Formation damage causes

Formation damage caused by clay migration may be observed when the injected brine replaces the connate water during operations such as water-flooding, chemical flooding including alkaline, and surfactant and polymer processes. These effects can be predicted by a physicochemical flow model based on cationic exchange reactions when the salinity decreases [1665]. Other models have also been presented [345,1245]. 

The primary purpose of matrix acidizing in sandstones is to remove formation damage caused by clay and other siliceous fine particles plugging near-wellbore permeability. Particles may be naturally occurring or may have been introduced into... 

Yang, X. M. Sharma, M. M. 1991. Formation damage caused by cement filtrates in sandstone cores. Society of Petroleum Engineers Production Engineering, November 1991 issue, 399-405. 

Despite all these safeguards to extend the service life of the antifreeze, fluid replacement is requited periodically. Typically, fluids are replaced because of irreversible damage caused by one of four conditions contamination, gel formation because of glycol/siUcate reaction, extensive glycol degradation caused by overheating or excessive oxygen exposure, or inhibitor depletion. 

A reduction in permeability around the wellbore mainly caused by contact with drilling fluid (formation damage]. 

The mechanism of action for liver toxicity and carcinogenicity may involve the formation of reactive products (Bonse and Henschler 1976 Bonse et al. 1975 Fisher et al. 1991 Larson and Bull 1992b). Methods for reducing the destructive damage caused by these intermediates, or for blocking their formation through inhibition of metabolic pathways may prove effective in reducing hepatic toxicity but are not currently available for clinical use. 

Polyacrylates are often added to drilling fluids to increase viscosity and limit formation damage. The filter-cake is critical in preventing reservoir invasion by mud filtrate. Polymer invasion of the reservoir has been shown to have a great impact on permeability reduction [98]. The invasion of filtrate and solids in drilling in fluid can cause serious reservoir damage. 

Filter-cakes are hard to remove and thus can cause considerable formation damage. Cakes with very low permeability can be broken up by reverse flow. No high-pressure spike occurs during the removal of the filter-cake. Typically a high-pressure spike indicates damage to the formation and wellbore surface because damage typically reduces the overall permeability of the formation. Often formation damage results from the incomplete back-production of viscous, fluid loss control pills, but there may be other reasons. 

Sometimes it may become necessary to shut-in a gas well when the demand for gas is low. In such instances, the well is shut-in for an indefinite period, after which it is reopened and production is resumed. It often has been found that the production rate of gas from the reopened well is substantially less than it was before the well was shut-in. During production, the inner wall of the production tubing will be coated with a film of condensed freshwater because of the geothermal gradient. This water flows down when production is interrupted and can cause formation damage. This may occur because clays are normally saturated with brine water and not with freshwater. This swelling can be prevented with the injection of some additive, for example, sodium chloride, potassium chloride, calcium chloride, or an alcohol or a similar organic material [1853]. 

Formation permeability damage caused by precipitation of dissolved minerals such as colloidal silica, aluminum hydroxide, and aluminum fluoride can reduce the benefits of acidizing (132-134). Careful treatment design, particularly in the concentration and amount of HF used is needed to minimize this problem. Hydrofluoric acid initially reacts with clays and feldspars to form silicon and aluminum fluorides. These species can react with additional clays and feldspars depositing hydrated silica in rock flow channels (106). This usually occurs before the spent acid can be recovered from the formation. However, some workers have concluded that permeability damage due to silica precipitation is much less than previously thought (135). 

Perhaps the key development that began to tip the balance in favor of water-base fluids was recognition that formation damage by water could be controlled. Control was first provided by inorganic salts dissolved in the water. Operators knew that native brine solutions (usually 6-37% NaCl) caused little or no damage to the formations they were produced from. 

Gray, D.H. Rex, R.W. "Formation Damage in Sandstones Caused by Clay Dispersion and Migration", 1966 Fourteenth National Conference on Clays and Clay Minerals, 355-366. 

Formation Damage. While the causes of formation damage are numerous and may vary from one field to another, they may be grouped into the following general categories ... 

Other minerals beside water-swelling clays have been found to undergo fines migration. The permeability damage caused by essentially non-swelling clays such as kaolinite and chlorite is a well-known phenomenon. Silica fines have been identified as a potential source of permeability damage in various poorly consolidated U.S. Gulf Coast formations (1). Other minerals identified as constituents of mobile fine particles include feldspar, calcite, dolomite, and siderite (4,5). 

Results indicated that poly(DADMAC) will reduce damage caused by contact of low salinity fluid lost from the cement slurry with swelling clays present in the formation. An increase in poly (DADMAC) molecular weight from 600,000 to 2.6 X 10 daltons resulted in a decreased polymer effectiveness. The test columns were of relatively high permeability so the thickness of the adsorbed polymer layer, predicted to be greater for the higher molecular weight polymer, would have little effect on the observed flow rates. 

In the simulations, a significant fraction (about 50% to 80%) of the alkali present in solution is consumed by reactions near the wellbore with the reservoir minerals (as shown in Reaction 30.6 for the NaOH flood), mostly by the production of analcime, paragonite, and dawsonite [NaAlC03(0H)2]. In the clastic reservoir considered, therefore, alkali floods might be expected to cause formation damage (mostly due to the precipitation of zeolites) and to be less effective at increasing oil mobility than in a reservoir where they do not react extensively with the formation. 

Making a Model Acid precipitation often falls to Earth hundreds of kilometers away from where the pollutant gases enter the atmosphere because the gases diffuse through the air and are carried by the wind. In this lab, you will model the formation of acid rain to observe how the damage caused by acid varies with the distance from the source of pollution. You also will observe another factor that affects the amount of damage caused by acid rain. 

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