Drilling fluids formation damage

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

The choice of drilling fluid has a major impact on the evaluation and" production of a well. Later in this section, we will investigate the interaction between drilling fluids, logging operations and the potential damage to well productivity caused by mud invasion into the formation. 

In most air and gas drilling operations, open-hole well completions are common. This type of completion is consistent with low pore pressure and the desire to avoid formation damage. It is often used for gas wells where nitrogen foam fracturing stimulation is necessary to provide production. In oil wells drilled with natural gas as the drilling fluid, the well is often an open hole completed with a screen set on a liner hanger to control sand influx to the well. 

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. 

Fluid loss from the wellbore to the formation may be reduced using the less permeability damaging drilling fluid loss additives described above. In saturated brines, carefully sized sodium chloride particles have been used to temporarily plug the formation face (35). The particles may be dissolved by pumping a less saline fluid down the wellbore. 

Tuttle, R.N. and Barkman, J.H. "The Need for Nondamaging Drilling and Completion Fluids," SPE paper 4791, 1974 SPE Symposium on Formation Damage Control, New Orleans, February 7-8. 

Specially designed drill-in fluids or workover and completion fluids, minimize formation damage. 

Foam was selected as the drilling fluid for the horizontal section. The necessity to maintain a low bottom hole pressure in order to remain underbalanced, relative to formation pore pressure, along with the imminent danger of lost circulation, made this project an excellent candidate for foam. Minimizing formation damage was of prime concern. 

Injection waters used in the oil industry may be taken from various sources seawater, fresh water, subterranean water, and production water, which was initially brought to the surface with the crude oil. Injection waters may contain different kinds of particulate materials (formation particles, corrosion products, insoluble carbonates, or sulfates, iron compounds, oil-in-water emulsions, and bacteria) that may be deposited in the rock pores. Because this deposition may lead to well impairment, injection water may have to be treated before it is injected. Oil-producing wells can also be damaged during drilling or workover. Solids present in drilling muds and workover fluids can invade the formation and damage the wellbore area (3, 10, 24, 25). 

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