In Situ Stress Magnitude and Orientation in an Onshore Field, Eastern Niger Delta: Implications for Directional Drilling

Abstract

Abstract In situ stress magnitude and orientation are necessary for oil and gas field development planning to achieve optimal well placement whether vertical, deviated or horizontal, wellbore stability analysis for safe and stable drilling to reduce non-productive time, fault stability and cap rock integrity modeling for CO2 geosequestration and stage placement of hydraulic fracture for optimum production in unconventional plays. These were evaluated using wireline logs, leak off test and vertical seismic profile data in an onshore field, Eastern Niger Delta whose stratigraphic sequence is the typical interlayered, normal to abnormal pressured shales and sandstones of the Agbada Formation. The vertical stress magnitude ranges from 23.08 - 25.57 MPa/km, minimum effective horizontal stress from 13.80 - 14.03 MPa/km and maximum effective horizontal stress from 16.06 - 17.65 MPa/km inferring a normal fault stress regime. The minimum horizontal stress orientation varies from 16° - 33° forming the most stable orientation for geosteering a directional well while the maximum horizontal stress orientation is N60°E - N123°E in agreement with the regional fault orientations in the Niger Delta. ENE – WSW, WNW – ESE and other maximum horizontal stress orientations suggest multiple sources of stress, and in situ stress rotation across fault surfaces depicts wellbore instability issues. Structural evolution depicts NE – SW and NW-SE trending faults in the direction of the maximum horizontal stress. Directional well inclination angles of 16° and 33° were predicted in wells 10 and 11 respectively and mud weight window predicted using 2D Mohr - Coulomb failure criterion yielded an optimum mud weight window of 10 - 14.0ppg with overpressure accounting for mud weights as high as 25ppg and minimum mud weight exceeding the maximum mud weight in some sections.