Controlling fluid losses to the formation, both before and after completions, is critical to optimizing production. Fluid-loss control can be achieved through the use of either mechanical or chemical means. Chemical methods control losses to the formation by increasing the base fluid viscosity with linear or crosslinked polymers or by forming a low-permeability filter cake on the formation face. However, performance limitations have prevented the use of such traditional ‘pills’ in high-stress environments, i. e., those that include high temperature, high density, low pH, high differential pressure, and high concentrations of divalent cations, Zn2+ and Ca2+. These limitations result in accepting excessive losses or employing less-than-ideal methods. This paper describes fluid-loss pills developed for high-stress applications for both solids-free and solids-laden systems. Among the new developments are linear gel-based fluids stable at high temperature for extended periods. For example, we present data on HEC-based fluids stable at temperatures as high as 300°F and in densities in excess of 16.5 lbm/gal. Solids-laden pills are presented that have been field tested under severe conditions including high-density zinc brines up to 18.7 lbm/gal and temperatures up to 325°F. Laboratory data are provided that demonstrate effective fluid-loss control for at least 5 days under these extreme conditions. Formation damage and filtercake cleanup results are included. Several solids-free and solids-laden systems are documented through both lab and field case histories. Introduction Fluid-loss control is an important aspect of the completion/workover operation. Perhaps more important than the relative cost associated with losing high-density completion fluid, is the production rate impairment that may be caused by excessive losses or poorly designed fluid-loss-control methods. Although a number of options exist for controlling losses during the completion process by mechanical means, these methods are not always applicable, or, in some cases, require chemical methods as backup in case of failure. Therefore, chemical fluid-loss-control pills (FLCP) will continue to maintain their important role as a fundamental control means and the need to push their performance limits will persist for the foreseeable future. Current performance limitations to chemical fluid loss systems include high temperature, high density, high concentration of Ca2+ and Zn2+, high differential pressure, low pH, and high shear. One of the key features to controlling fluid-losses is the ability of a FLCP to maintain viscosity at elevated temperatures. Viscosity reduction with increasing temperature is a consequence of either reduced molecular interactions or the degradation of polymer molecules into smaller, non-viscosity producing, fragments. In the first process, when the temperature is decreased, some fraction of the original viscosity is regained. This is seen in conventional, hydroxylethyl cellulose (HEC) solids-free FLCP. In the second process, the loss of viscosity due to polymer degradation is irreversible (Fig. 1).1 Technology has been developed to stabilize both conventional solids-free and solids-laden FLCP, however, even this technology is limited at elevated temperatures.2–3 This paper describes how conventional solids-free and solids-laden FLCPs can be stabilized for several hours to several days at temperatures that destroy conventionally formulated FLCP. It also shows that these stabilizing techniques have similar interaction with the formation as conventional systems. Finally, several solids-free and solids-laden systems are documented through both lab and field case histories.
fax 01-972-952-9435. AbstractWhile thiocyanates are useful corrosion inhibitors in some low-to-medium temperature ranges, at temperatures of 350ºF and upwards, thiocyanates are believed to be prone to thermal decomposition and subsequent environmentally induced corrosion cracking of tubular goods, especially of high strength corrosion-resistant alloys. Stress corrosion cracking has also been postulated to be a risk as a result of hydrogen sulfide production from the decomposition of thiocyanates.In the life cycle of completion brines, a stock brine is custom-blended with a variety of additives depending on the particular application. In the field, additional components may be introduced, sometimes as contaminants. Once used, completion fluid that is returned to the surface may optionally be subjected to reclamation processes for reuse in a subsequent application. Current API recommended practices specify the testing for such components as solids, pH, and iron; however, it seems reasonable that in the future the recommended practices will also include a specification on the maximum allowable thiocyanate content.Reclamation processes to date have not focused on the removal of thiocyanates from brines. This paper discusses the laboratory development and field implementation of processes for complete removal of thiocyanates from completion brines before any attempt is made to reuse them. This process works for a wide range of brines, is quite cost-effective, and enables buy-back of used completion brines with only a reasonable additional cost for thiocyanate removal.
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