A Real-Time Integration of 3D+ Geo-Mechanical Model to Optimize Mud Weight Across Weak Bedding Plane (A Field Applocation)

Abstract

Bedding plane is a surface that separates one stratum, layer, or bed of stratified rock from another and represents interruptions in the course of deposition of the rock mass. A number of models have been proposed in the attempt to solving the problem of wellbore instabilities due to weak bedding plane. Some of these models are developed to be used at the planning and design stages of the well while the accuracy and efficiency depend largely on the integrity of pre-drill data. The objective of this paper is to provide an integrated 3D ϩ geo-mechanical model that would help reduce non productive time (NPT) by combining minimum drilling conditions across weak bedding plane, time dependent brittle creep of rocks and optimum hydraulics parameters. The new model assumes anisotropy rock strength criteria in order to develop theory and models to predict rock physical behavior under specific load conditions. Also all in-situ stresses were assumed principal and directed horizontally and vertically. Analyses were achieved with the aid of DrillMax software newly developed and the results validated with Opti-Well software currently in use for the Niger-Delta Field. The intermediate hole section between 8000ft-12500ft of well-1 in the field was investigated. Analysis of the normal compaction trend showed that the well encountered abnormal pressure at the depth of (8500-11500ft). The sensitivity analysis of the field data showed that the overburden pressure lied within the range 16.84-17.92ppg while pore pressure was between 9.86-10.91ppg. The fracture pressure was between 12.84-13.95ppg while the collapse pressure was 10.92-11.68ppg equivalent mud weight. From the analysis of the hydraulics parameters, the pressure drop at the bit was estimated to be 1894Psi. The developed 3D ϩ integrated geo-mechanical model fell within optimum mud window and integrates time dependent brittle creep of rock and optimum drilling hydraulics.