1-D Assessment of Formation Pressure from Transit Time and Shale Diagenesis of an Onshore Field in Niger Delta
IOSR Journal of Applied Geology and Geophysics (IOSR-JAGG), Volume 4, Issue 6, Ver. I, PP 43-51, 2016
9 Pages Posted: 18 Nov 2016
Date Written: November 17, 2016
Abstract
Modeling formation pressures as an input by the engineers into drilling programs come in different styles and reliability. Kicks, loss of circulation, blowouts and even loss of lives are some of the major tragedies associated with poor modeling. The use of 1D has proved to be a sufficient tool; however, it has fallen short of modeling inflation in formation pressure alongside other pressures. The integration of 1D and clay diagenesis to infer formation pressure is robust. Gamma ray logs were loaded into the log panel for correlation, normal compaction was generated from sonic log while overburden stress (OBS) was estimated from density log. Transit time from sonic was used in obtaining Vertical Effective Stress (VES) by applying an exponent and deducting VES from the OBS to obtain formation pressure (FP). Percentage of Illite/Smectite + Illite (ILLISM) transformation and Kaolinite + Dickite + Halloysite transformation to illite were obtained from clay minerals analysed by X-Ray Diffraction (XRD). These percentages were then tied to formation pressures from the 1D assessment. In Well A, peak geopressures of 5549.12psi and 7873.07psi at8306.50ft and 11405ft respectively dropped to 6831.92psi at 11566ft. 29% weight of ILLSMrecorded at 8090ft,slightly deeper than 8027ft yielded 4407.85psi; 32% ILLISM was present at 8330ft close in depth to 8306ft of 5549.12psi. Depth of 11405ft with formation pressure 873.07psi was 250ft above 11630ft which recorded 25% ILLISM. Well E yielded high overpressures with 6077.89psi and 8085.33psi at the depths of8259.87ft and 10867.63ft respectively. Mild high formation pressure of 5853.26psi rose steadily at 8819.42ft. Depths of high illite/smectite mix in Well A tied well with its mildly high formation pressure depths. Well E is of high formation pressure.
Keywords: Formation Pressure, Transit Time, Clay Diagenesis, Illite/Smectite, Kaolinite, Dickite, Halloysite
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