Solvents and mutual solvents have been used for numerous years as stimulation treatments or as components of stimulation treatment packages. This paper presents the results of field case histories of stimulation treatments using a unique combination of selected solvents and mutual solvents to remove hydrocarbon based formation damage. Treatment with this chemical has been effective in removal of multi-continent hydrocarbon and hydrocarbon/water causeddamage. The removal of this damage in producing wells provides increased production at rates and lifetimes exceeding those obtained by conventional solvent or solvent/acid treatments, and hot oiling treatments.

References and illustrations at end of paper


The deposition of hydrocarbon material occurs in the near wellbore area, formation face and perforations. These deposits can consist of paraffins, asphaltenes, emulsions, oil wet scale or other solids, and combinations of any of these.1

Paraffin deposits can be caused by cooling of the well fluids as they are subjected to pressure decreases at the formation face and through the perforations.1 In this case the naturally occurring higher carbon number paraffins deposit because the accompanying crude oil cannot re-dissolve them at existing bottom hole temperature. Thus, when wells become older and their bottom hole temperature falls, the chances for paraffin deposition and plugging increases. Additional paraffin deposits occur downhole due to hot oiling for paraffin control.2 Addition of hot oil to bottom hole areas can leave paraffin deposits when the hot oil cools and it can no longer hold paraffin in solution at bottom hole conditions.

Asphaltenes can create plugging in the bottom-hole area by deposition from the crude oil. The asphaltenes can be destabilized from their normal dispersed state by many factors which occur in production systems. These include: pressure drop which changes the composition of the crude oil and causes turbulence,1,3,4,5 streaming potential caused by the fluid flow in the porous media of the formation which destabilizes asphaltenes by electrical potential,1,4 and by the addition of foreign agents. These agents can be acid or other stimulation or workover fluids,1 or recovery assist additives such as CO2 or other miscible gases.1,4,5 These materials can destabilize the asphaltenes in suspension by changing the pH or solubility characteristics of the crude oil resulting in deposit or sludge formation.

The presence of water in the formation can complicate the problem, as well as the solution, by forming emulsions or sludging with the crude oil and insoluble hydrocarbon materials. This creates additional formation damage, further reducing production rates. In addition, the water can form a protective mating that prevents the more common solvents from penetrating to the hydrocarbon deposit and dissolving oil. Oil and paraffin coated solids or scale can cause additional deposit problems. These solids are difficult to remove or dissolve when coated and make acid treatments less effective.

Laboratory Testing

Testing in the laboratory for these types of downhole damage is difficult because formation of the deposits under actual formation flow conditions is difficult and time consuming. Laboratory tests were conducted to demonstrate the effects of the solvent and mutual solvent mixture chosen for the field tests.

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