TKPP

Potassium Pyrophosphates. Tetrapotassium pyrophosphate (TKPP), is easily prepared by thermal dehydration of K HPO. TKPP... 

De-oiling, typically using a blend of chemical materials such as caustic and alkaline phosphates together with nonfoaming surfactants the phosphates employed are generally either trisodium phosphate (TSP) or tetrapotassium pyrophosphate (TKPP)... 

What has long been sought and badly needed is a soluble weighting agent less corrosive than, and equally non-damaging as, the popular calcium and zinc halides. Preliminary laboratory and field data indicate TKPP may be the solution. 

TKPP (K4P2O7) is a merchant chemical produced by many major companies throughout the world. It is available commercially as a free flowing, white, grsr.ular solid or as a 60% wt. solution. In addition to its widespread use in the liquid detergent formulations, TKPP is also utilized in the food industry. It has been certified by the U. S. Department of Transportation as nontoxic. The solubility of TKPP in water at 60° F is shown in Table I. It is possible to achieve increased density at temperatures above 60° F because of increased solubility. 

Similar tests were performed with 10% and 20% by weight aqueous solutions of TKPP having approximately the same potassium ion concentration... 

The damage potential of TKPP fluids was further reduced by the addition of multivalent cations. When these salts were added at approximately their solubility limit in TKPP solutions, damage decreased, lending additional credence to the observation that the addition potassium ions alone is not sufficient to completely eliminate formation damage. 

At the conclusion of a few selected damage tests, an additional experiment was performed in which solutions containing 10% TKPP, 0.1% calcium chloride, and 0.4% magnesium chloride were pumped through the damaged cores. In each instance, the permeability of the core recovered dramatically, as shown in Figure 1. 

No Visible Effect 2 - Cracks/Sloughing 3 - Complete Disintegration TKPP solutions contain 0.21% CaCl2 and 0.65% MgCl2... 

Tests were conducted to compare the effect of KC1 and TKPP on the rheology of an unweighted (nondispersed) and a weighted (dispersed) drilling fluid. All fluids were mixed in an industry standard Hamilton Beach mixer. The rheology of each fluid was then measured in a Fann viscometer at 120°F at 300 rpm and 600 rpm. 

The results of these tests and the fluid formulations axe shown in Table IV. The adverse effect on fluid rheology of adding potassium, KC1, Test B, and TKPP, Test C, is evident. Both salts cause increases in yield point, YP, and initial gel strength. TKPP produced only about half as much increase as did KC1 and can be added in much higher concentrations before the rheological properties of the drilling mud become unacceptable. 

When suitably viscosified, TKPP solutions become superior low solids drilling fluids. Many water-soluble polymers were tested to identify satisfactory viscosifiers. Most commercially available polymers were found to be insoluble in TKPP solutions at densities above 11 ppg. Only xanthan gum... 

Table V. Rheology of TKPP - Xanthan Drilling Muds...

TKPP Cone. Density Apparent Plastic Yield Point... 

Solutions of TKPP were mixed with aqueous fluids commonly encountered in drilling or completion of wells. Unlike saturated zinc bromide, concentrated TKPP solutions can be mixed in any proportion with fresh water with the only result being a decrease in solution density. Similar results were obtained with conventional oil field brines containing as much as 400 parts per million polyvalent cations, mostly calcium. Saturated solutions of calcium hydroxide also can be added to TKPP in any proportion without promoting precipitation as can concentrated hydrochloric acid solutions, conventionally used for well stimulation. The acid tends to generate a slight haze as the pH is reduced from 11.5 to approximately 8 however, this haze rapidly disappears as the pH is lowered by further addition of acid. 

The only fluid, common to oil field operations, that has a significant interaction with TKPP solutions was concentrated calcium chloride. Solutions of calcium chloride, spent acid, are generated during the acidization of a limestone or a dolomite formation. When solutions containing 10% calcium chloride were mixed in equal proportions with 14.5 ppg TKPP solutions, massive precipitation occurred. Similar precipitation was observed with oil field brines having calcium concentrations above 400 ppm. 

In normal operations, there is little chance for spent acid to contact the completion fluid as the well will usually be produced after perforation, effecting the removal of completion fluid prior to acidization. The fact that a calcium precipitation reaction can occur should be recognized by those using TKPP solutions as a clear completion fluid in well operations. A KC1 spacer is recommended to avoid completion problems in formations having high calcium brines. 

Not only should well fluids be compatible with reservoir fluids and minerals, but they must also be stable at surface conditions. One disadvantage of conventional halide fluids is their tendency to crystallize at ambient temperatures. Solutions containing varing amounts of TKPP were exposed to constant temperatures as low as -76°F (-60°C) for a period of 30 hours. No crystallization was observed at any temperature above 36°F (2°C) even at concentrations as high as 60% by weight. At low fluid densities, less than 11.7 ppg, there is no evidence of TKPP crystallization even at temperatures as low as 30°F(-1°C), the freezing point of most fresh water drilling fluids. 

The addition of TKPP lowers the freezing point of the fluid significantly. This offers the opportunity of using a subfreezing TKPP mud to drill through strata, i.e., the permafrost in Alaska and Canada, without thawing of the... 

Corrosion rates for TKPP solutions measured at 194°F were low, 2 mils/yeax. Data at 400°F are equally impressive, 14 mils/year for 1020 steel... 

At the request of an international petroleum company, a major manufacturer and supplier of down-hole equipment performed tests of the various elastomers commonly used in the construction of packers and other oil field tools. Seven of the nine most commonly used thermoplastic materials were found to be completely inert to TKPP solutions. The test included continual immersion in saturated TKPP for 21 days at 280°F. Only two elastomers, Vi-ton and Fluorel, showed any adverse reaction. O-rings made from these two elastomers showed minor cracking at the termination of the test. A listing of the elastomers that tested inert to TKPP solutions include nitrile, saturated nitrile (HNBR), Aflas, Kalrez, PEEK, Glass-filled Teflon, and Ryton. Several of these elastomers are attacked or degraded by conventional clear completion fluids containing calcium and zinc halides. The inertness of commonly employed elastomers to TKPP is an important advantage for TKPP fluids in normal operations. 

Although at high concentration, TKPP is toxic to fish and shrimp. When diluted, 500-1000 PPM, it is non-toxic and expected to be both environmentally acceptable and of low risk to humans. The widespread use of TKPP in detergent formulations supports this expectation. It is listed by the U. S. Department of Transportation as a nontoxic substance relative to shipping regulations. 

Solutions of TKPP have been shown to have unique and advantageous properties for use in formulating a wide variety of well fluids. Its reasonable cost, worldwide availability, and nontoxic properties make it a preferred additive for use in many petroleum applications. It has been shown to be a most effective salt with respect to inhibiting hydration and swelling of clay minerals commonly encountered in drilling operations and/or reservoirs. Avoiding clay problems is the major impetus for the incorporation of potassium ions in well fluids, and the use of TKPP provides advantages over and above those available from other potassium salts. 

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