpressured.…”

Evaluation of poisson’s ratio range for Fracture Pressure Gradient (FPG) prediction for Niger Delta formation

“…This study was carried out using six (6) well data from the Niger Delta region, the data used was well logs in American Standard Code for Information Interchange (ASCII) format. Because of the existing laws within the Oil companies in Nigeria, the exact location of the wells cannot be disclosed.…”

“…The Niger Delta is located in the Gulf of Guinea, Central West Africa at the culmination of the Benue Trough and is considered one of the most prolific hydrocarbon provinces in the world [5]. It is a thick accumulation of tertiary deltaic sediments bordering the Atlantic Ocean and extends from longitude 3 o E -9 o E and latitude 4 o 30'N -5 o 20'N [6]. The proto delta developed in the Northern part of the basin during the Campanian transgression and ended with the Paleocene transgression [7].…”

Pore Pressure Prediction in Offshore Niger Delta: Implications on Drilling and Reservoir Quality

“…Previous studies carried out in the Niger Delta have shown that abnormal pore fluid pressure generation is related to several factors: due to disequilibrium compaction (Ichara & Avbovbo, 1985;Weber & Daukoru, 1975;Nwankwo & Kalu, 2016;Adewole et al, 2016;Udo et al, 2020;Abijah & Tse, 2016;Emudianughe & Ogagarue, 2019;Alabere & Akangbe, 2021), stratigraphic and structural controls (Evamy et al, 1978;Opara et al, 2009;Ugwu & Nwankwo, 2014) and due to normal faulting, clay diapirism, Shale diagenesis and late hydrocarbon generation (Ugwu & Nwankwo, 2014;Opara et al, 2009;Evamy et al, 1978;Nwaufa W.A., 2006;Alabere & Akangbe, 2021). These studies used well logs, seismic data and leak-off test (LOT) to predict pore pressures in the Niger Delta.…”