Use Of Spent Sulfite Liquors In Enhanced On Recovery Operations

Abstract

Abstract Previous work has shown that commercially-refined lignosulfonates can considerably enhance the tertiary oil recovery efficacy of petroleum sulfonate surfactants. The present study examines the effects of using lignosulfonates in their unrefined form. i.e. as spent sulfite liquors which emanate as effluent from many Canadian pulp and paper mills. These liquors contain several inorganic and organic components in addition to lignosuljonotes, notably sugars. Interfacial tension, phase behaviour, and tertiary oil recovery data are presented for a wide range of surfactant mixtures containing spent sulfite liquors and petroleum sulfonates. It is shown that within certain concentration ranges significant increases in oil recovery can be achieved by adding spent sulfite liquors to petroleum sulfonate surfactants. Introduction It has been widely recognized that secondary or tertiary surfactant flooding of petroleum reservoirs is an effective means of recovering a fraction of the remaining oil, provided an ultralow interfacial tension (= 10−3 mN/m) between the oil and the surfactant solution can be attained. Several types of petroleum sulfonate surfactants have been investigated in the literature for the attainment of such low interfacial tensions. However, the high cost of petroleum sulfonate is one of the major drawbacks in surfactant flooding processes. The present authors have therefore been investigating the possibilities of using lignosulfonates (which are about four times cheaper than petroleum sulfonates) in enhanced oil recovery operations. Lignosulfonates were chosen as an alternate surfactant source because they are derived from wood, which is a renewable resource and abundantly available in Canada. Lignosulfonates are one of the major constituents of spent sulfite liquors which are discarded as effluents from pulp and paper plants. About 10% of the total spent sulfite liquors are currently being processed to recover useful products like lignosulfonates, which have a variety of uses such as dispersants, binders, emulsion stabilizers and industrial cleaners. Lignosulfonates in Enhanced Oil Recovery Lignosulfonate solutions are sub-colloidal, high molecular weight, polyelectrolyres which do not show any tendency to form micelles and do not reduce interfacial tension appreciably when used alone(1–2). Kalfoglou(3) patented a tertiary recovery process in which he proposed the use of lignosulfonates as sacrificial agents to reduce the adsorption loses of expensive petroleum sulfonate surfactants on the reservoir rock. However, in a recent study, Novosad(8) claimed that the beneficial effects of lignosulfonates do not result from their activity as sacrificial agents. In several studies performed ill our laboratory, increased interfacial activity was observed between oil and petroleum sulfonate solutions upon the addition of lignosulfonates(4–6). The lowering of interfacial tension produced by adding lignosulfonate was qualitatively similar to that observed when adding NaCI, provided the solution was below its optimal salinity level. However, the quantity of lignosulfonate required 10 produce a given lowering was much smaller(6). In a related study Son et al. (7) observed faster oil drop coalescence rates with these mixed surfactants than when using petroleum sulfonates alone.