Abstract

This paper presents a methodology to analyze sanding potential on clasticreservoirs by determining the critical drawdown pressure required to on-setsand production. The critical drawdown pressures are obtained from ananalytical model that describes the mechanical stability of a perforationcavity in a Mohr-Coulomb material under Darcy flow regime. The study wasperformed on several wells from different oil fields in South Oman with themain objective to identify the formation intervals with the greatest sandingpotential.

The critical drawdown assessment requires geomechanical characterization ofthe formations of interest. Static mechanical properties and strengths wereobtained from a log-based program. This program is based on FORMEL; which is aconstitutive model describing the microscopic processes occurring in a rocksample during triaxial loading. The basic inputs for running the model are welllog information, petrophysical volumes, and the pore fluid properties of theformation. The geomechanical characterization and the pore pressure profilewere used to calculate the maximum drawdown pressure needed before sandingoccurs on foot by foot basics. A clear correlation was found between lowstrength formations and the intervals with low critical drawdown pressurevalues.

The analysis allows identification of high sanding potential intervals for aselective perforation program, and it supports gravel pack decisions whererequired. Also, the critical drawdown profiles assist to choose a suitable sandcontrol completion technique, ranging from classic gravel packing tostate-of-the-art expandable sand screen installations.

Introduction

Knowledge of rock mechanical properties is important for the planning of bothdrilling and production strategies. Traditionally, rock mechanical propertiesare obtained directly from laboratory triaxial tests on core samples. Hence, mechanical properties are typically only defined at discrete depths were thecore samples were taken and lab values can be skewed due to the core handlingprocess. Accurate sand production prediction, however, requires a continuouspresentation of mechanical properties with depth including the cohesivestrength and internal friction angle of the rock.

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