American Journal of Chemical Engineering 2013; 1(1) : 1-5 Published online May 30, 2013 (http://www.sciencepublishinggroup.com/j/ajche) doi: 10.11648/j.ajche.20130101.11 Reservoir formation damage due to mud filtration Abdolreza Dabiri, Mohammad Afkhami, Hooman Fallah * Department of Petroleum Engineering, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran Email address: hooman.fallah2@gmail.com(H. Fallah) To cite this article: Abdolreza Dabiri, Mohammad Afkhami, Hooman Fallah. Reservoir Formation Damage due to Mud Filtration International Journal of Oil, Gas and Coal Engineering Vol. 1, No. 1, 2013, pp. 1-5. doi: 10.11648/j.ajche.20130101.11 Abstract: Transport of particle suspensions in oil reservoirs is an essential phenomenon in many oil industry processes. Solid and liquid particles dispersed in the drilling fluid (mud) are trapped by the rock (porous medium) and permeability decline takes place during drilling fluid invasion into reservoir resulting in formation damage. The formation damage due to mud filtration is explained by erosion of external filter cake. Nevertheless, the stabilization is observed in core floods, which evidences internal erosion. A new mathematical model for detachment of particles is based on mechanical equili- brium of a particle positioned on the internal cake or matrix surface in the pore space. In the current work the analytical solution obtained for mud filtration with one particle capture mechanism with damage stabilization. The particle torque equilibrium is determined by the dimensionless ratio between the drag and normal forces acting on the particle. The maxi- mum retention function of the dimensionless ratio closes system of governing equations for colloid transport through por- ous medium. Keywords: Formation Damage, Drilling Mud, Classical Filtration, Maximum Retention Function External Filter Cake 1. Introduction Formation damage is an undesirable operational and economic problem that can occurs during the various phas- es of oil and gas recovery from subsurface reservoirs in- cluding production, drilling, hydraulic fracturing, and work-over operations. Formation damage assessment, con- trol, and remediation are among the most important issues to be resolved for efficient exploitation of hydrocarbon reservoirs [1]. Formation damage indicators include permeability im- pairment, skin, damage and decrease of well performance. Flow of suspensions in rocks with particle capture and consequent permeability impairment is an essential pheno- menon in many oil industry processes. Particle capture by rock and permeability decline takes place during drilling fluid invasion into reservoir resulting in formation damage. It also occurs during fines migration, mostly in reservoirs with low consolidated sands and heavy oil. Deep bed filtration of fines with capture and permeabili- ty damage takes place near to production wells, in drilling operation. The particles in drilling fluid are captured by size exclusion (straining) or by different attachment me- chanisms (electric forces, gravity segregation and diffu- sion). The classical mathematical model for suspension flow in rocks consists of particle balance and capture kinetics equ- ations [2]. It is assumed that the mean particle speed is equal to carrier water velocity. Internal filtration is the phenomenon describing the cap- ture of suspended particles and droplets of a suspension flowing through a porous medium. Internal filtration of suspended and precipitating solids and the associated for- mation damage constitute fundamental components of the productivity decline problem. The phenomenon is complex and multiple parameters play a role. The characteristics of the porous medium play a role; for example the size distri- bution of the pore throats, the connectivity of the pore bo- dies and the surface chemistry of the grains comprising the porous medium. External filter cake is the term used to describe the par- ticles retained at the interface of porous medium. The re- tention of particles occurs due to different phenomena in- cluding size exclusion; i.e. at the wellbore (Barkman and Davidson 1972) [3]. An alternative mechanism for the de- velopment of an external filter cake is that of transitioning from internal filtration to external filter cake buildup. An example of external filter cake build-up due to size exclu- sion is that associated with drilling. When drilling, the cir- culating mud is designed to prevent fluid leak-off with mi- nimal internal filtration by forming external filter cakes due