Numerical Simulation of Solids Production Using Standard And Cosserat Continua

Muller, Andre Luis (Pontifical Catholic University) | do Amaral Vargas, Euripedes (Pontifical Catholic University) | Zambrano, Carolina (PDVSA-Intevep) | Goncalves, Clemente Jose (Petrobras)

OnePetro 

Solids/sand production is a serious problem faced by the petroleum industry during production stages. Particles or groups of particles of formation rock are produced together with oil or gas being pumped which has highly damaging effects on pipes and valves. Numerical simulation of sand/solids production presents a considerable challenge as intricacies of failure processes must be correctly simulated in order to correctly predict rates of solids production. This paper presents a finite element based procedure for simulating the process of sand production, considering fluid-mechanical coupling in both elasto-plastic Cosserat and standard continua. It is believed that the enhanced deformation modes included into Cosserat continua may contribute for proper modelling of the deformational behaviour and failure modes of the cemented/non cemented granular materials involved. This is made possible by the incorporation of enhanced kinematics and statics as compared to standard continua kinematics through additional degrees of freedom related to rotations of the microstructure, statics through the transfer of moment/couple stresses. For the modelling of the elasto-plastic/failure behaviour of the granular media involved, generalized Mohr-Coulomb constitutive model was implemented to Cosserat continua.

1. INTRODUCTION

The phenomenon of particle production during the extraction of oil producing wells is commonly called sand or solids production. According to Dusseault and Santarelli [1], this physical phenomenon usually occurs when the fluid/porous medium, previously stable, becomes unstable, reaches the strength limit of the porous matrix, with consequent breakdown of the its constituent parts thereafter. Field observations indicate that perturbations of flow gradients and of effective stress acting on the porous matrix of the formation, initiate tearing of small fractions of the rock.

This phenomenon is commonly seen in sandstones, especially in poorly or non consolidated ones. However, it does not occur exclusively in these rocks, as it is also observed in rocks of various natures, such as coal and limestones.

Sand production is one of the most frequent and serious problems observed during the extraction of oil or gas. The Society of Petroleum Engineers (SPE) indicates that much world''s hydrocarbon reserves are contained in sandstone, and thus potentially subject to this phenomenon. Also, if not properly controlled, this might make the development of borehole economically unfeasible, or provide their premature closure. According to Fjaer et al [2], it is estimated that seventy percent of the world''s hydrocarbon reserves are contained in reservoirs where sand production may occur.

Bianco [3] suggested that the sand production phenomenon in oil producing wells would be associated to three basic sets of factors: magnitude of the in-situ stresses and its variations, pressure gradients, fluid flow velocity and changes in fluid saturation; strength factor (strength of the material, inter-particle friction; arcs of sand, capillary forces); operational factors (strategies of drilling and completion, production procedures and depletion of the reservoir). A description of operational aspects and other mechanisms related to sand production are described in detail in Fjaer et al [2].