Abstract

The giant Rumaila oilfield in south Iraq has been plagued by a number of wellbore instabilities. The shaley formations in this field pose the greatest challenges to drilling operations, accounting for approximately 90% of the problems. Stuck pipe, tight hole, and borehole collapse are examples of the incidents commonly encountered even while drilling vertical wells. The main objectives of this study were to generate a mud weight window cube for different trajectory scenarios by examining the impact of depletion on field performance and drilling integrity for making life-of-reservoir decisions. The derived mechanical properties were taken from their respective 1D mechanical earth models (MEM) by utilizing the available mechanical core test data and populating in 3D space. The final 3D MEM has been calibrated against field observations. This paper presents a well planning tool for translating the geomechanical modeling results to operational parameters, and in so doing, informing well trajectory planning and optimization.

Introduction

Reservoir geomechanics play a vitally important role in minimizing drilling activity costs and informing field development planning. Comprehensive geomechanical models (1D, 3D and 4D) have been built in the Rumaila Field based on a wide array of inputs taken from 14 wells distributed across the field. The analysis examined the stress changes in the main reservoirs—namely: Mishrif and Zubair Main Pay—and addressed the instability issues in all Rumaila formations encountered while drilling, by using the available openhole logs, core mechanical test data, production data, and pressure data. The main objectives of this study were to build a fieldscale geomechanical model with a view to assessing the impact of production-induced stress changes on field performance and generating mud weight cubes at different timesteps (Al-Asadi 2021).

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