WELL SERVICING FLUIDS

Abstract: This invention relates to an aqueous well servicing fluid comprising in solution a potassium formate characterised in that said solution contains in addition potassium citrate. The potassium citrate, which can be added as a solid to a potassium formate solution, enhances the density of said fluid and minimises any risk of caking which may be experienced if solid potassium formate is used.

Description: WELL SERVICING FLUIDS The present invention relates to a composition for and method of enhancing the density of well servicing fluids prepared therefrom. It is well known that aqueous media, especially those containing oil field brines, are generally used as well servicing fluids such as drilling fluids, r > completion fluids, packer fluids, well treating fluids, subterranean formation testing fluids, spacer fluids and hole abandonment fluids. For all these uses, such brines desirably have relatively high density. In order to achieve this, various components have been added to such fluids. Examples of such additives include heavy brines such as zinc bromide or combinations thereof i n with eg hydrophilic polymeric materials such as hydroxyethyl cellulose. One of the problems with such brines currently used is that they contain zinc atoms which are not environmentally friendly. Moreover, the polymeric hydroxyethyl celluloses are poorly hydrated, solvated or dispersed in aqueous systems which contain water-soluble salts of multi valent metals. In order to Hi overcome the problems of toxicity it has been proposed to use a non-toxic carboxylates. The most important of these is potassium carboxylates, especially potassium formate and potassium acetate. However, one of the problems with a salt such as potassium formate it is highly susceptible to caking. This is particularly unsuitable if one attempts to transport solid 20 potassium formate to the drilling site in order to prepare the well servicing tluid on the spot either as a fresh solution of the desired density or to enhance the density of an used/depleted well servicing tluid for the purposes of recycling. Use of conventional anti-caking agents either have an adverse affect on the density of the well servicing tluid or the other components 2 C > thereof, or, the environment, or, contaminate the oils recovered It is an object of the present invention to devise a composition which provides the desired high density aqueous brine systems which are of much lower ecotoxicity and yet overcome the problems of caking experienced when using compounds such as potassium formate alone as density enhancers Accordingly, the pi esent invention is an aqueous well servicing fluid comprising in solution a potassium foi mate characterised in that said solution contains in addition potassium citrate Both potassium foimate and potassium citrate are readily available commercially A featui e of the pi esent invention is that solid potassium citrate can be added to aqueous solutions of potassium formate lo enhance the density thei eof din ing use as well servicing fluids This is particularly important because whilst, theoretically, solid potassium formate itself could be added to such solutions to achieve an equivalent increment in density, solid potassium formate is much more difficult to handle in view of its tendency to caking In compai ison, potassium citi ate is much less prone to caking and hence can be l eadily handled to ad|iιst the density of well servicing fluids at the point of use of such fluids Thus, when a potassium formate solution is mixed with potassium citi te, thei e is virtually no advei se effect on the density of the potassium foi ate solution, on the contrary, the density of the potassium formate solution is enhanced This is vei y surprising because an identical potassium foi mate solution when mixed with the same amount of potassium acetate oi sodium foi mate, results in a reduction of the density of the potassium formate solution The amount of potassium citi ate that may be added to a potassium foi mate solution can vai y ovei a wide l nge since they are miscible over such wide ranges but is suitably in the l nge fi om 5 to 30%, preferably from 10- 25% by weight Optionally, salts such as eg cesium foi mate, acetate, propionate, oxalate, cesium lactate, cesium citrate and cesium tartarate can be added to the aqueous bi es used in well sei vicing fluids By varying the relative concentrations of the cai boxyhc acid salts in the fluid it is possible to achieve the desu ed density of the bi ine oi the ultimate sei vicing fluid in which the bi ine is used Formulations containing the carboxylate and hydi oxy- cai boxylate salts as descπbed above ai e most desn able for density enhancing since they ai e envii nmentally safe and ai e usei fnendly Thus densities langing tiom I 6 to 2 61 g/cm-^ preferably from 1 8 to 2 g/cm-* can be achieved using the compositions of the present invention The well seivicmg fluids of the piesent invention can be prepared by mixing aqueous solutions of the individual salts Alternatively, a mixture of the aqueous solutions of the lespective bases of the alkali metals can first be piepaied to which the desiied caiboxylic acid is added to form the respective carboxylates The desiied concenti ation of the lespective salts in the aqueous solution so foi med can be adjusted by evapoiation of the water from the mixed solution The present invention is fuithei illustrated with leference to the following Example EXAMPLE: A 70 weight % contiol solution of potassium foi mate in water was piepaied and to this solution (density ! 8) othei salts ( 10% by weight each) wei e added to detei mine the effect of the added salts on the density of the lesultant solution All expei iments wei e conducted at loom temperature The lesults of these expenments ai e tabulated below The above iesults show that potassium formate and potassium citrate aie compatible and enhances the density of the solution containing both Whilst the addition of fui thei a quots of potassium formate also appears to give a similai density to that achieved by adding potassium citrate, it is not convenient to add potassium foi mate solid at the well diilling site due to its pi opensity foi caking

Claims: Claims 1 An aqueous well sei vicing fluid compiis g in solution a potassium foimate chaiactensed in that said solution contains in addition potassium citrate 2 An aqueous well sei vicing fluid accoiding to Claim 1 wheiein the potassium citi te enhances the density of said fluid 3 An aqueous well .sei vicing fluid accoiding to any one of the preceding Claims wheiein the amount of potassium citrate added to a potassium formate solution is in the lange fiom 5 to 30% by weight based on the total weight of potassium foimate and potassium citiate m said fluid 4 An aqueous well sei vicing fluid accoiding to any one of the preceding Claims wheiein said fluid optionally contains in addition, one oi moie salts selected fiom cesium foimate cesium acetate, cesium piυpionate cesium o\alate, cesium lactate, cesium citiate and cesium taitaiate 5 An aqueous well sei vicing fluid accoiding to any one ot the pieceding Claims wheiein the lelative concenti tions of potassium foimate and potassium citrate in the fluid is vaned to achieve fluids having densities in the lanye fiom I 6 to 263 g/cm '

Inventors: VAN OOYEN JOHANNES ADRIANUS CO, VAN OOYEN, JOHANNES, ADRIANUS, CORNELIS
Applicants: OOYEN JOHANNES ADRIANUS CORNEL, VERDUGT BV, VAN OOYEN, JOHANNES, ADRIANUS, CORNELIS, VERDUGT B.V.
Application year: 1997
Main classification: C09K7
IPC codes: C09K8